1.2.0: update version to release

- Implemented `extern` support for functions, classes, objects, enums, and properties in the `MiniAST`.
- Updated `MiniAST` to include `isExtern` field for applicable nodes.
- Enabled merging of `.lyng.d` declaration files into main `.lyng` scripts.
- Adjusted tests to validate `extern` behavior and documentation handling.
- Minor fixes to parser logic for improved robustness.

.gitattributes

@@ -0,0 +1 @@
+*.zip filter=lfs diff=lfs merge=lfs -text

.github/workflows/gradle.yml

@@ -1,54 +0,0 @@
-# This workflow uses actions that are not certified by GitHub.
-# They are provided by a third-party and are governed by
-# separate terms of service, privacy policy, and support
-# documentation.
-# This workflow will build a Java project with Gradle and cache/restore any dependencies to improve the workflow execution time
-# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-java-with-gradle
-
-name: Java CI with Gradle
-
-on:
-  push:
-    branches: [ "main" ]
-  pull_request:
-    branches: [ "main" ]
-  workflow_call:
-
-permissions:
-  contents: read
-
-jobs:
-  build:
-    strategy:
-      matrix:
-        include:
-          - target: iosSimulatorArm64Test
-            os: macos-latest
-          - target: jvmTest
-            os: ubuntu-latest
-          - target: linuxX64Test
-            os: ubuntu-latest
-          - target: testDebugUnitTest
-            os: ubuntu-latest
-          - target: testReleaseUnitTest
-            os: ubuntu-latest
-    runs-on: ${{ matrix.os }}
-
-    steps:
-    - uses: actions/checkout@v3
-    - name: Validate Gradle Wrapper
-      uses: gradle/actions/wrapper-validation@v3
-    - uses: actions/cache@v3
-      with:
-        path: |
-          ~/.konan
-        key: ${{ runner.os }}-${{ hashFiles('**/.lock') }}
-    - name: Set up JDK 17
-      uses: actions/setup-java@v3
-      with:
-        java-version: '17'
-        distribution: 'temurin'
-    - name: Build with Gradle
-      uses: gradle/gradle-build-action@ce999babab2de1c4b649dc15f0ee67e6246c994f
-      with:
-        arguments: ${{ matrix.target }}

.github/workflows/publish.yml

@@ -1,25 +0,0 @@
-name: Publish
-on:
-  release:
-    types: [released, prereleased]
-jobs:
-  publish:
-    name: Release build and publish
-    runs-on: macOS-latest
-    steps:
-      - name: Check out code
-        uses: actions/checkout@v4
-      - name: Set up JDK 21
-        uses: actions/setup-java@v4
-        with:
-          distribution: 'zulu'
-          java-version: 21
-      - name: Publish to MavenCentral
-        run: ./gradlew publishToMavenCentral --no-configuration-cache
-        env:
-          ORG_GRADLE_PROJECT_mavenCentralUsername: ${{ secrets.MAVEN_CENTRAL_USERNAME }}
-          ORG_GRADLE_PROJECT_mavenCentralPassword: ${{ secrets.MAVEN_CENTRAL_PASSWORD }}
-          ORG_GRADLE_PROJECT_signingInMemoryKeyId: ${{ secrets.SIGNING_KEY_ID }}
-          ORG_GRADLE_PROJECT_signingInMemoryKeyPassword: ${{ secrets.SIGNING_PASSWORD }}
-          ORG_GRADLE_PROJECT_signingInMemoryKey: ${{ secrets.GPG_KEY_CONTENTS }}
-

.gitignore

@@ -15,3 +15,15 @@ xcuserdata
 /kotlin-js-store/yarn.lock
 /test.lyng
 /sample_texts/1.txt.gz
+/kotlin-js-store/wasm/yarn.lock
+/distributables
+.output*.txt
+debug.log
+/build.log
+/test.md
+/build_output.txt
+/build_output_full.txt
+/check_output.txt
+/compile_jvm_output.txt
+/compile_metadata_output.txt
+test_output*.txt

.junie/guidelines.md

@@ -0,0 +1,11 @@
+# Lyng Project Guidelines
+
+This project uses the Lyng scripting language for multiplatform scripting.
+
+## Coding in Lyng
+When writing, refactoring, or analyzing Lyng code:
+- **Reference**: Always use `LYNG_AI_SPEC.md` in the project root as the primary source of truth for syntax and idioms.
+- **File Extensions**: Use `.lyng` for all script files.
+- **Implicit Coroutines**: Remember that all Lyng functions are implicitly coroutines; do not look for `async/await`.
+- **Everything is an Expression**: Leverage the fact that blocks, if-statements, and loops return values.
+- **Maps vs Blocks**: Be careful: `{}` is a block/lambda, use `Map()` for an empty map.

.run/Tests in 'lyng.lynglib.jvmTest'.run.xml

@@ -1,20 +1,3 @@
-<!--
-  ~ Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
-  ~
-  ~ Licensed under the Apache License, Version 2.0 (the "License");
-  ~ you may not use this file except in compliance with the License.
-  ~ You may obtain a copy of the License at
-  ~
-  ~     http://www.apache.org/licenses/LICENSE-2.0
-  ~
-  ~ Unless required by applicable law or agreed to in writing, software
-  ~ distributed under the License is distributed on an "AS IS" BASIS,
-  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  ~ See the License for the specific language governing permissions and
-  ~ limitations under the License.
-  ~
-  -->
-
 <component name="ProjectRunConfigurationManager">
   <configuration default="false" name="Tests in 'lyng.lynglib.jvmTest'" type="GradleRunConfiguration" factoryName="Gradle">
     <ExternalSystemSettings>
@@ -35,8 +18,11 @@
     </ExternalSystemSettings>
     <ExternalSystemDebugServerProcess>false</ExternalSystemDebugServerProcess>
     <ExternalSystemReattachDebugProcess>true</ExternalSystemReattachDebugProcess>
+    <ExternalSystemDebugDisabled>false</ExternalSystemDebugDisabled>
     <DebugAllEnabled>false</DebugAllEnabled>
     <RunAsTest>true</RunAsTest>
+    <GradleProfilingDisabled>false</GradleProfilingDisabled>
+    <GradleCoverageDisabled>false</GradleCoverageDisabled>
     <method v="2" />
   </configuration>
 </component>

.run/lyng_site [jsBrowserDevelopmentRun].run.xml

@@ -0,0 +1,44 @@
+<!--
+  ~ Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~     http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  ~
+  -->
+
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="lyng:site [jsBrowserDevelopmentRun]" type="GradleRunConfiguration" factoryName="Gradle">
+    <ExternalSystemSettings>
+      <option name="executionName" />
+      <option name="externalProjectPath" value="$PROJECT_DIR$/site" />
+      <option name="externalSystemIdString" value="GRADLE" />
+      <option name="scriptParameters" value="--continuous" />
+      <option name="taskDescriptions">
+        <list />
+      </option>
+      <option name="taskNames">
+        <list>
+          <option value="jsBrowserDevelopmentRun" />
+        </list>
+      </option>
+      <option name="vmOptions" />
+    </ExternalSystemSettings>
+    <ExternalSystemDebugServerProcess>true</ExternalSystemDebugServerProcess>
+    <ExternalSystemReattachDebugProcess>true</ExternalSystemReattachDebugProcess>
+    <ExternalSystemDebugDisabled>false</ExternalSystemDebugDisabled>
+    <DebugAllEnabled>false</DebugAllEnabled>
+    <RunAsTest>false</RunAsTest>
+    <GradleProfilingDisabled>true</GradleProfilingDisabled>
+    <GradleCoverageDisabled>true</GradleCoverageDisabled>
+    <method v="2" />
+  </configuration>
+</component>

CHANGELOG.md

@@ -0,0 +1,136 @@
+## Changelog
+
+### Unreleased
+
+- Language: Added `return` statement
+  - `return [expression]` exits the innermost enclosing callable (function or lambda).
+  - Supports non-local returns using `@label` syntax (e.g., `return@outer 42`).
+  - Named functions automatically provide their name as a label for non-local returns.
+  - Labeled lambdas: lambdas can be explicitly labeled using `@label { ... }`.
+  - Restriction: `return` is forbidden in shorthand function definitions (e.g., `fun f(x) = return x` is a syntax error).
+  - Control Flow: `return` and `break` are now protected from being caught by user-defined `try-catch` blocks in Lyng.
+  - Documentation: New `docs/return_statement.md` and updated `tutorial.md`.
+
+- Language: stdlib improvements
+  - Added `with(self, block)` function to `root.lyng` which executes a block with `this` set to the provided object.
+- Language: Abstract Classes and Interfaces
+  - Support for `abstract` modifier on classes, methods, and variables.
+  - Introduced `interface` as a synonym for `abstract class`, supporting full state (constructors, fields, `init` blocks) and implementation by parts via MI.
+  - New `closed` modifier (antonym to `open`) to prevent overriding class members.
+  - Refined `override` logic: mandatory keyword when re-declaring members that exist in the ancestor chain (MRO).
+  - MI Satisfaction: Abstract requirements are automatically satisfied by matching concrete members found later in the C3 MRO chain without requiring explicit proxy methods.
+  - Integration: Updated highlighters (lynglib, lyngweb, IDEA plugin), IDEA completion, and Grazie grammar checking.
+  - Documentation: Updated `docs/OOP.md` with sections on "Abstract Classes and Members", "Interfaces", and "Overriding and Virtual Dispatch".
+- IDEA plugin: Improved natural language support and spellchecking
+  - Disabled the limited built-in English and Technical dictionaries.
+  - Enforced usage of the platform's standard Natural Languages (Grazie) and Spellchecker components.
+  - Integrated `SpellCheckerManager` for word suggestions and validation, respecting users' personal and project dictionaries.
+  - Added project-specific "learned words" support via `Lyng Formatter` settings and quick-fixes.
+  - Enhanced fallback spellchecker for technical terms and Lyng-specific vocabulary.
+
+- Language: Class properties with accessors
+  - Support for `val` (read-only) and `var` (read-write) properties in classes.
+  - Syntax: `val name [ : Type ] get() { body }` or `var name [ : Type ] get() { body } set(value) { body }`.
+  - Laconic Expression Shorthand: `val prop get() = expression` and `var prop get() = read set(v) = write`.
+  - Properties are pure accessors and do **not** have automatic backing fields.
+  - Validation: `var` properties must have both accessors; `val` must have only a getter.
+  - Integration: Updated TextMate grammar and IntelliJ plugin (highlighting + keywords).
+  - Documentation: New "Properties" section in `docs/OOP.md`.
+
+- Language: Restricted Setter Visibility
+  - Support for `private set` and `protected set` modifiers on `var` fields and properties.
+  - Allows members to be publicly readable but only writable from within the declaring class or its subclasses.
+  - Enforcement at runtime: throws `AccessException` on unauthorized writes.
+  - Supported only for declarations in class bodies (fields and properties).
+  - Documentation: New "Restricted Setter Visibility" section in `docs/OOP.md`.
+
+- Language: Late-initialized `val` fields in classes
+  - Support for declaring `val` without an immediate initializer in class bodies.
+  - Compulsory initialization: every late-init `val` must be assigned at least once within the class body or an `init` block.
+  - Write-once enforcement: assigning to a `val` is allowed only if its current value is `Unset`.
+  - Access protection: reading a late-init `val` before it is assigned returns the `Unset` singleton; using `Unset` for most operations throws an `UnsetException`.
+  - Extension properties do not support late-init.
+  - Documentation: New "Late-initialized `val` fields" and "The `Unset` singleton" sections in `docs/OOP.md`.
+
+- Docs: OOP improvements
+  - New page: `docs/scopes_and_closures.md` detailing `ClosureScope` resolution order, recursion‑safe helpers (`chainLookupIgnoreClosure`, `chainLookupWithMembers`, `baseGetIgnoreClosure`), cycle prevention, and capturing lexical environments for callbacks (`snapshotForClosure`).
+  - Updated: `docs/advanced_topics.md` (link to the new page), `docs/parallelism.md` (closures in `launch`/`flow`), `docs/OOP.md` (visibility from closures with preserved `currentClassCtx`), `docs/exceptions_handling.md` (compatibility alias `SymbolNotFound`).
+  - Tutorial: added quick link to Scopes and Closures.
+
+- IDEA plugin: Lightweight autocompletion (experimental)
+  - Global completion: local declarations, in‑scope parameters, imported modules, and stdlib symbols.
+  - Member completion: after a dot, suggests only members of the inferred receiver type (incl. chained calls like `Path(".." ).lines().` → `Iterator` methods). No global identifiers appear after a dot.
+  - Inheritance-aware: direct class members first, then inherited (e.g., `List` includes `Collection`/`Iterable` methods).
+  - Heuristics: handles literals (`"…"` → `String`, numbers → `Int/Real`, `[...]` → `List`, `{...}` → `Dict`) and static `Namespace.` members.
+  - Performance: capped results, early prefix filtering, per‑document MiniAst cache, cancellation checks.
+  - Toggle: Settings | Lyng Formatter → "Enable Lyng autocompletion (experimental)" (default ON).
+  - Stabilization: DEBUG completion/Quick Doc logs are OFF by default; behavior aligned between IDE and isolated engine tests.
+
+- Language: Named arguments and named splats
+  - New call-site syntax for named arguments using colon: `name: value`.
+    - Positional arguments must come before named; positionals after a named argument inside parentheses are rejected.
+    - Trailing-lambda interaction: if the last parameter is already assigned by name (or via a named splat), a trailing `{ ... }` block is illegal.
+  - Named splats: `...` can now expand a Map into named arguments.
+    - Only string keys are allowed; non-string keys raise a clear error.
+    - Duplicate assignment across named args and named splats is an error.
+    - Ellipsis (variadic) parameters remain positional-only and cannot be named.
+  - Rationale: `=` is assignment and an expression in Lyng; `:` at call sites avoids ambiguity. Declarations keep `name: Type`; call-site casts continue to use `as` / `as?`.
+  - Documentation updated: proposals and declaring-arguments sections now cover named args/splats and error cases.
+  - Tests added covering success cases and errors for named args/splats and trailing-lambda interactions.
+
+- Tooling: Highlighters and TextMate bundle updated for named args
+  - Website/editor highlighter (lyngweb + site) works with `name: value` and `...Map("k" => v)`; added JS tests covering punctuation/operator spans for `:` and `...`.
+  - TextMate grammar updated to recognize named call arguments: `name: value` after `(` or `,` with `name` highlighted as `variable.parameter.named.lyng` and `:` as punctuation; excludes `::`.
+  - TextMate bundle version bumped to 0.0.3; README updated with details and guidance.
+
+- Multiple Inheritance (MI) completed and enabled by default:
+  - Active C3 Method Resolution Order (MRO) for deterministic, monotonic lookup across complex hierarchies and diamonds.
+  - Qualified dispatch:
+    - `this@Type.member(...)` inside class bodies starts lookup at the specified ancestor.
+    - Cast-based disambiguation: `(expr as Type).member(...)`, `(expr as? Type)?.member(...)` (works with existing safe-call `?.`).
+  - Field inheritance (`val`/`var`) under MI:
+    - Instance storage is disambiguated per declaring class; unqualified read/write resolves to the first match in MRO.
+    - Qualified read/write targets the chosen ancestor’s storage.
+  - Constructors and initialization:
+    - Direct bases are initialized left-to-right; each ancestor is initialized at most once (diamond-safe de-duplication).
+    - Header-specified constructor arguments are passed to direct bases.
+  - Visibility enforcement under MI:
+    - `private` visible only inside the declaring class body.
+    - `protected` visible inside the declaring class and any of its transitive subclasses; unrelated contexts cannot access it (qualification/casts do not bypass).
+  - Diagnostics improvements:
+    - Missing member/field messages include receiver class and linearization order; hints for `this@Type` or casts when helpful.
+    - Invalid `this@Type` reports that the qualifier is not an ancestor and shows the receiver lineage.
+    - `as`/`as?` cast errors include actual and target type names.
+
+- Documentation updated (docs/OOP.md and tutorial quick-start) to reflect MI with active C3 MRO.
+
+Notes:
+- Existing single-inheritance code continues to work; resolution reduces to the single base.
+- If code previously relied on non-deterministic parent set iteration, C3 MRO provides a predictable order; disambiguate explicitly if needed using `this@Type`/casts.
+
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+## Unreleased
+
+- CLI: Added `fmt` as a first-class Clikt subcommand.
+  - Default behavior: formats files to stdout (no in-place edits by default).
+  - Options:
+    - `--check`: check only; print files that would change; exit with code 2 if any changes are needed.
+    - `-i, --in-place`: write formatted result back to files.
+    - `--spacing`: apply spacing normalization.
+    - `--wrap`, `--wrapping`: enable line wrapping.
+  - Mutually exclusive: `--check` and `--in-place` together now produce an error and exit with code 1.
+  - Multi-file stdout prints headers `--- <path> ---` per file.
+  - `lyng --help` shows `fmt`; `lyng fmt --help` displays dedicated help.
+  - Fix: Property accessors (`get`, `set`, `private set`, `protected set`) are now correctly indented relative to the property declaration.
+  - Fix: Indentation now correctly carries over into blocks that start on extra‑indented lines (e.g., nested `if` statements or property accessor bodies).
+  - Fix: Formatting Markdown files no longer deletes content in `.lyng` code fences and works correctly with injected files (resolves clobbering, `StringIndexOutOfBoundsException`, and `nonempty text is not covered by block` errors).
+
+- CLI: Preserved legacy script invocation fast-paths:
+  - `lyng script.lyng [args...]` executes the script directly.
+  - `lyng -- -file.lyng [args...]` executes a script whose name begins with `-`.
+
+- CLI: Fixed a regression where the root help banner could print before subcommands.
+  - Root command no longer prints help when a subcommand (e.g., `fmt`) is invoked.

LYNG_AI_SPEC.md

@@ -0,0 +1,105 @@
+# Lyng Language AI Specification (V1.3)
+
+High-density specification for LLMs. Reference this for all Lyng code generation.
+
+## 1. Core Philosophy & Syntax
+- **Everything is an Expression**: Blocks, `if`, `when`, `for`, `while`, `do-while` return their last expression (or `void`).
+- **Loops with `else`**: `for`, `while`, and `do-while` support an optional `else` block.
+    - `else` executes **only if** the loop finishes normally (without a `break`).
+    - `break <value>` exits the loop and sets its return value.
+    - Loop Return Value:
+        1. Value from `break <value>`.
+        2. Result of `else` block (if loop finished normally and `else` exists).
+        3. Result of the last iteration (if loop finished normally and no `else`).
+        4. `void` (if loop body never executed and no `else`).
+- **Implicit Coroutines**: All functions are coroutines. No `async/await`. Use `launch { ... }` (returns `Deferred`) or `flow { ... }`.
+- **Variables**: `val` (read-only), `var` (mutable). Supports late-init `val` in classes (must be assigned in `init` or body).
+- **Null Safety**: `?` (nullable type), `?.` (safe access), `?( )` (safe invoke), `?{ }` (safe block invoke), `?[ ]` (safe index), `?:` or `??` (elvis), `?=` (assign-if-null).
+- **Equality**: `==` (equals), `!=` (not equals), `===` (ref identity), `!==` (ref not identity).
+- **Comparison**: `<`, `>`, `<=`, `>=`, `<=>` (shuttle/spaceship, returns -1, 0, 1).
+- **Destructuring**: `val [a, b, rest...] = list`. Supports nested `[a, [b, c]]` and splats.
+
+## 2. Object-Oriented Programming (OOP)
+- **Multiple Inheritance**: Supported with **C3 MRO** (Python-style). Diamond-safe.
+- **Header Arguments**: `class Foo(a, b) : Base(a)` defines fields `a`, `b` and passes `a` to `Base`.
+- **Members**: `fun name(args) { ... }`, `val`, `var`, `static val`, `static fun`.
+- **Properties (Get/Set)**: Pure accessors, no auto-backing fields.
+    ```lyng
+    var age
+        get() = _age
+        private set(v) { if(v >= 0) _age = v }
+    // Laconic syntax:
+    val area get = π * r * r
+    ```
+- **Mandatory `override`**: Required for all members existing in the ancestor chain.
+- **Visibility**: `public` (default), `protected` (subclasses), `private` (this class instance only). `private set` / `protected set` allowed on properties.
+- **Disambiguation**: `this@Base.member()` or `(obj as Base).member()`. `as` returns a qualified view.
+- **Abstract/Interface**: `interface` is a synonym for `abstract class`. Both support state and constructors.
+- **Extensions**: `fun Class.ext()` or `val Class.ext get = ...`. Scope-isolated.
+
+## 3. Delegation (`by`)
+Unified model for `val`, `var`, and `fun`.
+```lyng
+val x by MyDelegate()
+var y by Map() // Uses "y" as key in map
+fn f(a, b) by RemoteProxy() // Calls Proxy.invoke(thisRef, "f", a, b)
+```
+Delegate Methods:
+- `getValue(thisRef, name)`: for `val`/`var`.
+- `setValue(thisRef, name, val)`: for `var`.
+- `invoke(thisRef, name, args...)`: for `fn` (called if `getValue` is absent).
+- `bind(name, access, thisRef)`: optional hook called at declaration/binding time. `access` is `DelegateAccess.Val`, `Var`, or `Callable`.
+
+## 4. Standard Library & Functional Built-ins
+- **Scope Functions**:
+    - `obj.let { it... }`: result of block. `it` is `obj`.
+    - `obj.apply { this... }`: returns `obj`. `this` is `obj`.
+    - `obj.also { it... }`: returns `obj`. `it` is `obj`.
+    - `obj.run { this... }`: result of block. `this` is `obj`.
+    - `with(obj, { ... })`: result of block. `this` is `obj`.
+- **Functional**: `forEach`, `map`, `filter`, `any`, `all`, `sum`, `count`, `sortedBy`, `flatten`, `flatMap`, `associateBy`.
+- **Lazy**: `val x = cached { expensive() }` (call as `x()`) or `val x by lazy { ... }`.
+- **Collections**: `List` ( `[a, b]` ), `Map` ( `Map(k => v)` ), `Set` ( `Set(a, b)` ). `MapEntry` ( `k => v` ).
+
+## 5. Patterns & Shorthands
+- **Map Literals**: `{ key: value, identifier: }` (identifier shorthand `x:` is `x: x`). Empty map is `Map()`.
+- **Named Arguments**: `fun(y: 10, x: 5)`. Shorthand: `Point(x:, y:)`.
+- **Varargs & Splats**: `fun f(args...)`, `f(...otherList)`.
+- **Labels**: `loop@ for(x in list) { if(x == 0) break@loop }`.
+- **Dynamic**: `val d = dynamic { get { name -> ... } }` allows `d.anyName`.
+
+## 6. Operators & Methods to Overload
+| Op | Method | Op | Method |
+| :--- | :--- | :--- | :--- |
+| `+` | `plus` | `==` | `equals` |
+| `-` | `minus` | `<=>` | `compareTo` |
+| `*` | `mul` | `[]` | `getAt` / `putAt` |
+| `/` | `div` | `!` | `logicalNot` |
+| `%` | `mod` | `-` | `negate` (unary) |
+| `=~` | `operatorMatch` | `+=` | `plusAssign` |
+
+## 7. Common Snippets
+```lyng
+// Multiple Inheritance and Properties
+class Warrior(id, hp) : Character(id), HealthPool(hp) {
+    override fun toString() = "Warrior #%s (%s HP)"(id, hp)
+}
+
+// Map entry and merging
+val m = Map("a" => 1) + ("b" => 2)
+m += "c" => 3
+
+// Destructuring with splat
+val [first, middle..., last] = [1, 2, 3, 4, 5]
+
+// Safe Navigation and Elvis
+val companyName = person?.job?.company?.name ?? "Freelancer"
+```
+
+## 8. Standard Library Discovery
+To collect data on the standard library and available APIs, AI should inspect:
+- **Global Symbols**: `lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt` (root functions like `println`, `sqrt`, `assert`).
+- **Core Type Members**: `lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/*.kt` (e.g., `ObjList.kt`, `ObjString.kt`, `ObjMap.kt`) for methods on built-in types.
+- **Lyng-side Extensions**: `lynglib/stdlib/lyng/root.lyng` for high-level functional APIs (e.g., `map`, `filter`, `any`, `lazy`).
+- **I/O & Processes**: `lyngio/src/commonMain/kotlin/net/sergeych/lyng/io/` for `fs` and `process` modules.
+- **Documentation**: `docs/*.md` (e.g., `tutorial.md`, `lyngio.md`) for high-level usage and module overviews.

README.md

@@ -1,14 +1,26 @@
-# Lyng: modern scripting for kotlin multiplatform
+# Lyng: ideal scripting for kotlin multiplatform
+
+__Please visit the project homepage: [https://lynglang.com](https://lynglang.com) and a [telegram channel](https://t.me/lynglang).__
+
+__Main development site:__ [https://gitea.sergeych.net/SergeychWorks/lyng](https://gitea.sergeych.net/SergeychWorks/lyng)
+__github mirror__: [https://github.com/sergeych/lyng](https://github.com/sergeych/lyng)
+
+We keep github as a mirror and backup for the project, while the main development site is hosted on gitea.sergeych.net. We use gitea for issues and pull requests, and as a main point of trust, as github access now is a thing that can momentarily be revoked for no apparent reason.
+
+We encourage using the github if the main site is not accessible from your country and vice versa. We recommend to `publishToMavenLocal` and not depend on politics.
 
-A KMP library and a standalone interpreter
 
 - simple, compact, intuitive and elegant modern code:
 
-```
+```lyng
 class Point(x, y) {
    fun dist() { sqrt(x*x + y*y) } 
 }
-Point(3,4).dist() //< 5
+
+// Auto-named arguments shorthand (x: is x: x):
+val x = 3
+val y = 4
+Point(x:, y:).dist() //< 5
 
 fun swapEnds(first, args..., last, f) {
     f( last, ...args, first)
@@ -17,28 +29,21 @@ fun swapEnds(first, args..., last, f) {
 
 - extremely simple Kotlin integration on any platform (JVM, JS, WasmJS, Lunux, MacOS, iOS, Windows)
 - 100% secure: no access to any API you didn't explicitly provide
-- 100% coroutines! Every function/script is a coroutine, it does not block the thread, no async/await/suspend keyword garbage, see [parallelism]
-
-```
-  val deferred = launch {
-    delay(1.5) // coroutine is delayed for 1.5s, thread is not blocked!
-    "done"
-  }
-  // ...
-  // suspend current coroutine, no thread is blocked again,
-  // and wait for deferred to return something:
-  assertEquals("donw", deferred.await())
-```
-and it is multithreaded on platforms supporting it (automatically, no code changes required, just
-`launch` more coroutines and they will be executed concurrently if possible). See [parallelism]
-
-- functional style and OOP together, multiple inheritance, implementing interfaces for existing classes, writing extensions.
+- 100% coroutines! Every function/script is a coroutine, it does not block the thread, no async/await/suspend keyword garbage, see [parallelism]. it is multithreaded on platforms supporting it (automatically, no code changes required, just `launch` more coroutines and they will be executed concurrently if possible). See [parallelism]
+- functional style and OOP together: multiple inheritance (so you got it all - mixins, interfaces, etc.), delegation, sigletons, anonymous classes,extensions.
+- nice literals for maps and arrays, destructuring assignment, ranges.
 - Any Unicode letters can be used as identifiers: `assert( sin(π/2) == 1 )`.
 
  ## Resources: 
 
+- [Language home](https://lynglang.com)
 - [introduction and tutorial](docs/tutorial.md) - start here please
+- [Testing and Assertions](docs/Testing.md)
+- [Filesystem and Processes (lyngio)](docs/lyngio.md)
+- [Return Statement](docs/return_statement.md)
+- [Efficient Iterables in Kotlin Interop](docs/EfficientIterables.md)
 - [Samples directory](docs/samples)
+- [Formatter (core + CLI + IDE)](docs/formatter.md)
 - [Books directory](docs)
 
 ## Integration in Kotlin multiplatform
@@ -71,7 +76,7 @@ Now you can import lyng and use it:
 ### Execute script:
 
 ```kotlin
-import net.sergeyh.lyng.*
+import net.sergeych.lyng.*
 
 // we need a coroutine to start, as Lyng
 // is a coroutine based language, async topdown
@@ -87,9 +92,7 @@ Script is executed over some `Scope`. Create instance,
 add your specific vars and functions to it, and call:
 
 ```kotlin
-
-import com.sun.source.tree.Scope
-import new.sergeych.lyng.*
+import net.sergeych.lyng.*
 
 // simple function
 val scope = Script.newScope().apply {
@@ -115,6 +118,34 @@ scope.eval("sumOf(1,2,3)") // <- 6
 ```
 Note that the scope stores all changes in it so you can make calls on a single scope to preserve state between calls.
 
+## IntelliJ IDEA plugin: Lightweight autocompletion (experimental)
+
+The IDEA plugin provides a fast, lightweight BASIC completion for Lyng code (IntelliJ IDEA 2024.3+).
+
+What it does:
+- Global suggestions: in-scope parameters, same-file declarations (functions/classes/vals), imported modules, and stdlib symbols.
+- Member completion after dot: offers only members of the inferred receiver type. It works for chained calls like `Path(".." ).lines().` (suggests `Iterator` methods), and for literals like `"abc".` (String methods) or `[1,2,3].` (List/Iterable methods).
+- Inheritance-aware: shows direct class members first, then inherited. For example, `List` also exposes common `Collection`/`Iterable` methods.
+- Static/namespace members: `Name.` lists only static members when `Name` is a known class or container (e.g., `Math`).
+- Performance: suggestions are capped; prefix filtering is early; parsing is cached; computation is cancellation-friendly.
+
+What it does NOT do (yet):
+- No heavy resolve or project-wide indexing. It’s best-effort, driven by a tiny MiniAst + built-in docs registry.
+- No control/data-flow type inference.
+
+Enable/disable:
+- Settings | Lyng Formatter → "Enable Lyng autocompletion (experimental)" (default: ON).
+
+Tips:
+- After a dot, globals are intentionally suppressed (e.g., `lines().Path` is not valid), only the receiver’s members are suggested.
+- If completion seems sparse, make sure related modules are imported (e.g., `import lyng.io.fs` so that `Path` and its methods are known).
+
+## AI Assistant Support
+
+To help AI assistants (like Cursor, Windsurf, or GitHub Copilot) understand Lyng with minimal effort, we provide a high-density language specification:
+
+- **[LYNG_AI_SPEC.md](LYNG_AI_SPEC.md)**: A concise guide for AI models to learn Lyng syntax, idioms, and core philosophy. We recommend pointing your AI tool to this file or including it in your project's custom instructions.
+
 ## Why? 
 
 Designed to add scripting to kotlin multiplatform application in easy and efficient way. This is attempt to achieve what Lua is for C/++.
@@ -134,9 +165,8 @@ Designed to add scripting to kotlin multiplatform application in easy and effici
 
 # Language Roadmap
 
-## v1.0.0
-
-Planned autumn 2025. Complete dynamic language with sufficient standard library:
+We are now at **v1.0**: basic optimization performed, battery included: standard library is 90% here, initial
+support in HTML, popular editors, and IDEA; tools to syntax highlight and format code are ready. It was released closed to schedule.
 
 Ready features:
 
@@ -147,6 +177,7 @@ Ready features:
 - [x] ranges, lists, strings, interfaces: Iterable, Iterator, Collection, Array
 - [x] when(value), if-then-else
 - [x] exception handling: throw, try-catch-finally, exception classes.
+- [x] user-defined exception classes
 - [x] multiplatform maven publication
 - [x] documentation for the current state
 - [x] maps, sets and sequences (flows?)
@@ -159,26 +190,45 @@ Ready features:
 - [x] dynamic fields
 - [x] function annotations
 - [x] better stack reporting
+- [x] regular exceptions + extended `when`
+- [x] multiple inheritance for user classes
+- [x] class properties (accessors)
+- [x] `return` statement for local and non-local exit
+- [x] Unified Delegation model: val, var and fun
+- [x] `lazy val` using delegation
+- [x] singletons `object TheOnly { ... }`
+- [x] object expressions `object: List { ... }`
+- [x] late-init vals in classes
+- [x] properties with getters and setters
+- [x] assign-if-null operator `?=`
+- [x] user-defined exception classes
 
-###  Under way: 
+All of this is documented in the [language site](https://lynglang.com) and locally [docs/language.md](docs/tutorial.md). the current nightly builds published on the site and in the private maven repository.  
 
-- [ ] regular exceptions
-- [ ] multiple inheritance for user classes
-- [ ] site with integrated interpreter to give a try
-- [ ] kotlin part public API good docs, integration focused
-
-## v1.1+
-
-Planned features.
+## plan: towards v1.5 Enhancing
 
+- [x] site with integrated interpreter to give a try
+- [x] kotlin part public API good docs, integration focused
 - [ ] type specifications
+- [x] Textmate Bundle
+- [x] IDEA plugin
 - [ ] source docs and maybe lyng.md to a standard
 - [ ] metadata first class access from lyng
+- [x] aggressive optimizations
+- [ ] compile to JVM bytecode optimization
 
-Further
+## After 1.5 "Ideal scripting"
 
-- [ ] client with GUI support based on compose multiplatform somehow
-- [ ] notebook - style workbooks with graphs, formulae, etc.
-- [ ] language server or compose-based lyng-aware editor
+Estimated summer 2026
+
+- propose your feature! 
+
+## Authors
+
+@-links are for contacting authors on [project home](https://gitea.sergeych.net/SergeychWorks/lyng): this simplest s to open issue for the person you need to convey any information about this project.
+
+__Sergey Chernov__ @sergeych: Initial idea and architecture, language concept, design, implementation.
+
+__Yulia Nezhinskaya__ @AlterEgoJuliaN: System analysis, math and features design.
 
 [parallelism]: docs/parallelism.md

archived/README.md

@@ -0,0 +1,4 @@
+# Obsolete files
+
+
+__Do not rely on contents of the files in this directory. They are kept for historical reference only and may not be up-to-date or relevant.__

archived/development/String.md

@@ -0,0 +1,28 @@
+[//]: # (excludeFromIndex)
+
+# String
+
+# This document is for developer notes only
+
+--------------------------
+
+
+## Interpolation proposal
+
+"""no $iterpolation"""
+    
+    val inpterpolation1 = "foo"
+    "${interpolation1}"
+    >>> "foo"
+
+"$interpolation2"
+"no $$ interpolatino"
+
+
+## Regexp vs div / ?
+
+```EBNF
+regex_literal = "/", { regchar }, "/", [ flag ]
+foag = "i" | "n"....
+regchar = x`x`
+```

archived/development/including_modules.md

@@ -1,5 +1,7 @@
 # Modules inclusion
 
+[//]: # (excludeFromIndex)
+
 Module is, at the low level, a statement that modifies a given context by adding
 here local and exported symbols, performing some tasks and even returning some value
 we don't need for now.

archived/development/scope_resolution.md

@@ -1,3 +1,4 @@
+[//]: # (excludeFromIndex)
 
 
 Provide:

archived/proposals/delegates.lyng

@@ -0,0 +1,117 @@
+/*
+    This is a tech proposal under construction, please do not use it yet
+    for any purpose
+*/
+
+/*
+    Abstract delegate can be used to proxy read/wrtie field access
+    or method call. Default implementation reports error.
+*/
+interface Delegate {
+    fun getValue() = Unset
+    fun setValue(newValue) { throw NotImplementedException("delegate setter is not implemented") }
+    fun invoke(args...) { throw NotImplementedException("delegate setter is not implemented") }
+}
+
+/*
+    Delegate cam be used to implement a val, var or fun, so there are
+    access type enum to distinguish:
+*/
+enum DelegateAccess {
+    Val,
+    Var,
+    Callable
+}
+
+// Delegate can be associated by a val/var/fun in a declaraion site using `by` keyword
+
+val proxiedVal by proxy(1)
+var proxiedVar by proxy(2, 3)
+fun proxiedFun by proxy()
+
+// each proxy is a Lyng expression returning instance of the Proxy interface:
+
+/*
+    Proxy interface is connecting some named property of a given kind with the `Delegate`.
+    It removes the burden of dealing with property name and this ref on each get/set value
+    or invoke allowing having one delegate per instance, execution buff.
+*/
+interface Proxy {
+    fun getDelegate(propertyName: String,access: DelegateAccess,thisRef: Obj?): Delegate
+}
+
+// val, var and fun can be delegated, local or class instance:
+class TestProxy: Proxy {
+    override getDelegate(name,access,thisRef) {
+        Delegate()
+    }
+}
+
+val proxy = TestProxy()
+
+class Allowed {
+    val v1 by proxy
+    var v2 by proxy
+    fun f1 by proxy
+}
+val v3 by proxy
+var v4 by proxy
+fun f2 by proxy
+
+/*
+    It means that for example
+    Allowed().f1("foo")
+    would call a delegate.invoke("foo") on the `Delegate` instance supplied by `proxy`, etc.
+*/
+
+// The practic sample: lazy value
+
+/*
+    The delegate that caches single time evaluated value
+*/
+class LazyDelegate(creator): Delegate {
+    private var currentValue=Unset
+
+    override fun getValue() {
+        if( currentValue == Unset )
+            currentValue = creator()
+        currentValue
+    }
+}
+
+/*
+    The proxy to assign it
+*/
+class LazyProxy(creator) {
+    fun getDelegate(name,access,thisRef) {
+        if( access != DelegateAccess.Val )
+            throw IllegalArgumentException("only lazy val are allowed")
+        LazyDelegate(creator)
+    }
+}
+
+
+/*
+    A helper function to simplify creation:
+*/
+fun lazy(creator) {
+    LazyProxy(creator)
+}
+
+// Usage sample and the test:
+var callCounter = 0
+assertEquals(0, clallCounter)
+
+val lazyText by lazy { "evaluated text" }
+
+// the lazy property is not yet evaluated:
+assertEquals(0, clallCounter)
+// now evaluate it by using it:
+assertEquals("evaluated text", lazyText)
+assertEquals(1, callCounter)
+
+// lazy delegate should fail on vars or funs:
+assertThrows { var bad by lazy { "should not happen" } }
+assertThrows { fun bad by lazy { 42 } }
+
+

archived/proposals/map_literal.md

@@ -0,0 +1,95 @@
+
+# Map literals — refined proposal
+
+[//]: # (excludeFromIndex)
+
+Implement JavaScript-like literals for maps. The syntax and semantics align with named arguments in function calls, but map literals are expressions that construct `Map` values.
+
+Keys can be either:
+- string literals: `{ "some key": value }`, or
+- identifiers: `{ name: expr }`, where the key becomes the string `"name"`.
+
+Identifier shorthand inside map literals is supported:
+- `{ name: }` desugars to `{ "name": name }`.
+
+Property access sugar is not provided for maps: use bracket access only, e.g. `m["a"]`, not `m.a`.
+
+Examples:
+
+```lyng
+val x = 2
+val m = { "a": 1, x: x*10, y: }
+assertEquals(1, m["a"])      // string-literal key
+assertEquals(20, m["x"])     // identifier key
+assertEquals(2, m["y"])      // identifier shorthand
+```
+
+Spreads (splats) in map literals are allowed and merged left-to-right with “rightmost wins” semantics:
+
+```lyng
+val base = { a: 1, b: 2 }
+val m = { a: 0, ...base, b: 3, c: 4 }
+assertEquals(1, m["a"])  // base overwrites a:0
+assertEquals(3, m["b"])  // literal overwrites spread
+assertEquals(4, m["c"])  // new key
+```
+
+Trailing commas are allowed (optional):
+
+```lyng
+val m = {
+  "a": 1,
+  b: 2,
+  ...other,
+}
+```
+
+Duplicate keys among literal entries (including identifier shorthand) are a compile-time error:
+
+```lyng
+{ foo: 1, "foo": 2 }   // error: duplicate key "foo"
+{ foo:, foo: 2 }        // error: duplicate key "foo"
+```
+
+Spreads are evaluated at runtime. Overlaps from spreads are resolved by last write wins. If a spread is not a map, or yields a map with non-string keys, it’s a runtime error.
+
+Merging with `+`/`+=` and entries:
+
+```lyng
+("1" => 10) + ("2" => 20)     // Map("1"=>10, "2"=>20)
+{ "1": 10 } + ("2" => 20)     // same
+{ "1": 10 } + { "2": 20 }    // same
+
+var m = { "a": 1 }
+m += ("b" => 2)                 // m = { "a":1, "b":2 }
+```
+
+Rightmost wins on duplicates consistently across spreads and merges. All map merging operations require string keys; encountering a non-string key during merge is a runtime error.
+
+Empty map literal `{}` is not supported to avoid ambiguity with blocks/lambdas. Use `Map()` for an empty map.
+
+Lambda disambiguation
+- A `{ ... }` with typed lambda parameters must have a top-level `->` in its header. The compiler disambiguates by looking for a top-level `->`. If none is found, it attempts to parse a map literal; if that fails, it is parsed as a lambda or block.
+
+Grammar (EBNF)
+
+```
+ws                    = zero or more whitespace (incl. newline/comments)
+map_literal           = '{' ws map_entries ws '}'
+map_entries           = map_entry ( ws ',' ws map_entry )* ( ws ',' )?
+map_entry             = map_key ws ':' ws map_value_opt
+                      | '...' ws expression
+map_key               = string_literal | ID
+map_value_opt         = expression | ε   // ε allowed only if map_key is ID
+```
+
+Notes:
+- Identifier shorthand (`id:`) is allowed only for identifiers, not string-literal keys.
+- Spreads accept any expression; at runtime it must yield a `Map` with string keys.
+- Duplicate keys are detected at compile time among literal keys; spreads are merged at runtime with last-wins.
+
+Rationale
+- The `{ name: value }` style is familiar and ergonomic.
+- Disambiguation with lambdas leverages the required `->` in typed lambda headers.
+- Avoiding `m.a` sidesteps method/field shadowing and keeps semantics clear.
+

archived/proposals/named_args.md

@@ -0,0 +1,70 @@
+# Named arguments in calls
+
+[//]: # (excludeFromIndex)
+
+
+Extend function/method calls to allow setting arguments by name using colon syntax at call sites. This is especially convenient with many parameters and default values.
+
+Examples:
+
+```lyng
+    fun test(a="foo", b="bar", c="bazz") { [a, b, c] }
+
+    assertEquals(test(b: "b"), ["foo", "b", "bazz"])
+    assertEquals(test("a", c: "c"), ["a", "bar", "c"])
+```
+
+Rules:
+
+- Named arguments are optional. If named arguments are present, their order is not important.
+- Named arguments must follow positional arguments; positional arguments cannot follow named ones (the only exception is the syntactic trailing block outside parentheses, see below).
+- A named argument cannot reassign a parameter already set positionally.
+- If the last parameter is already assigned by a named argument (or named splat), the trailing-lambda rule must NOT apply: a following `{ ... }` after the call is an error.
+
+Rationale for using `:` instead of `=` in calls: in Lyng, assignment `=` is an expression; using `:` avoids ambiguity and keeps declarations (`name: Type`) distinct from call sites, where casting uses `as` / `as?`.
+
+Migration note: earlier drafts/examples used `name = value`. The final syntax is `name: value` at call sites.
+
+## Extended call argument splats: named splats
+
+With named arguments, splats (`...`) are extended to support maps as named splats. When a splat evaluates to a Map, its entries provide name→value assignments:
+
+```lyng
+    fun test(a="a", b="b", c="c", d="d") { [a, b, c, d] }
+
+    assertEquals(test("A?", ...Map("d" => "D!", "b" => "B!")), ["A?", "B!", "c", "D!"])
+```
+
+Constraints for named splats:
+
+- Only string keys are allowed in map splats; otherwise, a clean error is thrown.
+- Named splats cannot reassign parameters already set (positionally or by earlier named arguments/splats).
+- Named splats follow the same ordering as named arguments: they must appear after all positional arguments and positional splats.
+
+## Trailing-lambda interaction
+
+Lyng supports a syntactic trailing block after a call: `f(args) { ... }`. With named args/splats, if the last parameter is already assigned by name, the trailing block must not apply and the call is an error:
+
+```lyng
+    fun f(x, onDone) { onDone(x) }
+    f(x: 1) { 42 }    // ERROR: last parameter already assigned by name
+    f(1) { 42 }       // OK
+```
+
+## Errors (non-exhaustive)
+
+- Positional argument after any named argument inside parentheses: error.
+- Positional splat after any named argument: error.
+- Duplicate named assignment (directly or via map splats): error.
+- Unknown parameter name in a named argument/splat: error.
+- Map splat with non-string keys: error.
+- Attempt to target the ellipsis parameter by name: error.
+
+## Notes
+
+- Declarations continue to use `:` for types, while call sites use `:` for named arguments and `as` / `as?` for type casts/checks.
+
+
+
+
+

bin/deploy_all

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+#
+# Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+#
+
+set -e
+echo "publishing all artifacts"
+echo
+./gradlew publishToMavenLocal
+./gradlew publish
+
+echo
+echo "Creating plugin"
+echo
+./gradlew buildInstallablePlugin
+
+echo
+echo "building CLI tools"
+echo
+bin/local_jrelease
+bin/local_release
+
+echo
+echo "Deploying site"
+echo
+./bin/deploy_site

bin/deploy_plugin

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+#
+# Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+#
+
+set -e
+
+echo
+echo "Creating plugin"
+echo
+./gradlew buildInstallablePlugin
+deploy_site -u

bin/deploy_site

@@ -0,0 +1,189 @@
+#!/bin/bash
+
+#
+# Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+#
+
+upload_only=false
+for arg in "$@"; do
+  if [[ "$arg" == "-u" || "$arg" == "--upload-only" ]]; then
+    upload_only=true
+    break
+  fi
+done
+
+function checkState() {
+  if [[ $? != 0 ]]; then
+    echo
+    echo -- rsync failed. deploy was not finished. deployed version has not been affected
+    echo
+    exit 100
+  fi
+}
+
+
+
+# Update docs/idea_plugin.md to point to the latest built IDEA plugin zip
+# from ./distributables before building the site. The change is temporary and
+# the original file is restored right after the build.
+DOC_IDEA_PLUGIN="docs/idea_plugin.md"
+DOC_IDEA_PLUGIN_BACKUP="${DOC_IDEA_PLUGIN}.deploy_backup"
+
+function updateIdeaPluginDownloadLink() {
+  if [[ ! -f "$DOC_IDEA_PLUGIN" ]]; then
+    echo "WARN: $DOC_IDEA_PLUGIN not found; skipping plugin link update"
+    return 0
+  fi
+
+  # Find the most recently modified plugin zip
+  local latest
+  latest=$(ls -t distributables/lyng-idea-*.zip 2>/dev/null | head -n 1)
+  if [[ -z "$latest" ]]; then
+    echo "WARN: no distributables/lyng-idea-*.zip found; leaving $DOC_IDEA_PLUGIN unchanged"
+    return 0
+  fi
+
+  local base
+  base=$(basename "$latest")
+  local version
+  version="${base#lyng-idea-}"
+  version="${version%.zip}"
+  local url
+  url="https://lynglang.com/distributables/${base}"
+  local newline
+  newline="### [Download plugin v${version}](${url})"
+
+  # Backup and rewrite the specific markdown line if present
+  cp "$DOC_IDEA_PLUGIN" "$DOC_IDEA_PLUGIN_BACKUP" || {
+    echo "ERROR: can't backup $DOC_IDEA_PLUGIN"; return 1; }
+
+  # Replace the line that starts with the download header; if not found, append it
+  awk -v repl="$newline" 'BEGIN{done=0} \
+    /^### \[Download plugin v/ { print repl; done=1; next } \
+    { print } \
+    END { if (done==0) exit 42 }' "$DOC_IDEA_PLUGIN_BACKUP" > "$DOC_IDEA_PLUGIN"
+
+  local rc=$?
+  if [[ $rc -eq 42 ]]; then
+    echo "WARN: download link not found in $DOC_IDEA_PLUGIN; appending generated link"
+    echo >> "$DOC_IDEA_PLUGIN"
+    echo "$newline" >> "$DOC_IDEA_PLUGIN"
+  elif [[ $rc -ne 0 ]]; then
+    echo "ERROR: failed to update $DOC_IDEA_PLUGIN; restoring original"
+    mv -f "$DOC_IDEA_PLUGIN_BACKUP" "$DOC_IDEA_PLUGIN" 2>/dev/null
+    return 1
+  fi
+}
+
+# default target settings
+case "com" in
+  com)
+    SSH_HOST=sergeych@d.lynglang.com # host to deploy to
+    SSH_PORT=22                             # ssh port on it
+    ROOT=/bigstore/sergeych_pub/lyng                 # directory to rsync to
+    ;;
+#  com)
+#    SSH_HOST=vvk@front-01.neurodatalab.com
+#    ROOT=/home/vvk
+#    ;;
+  *)
+    echo "*** ERROR: target not specified (use deploy com | dev)"
+    echo "*** stop"
+    exit 101
+esac
+
+die() { echo "ERROR: $*" 1>&2 ; exit 1; }
+
+function refreshTextmateZip() {
+  echo "Refreshing distributables/lyng-textmate.zip from editors/..."
+  mkdir -p distributables
+  # We use -r for recursive and -q for quiet (optional)
+  # -j can be used if we want to junk paths, but the request says "contents of editors/"
+  # usually we want to preserve the structure inside editors/
+  (cd editors && zip -rq ../distributables/lyng-textmate.zip .)
+}
+
+
+if [[ "$upload_only" == false ]]; then
+  # Update the IDEA plugin download link in docs (temporarily), then build, then restore the doc
+  refreshTextmateZip
+  updateIdeaPluginDownloadLink || echo "WARN: proceeding without updating IDEA plugin download link"
+
+  ./gradlew site:jsBrowserDistribution
+  BUILD_RC=$?
+
+  # Always restore original doc if backup exists
+  if [[ -f "$DOC_IDEA_PLUGIN_BACKUP" ]]; then
+    mv -f "$DOC_IDEA_PLUGIN_BACKUP" "$DOC_IDEA_PLUGIN"
+  fi
+
+  if [[ $BUILD_RC -ne 0 ]]; then
+    echo
+    echo -- build failed. deploy aborted.
+    echo
+    exit 100
+  fi
+fi
+
+# Prepare working dir
+ssh -p ${SSH_PORT} ${SSH_HOST} "
+  cd ${ROOT}
+  rm -rd build 2>/dev/null
+  if [ -d release ]; then
+    echo copying current release
+    cp -r release build
+  else
+    echo creating first release
+    mkdir release
+    mkdir build
+  fi
+";
+
+if [[ "$upload_only" == false ]]; then
+  # sync files
+  SRC=./site/build/dist/js/productionExecutable
+  rsync -e "ssh -p ${SSH_PORT}" -avz -r -d --delete ${SRC}/* ${SSH_HOST}:${ROOT}/build/dist
+  checkState
+  #rsync -e "ssh -p ${SSH_PORT}" -avz  ./static/* ${SSH_HOST}:${ROOT}/build/dist
+  #checkState
+fi
+
+rsync -e "ssh -p ${SSH_PORT}" -avz -r -d --delete distributables/* ${SSH_HOST}:${ROOT}/build/dist/distributables
+checkState
+
+echo
+echo finalizing the deploy...
+ssh -p ${SSH_PORT} ${SSH_HOST} "
+  cd ${ROOT}
+  rm -rd release~
+  mv release release~
+  mv build release
+  cd release
+  # in this project we needn't restart back when we deploy the front
+  #  ~/bin/restart_service
+";
+
+if [[ $? != 0 ]]; then
+  echo
+  echo -- finalization failed. the rease might be corrupt. rolling back is not yet implemented.
+  echo
+  exit 100
+fi
+
+echo
+echo Deploy successful
+echo
+

bin/generate_docs.sh

@@ -0,0 +1,256 @@
+#!/bin/bash
+#
+# Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+#
+
+set -e
+
+# Configuration
+DOCS_DIR="docs"
+OUTPUT_DIR="distributables"
+TEMP_DIR="build/temp_docs"
+MERGED_MD="$TEMP_DIR/merged.md"
+OUTPUT_HTML="$OUTPUT_DIR/lyng_documentation.html"
+
+mkdir -p "$OUTPUT_DIR"
+mkdir -p "$TEMP_DIR"
+
+# Files that should come first in specific order
+PRIORITY_FILES=(
+    "tutorial.md"
+    "OOP.md"
+    "advanced_topics.md"
+    "declaring_arguments.md"
+    "scopes_and_closures.md"
+    "exceptions_handling.md"
+    "when.md"
+    "parallelism.md"
+    "Testing.md"
+)
+
+# Files that should come next (reference)
+REFERENCE_FILES=(
+    "Collection.md"
+    "Iterable.md"
+    "Iterator.md"
+    "List.md"
+    "Set.md"
+    "Map.md"
+    "Array.md"
+    "Buffer.md"
+    "RingBuffer.md"
+    "Range.md"
+    "Real.md"
+    "Regex.md"
+    "math.md"
+    "time.md"
+)
+
+# Files that are about integration/tools
+INTEGRATION_FILES=(
+    "serialization.md"
+    "json_and_kotlin_serialization.md"
+    "embedding.md"
+    "lyng_cli.md"
+    "lyng.io.fs.md"
+    "formatter.md"
+    "EfficientIterables.md"
+)
+
+# Tracking processed files to avoid duplicates
+PROCESSED_PATHS=()
+
+is_excluded() {
+    local full_path="$1"
+    if grep -q "excludeFromIndex" "$full_path"; then
+        return 0 # true in bash
+    fi
+    return 1 # false
+}
+
+process_file() {
+    local rel_path="$1"
+    local full_path="$DOCS_DIR/$rel_path"
+    
+    if [[ ! -f "$full_path" ]]; then
+        return
+    fi
+    
+    if is_excluded "$full_path"; then
+        echo "Skipping excluded: $rel_path"
+        return
+    fi
+
+    # Check for duplicates
+    for p in "${PROCESSED_PATHS[@]}"; do
+        if [[ "$p" == "$rel_path" ]]; then
+            return
+        fi
+    done
+    PROCESSED_PATHS+=("$rel_path")
+
+    echo "Processing: $rel_path"
+    
+    # 1. Add an anchor for the file based on its path
+    local anchor_name=$(echo "$rel_path" | sed 's/\//_/g')
+    echo "<div id=\"$anchor_name\"></div>" >> "$MERGED_MD"
+    echo "" >> "$MERGED_MD"
+    
+    # 2. Append content with fixed links
+    # - [text](file.md) -> [text](#file.md)
+    # - [text](dir/file.md) -> [text](#dir_file.md)
+    # - [text](file.md#anchor) -> [text](#anchor)
+    # - Fix image links: [alt](../images/...) -> [alt](images/...) if needed, but none found yet.
+    
+    cat "$full_path" | \
+    perl -pe 's/\[([^\]]+)\]\(([^)]+)\.md\)/"[$1](#" . ($2 =~ s|\/|_|gr) . ".md)"/ge' | \
+    perl -pe 's/\[([^\]]+)\]\(([^)]+)\.md#([^)]+)\)/[$1](#$3)/g' >> "$MERGED_MD"
+    
+    echo -e "\n\n---\n\n" >> "$MERGED_MD"
+}
+
+# Start with an empty merged file
+echo "% Lyng Language Documentation" > "$MERGED_MD"
+echo "" >> "$MERGED_MD"
+
+# 1. Process priority files
+for f in "${PRIORITY_FILES[@]}"; do
+    process_file "$f"
+done
+
+# 2. Process reference files
+for f in "${REFERENCE_FILES[@]}"; do
+    process_file "$f"
+done
+
+# 3. Process integration files
+for f in "${INTEGRATION_FILES[@]}"; do
+    process_file "$f"
+done
+
+# 4. Process remaining files in docs root
+for f in "$DOCS_DIR"/*.md; do
+    rel_f=${f#"$DOCS_DIR/"}
+    process_file "$rel_f"
+done
+
+# 5. Process remaining files in subdirs (like samples)
+find "$DOCS_DIR" -name "*.md" | sort | while read -r f; do
+    rel_f=${f#"$DOCS_DIR/"}
+    process_file "$rel_f"
+done
+
+echo "Running pandoc to generate $OUTPUT_HTML..."
+
+# Use a basic but clean CSS
+pandoc "$MERGED_MD" -o "$OUTPUT_HTML" \
+    --toc --toc-depth=2 \
+    --standalone \
+    --embed-resources \
+    --metadata title="Lyng Language Documentation" \
+    --css <(echo "
+        body { 
+            font-family: -apple-system, BlinkMacSystemFont, \"Segoe UI\", Helvetica, Arial, sans-serif;
+            line-height: 1.6; 
+            max-width: 1000px; 
+            margin: 0 auto; 
+            padding: 2em; 
+            color: #24292e;
+            background-color: #fff;
+        }
+        code { 
+            background-color: rgba(27,31,35,0.05); 
+            padding: 0.2em 0.4em; 
+            border-radius: 3px; 
+            font-family: SFMono-Regular, Consolas, \"Liberation Mono\", Menlo, monospace;
+            font-size: 85%;
+        }
+        pre { 
+            background-color: #f6f8fa; 
+            padding: 16px; 
+            overflow: auto; 
+            border-radius: 3px;
+            line-height: 1.45;
+        }
+        pre code {
+            background-color: transparent;
+            padding: 0;
+            font-size: 100%;
+        }
+        h1 { 
+            border-bottom: 1px solid #eaecef; 
+            padding-bottom: 0.3em; 
+            margin-top: 24px;
+            margin-bottom: 16px;
+            font-weight: 600;
+        }
+        h2 { 
+            border-bottom: 1px solid #eaecef; 
+            padding-bottom: 0.3em; 
+            margin-top: 24px;
+            margin-bottom: 16px;
+            font-weight: 600;
+        }
+        hr { 
+            height: 0.25em;
+            padding: 0;
+            margin: 24px 0;
+            background-color: #e1e4e8;
+            border: 0;
+        }
+        blockquote {
+            padding: 0 1em;
+            color: #6a737d;
+            border-left: 0.25em solid #dfe2e5;
+            margin: 0 0 16px 0;
+        }
+        nav#TOC { 
+            background: #f9f9f9; 
+            padding: 1em; 
+            border: 1px solid #eee; 
+            margin-bottom: 2.5em; 
+            border-radius: 6px;
+        }
+        nav#TOC ul { 
+            list-style: none; 
+            padding-left: 1.5em; 
+        }
+        nav#TOC > ul {
+            padding-left: 0;
+        }
+        table {
+            border-spacing: 0;
+            border-collapse: collapse;
+            margin-top: 0;
+            margin-bottom: 16px;
+        }
+        table th, table td {
+            padding: 6px 13px;
+            border: 1px solid #dfe2e5;
+        }
+        table tr {
+            background-color: #fff;
+            border-top: 1px solid #c6cbd1;
+        }
+        table tr:nth-child(2n) {
+            background-color: #f6f8fa;
+        }
+    ")
+
+echo "-------------------------------------------------------"
+echo "Done! Documentation generated successfully."
+echo "Location: $OUTPUT_HTML"
+echo "-------------------------------------------------------"

bin/local_release

@@ -25,3 +25,6 @@ file=./lyng/build/bin/linuxX64/releaseExecutable/lyng.kexe
 strip $file
 upx   $file
 cp $file ~/bin/lyng
+cp $file ./distributables/lyng
+zip ./distributables/lyng-linuxX64 ./distributables/lyng
+rm ./distributables/lyng

build.gradle.kts

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,3 +20,18 @@ plugins {
     alias(libs.plugins.kotlinMultiplatform) apply  false
     alias(libs.plugins.vanniktech.mavenPublish) apply false
 }
+
+// Convenience alias to run the IntelliJ IDE with the Lyng plugin from the project root.
+// Usage: ./gradlew runIde
+// It simply delegates to :lyng-idea:runIde provided by the Gradle IntelliJ Plugin.
+tasks.register<org.gradle.api.DefaultTask>("runIde") {
+    group = "intellij"
+    description = "Run IntelliJ IDEA with the Lyng plugin (:lyng-idea)"
+    dependsOn(":lyng-idea:runIde")
+}
+
+tasks.register<Exec>("generateDocs") {
+    group = "documentation"
+    description = "Generates a single-file documentation HTML using bin/generate_docs.sh"
+    commandLine("./bin/generate_docs.sh")
+}

docs/Buffer.md

@@ -23,11 +23,11 @@ There are a lo of ways to construct a buffer:
     assertEquals( 5, Buffer("hello").size )
 
     // from bytes, e.g. integers in range 0..255
-    assertEquals( 255, Buffer(1,2,3,255).last() )
+    assertEquals( 255, Buffer(1,2,3,255).last )
 
     // from whatever iterable that produces bytes, e.g.
     // integers in 0..255 range:
-    assertEquals( 129, Buffer([1,2,129]).last() )
+    assertEquals( 129, Buffer([1,2,129]).last )
 
     // Empty buffer of fixed size:
     assertEquals(100, Buffer(100).size)

docs/Collection.md

@@ -12,7 +12,7 @@ Is a [Iterable] with known `size`, a finite [Iterable]:
 (1)
 : `comparator(a,b)` should return -1 if `a < b`, +1 if `a > b` or zero.
 
-See [List], [Set] and [Iterable]
+See [List], [Set], [Iterable] and [Efficient Iterables in Kotlin Interop](EfficientIterables.md)
 
 [Iterable]: Iterable.md
 [List]: List.md

docs/EfficientIterables.md

@@ -0,0 +1,92 @@
+# Efficient Iterables in Kotlin Interop
+
+Lyng provides high-performance iteration mechanisms that allow Kotlin-side code to interact with Lyng iterables efficiently and vice versa.
+
+## 1. Enumerating Lyng Objects from Kotlin
+
+To iterate over a Lyng object (like a `List`, `Set`, or `Range`) from Kotlin code, use the virtual `enumerate` method:
+
+```kotlin
+val lyngList: Obj = ... 
+lyngList.enumerate(scope) { item ->
+    println("Processing $item")
+    true // return true to continue, false to break
+}
+```
+
+### Why it's efficient:
+- **Zero allocation**: Unlike traditional iterators, it doesn't create a `LyngIterator` object or any intermediate wrappers.
+- **Direct access**: Subclasses like `ObjList` override `enumerate` to iterate directly over their internal Kotlin collections.
+- **Reduced overhead**: It avoids multiple `invokeInstanceMethod` calls for `hasNext()` and `next()` on every step, which would normally involve dynamic dispatch and scope overhead.
+
+## 2. Reactive Enumeration with Flow
+
+If you prefer a reactive approach or need to integrate with Kotlin Coroutines flows, use `toFlow()`:
+
+```kotlin
+lyngList.toFlow(scope).collect { item ->
+    // ...
+}
+```
+*Note: `toFlow()` internally uses the Lyng iterator protocol (`iterator()`, `hasNext()`, `next()`), so it's slightly less efficient than `enumerate()` for performance-critical loops, but more idiomatic for flow-based processing.*
+
+## 3. Creating Efficient Iterables for Lyng in Kotlin
+
+When implementing a custom object in Kotlin that should be iterable in Lyng (e.g., usable in `for (x in myObj) { ... }`), follow these steps to ensure maximum performance.
+
+### A. Inherit from `Obj` and use `ObjIterable`
+Ensure your object's class has `ObjIterable` as a parent so the Lyng compiler recognizes it as an iterable.
+
+```kotlin
+class MyCollection(val items: List<Obj>) : Obj() {
+    override val objClass = MyCollection.type
+
+    companion object {
+        val type = ObjClass("MyCollection", ObjIterable).apply {
+            // Provide a Lyng-side iterator for compatibility with 
+            // manual iterator usage in Lyng scripts.
+            // Using ObjKotlinObjIterator if items are already Obj instances:
+            addFn("iterator") { 
+                ObjKotlinObjIterator(thisAs<MyCollection>().items.iterator()) 
+            }
+        }
+    }
+}
+```
+
+### B. Override `enumerate` for Maximum Performance
+The Lyng compiler's `for` loops use the `enumerate` method. By overriding it in your Kotlin class, you provide a "fast path" for iteration.
+
+```kotlin
+class MyCollection(val items: List<Obj>) : Obj() {
+    // ...
+    override suspend fun enumerate(scope: Scope, callback: suspend (Obj) -> Boolean) {
+        for (item in items) {
+            // If callback returns false, it means 'break' was called in Lyng
+            if (!callback(item)) break
+        }
+    }
+}
+```
+
+### C. Use `ObjInt.of()` for Numeric Data
+If your iterable contains integers, always use `ObjInt.of(Long)` instead of the `ObjInt(Long)` constructor. Lyng maintains a cache for small integers (-128 to 127), which significantly reduces object allocations and GC pressure during tight loops.
+
+```kotlin
+// Efficiently creating an integer object
+val obj = ObjInt.of(42L) 
+
+// Or using extension methods which also use the cache:
+val obj2 = 42.toObj()
+val obj3 = 42L.toObj()
+```
+
+#### Note on `toObj()` extensions:
+While `<reified T> T.toObj()` is convenient, using specific extensions like `Int.toObj()` or `Long.toObj()` is slightly more efficient as they use the `ObjInt` cache.
+
+## 4. Summary of Best Practices
+
+- **To Consume**: Use `enumerate(scope) { item -> ... true }`.
+- **To Implement**: Override `enumerate` in your `Obj` subclass.
+- **To Register**: Use `ObjIterable` (or `ObjCollection`) as a parent class in your `ObjClass` definition.
+- **To Optimize**: Use `ObjInt.of()` (or `.toObj()`) for all integer object allocations.

docs/Iterable.md

@@ -40,13 +40,13 @@ available, for example
 ## joinToString
 
 This methods convert any iterable to a string joining string representation of each element, optionally transforming it
-and joining using specified suffix.
+and joining using specified separator.
 
-    Iterable.joinToString(suffux=' ', transform=null)
+    Iterable.joinToString(separator=' ', transformer=null)
 
 - if `Iterable` `isEmpty`, the empty string `""` is returned.
-- `suffix` is inserted between items when there are more than one.
-- `transform` of specified is applied to each element, otherwise its `toString()` method is used.
+- `separator` is inserted between items when there are more than one.
+- `transformer` of specified is applied to each element, otherwise its `toString()` method is used.
 
 Here is the sample:
 
@@ -55,7 +55,7 @@ Here is the sample:
     assertEquals( (1..3).joinToString { it * 10 }, "10 20 30")
     >>> void
 
-## `sum` and `sumBy`
+## `sum` and `sumOf`
 
 These, again, does the thing:
 
@@ -68,6 +68,80 @@ These, again, does the thing:
 
     >>> void
 
+## map, filter and their variations
+
+Used to transform or filter the whole iterable stream:
+
+    val source = [1,2,3,4]
+    
+    // map: transform every element to something else
+    assertEquals(["n1", "n2", "n3", "n4"], source.map { "n"+it } )
+    
+    // filter: keep only elements matching the predicate
+    assertEquals([2, 4], source.filter { it % 2 == 0 } )
+
+    // count: count elements matching the predicate
+    assertEquals(2, source.count { it % 2 == 0 } )
+
+    // mapNotNull: transform every element, skipping null results:
+    assertEquals(["n1", "n2", "n4"], source.mapNotNull { if( it == 3 ) null else "n"+it } )
+    
+    // filterNotNull: skip all null elements:
+    assertEquals([1, 2, 4], [1, 2, null, 4].filterNotNull())
+
+    >>> void
+
+You can also use flow variations that return a cold `Flow` instead of a `List`, which is useful for large or infinite sequences:
+
+    val source = [1, 2, 3, 4]
+    
+    // filterFlow: returns a Flow of filtered elements
+    assert( source.filterFlow { it % 2 == 0 } is Flow )
+    
+    // filterFlowNotNull: returns a Flow of non-null elements
+    assert( [1, null, 2].filterFlowNotNull() is Flow )
+    
+    >>> void
+
+## minOf and maxOf
+
+Find the minimum or maximum value of a function applied to each element:
+
+    val source = ["abc", "de", "fghi"]
+    assertEquals(2, source.minOf { it.length })
+    assertEquals(4, source.maxOf { it.length })
+    >>> void
+
+## flatten and flatMap
+
+Work with nested collections:
+
+    val nested = [[1, 2], [3, 4]]
+    
+    // flatten: combine nested collections into one list
+    assertEquals([1, 2, 3, 4], nested.flatten())
+    
+    // flatMap: map each element to a collection and flatten the result
+    assertEquals([1, 10, 2, 20], [1, 2].flatMap { [it, it*10] })
+    
+    >>> void
+
+## findFirst and findFirstOrNull
+
+Search for the first element that satisfies the given predicate:
+
+    val source = [1, 2, 3, 4]
+    assertEquals( 2, source.findFirst { it % 2 == 0 } )
+    assertEquals( 2, source.findFirstOrNull { it % 2 == 0 } )
+    
+    // findFirst throws if not found:
+    assertThrows( NoSuchElementException ) { source.findFirst { it > 10 } }
+    
+    // findFirstOrNull returns null if not found:
+    assertEquals( null, source.findFirstOrNull { it > 10 } )
+    
+    >>> void
+
 ## Instance methods:
 
 | fun/method             | description                                                                     |
@@ -75,52 +149,56 @@ These, again, does the thing:
 | toList()               | create a list from iterable                                                     |
 | toSet()                | create a set from iterable                                                      |
 | contains(i)            | check that iterable contains `i`                                                |
-| `i in iterator`        | same as `contains(i)`                                                           |
+| `i in iterable`        | same as `contains(i)`                                                           |
 | isEmpty()              | check iterable is empty                                                         |
 | forEach(f)             | call f for each element                                                         |
 | toMap()                | create a map from list of key-value pairs (arrays of 2 items or like)           |
+| any(p)                 | true if any element matches predicate `p`                        |
+| all(p)                 | true if all elements match predicate `p`                         |
 | map(f)                 | create a list of values returned by `f` called for each element of the iterable |
 | indexOf(i)             | return index if the first encounter of i or a negative value if not found       |
 | associateBy(kf)        | create a map where keys are returned by kf that will be called for each element |
+| filter(p)              | create a list of elements matching predicate `p`                |
+| count(p)               | count elements matching predicate `p`                            |
+| filterFlow(p)          | create a [Flow] of elements matching predicate `p`               |
+| filterNotNull()        | create a list of non-null elements                               |
+| filterFlowNotNull()    | create a [Flow] of non-null elements                             |
+| minOf(f)               | return minimum value of `f` applied to elements                  |
+| maxOf(f)               | return maximum value of `f` applied to elements                  |
+| flatten()              | flatten nested collections into a single [List]                  |
+| flatMap(f)             | map each element with `f` and flatten results into a [List]      |
+| findFirst(p)           | return first element matching predicate `p` or throw (1)         |
+| findFirstOrNull(p)     | return first element matching predicate `p` or `null`                            |
 | first                  | first element (1)                                                               |
 | last                   | last element (1)                                                                |
 | take(n)                | return [Iterable] of up to n first elements                                     |
-| taleLast(n)            | return [Iterable] of up to n last elements                                      |
+| takeLast(n)            | return [Iterable] of up to n last elements                                      |
 | drop(n)                | return new [Iterable] without first n elements                                  |
 | dropLast(n)            | return new [Iterable] without last n elements                                   |
 | sum()                  | return sum of the collection applying `+` to its elements (3)                   |
-| sumOf(predicate)       | sum of the modified collection items (3)                                        |
+| sumOf(f)               | sum of the modified collection items (3)                                        |
 | sorted()               | return [List] with collection items sorted naturally                            |
 | sortedWith(comparator) | sort using a comparator that compares elements (1)                              |
 | sortedBy(predicate)    | sort by comparing results of the predicate function                             |
 | joinToString(s,t)      | convert iterable to string, see (2)                                             |
 | reversed()             | create a list containing items from this in reverse order                       |
-| shuffled()             | create a listof shiffled elements                                               |
+| shuffled()             | create a list of shuffled elements                                              |
 
 (1)
-: throws `NoSuchElementException` if there is no such element
+:: throws `NoSuchElementException` if there is no such element
 
 (2)
-: `joinToString(suffix=" ",transform=null)`: suffix is inserted between items if there are more than one, trasnfom is
+:: `joinToString(separator=" ", transformer=null)`: separator is inserted between items if there are more than one, transformer is
 optional function applied to each item that must return result string for an item, otherwise `item.toString()` is used.
 
 (3)
-: sum of empty collection is `null`
-
-    fun Iterable.toList(): List
-    fun Iterable.toSet(): Set
-    fun Iterable.indexOf(element): Int
-    fun Iterable.contains(element): Bool
-    fun Iterable.isEmpty(element): Bool
-    fun Iterable.forEach(block: (Any?)->Void ): Void
-    fun Iterable.map(block: (Any?)->Void ): List
-    fun Iterable.associateBy( keyMaker: (Any?)->Any): Map
+:: sum of empty collection is `null`
 
 ## Abstract methods:
 
     fun iterator(): Iterator
 
-Creates a list by iterating to the end. So, the Iterator should be finite to be used with it.
+For high-performance Kotlin-side interop and custom iterable implementation details, see [Efficient Iterables in Kotlin Interop](EfficientIterables.md).
 
 ## Included in interfaces:
 
@@ -134,6 +212,8 @@ Creates a list by iterating to the end. So, the Iterator should be finite to be
 
 [List]: List.md
 
+[Flow]: parallelism.md#flow
+
 [Range]: Range.md
 
 [Set]: Set.md

docs/Iterator.md

@@ -9,6 +9,9 @@ To implement the iterator you need to implement only two abstract methods:
 
 ### hasNext(): Bool
 
+    // lets test
+    // offset
+
 Should return `true` if call to `next()` will return valid next element.
 
 ### next(): Obj
@@ -20,6 +23,8 @@ must throw `ObjIterationFinishedError`.
 
 Iterators are returned when implementing [Iterable] interface.
 
+For high-performance Kotlin-side interop and custom iterable implementation details, see [Efficient Iterables in Kotlin Interop](EfficientIterables.md).
+
 ## Implemented for classes:
 
 - [List], [Range]

docs/List.md

@@ -92,6 +92,34 @@ Open end ranges remove head and tail elements:
     assert( [1, 2, 3] !== [1, 2, 3])
     >>> void
 
+## Destructuring
+
+Lists can be used as L-values for destructuring assignments. This allows you to unpack list elements into multiple variables.
+
+### Basic Destructuring
+```lyng
+val [a, b, c] = [1, 2, 3]
+```
+
+### With Splats (Variadic)
+A single ellipsis `...` can be used to capture remaining elements into a list. It can be placed at the beginning, middle, or end of the pattern.
+```lyng
+val [head, rest...] = [1, 2, 3] // head=1, rest=[2, 3]
+val [first, middle..., last] = [1, 2, 3, 4, 5] // first=1, middle=[2, 3, 4], last=5
+```
+
+### Nested Patterns
+Destructuring patterns can be nested to unpack multi-dimensional lists.
+```lyng
+val [a, [b, c...], d] = [1, [2, 3, 4], 5]
+```
+
+### Reassignment
+Destructuring can also be used to reassign existing variables:
+```lyng
+[x, y] = [y, x] // Swap values
+```
+
 ## In-place sort
 
 List could be sorted in place, just like [Collection] provide sorted copies, in a very like way:
@@ -130,7 +158,8 @@ List could be sorted in place, just like [Collection] provide sorted copies, in
 | `sort()`                      | in-place sort, natural order                 | void        |
 | `sortBy(predicate)`           | in-place sort bu `predicate` call result (3) | void        |
 | `sortWith(comparator)`        | in-place sort using `comarator` function (4) | void        |
-| `shiffle()`                   | in-place shiffle contents                    |             |
+| `shuffle()`                   | in-place shuffle contents                    |             |
+| `toString()`                 | string representation like `[a,b,c]`         |             |
 
 (1)
 : optimized implementation that override `Array` one

docs/Map.md

@@ -1,19 +1,22 @@
 # Map
 
-Map is a mutable collection of key-value pars, where keys are unique. Maps could be created with
-constructor or `.toMap` methods. When constructing from a list, each list item must be a [Collection] with exactly 2 elements, for example, a [List].
+Map is a mutable collection of key-value pairs, where keys are unique. You can create maps in two ways:
+- with the constructor `Map(...)` or `.toMap()` helpers; and
+- with map literals using braces: `{ "key": value, id: expr, id: }`.
+
+When constructing from a list, each list item must be a [Collection] with exactly 2 elements, for example, a [List].
 
 Important thing is that maps can't contain `null`: it is used to return from missing elements.
 
-Constructed map instance is of class `Map` and implements `Collection` (and therefore `Iterable`)
+Constructed map instance is of class `Map` and implements `Collection` (and therefore `Iterable`).
 
-    val map = Map( "foo" => 1, "bar" => "buzz" )
-    assert(map is Map)
-    assert(map.size == 2)
-    assert(map is Iterable)
+    val oldForm = Map( "foo" => 1, "bar" => "buzz" )
+    assert(oldForm is Map)
+    assert(oldForm.size == 2)
+    assert(oldForm is Iterable)
     >>> void
 
-Notice usage of the `=>` operator that creates `MapEntry`, which implements also [Collection] of
+Notice usage of the `=>` operator that creates `MapEntry`, which also implements [Collection] of
 two items, first, at index zero, is a key, second, at index 1, is the value. You can use lists too.
 Map keys could be any objects (hashable, e.g. with reasonable hashCode, most of standard types are). You can access elements with indexing operator:
 
@@ -29,6 +32,36 @@ Map keys could be any objects (hashable, e.g. with reasonable hashCode, most of
     assert( map["foo"] == -1)
     >>> void
 
+## Map literals { ... }
+
+Lyng supports JavaScript-like map literals. Keys can be string literals or identifiers, and there is a handy identifier shorthand:
+
+- String key: `{ "a": 1 }`
+- Identifier key: `{ foo: 2 }` is the same as `{ "foo": 2 }`
+- Identifier shorthand: `{ foo: }` is the same as `{ "foo": foo }`
+
+Access uses brackets: `m["a"]`.
+
+    val x = 10
+    val y = 10
+    val m = { "a": 1, x: x * 2, y: }
+    assertEquals(1, m["a"])      // string-literal key
+    assertEquals(20, m["x"])     // identifier key
+    assertEquals(10, m["y"])     // identifier shorthand expands to y: y
+    >>> void
+
+Trailing commas are allowed for nicer diffs and multiline formatting:
+
+    val m = {
+        "a": 1,
+        b: 2,
+    }
+    assertEquals(1, m["a"]) 
+    assertEquals(2, m["b"]) 
+    >>> void
+
+Empty `{}` is reserved for blocks/lambdas; use `Map()` for an empty map.
+
 To remove item from the collection. use `remove`. It returns last removed item or null. Be careful if you 
 hold nulls in the map - this is not a recommended practice when using `remove` returned value. `clear()` 
 removes all.
@@ -110,4 +143,36 @@ is equal.
     assert( m1 != m3 )
     >>> void
 
+## Spreads and merging
+
+Inside map literals you can spread another map with `...` and items will be merged left-to-right; rightmost wins:
+
+    val base = { a: 1, b: 2 }
+    val m = { a: 0, ...base, b: 3, c: 4 }
+    assertEquals(1, m["a"])  // base overwrites a:0
+    assertEquals(3, m["b"])  // literal overwrites spread
+    assertEquals(4, m["c"])  // new key
+    >>> void
+
+Maps and entries can also be merged with `+` and `+=`:
+
+    val m1 = ("x" => 1) + ("y" => 2)
+    assertEquals(1, m1["x"])
+    assertEquals(2, m1["y"])
+
+    val m2 = { "a": 10 } + ("b" => 20)
+    assertEquals(10, m2["a"])
+    assertEquals(20, m2["b"])
+
+    var m3 = { a: 1 }
+    m3 += ("b" => 2)
+    assertEquals(1, m3["a"])
+    assertEquals(2, m3["b"])
+    >>> void
+
+Notes:
+- Map literals always use string keys (identifier keys are converted to strings).
+- Spreads inside map literals and `+`/`+=` merges allow any objects as keys.
+- When you need computed or non-string keys, use the constructor form `Map(...)`, map literals with computed keys (if supported), or build entries with `=>` and then merge.
+
 [Collection](Collection.md)

docs/OOP.md

@@ -1,6 +1,10 @@
-# OO implementation in Lyng
+# Object-oriented programming
 
-## Declaration 
+[//]: # (topMenu)
+
+Lyng supports first class OOP constructs, based on classes with multiple inheritance.
+
+## Class Declaration 
 
 The class clause looks like
 
@@ -38,6 +42,229 @@ a _constructor_ that requires two parameters for fields. So when creating it wit
 Form now on `Point` is a class, it's type is `Class`, and we can create instances with it as in the
 example above.
 
+## Singleton Objects
+
+Singleton objects are declared using the `object` keyword. An `object` declaration defines both a class and a single instance of that class at the same time. This is perfect for stateless utilities, global configuration, or shared delegates.
+
+```lyng
+object Config {
+    val version = "1.0.0"
+    val debug = true
+    
+    fun printInfo() {
+        println("App version: " + version)
+    }
+}
+
+// Usage:
+println(Config.version)
+Config.printInfo()
+```
+
+Objects can also inherit from classes or interfaces:
+
+```lyng
+object DefaultLogger : Logger("Default") {
+    override fun log(msg) {
+        println("[DEFAULT] " + msg)
+    }
+}
+```
+
+## Object Expressions
+
+Object expressions allow you to create an instance of an anonymous class. This is useful when you need to provide a one-off implementation of an interface or inherit from a class without declaring a new named subclass.
+
+```lyng
+val worker = object : Runnable {
+    override fun run() {
+        println("Working...")
+    }
+}
+```
+
+Object expressions can implement multiple interfaces and inherit from one class:
+
+```lyng
+val x = object : Base(arg1), Interface1, Interface2 {
+    val property = 42
+    override fun method() = property * 2
+}
+```
+
+### Scoping and `this@object`
+
+Object expressions capture their lexical scope, meaning they can access local variables and members of the outer class. When `this` is rebound (for example, inside an `apply` block), you can use the reserved alias `this@object` to refer to the innermost anonymous object instance.
+
+```lyng
+val handler = object {
+    fun process() {
+        this@object.apply {
+            // here 'this' is rebound to the map/context
+            // but we can still access the anonymous object via this@object
+            println("Processing in " + this@object)
+        }
+    }
+}
+```
+
+### Serialization and Identity
+
+- **Serialization**: Anonymous objects are **not serializable**. Attempting to encode an anonymous object via `Lynon` will throw a `SerializationException`. This is because their class definition is transient and cannot be safely restored in a different session or process.
+- **Type Identity**: Every object expression creates a unique anonymous class. Two identical object expressions will result in two different classes with distinct type identities.
+
+## Properties
+
+Properties allow you to define member accessors that look like fields but execute code when read or written. Unlike regular fields, properties in Lyng do **not** have automatic backing fields; they are pure accessors.
+
+### Basic Syntax
+
+Properties are declared using `val` (read-only) or `var` (read-write) followed by a name and a `get` (and optionally `set`) accessor. Unlike fields, properties do not have automatic storage and must compute their values or delegate to other members.
+
+The standard syntax uses parentheses:
+```lyng
+class Person(private var _age: Int) {
+    // Read-only property
+    val ageCategory 
+        get() {
+            if (_age < 18) "Minor" else "Adult"
+        }
+
+    // Read-write property
+    var age: Int
+        get() { _age }
+        set(value) {
+            if (value >= 0) _age = value
+        }
+}
+```
+
+### Laconic Syntax (Optional Parentheses)
+
+For even cleaner code, you can omit the parentheses for `get` and `set`. This is especially useful for simple expression shorthand:
+
+```lyng
+class Circle(val radius: Real) {
+    // Laconic expression shorthand
+    val area get = π * radius * radius
+    val circumference get = 2 * π * radius
+    
+    fun diameter() = radius * 2
+}
+
+fun median(a, b) = (a + b) / 2
+
+class Counter {
+    private var _count = 0
+    var count get = _count set(v) = _count = v
+}
+```
+
+### Key Rules
+
+- **`val` properties** must have a `get` accessor (with or without parentheses) and cannot have a `set`.
+- **`var` properties** must have both `get` and `set` accessors.
+- **Functions and methods** can use the `=` shorthand to return the result of a single expression.
+- **`override` is mandatory**: If you are overriding a member from a base class, you MUST use the `override` keyword.
+- **No Backing Fields**: There is no magic `field` identifier. If you need to store state, you must declare a separate (usually `private`) field.
+- **Type Inference**: You can omit the type declaration if it can be inferred or if you don't need strict typing.
+
+### Lazy Properties with `cached`
+
+When you want to define a property that is computed only once (on demand) and then remembered, use the built-in `cached` function. This is more efficient than a regular property with `get()` if the computation is expensive, as it avoids re-calculating the value on every access.
+
+```lyng
+class DataService(val id: Int) {
+    // The lambda passed to cached is only executed once, the first time data() is called.
+    val data = cached {
+        println("Fetching data for " + id)
+        // Perform expensive operation
+        "Record " + id
+    }
+}
+
+val service = DataService(42)
+// No printing yet
+println(service.data()) // Prints "Fetching data for 42", then returns "Record 42"
+println(service.data()) // Returns "Record 42" immediately (no second fetch)
+```
+
+Note that `cached` returns a lambda, so you access the value by calling it like a method: `service.data()`. This is a powerful pattern for lazy-loading resources, caching results of database queries, or delaying expensive computations until they are truly needed.
+
+## Delegation
+
+Delegation allows you to hand over the logic of a property or function to another object. This is done using the `by` keyword.
+
+### Property Delegation
+
+Instead of providing `get()` and `set()` accessors, you can delegate them to an object that implements the `getValue` and `setValue` methods.
+
+```lyng
+class User {
+    var name by MyDelegate()
+}
+```
+
+### Function Delegation
+
+You can also delegate a whole function to an object. When the function is called, it will invoke the delegate's `invoke` method.
+
+```lyng
+fun remoteAction by RemoteProxy("actionName")
+```
+
+### The Unified Delegate Interface
+
+A delegate is any object that provides the following methods (all optional depending on usage):
+
+- `getValue(thisRef, name)`: Called when a delegated `val` or `var` is read.
+- `setValue(thisRef, name, newValue)`: Called when a delegated `var` is written.
+- `invoke(thisRef, name, args...)`: Called when a delegated `fun` is invoked.
+- `bind(name, access, thisRef)`: Called once during initialization to configure or validate the delegate.
+
+### Map as a Delegate
+
+Maps can also be used as delegates. When delegated to a property, the map uses the property name as the key:
+
+```lyng
+val settings = { "theme": "dark", "fontSize": 14 }
+val theme by settings
+var fontSize by settings
+
+println(theme)    // "dark"
+fontSize = 16     // Updates settings["fontSize"]
+```
+
+For more details and advanced patterns (like `lazy`, `observable`, and shared stateless delegates), see the [Delegation Guide](delegation.md).
+
+## Instance initialization: init block
+
+In addition to the primary constructor arguments, you can provide an `init` block that runs on each instance creation. This is useful for more complex initializations, side effects, or setting up fields that depend on multiple constructor parameters.
+
+    class Point(val x, val y) {
+       var magnitude
+       
+       init {
+          magnitude = Math.sqrt(x*x + y*y)
+       }
+    }
+
+Key features of `init` blocks:
+- **Scope**: They have full access to `this` members and all primary constructor parameters.
+- **Order**: In a single-inheritance scenario, `init` blocks run immediately after the instance fields are prepared but before the primary constructor body logic.
+- **Multiple blocks**: You can have multiple `init` blocks; they will be executed in the order they appear in the class body.
+
+### Initialization in Multiple Inheritance
+
+In cases of multiple inheritance, `init` blocks are executed following the constructor chaining rule:
+1. All ancestors are initialized first, following the inheritance hierarchy (diamond-safe: each ancestor is initialized exactly once).
+2. The `init` blocks of each class are executed after its parents have been fully initialized.
+3. For a hierarchy `class D : B, C`, the initialization order is: `B`'s chain, then `C`'s chain (skipping common ancestors with `B`), and finally `D`'s own `init` blocks.
+
+### Initialization during Deserialization
+
+When an object is restored from a serialized form (e.g., using `Lynon`), `init` blocks are **re-executed**. This ensures that transient state or derived fields are correctly recalculated upon restoration. However, primary constructors are **not** re-called during deserialization; only the `init` blocks and field initializers are executed to restore the instance state.
+
 Class point has a _method_, or a _member function_ `length()` that uses its _fields_ `x` and `y` to
 calculate the magnitude. Length is called
 
@@ -49,8 +276,58 @@ statements discussed later, there could be default values, ellipsis, etc.
     class Point(x=0,y=0) 
     val p = Point()
     assert( p.x == 0 && p.y == 0 )
+    
+    // Named arguments in constructor calls use colon syntax:
+    val p2 = Point(y: 10, x: 5)
+    assert( p2.x == 5 && p2.y == 10 )
+    
+    // Auto-substitution shorthand for named arguments:
+    val x = 1
+    val y = 2
+    val p3 = Point(x:, y:)
+    assert( p3.x == 1 && p3.y == 2 )
     >>> void
 
+Note that unlike **Kotlin**, which uses `=` for named arguments, Lyng uses `:` to avoid ambiguity with assignment expressions.
+
+### Late-initialized `val` fields
+
+You can declare a `val` field without an immediate initializer if you provide an assignment for it within an `init` block or the class body. This is useful when the initial value depends on logic that cannot be expressed in a single expression.
+
+```lyng
+class DataProcessor(data: Object) {
+    val result: Object
+    
+    init {
+        // Complex initialization logic
+        result = transform(data)
+    }
+}
+```
+
+Key rules for late-init `val`:
+- **Compile-time Check**: The compiler ensures that every `val` declared without an initializer in a class body has at least one assignment within that class body (including `init` blocks). Failing to do so results in a syntax error.
+- **Write-Once**: A `val` can only be assigned once. Even if it was declared without an initializer, once it is assigned a value (e.g., in `init`), any subsequent assignment will throw an `IllegalAssignmentException`.
+- **Access before Initialization**: If you attempt to read a late-init `val` before it has been assigned (for example, by calling a method in `init` that reads the field before its assignment), it will hold a special `Unset` value. Using `Unset` for most operations (like arithmetic or method calls) will throw an `UnsetException`.
+- **No Extensions**: Extension properties do not support late initialization as they do not have per-instance storage. Extension `val`s must always have an initializer or a `get()` accessor.
+
+### The `Unset` singleton
+
+The `Unset` singleton represents a field that has been declared but not yet initialized. While it can be compared and converted to a string, most other operations on it are forbidden to prevent accidental use of uninitialized data.
+
+```lyng
+class T {
+    val x
+    fun check() {
+        if (x == Unset) println("Not ready")
+    }
+    init {
+        check() // Prints "Not ready"
+        x = 42
+    }
+}
+```
+
 ## Methods
 
 Functions defined inside a class body are methods, and unless declared
@@ -71,6 +348,393 @@ Functions defined inside a class body are methods, and unless declared
     void
     >>> void
 
+## Multiple Inheritance (MI)
+
+Lyng supports declaring a class with multiple direct base classes. The syntax is:
+
+```lyng
+class Foo(val a) {
+    var tag = "F"
+    fun runA() { "ResultA:" + a }
+    fun common() { "CommonA" }
+    private fun privateInFoo() {}
+    protected fun protectedInFoo() {}
+}
+
+class Bar(val b) {
+    var tag = "B"
+    fun runB() { "ResultB:" + b }
+    fun common() { "CommonB" }
+}
+
+// Multiple inheritance with per‑base constructor arguments
+class FooBar(a, b) : Foo(a), Bar(b) {
+    // You can disambiguate via qualified this or casts
+    fun fromFoo() { this@Foo.common() }
+    fun fromBar() { this@Bar.common() }
+}
+
+val fb = FooBar(1, 2)
+assertEquals("ResultA:1", fb.runA())
+assertEquals("ResultB:2", fb.runB())
+// Unqualified ambiguous member resolves to the first base (leftmost)
+assertEquals("CommonA", fb.common())
+// Disambiguation via casts
+assertEquals("CommonB", (fb as Bar).common())
+assertEquals("CommonA", (fb as Foo).common())
+
+// Field inheritance with name collisions
+assertEquals("F", fb.tag)            // unqualified: leftmost base
+assertEquals("F", (fb as Foo).tag)   // qualified read: Foo.tag
+assertEquals("B", (fb as Bar).tag)   // qualified read: Bar.tag
+
+fb.tag = "X"                         // unqualified write updates leftmost base
+assertEquals("X", (fb as Foo).tag)
+assertEquals("B", (fb as Bar).tag)
+
+(fb as Bar).tag = "Y"                 // qualified write updates Bar.tag
+assertEquals("X", (fb as Foo).tag)
+assertEquals("Y", (fb as Bar).tag)
+```
+
+Key rules and features:
+
+- Syntax
+  - `class Derived(args) : Base1(b1Args), Base2(b2Args)`
+  - Each direct base may receive constructor arguments specified in the header. Only direct bases receive header args; indirect bases must either be default‑constructible or receive their args through their direct child.
+
+- Resolution order (C3 MRO)
+  - Member lookup is deterministic and follows C3 linearization (Python‑like), which provides a monotonic, predictable order for complex hierarchies and diamonds.
+  - Intuition: for `class D() : B(), C()` where `B()` and `C()` both derive from `A()`, the C3 order is `D → B → C → A`.
+  - The first visible match along this order wins.
+
+- Qualified dispatch
+  - Inside a class body, use `this@Type.member(...)` to start lookup at the specified ancestor.
+  - For arbitrary receivers, use casts: `(expr as Type).member(...)` or `(expr as? Type)?.member(...)`.
+  - Qualified access does not relax visibility.
+
+- Field inheritance (`val`/`var`) and collisions
+  - Instance storage is kept per declaring class, internally disambiguated; unqualified read/write resolves to the first match in the resolution order (leftmost base).
+  - Qualified read/write (via `this@Type` or casts) targets the chosen ancestor’s storage.
+  - `val` remains read‑only; attempting to write raises an error as usual.
+
+- Constructors and initialization
+  - During construction, direct bases are initialized left‑to‑right in the declaration order. Each ancestor is initialized at most once (diamond‑safe de‑duplication).
+  - Arguments in the header are evaluated in the instance scope and passed to the corresponding direct base constructor.
+  - The most‑derived class’s constructor runs after the bases.
+
+- Visibility
+  - `private`: accessible only inside the declaring class body; not visible in subclasses and cannot be accessed via `this@Type` or casts.
+  - `protected`: accessible in the declaring class and in any of its transitive subclasses (including MI), but not from unrelated contexts; qualification/casts do not bypass it.
+
+## Abstract Classes and Members
+
+An `abstract` class is a class that cannot be instantiated and is intended to be inherited by other classes. It can contain `abstract` members that have no implementation and must be implemented by concrete subclasses.
+
+### Abstract Classes
+
+To declare an abstract class, use the `abstract` modifier:
+
+```lyng
+abstract class Shape {
+    abstract fun area(): Real
+}
+```
+
+Abstract classes can have constructors, fields, and concrete methods, just like regular classes.
+
+### Abstract Members
+
+Methods and variables (`val`/`var`) can be marked as `abstract`. Abstract members must not have a body or initializer.
+
+```lyng
+abstract class Base {
+    abstract fun foo(): Int
+    abstract var bar: String
+}
+```
+
+- **Safety**: `abstract` members cannot be `private`, as they must be visible to subclasses for implementation.
+- **Contract of Capability**: An `abstract val/var` represents a requirement for a capability. It can be implemented by either a **field** (storage) or a **property** (logic) in a subclass.
+
+## Interfaces
+
+An `interface` in Lyng is a synonym for an `abstract class`. Following the principle that Lyng's Multiple Inheritance system is powerful enough to handle stateful contracts, interfaces support everything classes do, including constructors, fields, and `init` blocks.
+
+```lyng
+interface Named(val name: String) {
+    fun greet() { "Hello, " + name }
+}
+
+class Person(name) : Named(name)
+```
+
+Using `interface` instead of `abstract class` is a matter of semantic intent, signaling that the class is primarily intended to be used as a contract in MI.
+
+### Implementation by Parts
+
+One of the most powerful benefits of Lyng's Multiple Inheritance and C3 MRO is the ability to satisfy an interface's requirements "by parts" from different parent classes. Since an `interface` can have state and requirements, a subclass can inherit these requirements and satisfy them using members inherited from other parents in the MRO chain.
+
+Example:
+
+```lyng
+// Interface with state (id) and abstract requirements
+interface Character(val id) {
+    var health
+    var mana
+    
+    fun isAlive() = health > 0
+    fun status() = name + " (#" + id + "): " + health + " HP, " + mana + " MP"
+}
+
+// Parent class 1: provides health
+class HealthPool(var health)
+
+// Parent class 2: provides mana and name
+class ManaPool(var mana) {
+    val name = "Hero"
+}
+
+// Composite class: implements Character by combining HealthPool and ManaPool
+class Warrior(id, h, m) : HealthPool(h), ManaPool(m), Character(id)
+
+val w = Warrior(1, 100, 50)
+assertEquals("Hero (#1): 100 HP, 50 MP", w.status())
+```
+
+In this example, `Warrior` inherits from `HealthPool`, `ManaPool`, and `Character`. The abstract requirements `health` and `mana` from `Character` are automatically satisfied by the matching members inherited from `HealthPool` and `ManaPool`. The `status()` method also successfully finds the `name` field from `ManaPool`. This pattern allows for highly modular and reusable "trait-like" classes that can be combined to fulfill complex contracts without boilerplate proxy methods.
+
+## Overriding and Virtual Dispatch
+
+When a class defines a member that already exists in one of its parents, it is called **overriding**.
+
+### The `override` Keyword
+
+In Lyng, the `override` keyword is **mandatory when declaring a member** that exists in the ancestor chain (MRO).
+
+```lyng
+class Parent {
+    fun foo() = 1
+}
+
+class Child : Parent() {
+    override fun foo() = 2 // Mandatory override keyword
+}
+```
+
+- **Implicit Satisfaction**: If a class inherits an abstract requirement and a matching implementation from different parents, the requirement is satisfied automatically without needing an explicit `override` proxy.
+- **No Accidental Overrides**: If you define a member that happens to match a parent's member but you didn't use `override`, the compiler will throw an error. This prevents the "Fragile Base Class" problem.
+- **Private Members**: Private members in parent classes are NOT part of the virtual interface and cannot be overridden. Defining a member with the same name in a subclass is allowed without `override` and is treated as a new, independent member.
+
+### Visibility Widening
+
+A subclass can increase the visibility of an overridden member (e.g., `protected` → `public`), but it is strictly forbidden from narrowing it (e.g., `public` → `protected`).
+
+### The `closed` Modifier
+
+To prevent a member from being overridden in subclasses, use the `closed` modifier (equivalent to `final` in other languages).
+
+```lyng
+class Critical {
+    closed fun secureStep() { ... }
+}
+```
+
+Attempting to override a `closed` member results in a compile-time error.
+
+## Operator Overloading
+
+Lyng allows you to overload standard operators by defining specific named methods in your classes. When an operator expression is evaluated, Lyng delegates the operation to these methods if they are available.
+
+### Binary Operators
+
+To overload a binary operator, define the corresponding method that takes one argument:
+
+| Operator | Method Name |
+| :--- | :--- |
+| `a + b` | `plus(other)` |
+| `a - b` | `minus(other)` |
+| `a * b` | `mul(other)` |
+| `a / b` | `div(other)` |
+| `a % b` | `mod(other)` |
+| `a && b` | `logicalAnd(other)` |
+| `a \|\| b` | `logicalOr(other)` |
+| `a =~ b` | `operatorMatch(other)` |
+| `a & b` | `bitAnd(other)` |
+| `a \| b` | `bitOr(other)` |
+| `a ^ b` | `bitXor(other)` |
+| `a << b` | `shl(other)` |
+| `a >> b` | `shr(other)` |
+
+Example:
+```lyng
+class Vector(val x, val y) {
+    fun plus(other) = Vector(x + other.x, y + other.y)
+    override fun toString() = "Vector(${x}, ${y})"
+}
+
+val v1 = Vector(1, 2)
+val v2 = Vector(3, 4)
+assertEquals(Vector(4, 6), v1 + v2)
+```
+
+### Unary Operators
+
+Unary operators are overloaded by defining methods with no arguments:
+
+| Operator | Method Name |
+| :--- | :--- |
+| `-a` | `negate()` |
+| `!a` | `logicalNot()` |
+| `~a` | `bitNot()` |
+
+### Assignment Operators
+
+Assignment operators like `+=` first attempt to call a specific assignment method. If that method is not defined, they fall back to a combination of the binary operator and a regular assignment (e.g., `a = a + b`).
+
+| Operator | Method Name | Fallback |
+| :--- | :--- | :--- |
+| `a += b` | `plusAssign(other)` | `a = a + b` |
+| `a -= b` | `minusAssign(other)` | `a = a - b` |
+| `a *= b` | `mulAssign(other)` | `a = a * b` |
+| `a /= b` | `divAssign(other)` | `a = a / b` |
+| `a %= b` | `modAssign(other)` | `a = a % b` |
+
+Example of in-place mutation:
+```lyng
+class Counter(var value) {
+    fun plusAssign(n) {
+        value = value + n
+    }
+}
+
+val c = Counter(10)
+c += 5
+assertEquals(15, c.value)
+```
+
+### Comparison Operators
+
+Comparison operators use `compareTo` and `equals`.
+
+| Operator | Method Name |
+| :--- | :--- |
+| `a == b`, `a != b` | `equals(other)` |
+| `<`, `>`, `<=`, `>=`, `<=>` | `compareTo(other)` |
+
+- `compareTo` should return:
+  - `0` if `a == b`
+  - A negative integer if `a < b`
+  - A positive integer if `a > b`
+- The `<=>` (shuttle) operator returns the result of `compareTo` directly.
+- `equals` returns a `Bool`. If `equals` is not explicitly defined, Lyng falls back to `compareTo(other) == 0`.
+
+> **Note**: Methods that are already defined in the base `Obj` class (like `equals`, `toString`, or `contains`) require the `override` keyword when redefined in your class or as an extension. Other operator methods (like `plus` or `negate`) do not require `override` unless they are already present in your class's hierarchy.
+
+### Increment and Decrement
+
+`++` and `--` operators are implemented using `plus(1)` or `minus(1)` combined with an assignment back to the variable. If the variable is a field or local variable, it will be updated with the result of the operation.
+
+Compatibility notes:
+
+- Existing single‑inheritance code continues to work unchanged; its resolution order reduces to the single base.
+- If your previous code accidentally relied on non‑deterministic parent set iteration, it may change behavior — the new deterministic order is a correctness fix.
+
+### Migration note (declaration‑order → C3)
+
+Earlier drafts and docs described a declaration‑order depth‑first linearization. Lyng now uses C3 MRO for member lookup and disambiguation. Most code should continue to work unchanged, but in rare edge cases involving diamonds or complex multiple inheritance, the chosen base for an ambiguous member may change to reflect C3. If needed, disambiguate explicitly using `this@Type.member(...)` inside class bodies or casts `(expr as Type).member(...)` from outside.
+
+## Enums
+
+Lyng provides lightweight enums for representing a fixed set of named constants. Enums are classes whose instances are predefined and singletons.
+
+Current syntax supports simple enum declarations with just entry names:
+
+    enum Color {
+        RED, GREEN, BLUE
+    }
+
+Usage:
+
+- Type of entries: every entry is an instance of its enum type.
+
+      assert( Color.RED is Color )
+
+- Order and names: each entry has zero‑based `ordinal` and string `name`.
+
+      assertEquals(0, Color.RED.ordinal)
+      assertEquals("BLUE", Color.BLUE.name)
+
+- All entries as a list in declaration order: `EnumType.entries`.
+
+      assertEquals([Color.RED, Color.GREEN, Color.BLUE], Color.entries)
+
+- Lookup by name: `EnumType.valueOf("NAME")` → entry.
+
+      assertEquals(Color.GREEN, Color.valueOf("GREEN"))
+
+- Equality and comparison:
+  - Equality uses identity of entries, e.g., `Color.RED == Color.valueOf("RED")`.
+  - Cross‑enum comparisons are not allowed.
+  - Ordering comparisons use `ordinal`.
+
+      assert( Color.RED == Color.valueOf("RED") )
+      assert( Color.RED.ordinal < Color.BLUE.ordinal )
+      >>> void
+
+### Enums with `when`
+
+Use `when(subject)` with equality branches for enums. See full `when` guide: [The `when` statement](when.md).
+
+    enum Color { RED, GREEN, BLUE }
+
+    fun describe(c) {
+        when(c) {
+            Color.RED, Color.GREEN -> "primary-like"
+            Color.BLUE -> "blue"
+            else -> "unknown"   // if you pass something that is not a Color
+        }
+    }
+    assertEquals("primary-like", describe(Color.RED))
+    assertEquals("blue", describe(Color.BLUE))
+    >>> void
+
+### Serialization
+
+Enums are serialized compactly with Lynon: the encoded value stores just the entry ordinal within the enum type, which is both space‑efficient and fast.
+
+    import lyng.serialization
+
+    enum Color { RED, GREEN, BLUE }
+
+    val e = Lynon.encode(Color.BLUE)
+    val decoded = Lynon.decode(e)
+    assertEquals(Color.BLUE, decoded)
+    >>> void
+
+Notes and limitations (current version):
+
+- Enum declarations support only simple entry lists: no per‑entry bodies, no custom constructors, and no user‑defined methods/fields on the enum itself yet.
+- `name` and `ordinal` are read‑only properties of an entry.
+- `entries` is a read‑only list owned by the enum type.
+
+## Exception Classes
+
+You can define your own exception classes by inheriting from the built-in `Exception` class. User-defined exceptions are regular classes and can have their own properties and methods.
+
+```lyng
+class MyError(val code, m) : Exception(m)
+
+try {
+    throw MyError(500, "Internal Server Error")
+}
+catch(e: MyError) {
+    println("Error " + e.code + ": " + e.message)
+}
+```
+
+For more details on error handling, see the [Exceptions Handling Guide](exceptions_handling.md).
+
 ## fields and visibility
 
 It is possible to add non-constructor fields:
@@ -103,6 +767,69 @@ Are declared with var
     assert( p.isSpecial == true )
     >>> void
 
+### Restricted Setter Visibility
+
+You can restrict the visibility of a `var` field's or property's setter by using `private set` or `protected set` modifiers. This allows the member to be publicly readable but only writable from within the class or its subclasses.
+
+#### On Fields
+
+```lyng
+class SecretCounter {
+    var count = 0
+        private set // Can be read anywhere, but written only in SecretCounter
+        
+    fun increment() { count++ }
+}
+
+val c = SecretCounter()
+println(c.count) // OK
+c.count = 10     // Throws IllegalAccessException
+c.increment()    // OK
+```
+
+#### On Properties
+
+You can also apply restricted visibility to custom property setters:
+
+```lyng
+class Person(private var _age: Int) {
+    var age
+        get() = _age
+        private set(v) { if (v >= 0) _age = v }
+}
+```
+
+#### Protected Setters and Inheritance
+
+A `protected set` allows subclasses to modify a field that is otherwise read-only to the public:
+
+```lyng
+class Base {
+    var state = "initial"
+        protected set
+}
+
+class Derived : Base() {
+    fun changeState(newVal) {
+        state = newVal // OK: protected access from subclass
+    }
+}
+
+val d = Derived()
+println(d.state) // OK: "initial"
+d.changeState("updated")
+println(d.state) // OK: "updated"
+d.state = "bad"  // Throws IllegalAccessException: public write not allowed
+```
+
+### Key Rules and Limitations
+
+- **Only for `var`**: Restricted setter visibility cannot be used with `val` declarations, as they are inherently read-only. Attempting to use it with `val` results in a syntax error.
+- **Class Body Only**: These modifiers can only be used on members declared within the class body. They are not supported for primary constructor parameters.
+- **`private set`**: The setter is only accessible within the same class context (specifically, when `this` is an instance of that class).
+- **`protected set`**: The setter is accessible within the declaring class and all its transitive subclasses.
+- **Multiple Inheritance**: In MI scenarios, visibility is checked against the class that actually declared the member. Qualified access (e.g., `this@Base.field = value`) also respects restricted setter visibility.
+
 ### Private fields
 
 Private fields are visible only _inside the class instance_:
@@ -130,6 +857,25 @@ Private fields are visible only _inside the class instance_:
     void
     >>> void
 
+### Protected members
+
+Protected members are available to the declaring class and all of its transitive subclasses (including via MI), but not from unrelated contexts:
+
+```
+class A() {
+    protected fun ping() { "pong" }
+}
+class B() : A() {
+    fun call() { this@A.ping() }
+}
+
+val b = B()
+assertEquals("pong", b.call())
+
+// Unrelated access is forbidden, even via cast
+assertThrows { (b as A).ping() }
+```
+
 It is possible to provide private constructor parameters so they can be
 set at construction but not available outside the class:
 
@@ -203,9 +949,11 @@ As usual, private statics are not accessible from the outside:
 
 # Extending classes
 
-It sometimes happen that the class is missing some particular functionality that can be _added to it_ without rewriting its inner logic and using its private state. In this case _extension methods_ could be used, for example. we want to create an extension method
-that would test if some object of unknown type contains something that can be interpreted
-as an integer. In this case we _extend_ class `Object`, as it is the parent class for any instance of any type:
+It sometimes happen that the class is missing some particular functionality that can be _added to it_ without rewriting its inner logic and using its private state. In this case _extension members_ could be used.
+
+## Extension methods
+
+For example, we want to create an extension method that would test if some object of unknown type contains something that can be interpreted as an integer. In this case we _extend_ class `Object`, as it is the parent class for any instance of any type:
 
         fun Object.isInteger() {
             when(this) {
@@ -230,10 +978,67 @@ as an integer. In this case we _extend_ class `Object`, as it is the parent clas
         assert( ! "5.2".isInteger() )
         >>> void
 
-__Important note__ as for version 0.6.9, extensions are in __global scope__. It means, that once applied to a global type (Int in our sample), they will be available for _all_ contexts, even new created, 
-as they are modifying the type, not the context.
+## Extension properties
 
-Beware of it. We might need to reconsider it later.
+Just like methods, you can extend existing classes with properties. These can be defined using simple initialization (for `val` only) or with custom accessors.
+
+### Simple val extension
+
+A read-only extension can be defined by assigning an expression:
+
+```lyng
+val String.isLong = length > 10
+
+val s = "Hello, world!"
+assert(s.isLong)
+```
+
+### Properties with accessors
+
+For more complex logic, use `get()` and `set()` blocks:
+
+```lyng
+class Box(var value: Int)
+
+var Box.doubledValue
+    get() = value * 2
+    set(v) = value = v / 2
+
+val b = Box(10)
+assertEquals(20, b.doubledValue)
+b.doubledValue = 30
+assertEquals(15, b.value)
+```
+
+Extension members are strictly barred from accessing private members of the class they extend, maintaining encapsulation.
+
+### Extension Scoping and Isolation
+
+Extensions in Lyng are **scope-isolated**. This means an extension is only visible within the scope where it is defined and its child scopes. This reduces the "attack surface" and prevents extensions from polluting the global space or other modules.
+
+#### Scope Isolation Example
+
+You can define different extensions with the same name in different scopes:
+
+```lyng
+fun scopeA() {
+    val Int.description = "Number: " + toString()
+    assertEquals("Number: 42", 42.description)
+}
+
+fun scopeB() {
+    val Int.description = "Value: " + toString()
+    assertEquals("Value: 42", 42.description)
+}
+
+scopeA()
+scopeB()
+
+// Outside those scopes, Int.description is not defined
+assertThrows { 42.description }
+```
+
+This isolation ensures that libraries can use extensions internally without worrying about name collisions with other libraries or the user's code. When a module is imported using `use`, its top-level extensions become available in the importing scope.
 
 ## dynamic symbols
 
@@ -266,7 +1071,7 @@ The same we can provide writable dynamic fields (var-type), adding set method:
                 // constant field
                 "foo" -> "bar"
                 // mutable field
-                "bar" -> setValueForBar 
+                "bar" -> storedValueForBar 
 
                 else -> throw SymbolNotFoundException()
             }
@@ -289,9 +1094,56 @@ The same we can provide writable dynamic fields (var-type), adding set method:
     assertThrows {
         accessor.bad = "!23"
     }
+    void
+    >>> void
 
 Of course, you can return any object from dynamic fields; returning lambdas let create _dynamic methods_ - the callable method. It is very convenient to implement libraries with dynamic remote interfaces, etc.
 
+### Dynamic indexers
+
+Index access for dynamics is passed to the same getter and setter, so it is
+generally the same:
+
+    var storedValue = "bar"
+    val x = dynamic {
+        get { 
+            if( it == "foo" ) storedValue
+            else null
+        }
+    }
+    assertEquals("bar", x["foo"] )
+    assertEquals("bar", x.foo )
+    >>> void
+
+And assigning them works the same. You can make it working
+mimicking arrays, but remember, it is not Collection so
+collection's sugar won't work with it:
+
+    var storedValue = "bar"
+    val x = dynamic {
+        get { 
+            when(it) {
+                "size" -> 1
+                0 -> storedValue
+                else -> null
+            }
+        }
+        set { index, value -> 
+            if( index == 0 ) storedValue = value
+            else throw "Illegal index: "+index
+        }
+    }
+    assertEquals("bar", x[0] )
+    assertEquals(1, x.size )
+    x[0] = "buzz"
+    assertThrows { x[1] = 1 }
+    assertEquals("buzz", storedValue)
+    assertEquals("buzz", x[0])
+    >>> void
+
+If you want dynamic to function like an array, create a [feature
+request](https://gitea.sergeych.net/SergeychWorks/lyng/issues).
+
 # Theory
 
 ## Basic principles:
@@ -305,12 +1157,12 @@ Of course, you can return any object from dynamic fields; returning lambdas let
 - ObjClass sole parent is Obj
 - ObjClass contains code for instance methods, class fields, hierarchy information.
 - Class information is also scoped. 
-- We acoid imported classes duplication using packages and import caching, so the same imported module is the same object in all its classes.
+- We avoid imported classes duplication using packages and import caching, so the same imported module is the same object in all its classes.
 
 ## Instances
 
 Result of executing of any expression or statement in the Lyng is the object that
-inherits `Obj`, but is not `Obj`. For example it could be Int, void, null, real, string, bool, etc.
+inherits `Obj`, but is not `Obj`. For example, it could be Int, void, null, real, string, bool, etc.
 
 This means whatever expression returns or the variable holds, is the first-class
 object, no differenes. For example:
@@ -367,3 +1219,8 @@ Regular methods are called on instances as usual `instance.method()`. The method
 TBD
 
 [argument list](declaring_arguments.md)
+### Visibility from within closures and instance scopes
+
+When a closure executes within a method, the closure retains the lexical class context of its creation site. This means private/protected members of that class remain accessible where expected (subject to usual visibility rules). Field resolution checks the declaring class and validates access using the preserved `currentClassCtx`.
+
+See also: [Scopes and Closures: resolution and safety](scopes_and_closures.md)

docs/Regex.md

@@ -0,0 +1,91 @@
+# Regular expressions
+
+In lyng, you create regular expressions using class `Regex` or `String.re` methods:
+
+    assert( "\d*".re is Regex )
+    assert( Regex("\d*") is Regex )
+    >>> void
+
+We plan to add slash syntax at some point.
+
+To check that some string matches as whole to some regex:
+
+    assert( "123".matches("\d{3}".re) )
+    assert( !"123".matches("\d{4}".re) )
+    assert( !"1234".matches("\d".re) )
+    >>> void
+
+To check that _part of the string_ matches some regular expession, use _match operator_ `=~` just like in Ruby, and its
+counterpart, _not match_ operator `!~`:
+
+    assert( "abc123def" =~ "\d\d\d".re )
+    assert( "abc" !~ "\d\d\d".re )
+    >>> void
+
+When you need to find groups, and more detailed match information, use `Regex.find`:
+
+    val result = Regex("abc(\d)(\d)(\d)").find( "bad456 good abc123")
+    assert( result  != null )
+    assertEquals( 12 .. 17, result.range )
+    assertEquals( "abc123", result[0] )
+    assertEquals( "1", result[1] )
+    assertEquals( "2", result[2] )
+    assertEquals( "3", result[3] )
+    >>> void
+
+Note that the object `RegexMatch`, returned by [Regex.find], behaves much like in many other languages: it provides the
+index range and groups matches as indexes.
+
+Match operator actually also provides `RegexMatch` in `$~` reserved variable (borrowed from Ruby too):
+
+    assert( "bad456 good abc123" =~ "abc(\d)(\d)(\d)".re )
+    assertEquals( 12 .. 17, $~.range )
+    assertEquals( "abc123", $~[0] )
+    assertEquals( "1", $~[1] )
+    assertEquals( "2", $~[2] )
+    assertEquals( "3", $~[3] )
+    >>> void
+
+This is often more readable than calling `find`.
+
+Note that `=~` and `!~` operators against strings and regular expressions are commutative, e.g. regular expression and a
+string can be either left or right operator, but not both:
+
+    assert( "abc" =~ "\wc".re )
+    assert( "abc" !~ "\w1c".re )
+    assert( "a\wc".re =~ "abcd" )
+    assert( "a[a-z]c".re !~ "a2cd" )
+    >>> void
+
+Also, string indexing is Regex-aware, and works like `Regex.find` (_not findall!_):
+
+    assert( "cd" == "abcdef"[ "c.".re ].value )
+    >>> void
+
+
+# Regex class reference
+
+| name         | description                         | notes |
+|--------------|-------------------------------------|-------|
+| matches(str) | true if the whole `str` matches     |       |
+| find(str)    | find first match in `str` or null   | (1)   |
+| findAll(str) | find all matches in `str` as [List] | (1)   |
+
+(1)
+:: See `RegexMatch` class description below
+
+# RegexMatch
+
+| name  | description                               | notes |
+|-------|-------------------------------------------|-------|
+| range | the [Range] of the match in source string |       |
+| value | the value that matches                    |       |
+| [n]   | [List] of group matches                   | (1)   |
+
+(1)
+:: the [0] element is always value, [1] is group 1 match of any, etc.
+
+[List]: List.md
+
+[Range]: Range.md
+

docs/Testing.md

@@ -0,0 +1,121 @@
+# Testing and Assertions
+
+Lyng provides several built-in functions for testing and verifying code behavior. These are available in all scripts.
+
+## Basic Assertions
+
+### `assert`
+
+Assert that a condition is true.
+
+    assert(condition, message=null)
+
+- `condition`: A boolean expression.
+- `message` (optional): A string message to include in the exception if the assertion fails.
+
+If the condition is false, it throws an `AssertionFailedException`.
+
+```lyng
+assert(1 + 1 == 2)
+assert(true, "This should be true")
+```
+
+### `assertEquals` and `assertEqual`
+
+Assert that two values are equal. `assertEqual` is an alias for `assertEquals`.
+
+    assertEquals(expected, actual)
+    assertEqual(expected, actual)
+
+If `expected != actual`, it throws an `AssertionFailedException` with a message showing both values.
+
+```lyng
+assertEquals(4, 2 * 2)
+assertEqual("hello", "hel" + "lo")
+```
+
+### `assertNotEquals`
+
+Assert that two values are not equal.
+
+    assertNotEquals(unexpected, actual)
+
+If `unexpected == actual`, it throws an `AssertionFailedException`.
+
+```lyng
+assertNotEquals(5, 2 * 2)
+```
+
+## Exception Testing
+
+### `assertThrows`
+
+Assert that a block of code throws an exception.
+
+    assertThrows(code)
+    assertThrows(expectedExceptionClass, code)
+
+- `expectedExceptionClass` (optional): The class of the exception that is expected to be thrown.
+- `code`: A lambda block or statement to execute.
+
+If the code does not throw an exception, an `AssertionFailedException` is raised. 
+If an `expectedExceptionClass` is provided, the thrown exception must be of that class (or its subclass), otherwise an error is raised.
+
+`assertThrows` returns the caught exception object if successful.
+
+```lyng
+// Just assert that something is thrown
+assertThrows { 1 / 0 }
+
+// Assert that a specific exception class is thrown
+assertThrows(NoSuchElementException) { 
+    [1, 2, 3].findFirst { it > 10 } 
+}
+
+// You can use the returned exception
+val ex = assertThrows { throw Exception("custom error") }
+assertEquals("custom error", ex.message)
+```
+
+## Other Validation Functions
+
+While not strictly for testing, these functions help in defensive programming:
+
+### `require`
+
+    require(condition, message="requirement not met")
+
+Throws an `IllegalArgumentException` if the condition is false. Use this for validating function arguments.
+
+If we want to evaluate the message lazily:
+
+    require(condition) { "requirement not met: %s"(someData) }
+
+In this case, formatting will only occur if the condition is not met.
+
+### `check`
+
+    check(condition, message="check failed")
+
+Throws an `IllegalStateException` if the condition is false. Use this for validating internal state.
+
+With lazy message evaluation:
+
+    check(condition) { "check failed: %s"(someData) }
+
+In this case, formatting will only occur if the condition is not met.
+
+### TODO
+
+It is easy to mark some code and make it throw a special exception at cone with:
+
+    TODO()
+
+or
+
+    TODO("some message")
+
+It raises an `NotImplementedException` with the given message. You can catch it
+as any other exception when necessary.
+
+Many IDE and editors have built-in support for marking code with TODOs.

docs/advanced_topics.md

@@ -158,3 +158,9 @@ Function annotation can have more args specified at call time. There arguments m
     >>> void
 
 [parallelism]: parallelism.md
+
+## Scopes and Closures: resolution and safety
+
+Closures and dynamic scope graphs require care to avoid accidental recursion and to keep name resolution predictable. See the dedicated page for detailed rules, helper APIs, and best practices:
+
+- Scopes and Closures: resolution and safety → [scopes_and_closures.md](scopes_and_closures.md)

docs/class_reference.md

@@ -1,24 +0,0 @@
-# Classes
-
-## Declaring
-
-    class Foo1
-    class Foo2() // same, empty constructor
-    class Foo3() { // full
-    }
-    class Foo4 { // Only body
-    }
-
-```
-class_declaration = ["abstract",] "class" [, constructor] [, body]
-constructor = "(", [field [, field]] ")
-field = [visibility ,] [access ,] name [, typedecl]
-body = [visibility] ("var", vardecl) | ("val", vardecl) | ("fun", fundecl)
-visibility = "private" | "protected" | "internal"
-```
-
-### Abstract classes
-
-Contain one pr more abstract methods which must be implemented; though they
-can have constructors, the instances of the abstract classes could not be
-created independently

docs/declaring_arguments.md

@@ -1,11 +1,13 @@
 # Declaring arguments in Lyng
 
+[//]: # (topMenu)
+
 It is a common thing that occurs in many places in Lyng, function declarations, 
 lambdas and class declarations.
 
 ## Regular
 
-## default values
+## Default values
 
 Default parameters should not be mixed with mandatory ones:
 
@@ -73,6 +75,13 @@ destructuring arrays when calling functions and lambdas:
     getFirstAndLast( ...(1..10) ) // see "splats" section below
     >>> [1,10]
 
+Note that array destructuring can also be used in assignments:
+
+    val [first, middle..., last] = [1, 2, 3, 4, 5]
+    [x, y] = [y, x] // Swap
+
+See [tutorial] and [List] documentation for more details on destructuring assignments.
+
 # Splats
 
 Ellipsis allows to convert argument lists to lists. The inversa algorithm that converts [List],
@@ -96,5 +105,73 @@ There could be any number of splats at any positions. You can splat any other [I
     >>> [start,1,2,3,end]
     >>> void
 
+## Named arguments in calls
+
+Lyng supports named arguments at call sites using colon syntax `name: value`. 
+
+### Shorthand for Named Arguments
+
+If you want to pass a variable as a named argument and the variable has the same name as the parameter, you can omit the value and use the shorthand `name:`. This is highly readable and matches the shorthand for map literals.
+
+```lyng
+    fun test(a, b, c) { [a, b, c] }
+    
+    val a = 1
+    val b = 2
+    val c = 3
+    
+    // Explicit:
+    assertEquals([1, 2, 3], test(a: a, b: b, c: c))
+    
+    // Shorthand (preferred):
+    assertEquals([1, 2, 3], test(a:, b:, c:))
+```
+
+This shorthand is elegant, reduces boilerplate, and is consistent with Lyng's map literal syntax. It works for both function calls and class constructors.
+
+Rules for named arguments:
+
+- Named arguments must follow positional arguments. After the first named argument, no positional arguments may appear inside the parentheses.
+- The only exception is the syntactic trailing block after the call: `f(args) { ... }`. This block is outside the parentheses and is handled specially (see below).
+- A named argument cannot reassign a parameter already set positionally.
+- If the last parameter has already been assigned by a named argument (or named splat), a trailing block is not allowed and results in an error.
+
+Why `:` and not `=` at call sites? In Lyng, `=` is an expression (assignment), so we use `:` to avoid ambiguity. This is a key difference from **Kotlin**, which uses `=` for named arguments. Declarations in Lyng continue to use `:` for types, while call sites use `as` / `as?` for type operations.
+
+## Named splats (map splats)
+
+Splat (`...`) of a Map provides named arguments to the call. Only string keys are allowed. You can use the same auto-substitution shorthand inside map literals used for splats:
+
+```lyng
+    fun test(a="a", b="b", c="c", d="d") { [a, b, c, d] }
+    
+    val b = "B!"
+    val d = "D!"
+    
+    // Auto-substitution in map literal:
+    val patch = { d:, b: }
+    
+    val r = test("A?", ...patch)
+    assertEquals(["A?","B!","c","D!"], r)
+```
+
+Constraints:
+
+- Map splat keys must be strings; otherwise, a clean error is thrown.
+- Named splats cannot duplicate parameters already assigned (by positional or named arguments).
+- Named splats must follow all positional arguments and positional splats.
+- Ellipsis parameters (variadic) remain positional-only and cannot be assigned by name.
+
+## Trailing-lambda rule interaction
+
+If a call is immediately followed by a block `{ ... }`, it is treated as an extra last argument and bound to the last parameter. However, if the last parameter is already assigned by a named argument or a named splat, using a trailing block is an error:
+
+```lyng
+    fun f(x, onDone) { onDone(x) }
+    f(x: 1) { 42 }   // ERROR
+    f(1) { 42 }      // OK
+```
+    
 
 [tutorial]: tutorial.md
+[List]: List.md

docs/delegation.md

@@ -0,0 +1,194 @@
+# Delegation in Lyng
+
+Delegation is a powerful pattern that allows you to outsource the logic of properties (`val`, `var`) and functions (`fun`) to another object. This enables code reuse, separation of concerns, and the implementation of common patterns like lazy initialization, observable properties, and remote procedure calls (RPC) with minimal boilerplate.
+
+## The `by` Keyword
+
+Delegation is triggered using the `by` keyword in a declaration. The expression following `by` is evaluated once when the member is initialized, and the resulting object becomes the **delegate**.
+
+```lyng
+val x by MyDelegate()
+var y by MyDelegate()
+fun f by MyDelegate()
+```
+
+## The Unified Delegate Model
+
+A delegate object can implement any of the following methods to intercept member access. All methods receive the `thisRef` (the instance containing the member) and the `name` of the member.
+
+```lyng
+interface Delegate {
+    // Called when a 'val' or 'var' is read
+    fun getValue(thisRef, name)
+    
+    // Called when a 'var' is assigned
+    fun setValue(thisRef, name, newValue)
+    
+    // Called when a 'fun' is invoked
+    fun invoke(thisRef, name, args...)
+    
+    // Optional: Called once during initialization to "bind" the delegate
+    // Can be used for validation or to return a different delegate instance
+    fun bind(name, access, thisRef) = this
+}
+```
+
+### Delegate Access Types
+
+The `bind` method receives an `access` parameter of type `DelegateAccess`, which can be one of:
+- `DelegateAccess.Val`
+- `DelegateAccess.Var`
+- `DelegateAccess.Callable` (for `fun`)
+
+## Usage Cases and Examples
+
+### 1. Lazy Initialization
+
+The classic `lazy` pattern ensures a value is computed only when first accessed and then cached. In Lyng, `lazy` is implemented as a class that follows this pattern. While classes typically start with an uppercase letter, `lazy` is an exception to make its usage feel like a native language feature.
+
+```lyng
+class lazy(val creator) : Delegate {
+    private var value = Unset
+
+    override fun bind(name, access, thisRef) {
+        if (access != DelegateAccess.Val) throw "lazy delegate can only be used with 'val'"
+        this
+    }
+
+    override fun getValue(thisRef, name) {
+        if (value == Unset) {
+            // calculate value using thisRef as this:
+            value = with(thisRef) creator()
+        }
+        value
+    }
+}
+
+// Usage:
+val expensiveData by lazy {
+    println("Performing expensive computation...")
+    42
+}
+
+println(expensiveData) // Computes and prints 42
+println(expensiveData) // Returns 42 immediately
+```
+
+### 2. Observable Properties
+
+Delegates can be used to react to property changes.
+
+```lyng
+class Observable(initialValue, val onChange) {
+    private var value = initialValue
+
+    fun getValue(thisRef, name) = value
+    
+    fun setValue(thisRef, name, newValue) {
+        val oldValue = value
+        value = newValue
+        onChange(name, oldValue, newValue)
+    }
+}
+
+class User {
+    var name by Observable("Guest") { name, old, new ->
+        println("Property %s changed from %s to %s"(name, old, new))
+    }
+}
+
+val u = User()
+u.name = "Alice" // Prints: Property name changed from Guest to Alice
+```
+
+### 3. Function Delegation (Proxies)
+
+You can delegate an entire function to an object. This is particularly useful for implementing decorators or RPC clients.
+
+```lyng
+object LoggerDelegate {
+    fun invoke(thisRef, name, args...) {
+        println("Calling function: " + name + " with args: " + args)
+        // Logic here...
+        "Result of " + name
+    }
+}
+
+fun remoteAction by LoggerDelegate
+
+println(remoteAction(1, 2, 3))
+// Prints: Calling function: remoteAction with args: [1, 2, 3]
+// Prints: Result of remoteAction
+```
+
+### 4. Stateless Delegates (Shared Singletons)
+
+Because `getValue`, `setValue`, and `invoke` receive `thisRef`, a single object can act as a delegate for multiple properties across many instances without any per-property memory overhead.
+
+```lyng
+object Constant42 {
+    fun getValue(thisRef, name) = 42
+}
+
+class Foo {
+    val a by Constant42
+    val b by Constant42
+}
+
+val f = Foo()
+assertEquals(42, f.a)
+assertEquals(42, f.b)
+```
+
+### 5. Local Delegation
+
+Delegation is not limited to class members; you can also use it for local variables inside functions.
+
+```lyng
+fun test() {
+    val x by LocalProxy(123)
+    println(x)
+}
+```
+
+### 6. Map as a Delegate
+
+Maps can be used as delegates for `val` and `var` properties. When a map is used as a delegate, it uses the property name as a key to read from or write to the map.
+
+```lyng
+val m = { "a": 1, "b": 2 }
+val a by m
+var b by m
+
+println(a) // 1
+println(b) // 2
+
+b = 42
+println(m["b"]) // 42
+```
+
+Because `Map` implements `getValue` and `setValue`, it works seamlessly with any object that needs to store its properties in a map (e.g., when implementing dynamic schemas or JSON-backed objects).
+
+## The `bind` Hook
+
+The `bind(name, access, thisRef)` method is called exactly once when the member is being initialized. It allows the delegate to:
+1.  **Validate usage**: Throw an error if the delegate is used with the wrong member type (e.g., `lazy` on a `var`).
+2.  **Initialize state**: Set up internal state based on the property name or the containing instance.
+3.  **Substitute itself**: Return a different object that will act as the actual delegate.
+
+```lyng
+class ValidatedDelegate() {
+    fun bind(name, access, thisRef) {
+        if (access == DelegateAccess.Var) {
+            throw "This delegate cannot be used with 'var'"
+        }
+        this
+    }
+    
+    fun getValue(thisRef, name) = "Validated"
+}
+```
+
+## Summary
+
+Delegation in Lyng combines the elegance of Kotlin-style properties with the flexibility of dynamic function interception. By unifying `val`, `var`, and `fun` delegation into a single model, Lyng provides a consistent and powerful tool for meta-programming and code reuse.

docs/embedding.md

@@ -0,0 +1,349 @@
+# Embedding Lyng in your Kotlin project
+
+Lyng is a tiny, embeddable, Kotlin‑first scripting language. This page shows, step by step, how to:
+
+- add Lyng to your build
+- create a runtime and execute scripts
+- define functions and variables from Kotlin
+- read variable values back in Kotlin
+- call Lyng functions from Kotlin
+- create your own packages and import them in Lyng
+
+All snippets below use idiomatic Kotlin and rely on Lyng public APIs. They work on JVM and other Kotlin Multiplatform targets supported by `lynglib`.
+
+Note: all Lyng APIs shown are `suspend`, because script evaluation is coroutine‑friendly and can suspend.
+
+### 1) Add Lyng to your build
+
+Add the repository where you publish Lyng artifacts and the dependency on the core library `lynglib`.
+
+Gradle Kotlin DSL (build.gradle.kts):
+
+```kotlin
+repositories {
+    // Your standard repos
+    mavenCentral()
+
+    // If you publish to your own Maven (example: Gitea packages). Adjust URL/token as needed.
+    maven(url = uri("https://gitea.sergeych.net/api/packages/SergeychWorks/maven"))
+}
+
+dependencies {
+    // Multiplatform: place in appropriate source set if needed
+    implementation("net.sergeych:lynglib:1.0.0-SNAPSHOT")
+}
+```
+
+If you use Kotlin Multiplatform, add the dependency in the `commonMain` source set (and platform‑specific sets if you need platform APIs).
+
+### 2) Create a runtime (Scope) and execute scripts
+
+The easiest way to get a ready‑to‑use scope with standard packages is via `Script.newScope()`.
+
+```kotlin
+fun main() = kotlinx.coroutines.runBlocking {
+    val scope = Script.newScope() // suspends on first init
+
+    // Evaluate a one‑liner
+    val result = scope.eval("1 + 2 * 3")
+    println("Lyng result: $result") // ObjReal/ObjInt etc.
+}
+```
+
+You can also pre‑compile a script and execute it multiple times:
+
+```kotlin
+val script = Compiler.compile("""
+    // any Lyng code
+    val x = 40 + 2
+    x
+""")
+
+val run1 = script.execute(scope)
+val run2 = script.execute(scope)
+```
+
+`Scope.eval("...")` is a shortcut that compiles and executes on the given scope.
+
+### 3) Define variables from Kotlin
+
+To expose data to Lyng, add constants (read‑only) or mutable variables to the scope. All values in Lyng are `Obj` instances; the core types live in `net.sergeych.lyng.obj`.
+
+```kotlin
+// Read‑only constant
+scope.addConst("pi", ObjReal(3.14159))
+
+// Mutable variable: create or update
+scope.addOrUpdateItem("counter", ObjInt(0))
+
+// Use it from Lyng
+scope.eval("counter = counter + 1")
+```
+
+Tip: Lyng values can be converted back to Kotlin with `toKotlin(scope)`:
+
+```kotlin
+val current = (scope.eval("counter")).toKotlin(scope) // Any? (e.g., Int/Double/String/List)
+```
+
+### 4) Add Kotlin‑backed functions
+
+Use `Scope.addFn`/`addVoidFn` to register functions implemented in Kotlin. Inside the lambda, use `this.args` to access arguments and return an `Obj`.
+
+```kotlin
+// A function returning value
+scope.addFn<ObjInt>("inc") {
+    val x = args.firstAndOnly() as ObjInt
+    ObjInt(x.value + 1)
+}
+
+// A void function (returns Lyng Void)
+scope.addVoidFn("log") {
+    val items = args.list // List<Obj>
+    println(items.joinToString(" ") { it.toString(this).value })
+}
+
+// When adding a member function to a class, you can use isOverride = true
+// myClass.addFn("toString", isOverride = true) {
+//     ObjString("Custom string representation")
+// }
+
+// Call them from Lyng
+scope.eval("val y = inc(41); log('Answer:', y)")
+```
+
+You can register multiple names (aliases) at once: `addFn<ObjInt>("inc", "increment") { ... }`.
+
+### 5) Add Kotlin‑backed fields
+
+If you need a simple field (with a value) instead of a computed property, use `createField`. This adds a field to the class that will be present in all its instances.
+
+```kotlin
+val myClass = ObjClass("MyClass")
+
+// Add a read-only field (constant)
+myClass.createField("version", ObjString("1.0.0"), isMutable = false)
+
+// Add a mutable field with an initial value
+myClass.createField("count", ObjInt(0), isMutable = true)
+
+// If you are overriding a field from a base class, use isOverride = true
+// myClass.createField("someBaseField", ObjInt(42), isOverride = true)
+
+scope.addConst("MyClass", myClass)
+```
+
+In Lyng:
+```lyng
+val instance = MyClass()
+println(instance.version) // -> "1.0.0"
+instance.count = 5
+println(instance.count)   // -> 5
+```
+
+### 6) Add Kotlin‑backed properties
+
+Properties in Lyng are pure accessors (getters and setters) and do not have automatic backing fields. You can add them to a class using `addProperty`.
+
+```kotlin
+val myClass = ObjClass("MyClass")
+var internalValue: Long = 10
+
+myClass.addProperty(
+    name = "value",
+    getter = { 
+        // Return current value as a Lyng object
+        ObjInt(internalValue) 
+    },
+    setter = { newValue ->
+        // newValue is passed as a Lyng object (the first and only argument)
+        internalValue = (newValue as ObjInt).value
+    }
+)
+
+// You can also create an ObjProperty explicitly
+val explicitProp = ObjProperty(
+    name = "hexValue",
+    getter = statement { ObjString(internalValue.toString(16)) }
+)
+myClass.addProperty("hexValue", prop = explicitProp)
+
+// Use isOverride = true when overriding a property from a base class
+// myClass.addProperty("baseProp", getter = { ... }, isOverride = true)
+
+scope.addConst("MyClass", myClass)
+```
+
+Usage in Lyng:
+```lyng
+val instance = MyClass()
+println(instance.value) // -> 10
+instance.value = 42
+println(instance.value) // -> 42
+```
+
+### 7) Read variable values back in Kotlin
+
+The simplest approach: evaluate an expression that yields the value and convert it.
+
+```kotlin
+val kotlinAnswer = scope.eval("(1 + 2) * 3").toKotlin(scope) // -> 9 (Int)
+
+// After scripts manipulate your vars:
+scope.addOrUpdateItem("name", ObjString("Lyng"))
+scope.eval("name = name + ' rocks!'")
+val kotlinName = scope.eval("name").toKotlin(scope) // -> "Lyng rocks!"
+```
+
+Advanced: you can also grab a variable record directly via `scope.get(name)` and work with its `Obj` value, but evaluating `"name"` is often clearer and enforces Lyng semantics consistently.
+
+### 8) Execute scripts with parameters; call Lyng functions from Kotlin
+
+There are two convenient patterns.
+
+1) Evaluate a Lyng call expression directly:
+
+```kotlin
+// Suppose Lyng defines: fun add(a, b) = a + b
+scope.eval("fun add(a, b) = a + b")
+
+val sum = scope.eval("add(20, 22)").toKotlin(scope) // -> 42
+```
+
+2) Call a Lyng function by name via a prepared call scope:
+
+```kotlin
+// Ensure the function exists in the scope
+scope.eval("fun add(a, b) = a + b")
+
+// Look up the function object
+val addFn = scope.get("add")!!.value as Statement
+
+// Create a child scope with arguments (as Lyng Objs)
+val callScope = scope.createChildScope(
+    args = Arguments(listOf(ObjInt(20), ObjInt(22)))
+)
+
+val resultObj = addFn.execute(callScope)
+val result = resultObj.toKotlin(scope) // -> 42
+```
+
+If you need to pass complex data (lists, maps), construct the corresponding Lyng `Obj` types (`ObjList`, `ObjMap`, etc.) and pass them in `Arguments`.
+
+### 9) Create your own packages and import them in Lyng
+
+Lyng supports packages that are imported from scripts. You can register packages programmatically via `ImportManager` or by providing source texts that declare `package ...`.
+
+Key concepts:
+
+- `ImportManager` holds package registrations and lazily builds `ModuleScope`s when first imported.
+- Every `Scope` has `currentImportProvider` and (if it’s an `ImportManager`) a convenience `importManager` to register packages.
+
+Register a Kotlin‑built package:
+
+```kotlin
+val scope = Script.newScope()
+
+// Access the import manager behind this scope
+val im: ImportManager = scope.importManager
+
+// Register a package "my.tools"
+im.addPackage("my.tools") { module: ModuleScope ->
+    // Expose symbols inside the module scope
+    module.addConst("version", ObjString("1.0"))
+    module.addFn<ObjInt>("triple") {
+        val x = args.firstAndOnly() as ObjInt
+        ObjInt(x.value * 3)
+    }
+}
+
+// Use it from Lyng
+scope.eval("""
+    import my.tools.*
+    val v = triple(14)
+""")
+val v = scope.eval("v").toKotlin(scope) // -> 42
+```
+
+Register a package from Lyng source text:
+
+```kotlin
+val pkgText = """
+    package math.extra
+
+    fun sqr(x) = x * x
+""".trimIndent()
+
+scope.importManager.addTextPackages(pkgText)
+
+scope.eval("""
+    import math.extra.*
+    val s = sqr(12)
+""")
+val s = scope.eval("s").toKotlin(scope) // -> 144
+```
+
+You can also register from parsed `Source` instances via `addSourcePackages(source)`.
+
+### 10) Executing from files, security, and isolation
+
+- To run code from a file, read it and pass to `scope.eval(text)` or compile with `Compiler.compile(Source(fileName, text))`.
+- `ImportManager` takes an optional `SecurityManager` if you need to restrict what packages or operations are available. By default, `Script.defaultImportManager` allows everything suitable for embedded use; clamp it down in sandboxed environments.
+- For isolation, create fresh modules/scopes via `Scope.new()` or `Script.newScope()` when you need a clean environment per request.
+
+```kotlin
+// Fresh module based on the default manager, without the standard prelude
+val isolated = net.sergeych.lyng.Scope.new()
+```
+
+### 11) Tips and troubleshooting
+
+- All values that cross the boundary must be Lyng `Obj` instances. Convert Kotlin values explicitly (e.g., `ObjInt`, `ObjReal`, `ObjString`).
+- Use `toKotlin(scope)` to get Kotlin values back. Collections convert to Kotlin collections recursively.
+- Most public API in Lyng is suspendable. If you are not already in a coroutine, wrap calls in `runBlocking { ... }` on the JVM for quick tests.
+- When registering packages, names must be unique. Register before you compile/evaluate scripts that import them.
+- To debug scope content, `scope.toString()` and `scope.trace()` can help during development.
+
+### 12) Handling and serializing exceptions
+
+When Lyng code throws an exception, it is caught in Kotlin as an `ExecutionError`. This error wraps the actual Lyng `Obj` that was thrown (which could be a built-in `ObjException` or a user-defined `ObjInstance`).
+
+To simplify handling these objects from Kotlin, several extension methods are provided on the `Obj` class. These methods work uniformly regardless of whether the exception is built-in or user-defined.
+
+#### Uniform Exception API
+
+| Method | Description |
+| :--- | :--- |
+| `obj.isLyngException()` | Returns `true` if the object is an instance of `Exception`. |
+| `obj.isInstanceOf("ClassName")` | Returns `true` if the object is an instance of the named Lyng class or its ancestors. |
+| `obj.getLyngExceptionMessage(scope?=null)` | Returns the exception message as a Kotlin `String`. |
+| `obj.getLyngExceptionMessageWithStackTrace(scope?=null)` | Returns a detailed message with a formatted stack trace. |
+| `obj.getLyngExceptionString(scope)` | Returns a formatted string including the class name, message, and primary throw site. |
+| `obj.getLyngExceptionStackTrace(scope)` | Returns the stack trace as an `ObjList` of `StackTraceEntry`. |
+| `obj.getLyngExceptionExtraData(scope)` | Returns the extra data associated with the exception. |
+| `obj.raiseAsExecutionError(scope?=null)` | Rethrows the object as a Kotlin `ExecutionError`. |
+
+#### Example: Serialization and Rethrowing
+
+You can serialize Lyng exception objects using `Lynon` to transmit them across boundaries and then rethrow them.
+
+```kotlin
+try {
+    scope.eval("throw MyUserException(404, \"Not Found\")")
+} catch (e: ExecutionError) {
+    // 1. Serialize the Lyng exception object
+    val encoded: UByteArray = lynonEncodeAny(scope, e.errorObject)
+
+    // ... (transmit 'encoded' byte array) ...
+
+    // 2. Deserialize it back to an Obj in a different context
+    val decoded: Obj = lynonDecodeAny(scope, encoded)
+
+    // 3. Properly rethrow it on the Kotlin side using the uniform API
+    decoded.raiseAsExecutionError(scope)
+}
+```
+
+---
+
+That’s it. You now have Lyng embedded in your Kotlin app: you can expose your app’s API, evaluate user scripts, and organize your own packages to import from Lyng code.

docs/exceptions_handling.md

@@ -129,14 +129,16 @@ Serializable class that conveys information about the exception. Important membe
 | name              | description                                            |
 |-------------------|--------------------------------------------------------|
 | message           | String message                                           |
-| stackTrace        | lyng stack trace, list of `StackTraceEntry`, see below |
+| stackTrace()      | lyng stack trace, list of `StackTraceEntry`, see below   |
 | printStackTrace() | format and print stack trace using println()             |
 
+> **Note for Kotlin users**: When working with Lyng exceptions from Kotlin, you can use extension methods like `getLyngExceptionMessageWithStackTrace()`. See [Embedding Lyng](embedding.md#12-handling-and-serializing-exceptions) for the full API.
+
 ## StackTraceEntry
 
 A simple structire that stores single entry in Lyng stack, it is created automatically on exception creation:
 
-```kotlin
+```lyng
 class StackTraceEntry(
     val sourceName: String,
     val line: Int,
@@ -150,22 +152,116 @@ class StackTraceEntry(
 
 # Custom error classes
 
-_this functionality is not yet released_
+You can define your own exception classes by inheriting from the built-in `Exception` class. This allows you to create specific error types for your application logic and catch them specifically.
+
+## Defining a custom exception
+
+To define a custom exception, create a class that inherits from `Exception`:
+
+```lyng
+class MyUserException : Exception("something went wrong")
+```
+
+You can also pass the message dynamically:
+
+```lyng
+class MyUserException(m) : Exception(m)
+
+throw MyUserException("custom error message")
+```
+
+If you don't provide a message to the `Exception` constructor, the class name will be used as the default message:
+
+```lyng
+class SimpleException : Exception
+
+val e = SimpleException()
+assertEquals("SimpleException", e.message)
+```
+
+## Throwing and catching custom exceptions
+
+Custom exceptions are thrown using the `throw` keyword and can be caught using `catch` blocks, just like standard exceptions:
+
+```lyng
+class ValidationException(m) : Exception(m)
+
+try {
+    throw ValidationException("Invalid input")
+}
+catch(e: ValidationException) {
+    println("Caught validation error: " + e.message)
+}
+catch(e: Exception) {
+    println("Caught other exception: " + e.message)
+}
+```
+
+Since user exceptions are real classes, inheritance works as expected:
+
+```lyng
+class BaseError : Exception
+class DerivedError : BaseError
+
+try {
+    throw DerivedError()
+}
+catch(e: BaseError) {
+    // This will catch DerivedError as well
+    assert(e is DerivedError)
+}
+```
+
+## Accessing extra data
+
+You can add your own fields to custom exception classes to carry additional information:
+
+```lyng
+class NetworkException(m, val statusCode) : Exception(m)
+
+try {
+    throw NetworkException("Not Found", 404)
+}
+catch(e: NetworkException) {
+    println("Error " + e.statusCode + ": " + e.message)
+}
+```
 
 # Standard exception classes
 
 | class                      | notes                                                 |
 |----------------------------|-------------------------------------------------------|
-| Exception                  | root of al throwable objects                          |
+| Exception                  | root of all throwable objects                         |
 | NullReferenceException     |                                                       |
 | AssertionFailedException   |                                                       | 
 | ClassCastException         |                                                       |
 | IndexOutOfBoundsException  |                                                       |
 | IllegalArgumentException   |                                                       | 
+| IllegalStateException      |                                                       |
+| NoSuchElementException     |                                                       |
 | IllegalAssignmentException | assigning to val, etc.                                |
 | SymbolNotDefinedException  |                                                       |
 | IterationEndException      | attempt to read iterator past end, `hasNext == false` |
-| AccessException            | attempt to access private members or like             |
-| UnknownException           | unexpected kotlin exception caught                    |
-|                            |                                                       |
+| IllegalAccessException     | attempt to access private members or like             |
+| UnknownException           | unexpected internal exception caught                  |
+| NotFoundException          |                                                       |
+| IllegalOperationException  |                                                       |
+| UnsetException             | access to uninitialized late-init val                 |
+| NotImplementedException    | used by `TODO()`                                      |
+| SyntaxError                |                                                       |
 
+
+### Symbol resolution errors
+
+For compatibility, `SymbolNotFound` is an alias of `SymbolNotDefinedException`. You can catch either name in examples and tests.
+
+Example:
+
+```lyng
+try {
+    nonExistingMethod()
+}
+catch(e: SymbolNotFound) {
+    // handle
+}
+```

docs/fix-scope-parent-cycle.md

@@ -0,0 +1,34 @@
+## Fix: prevent cycles in scope parent chain during pooled frame reuse
+
+### What changed
+- Scope.resetForReuse now fully detaches a reused scope from its previous chain/state before re-parenting:
+  - sets `parent = null` and regenerates `frameId`
+  - clears locals/slots/bindings caches
+  - only after that, validates the new parent with `ensureNoCycle` and assigns it
+- ScopePool.borrow on all targets (JVM, Android, JS, Native, Wasm) now has a defensive fallback:
+  - if `resetForReuse` throws `IllegalStateException` indicating a parent-chain cycle, the pool allocates a fresh `Scope` instead of failing.
+
+### Why
+In some nested call patterns (notably instance method calls where an instance is produced by another function and immediately used), the same pooled `Scope` object can be rebound into a chain that already (transitively) contains it. Reassigning `parent` in that case forms a structural cycle, which `ensureNoCycle` correctly detects and throws. This could surface as:
+
+```
+IllegalStateException: cycle detected in scope parent chain assignment
+  at net.sergeych.lyng.Scope.ensureNoCycle(...)
+  at net.sergeych.lyng.Scope.resetForReuse(...)
+  at net.sergeych.lyng.ScopePool.borrow(...)
+  ... during instance method invocation
+```
+
+The fix removes the failure mode by:
+1) Detaching the reused frame from its prior chain/state before validating and assigning the new parent.
+2) Falling back to a new frame allocation if a cycle is still detected (extremely rare and cheap vs. a crash).
+
+### Expected effects
+- Eliminates sporadic `cycle detected in scope parent chain` crashes during instance method invocation.
+- No change to public API or normal semantics.
+- Pooling remains enabled by default; the fallback only triggers on the detected cycle edge case.
+- Negligible performance impact: fresh allocation is used only when a cycle would have crashed the VM previously.
+
+### Notes
+- The fix is platform-wide (all ScopePool actuals are covered).
+- We recommend adding/keeping a regression test that exercises: a class with a method, a function returning an instance, and an exported function calling the instance method. The test should pass without exceptions.

docs/formatter.md

@@ -0,0 +1,62 @@
+# Lyng formatter (core, CLI, and IDE)
+
+This document describes the Lyng code formatter included in this repository. The formatter lives in the core library (`:lynglib`), is available from the CLI (`lyng fmt`), and is used by the IntelliJ plugin.
+
+## Core library
+
+Package: `net.sergeych.lyng.format`
+
+- `LyngFormatConfig`
+  - `indentSize` (default 4)
+  - `useTabs` (default false)
+  - `continuationIndentSize` (default 8)
+  - `maxLineLength` (default 120)
+  - `applySpacing` (default false)
+  - `applyWrapping` (default false)
+- `LyngFormatter`
+  - `reindent(text, config)` — recomputes indentation from scratch (braces, `else/catch/finally` alignment, continuation indent under `(` `)` and `[` `]`), idempotent.
+  - `format(text, config)` — runs `reindent` and, depending on `config`, optionally applies:
+    - a safe spacing pass (commas/operators/colons/keyword parens; member access `.` remains tight; no changes to strings/comments), and
+    - a controlled wrapping pass for long call arguments (no trailing commas).
+
+Both passes are designed to be idempotent. Extensive tests live under `:lynglib/src/commonTest/.../format`.
+
+## CLI formatter
+
+```
+lyng fmt [--check] [--in-place|-i] [--spacing] [--wrap] <file1.lyng> [file2.lyng ...]
+```
+
+- Defaults: indent-only; spacing and wrapping are OFF unless flags are provided.
+- `--check` prints files that would change and exits with code 2 if any changes are detected.
+- `--in-place`/`-i` rewrites files in place (default if not using `--check`).
+- `--spacing` enables the safe spacing pass (commas/operators/colons/keyword parens).
+- `--wrap` enables controlled wrapping of long call argument lists (respects `maxLineLength`, no trailing commas).
+
+Examples:
+
+```
+# check formatting without modifying files
+lyng fmt --check docs/samples/fs_sample.lyng
+
+# format in place with spacing rules enabled
+lyng fmt --spacing -i docs/samples/fs_sample.lyng
+
+# format in place with spacing + wrapping
+lyng fmt --spacing --wrap -i src/**/*.lyng
+```
+
+## IntelliJ plugin
+
+- Indentation: always enabled, idempotent; the plugin computes per-line indent via the core formatter.
+- Spacing/wrapping: optional and OFF by default.
+  - Settings/Preferences → Lyng Formatter provides toggles:
+    - "Enable spacing normalization (commas/operators/colons/keyword parens)"
+    - "Enable line wrapping (120 cols) [experimental]"
+  - Reformat Code applies: indentation first, then spacing, then wrapping if toggled.
+
+## Design notes
+
+- Single source of truth: The core formatter is used by CLI and IDE to keep behavior consistent.
+- Stability first: Spacing/wrapping are gated by flags/toggles; indentation from scratch is always safe and idempotent.
+- Non-destructive: The formatter carefully avoids changing string/char literals and comment contents.

docs/idea_plugin.md

@@ -0,0 +1,29 @@
+# Plugin for IntelliJ IDEA
+
+[//]: # (excludeFromIndex)
+
+We introduce the alpha version of the plugin for IntelliJ IDEA 2024.3.x+ IDE variants. It is compatible with 2025.x and
+should be compatible with other IDEA flavors, notably [OpenIDE](https://openide.ru/). It supports the following features:
+
+- syntax highlighting (2 stage, fast and more accurate that analyses in background)
+- reformat code (indents, spaces)
+- reformat on paste
+- smart enter key
+
+Features are configurable via the plugin settings page, in system settings.
+
+> Recommended for IntelliJ-based IDEs: While IntelliJ can import TextMate bundles
+> (Settings/Preferences → Editor → TextMate Bundles), the native Lyng plugin provides
+> better support (formatting, smart enter, background analysis, etc.). Prefer installing
+> this plugin over using a TextMate bundle.
+
+### Install
+
+- From ZIP: download the archive below, then in IntelliJ IDEA open Settings/Preferences → Plugins →
+  gear icon → Install Plugin from Disk… and select the downloaded ZIP. Restart IDE if prompted.
+- Alternatively, if/when the plugin is published to a marketplace, you will be able to install it
+  directly from the “Marketplace” tab (not yet available).
+
+### [Download plugin v0.0.2-SNAPSHOT](https://lynglang.com/distributables/lyng-idea-0.0.2-SNAPSHOT.zip)
+
+Your ideas and bugreports are welcome on the [project gitea page](https://gitea.sergeych.net/SergeychWorks/lyng/issues)

docs/json_and_kotlin_serialization.md

@@ -0,0 +1,167 @@
+# Json support
+
+Since 1.0.5 we start adding JSON support. Versions 1,0,6* support serialization of the basic types, including lists and
+maps, and simple classes. Multiple inheritance may produce incorrect results, it is work in progress.
+
+## Serialization in Lyng
+
+    // in lyng
+    assertEquals("{\"a\":1}", {a: 1}.toJsonString())
+    void
+    >>> void
+
+Simple classes serialization is supported:
+
+    import lyng.serialization
+    class Point(foo,bar) {
+        val t = 42
+    }
+    // val is not serialized
+    assertEquals( "{\"foo\":1,\"bar\":2}", Point(1,2).toJsonString() )
+    >>> void
+
+Note that mutable members are serialized:
+
+    import lyng.serialization
+    
+    class Point2(foo,bar) {
+        var reason = 42
+        // but we override json serialization:
+        fun toJsonObject() {
+            { "custom": true }
+        }
+    }
+    // var is serialized instead
+    assertEquals( "{\"custom\":true}", Point2(1,2).toJsonString() )
+    >>> void
+
+Custom serialization of user classes is possible by overriding `toJsonObject` method. It must return an object which is
+serializable to Json. Most often it is a map, but any object is accepted, that makes it very flexible:
+
+    import lyng.serialization
+    
+    class Point2(foo,bar) {
+        var reason = 42
+        // but we override json serialization:
+        fun toJsonObject() {
+            { "custom": true }
+        }
+    }
+    class Custom {
+        fun toJsonObject() {
+            "full freedom"
+        }
+    }
+    // var is serialized instead
+    assertEquals( "\"full freedom\"", Custom().toJsonString() )
+    >>> void
+
+Please note that `toJsonString` should be used to get serialized string representation of the object. Don't call
+`toJsonObject` directly, it is not intended to be used outside the serialization library.
+
+## Kotlin side interfaces
+
+The "Batteries included" principle is also applied to serialization.
+
+- `Obj.toJson()` provides Kotlin `JsonElement`
+- `Obj.toJsonString()` provides Json string representation
+- `Obj.decodeSerializableWith()` and `Obj.decodeSerializable()` allows to decode Lyng classes as Kotlin objects using
+  `kotlinx.serialization`:
+
+```kotlin
+/**
+ * Decodes the current object into a deserialized form using the provided deserialization strategy.
+ * It is based on [Obj.toJson] and uses existing Kotlin Json serialization, without string representation
+ * (only `JsonElement` to carry information between Kotlin and Lyng serialization worlds), thus efficient.
+ *
+ * @param strategy The deserialization strategy that defines how the object should be decoded.
+ * @param scope An optional scope used during deserialization to define the context. Defaults to a new instance of Scope.
+ * @return The deserialized object of type T.
+ */
+suspend fun <T> Obj.decodeSerializableWith(strategy: DeserializationStrategy<T>, scope: Scope = Scope()): T =
+    Json.decodeFromJsonElement(strategy, toJson(scope))
+
+/**
+ * Decodes a serializable object of type [T] using the provided decoding scope. The deserialization uses
+ * [Obj.toJson] and existing Json based serialization ithout using actual string representation, thus
+ * efficient.
+ *
+ * @param T The type of the object to be decoded. Must be a reified type.
+ * @param scope The scope used during decoding. Defaults to a new instance of [Scope].
+ */
+suspend inline fun <reified T> Obj.decodeSerializable(scope: Scope = Scope()) =
+    decodeSerializableWith<T>(serializer<T>(), scope)
+```
+
+Note that lyng-2-kotlin deserialization with `kotlinx.serialization` uses JsonElement as information carrier without
+formatting and parsing actual Json strings. This is why we use `Json.decodeFromJsonElement` instead of
+`Json.decodeFromString`. Such an approach gives satisfactory performance without writing and supporting custom
+`kotlinx.serialization` codecs.
+
+### Pitfall: JSON objects and Map<String, Any?>
+
+Kotlin serialization does not support `Map<String, Any?>` as a serializable type, more general, it can't serialize `Any`. This in particular means that you can deserialize Kotlin `Map<String, T>` as long as `T` is `@Serializable` in Kotlin: 
+
+```kotlin
+@Serializable
+data class TestJson2(
+    val value: Int,
+    val inner: Map<String,Int>
+)
+
+@Test
+fun deserializeMapWithJsonTest() = runTest {
+    val x = eval("""
+        import lyng.serialization
+        { value: 1, inner: { "foo": 1, "bar": 2 }}
+    """.trimIndent()).decodeSerializable<TestJson2>()
+    // That works perfectly well:
+    assertEquals(TestJson2(1, mapOf("foo" to 1, "bar" to 2)), x)
+}
+```
+
+But what if your map has objects of different types? The approach of using polymorphism is partially applicable, but what to do with `{ one: 1, two: "two" }`?
+
+The answer is pretty simple: use `JsonObject` in your deserializable object. This class is capable of holding any JSON types and structures and is sort of a silver bullet for such cases:
+
+~~~kotlin
+@Serializable
+data class TestJson3(
+    val value: Int,
+    val inner: JsonObject
+)
+@Test
+fun deserializeAnyMapWithJsonTest() = runTest {
+    val x = eval("""
+        import lyng.serialization
+        { value: 12, inner: { "foo": 1, "bar": "two" }}
+    """.trimIndent()).decodeSerializable<TestJson3>()
+    assertEquals(TestJson3(12, JsonObject(mapOf("foo" to JsonPrimitive(1), "bar" to Json.encodeToJsonElement("two")))), x)
+}
+~~~
+
+
+# List of supported types
+
+| Lyng type | JSON type | notes       |
+|-----------|-----------|-------------|
+| `Int`     | number    |             |
+| `Real`    | number    |             |
+| `String`  | string    |             |
+| `Bool`    | boolean   |             |
+| `null`    | null      |             |
+| `Instant` | string    | ISO8601 (1) |
+| `List`    | array     | (2)         |
+| `Map`     | object    | (2)         |
+
+
+(1)
+: ISO8601 flavor 1970-05-06T06:00:00.000Z in used; number of fractional digits depends on the truncation
+on [Instant](time.md), see `Instant.truncateTo...` functions.
+
+(2)
+: List may contain any objects serializable to Json.
+
+(3)
+: Map keys must be strings, map values may be any objects serializable to Json.
+

docs/lyng.io.fs.md

@@ -0,0 +1,232 @@
+### lyng.io.fs — async filesystem access for Lyng scripts
+
+This module provides a uniform, suspend-first filesystem API to Lyng scripts, backed by Kotlin Multiplatform implementations.
+
+- JVM/Android/Native: Okio `FileSystem.SYSTEM` (non-blocking via coroutine dispatcher)
+- JS/Node: Node filesystem (currently via Okio node backend; a native `fs/promises` backend is planned)
+- JS/Browser and Wasm: in-memory virtual filesystem for now
+
+It exposes a Lyng class `Path` with methods for file and directory operations, including streaming readers for large files.
+
+It is a separate library because access to the filesystem is a security risk we compensate with a separate API that user must explicitly include to the dependency and allow. Together with `FsAccessPolicy` that is required to `createFs()` which actually adds the filesystem to the scope, the security risk is isolated.
+
+Also, it helps keep Lyng core small and focused.
+
+---
+
+#### Add the library to your project (Gradle)
+
+If you use this repository as a multi-module project, add a dependency on `:lyngio`:
+
+```kotlin
+dependencies {
+    implementation("net.sergeych:lyngio:0.0.1-SNAPSHOT")
+}
+```
+Note on maven repository. Lyngio uses the same maven as Lyng code (`lynglib`) so it is most likely already in your project. If not, add it to the proper section of your `build.gradle.kts` or settings.gradle.kts:
+
+```kotlin
+    repositories {
+        maven("https://gitea.sergeych.net/api/packages/SergeychWorks/maven")
+    }
+```
+
+This brings in:
+
+- `:lynglib` (Lyng engine)
+- Okio (`okio`, `okio-fakefilesystem`, and `okio-nodefilesystem` for JS)
+- Kotlin coroutines
+
+---
+
+#### Install the module into a Lyng Scope
+
+The filesystem module is not installed automatically. You must explicitly register it in the scope’s `ImportManager` using the installer. You can customize access control via `FsAccessPolicy`.
+
+Kotlin (host) bootstrap example:
+
+```kotlin
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.io.fs.createFs
+import net.sergeych.lyngio.fs.security.PermitAllAccessPolicy
+
+val scope: Scope = Scope.new()
+val installed: Boolean = createFs(PermitAllAccessPolicy, scope)
+// installed == true on first registration in this ImportManager, false on repeats
+
+// In scripts (or via scope.eval), import the module to use its symbols:
+scope.eval("import lyng.io.fs")
+```
+
+You can install with a custom policy too (see Access policy below).
+
+---
+
+#### Using from Lyng scripts
+
+```lyng
+val p = Path("/tmp/hello.txt")
+
+// Text I/O
+p.writeUtf8("Hello Lyng!\n")
+println(p.readUtf8())
+
+// Binary I/O
+val data = Buffer.fromHex("deadbeef")
+p.writeBytes(data)
+
+// Existence and directories
+assertTrue(p.exists())
+Path("/tmp/work").mkdirs()
+
+// Listing
+for (entry in Path("/tmp").list()) {
+    println(entry)
+}
+
+// Globbing
+val txts = Path("/tmp").glob("**/*.txt").toList()
+
+// Copy / Move / Delete
+Path("/tmp/a.txt").copy("/tmp/b.txt", overwrite=true)
+Path("/tmp/b.txt").move("/tmp/c.txt", overwrite=true)
+Path("/tmp/c.txt").delete()
+
+// Streaming large files (does not load whole file into memory)
+var bytes = 0
+val it = Path("/tmp/big.bin").readChunks(1_048_576) // 1MB chunks
+val iter = it.iterator()
+while (iter.hasNext()) {
+    val chunk = iter.next()
+    bytes = bytes + chunk.size()
+}
+
+// Text chunks and lines
+for (s in Path("/tmp/big.txt").readUtf8Chunks(64_000)) {
+    // process each string chunk
+}
+
+for (ln in Path("/tmp/big.txt").lines()) {
+    // process line by line
+}
+```
+
+---
+
+#### API (Lyng class `Path`)
+
+Constructor:
+- `Path(path: String)` — creates a Path object
+- `Paths(path: String)` — alias
+
+File and directory operations (all suspend under the hood):
+- `name`: name, `String`
+- `segments`: list of parsed path segments (directories)
+- `parent`: parent directory, `Path?`; null if root
+- `exists(): Bool`
+- `isFile(): Bool` — true if the path points to a regular file (cached metadata)
+- `isDirectory(): Bool` — true if the path points to a directory (cached metadata)
+- `size(): Int?` — size in bytes or null if unknown (cached metadata)
+- `createdAt(): Instant?` — creation time as Lyng `Instant`, or null (cached metadata)
+- `createdAtMillis(): Int?` — creation time in epoch milliseconds, or null (cached metadata)
+- `modifiedAt(): Instant?` — last modification time as Lyng `Instant`, or null (cached metadata)
+- `modifiedAtMillis(): Int?` — last modification time in epoch milliseconds, or null (cached metadata)
+- `list(): List<Path>` — children of a directory
+- `readBytes(): Buffer`
+- `writeBytes(bytes: Buffer)`
+- `appendBytes(bytes: Buffer)`
+- `readUtf8(): String`
+- `writeUtf8(text: String)`
+- `appendUtf8(text: String)`
+- `metadata(): Map` — keys: `isFile`, `isDirectory`, `size`, `createdAtMillis`, `modifiedAtMillis`, `isSymlink`
+- `mkdirs(mustCreate: Bool = false)`
+- `move(to: Path|String, overwrite: Bool = false)`
+- `delete(mustExist: Bool = false, recursively: Bool = false)`
+- `copy(to: Path|String, overwrite: Bool = false)`
+- `glob(pattern: String): List<Path>` — supports `**`, `*`, `?` (POSIX-style)
+
+Streaming readers for big files:
+- `readChunks(size: Int = 65536): Iterator<Buffer>` — iterate fixed-size byte chunks
+- `readUtf8Chunks(size: Int = 65536): Iterator<String>` — iterate text chunks by character count
+- `lines(): Iterator<String>` — line iterator built on `readUtf8Chunks`
+
+Notes:
+- Iterators implement Lyng iterator protocol. If you break early from a loop, the runtime will attempt to call `cancelIteration()` when available.
+- Current implementations chunk in memory. The public API is stable; internals will evolve to true streaming on all platforms.
+- Attribute accessors (`isFile`, `isDirectory`, `size`, `createdAt*`, `modifiedAt*`) cache a metadata snapshot inside the `Path` instance to avoid repeated filesystem calls during a sequence of queries. `metadata()` remains available for bulk access.
+
+---
+
+#### Access policy (security)
+
+Access control is enforced by `FsAccessPolicy`. You pass a policy at installation time. The module wraps the filesystem with a secured decorator that consults the policy for each primitive operation.
+
+Main types:
+- `FsAccessPolicy` — your policy implementation
+- `PermitAllAccessPolicy` — allows all operations (default for testing)
+- `AccessOp` (sealed) — operations the policy can decide on:
+  - `ListDir(path)`
+  - `CreateFile(path)`
+  - `OpenRead(path)`
+  - `OpenWrite(path)`
+  - `OpenAppend(path)`
+  - `Delete(path)`
+  - `Rename(from, to)`
+  - `UpdateAttributes(path)` — defaults to write-level semantics
+
+Minimal denying policy example (imports omitted for brevity):
+
+```kotlin
+val denyWrites = object : FsAccessPolicy {
+    override suspend fun check(op: AccessOp, ctx: AccessContext): AccessDecision = when (op) {
+        is AccessOp.OpenRead, is AccessOp.ListDir -> AccessDecision(Decision.Allow)
+        else -> AccessDecision(Decision.Deny, reason = "read-only policy")
+    }
+}
+
+createFs(denyWrites, scope)
+scope.eval("import lyng.io.fs")
+```
+
+Composite operations like `copy` and `move` are checked as a set of primitives (e.g., `OpenRead(src)` + `Delete(dst)` if overwriting + `CreateFile(dst)` + `OpenWrite(dst)`).
+
+---
+
+#### Errors and exceptions
+
+Policy denials are surfaced as Lyng runtime errors, not raw Kotlin exceptions:
+- Internally, a denial throws `AccessDeniedException`. The module maps it to `ObjIllegalOperationException` wrapped into an `ExecutionError` visible to scripts.
+
+Examples (Lyng):
+
+```lyng
+import lyng.io.fs
+val p = Path("/protected/file.txt")
+try {
+    p.writeUtf8("x")
+    fail("expected error")
+} catch (e) {
+    // e is an ExecutionError; message contains the policy reason
+}
+```
+
+Other I/O failures (e.g., not found, not a directory) are also raised as Lyng errors (`ObjIllegalStateException`, `ObjIllegalArgumentException`, etc.) depending on context.
+
+---
+
+#### Platform notes
+
+- JVM/Android/Native: synchronous Okio calls are executed on `Dispatchers.IO` (JVM/Android) or `Dispatchers.Default` (Native) to avoid blocking the main thread.
+- NodeJS: currently uses Okio’s Node backend. For heavy I/O, a native `fs/promises` backend is planned to fully avoid event-loop blocking.
+- Browser/Wasm: uses an in-memory filesystem for now. Persistent backends (IndexedDB or File System Access API) are planned.
+
+---
+
+#### Roadmap
+
+- Native NodeJS backend using `fs/promises`
+- Browser persistent storage (IndexedDB)
+- Streaming readers/writers over real OS streams
+- Attribute setters and richer metadata
+
+If you have specific needs (e.g., sandboxing, virtual roots), implement a custom `FsAccessPolicy` or ask us to add a helper.

docs/lyng.io.process.md

@@ -0,0 +1,136 @@
+### lyng.io.process — Process execution and control for Lyng scripts
+
+This module provides a way to run external processes and shell commands from Lyng scripts. It is designed to be multiplatform and uses coroutines for non-blocking execution.
+
+> **Note:** `lyngio` is a separate library module. It must be explicitly added as a dependency to your host application and initialized in your Lyng scopes.
+
+---
+
+#### Add the library to your project (Gradle)
+
+If you use this repository as a multi-module project, add a dependency on `:lyngio`:
+
+```kotlin
+dependencies {
+    implementation("net.sergeych:lyngio:0.0.1-SNAPSHOT")
+}
+```
+
+For external projects, ensure you have the appropriate Maven repository configured (see `lyng.io.fs` documentation).
+
+---
+
+#### Install the module into a Lyng Scope
+
+The process module is not installed automatically. You must explicitly register it in the scope’s `ImportManager` using `createProcessModule`. You can customize access control via `ProcessAccessPolicy`.
+
+Kotlin (host) bootstrap example:
+
+```kotlin
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.Script
+import net.sergeych.lyng.io.process.createProcessModule
+import net.sergeych.lyngio.process.security.PermitAllProcessAccessPolicy
+
+// ... inside a suspend function or runBlocking
+val scope: Scope = Script.newScope()
+createProcessModule(PermitAllProcessAccessPolicy, scope)
+
+// In scripts (or via scope.eval), import the module:
+scope.eval("import lyng.io.process")
+```
+
+---
+
+#### Using from Lyng scripts
+
+```lyng
+import lyng.io.process
+
+// Execute a process with arguments
+val p = Process.execute("ls", ["-l", "/tmp"])
+for (line in p.stdout) {
+    println("OUT: " + line)
+}
+val exitCode = p.waitFor()
+println("Process exited with: " + exitCode)
+
+// Run a shell command
+val sh = Process.shell("echo 'Hello from shell' | wc -w")
+for (line in sh.stdout) {
+    println("Word count: " + line.trim())
+}
+
+// Platform information
+val details = Platform.details()
+println("OS: " + details.name + " " + details.version + " (" + details.arch + ")")
+if (details.kernelVersion != null) {
+    println("Kernel: " + details.kernelVersion)
+}
+
+if (Platform.isSupported()) {
+    println("Processes are supported!")
+}
+```
+
+---
+
+#### API Reference
+
+##### `Process` (static methods)
+- `execute(executable: String, args: List<String>): RunningProcess` — Start an external process.
+- `shell(command: String): RunningProcess` — Run a command through the system shell (e.g., `/bin/sh` or `cmd.exe`).
+
+##### `RunningProcess` (instance methods)
+- `stdout: Flow` — Standard output stream as a Lyng Flow of lines.
+- `stderr: Flow` — Standard error stream as a Lyng Flow of lines.
+- `waitFor(): Int` — Wait for the process to exit and return the exit code.
+- `signal(name: String)` — Send a signal to the process (e.g., `"SIGINT"`, `"SIGTERM"`, `"SIGKILL"`).
+- `destroy()` — Forcefully terminate the process.
+
+##### `Platform` (static methods)
+- `details(): Map` — Get platform details. Returned map keys: `name`, `version`, `arch`, `kernelVersion`.
+- `isSupported(): Bool` — True if process execution is supported on the current platform.
+
+---
+
+#### Security Policy
+
+Process execution is a sensitive operation. `lyngio` uses `ProcessAccessPolicy` to control access to `execute` and `shell` operations.
+
+- `ProcessAccessPolicy` — Interface for custom policies.
+- `PermitAllProcessAccessPolicy` — Allows all operations.
+- `ProcessAccessOp` (sealed) — Operations to check:
+    - `Execute(executable, args)`
+    - `Shell(command)`
+
+Example of a restricted policy in Kotlin:
+
+```kotlin
+import net.sergeych.lyngio.fs.security.AccessDecision
+import net.sergeych.lyngio.fs.security.Decision
+import net.sergeych.lyngio.process.security.ProcessAccessOp
+import net.sergeych.lyngio.process.security.ProcessAccessPolicy
+
+val restrictedPolicy = object : ProcessAccessPolicy {
+    override suspend fun check(op: ProcessAccessOp, ctx: AccessContext): AccessDecision {
+        return when (op) {
+            is ProcessAccessOp.Execute -> {
+                if (op.executable == "ls") AccessDecision(Decision.Allow)
+                else AccessDecision(Decision.Deny, "Only 'ls' is allowed")
+            }
+            is ProcessAccessOp.Shell -> AccessDecision(Decision.Deny, "Shell is forbidden")
+        }
+    }
+}
+createProcessModule(restrictedPolicy, scope)
+```
+
+---
+
+#### Platform Support
+
+- **JVM:** Full support using `ProcessBuilder`.
+- **Native (Linux/macOS):** Support via POSIX.
+- **Windows:** Support planned.
+- **Android/JS/iOS/Wasm:** Currently not supported; `isSupported()` returns `false` and attempts to run processes will throw `UnsupportedOperationException`.

docs/lyng_cli.md

@@ -0,0 +1,141 @@
+### Lyng CLI (`lyng`)
+
+The Lyng CLI is the reference command-line tool for the Lyng language. It lets you:
+
+- Run Lyng scripts from files or inline strings (shebangs accepted)
+- Use standard argument passing (`ARGV`) to your scripts.
+- Format Lyng source files via the built-in `fmt` subcommand.
+
+
+#### Building on Linux
+
+Requirements:
+- JDK 17+ (for Gradle and the JVM distribution)
+- GNU zip utilities (for packaging the native executable)
+- upx tool (executable in-place compression)
+
+The repository provides convenience scripts in `bin/` for local builds and installation into `~/bin`.
+
+Note: In this repository the scripts are named `bin/local_release` and `bin/local_jrelease`. In some environments these may be aliased as `bin/release` and `bin/jrelease`. The steps below use the actual file names present here.
+
+
+##### Option A: Native linuxX64 executable (`lyng`)
+
+1) Build the native binary:
+
+```
+./gradlew :lyng:linkReleaseExecutableLinuxX64
+```
+
+2) Install and package locally:
+
+```
+bin/local_release
+```
+
+What this does:
+- Copies the built executable to `~/bin/lyng` for easy use in your shell.
+- Produces `distributables/lyng-linuxX64.zip` containing the `lyng` executable.
+
+
+##### Option B: JVM distribution (`jlyng` launcher)
+
+This creates a JVM distribution with a launcher script and links it to `~/bin/jlyng`.
+
+```
+bin/local_jrelease
+```
+
+What this does:
+- Runs `./gradlew :lyng:installJvmDist` to build the JVM app distribution to `lyng/build/install/lyng-jvm`.
+- Copies the distribution under `~/bin/jlyng-jvm`.
+- Creates a symlink `~/bin/jlyng` pointing to the launcher script.
+
+
+#### Usage
+
+Once installed, ensure `~/bin` is on your `PATH`. You can then use either the native `lyng` or the JVM `jlyng` launcher (both have the same CLI surface).
+
+
+##### Running scripts
+
+- Run a script by file name and pass arguments to `ARGV`:
+
+```
+lyng path/to/script.lyng arg1 arg2
+```
+
+- Run a script whose name starts with `-` using `--` to stop option parsing:
+
+```
+lyng -- -my-script.lyng arg1 arg2
+```
+
+- Execute inline code with `-x/--execute` and pass positional args to `ARGV`:
+
+```
+lyng -x "println(\"Hello\")" more args
+```
+
+- Print version/help:
+
+```
+lyng --version
+lyng --help
+```
+
+### Use in shell scripts
+
+Standard unix shebangs (`#!`) are supported, so you can make Lyng scripts directly executable on Unix-like systems. For example:
+
+    #!/usr/bin/env lyng
+    println("Hello, world!")
+
+
+##### Formatting source: `fmt` subcommand
+
+Format Lyng files with the built-in formatter.
+
+Basic usage:
+
+```
+lyng fmt [OPTIONS] FILE...
+```
+
+Options:
+- `--check` — Check-only mode. Prints file paths that would change and exits with code 2 if any changes are needed, 0 otherwise.
+- `-i, --in-place` — Write formatted content back to the source files (off by default).
+- `--spacing` — Apply spacing normalization.
+- `--wrap`, `--wrapping` — Enable line wrapping.
+
+Semantics and exit codes:
+- Default behavior is to write formatted content to stdout. When multiple files are provided, the output is separated with `--- <path> ---` headers.
+- `--check` and `--in-place` are mutually exclusive; using both results in an error and exit code 1.
+- `--check` exits with 2 if any file would change, with 0 otherwise.
+- Other errors (e.g., I/O issues) result in a non-zero exit code.
+
+Examples:
+
+```
+# Print formatted content to stdout
+lyng fmt src/file.lyng
+
+# Format multiple files to stdout with headers
+lyng fmt src/a.lyng src/b.lyng
+
+# Check mode: list files that would change; exit 2 if changes are needed
+lyng fmt --check src/**/*.lyng
+
+# In-place formatting
+lyng fmt -i src/**/*.lyng
+
+# Enable spacing normalization and wrapping
+lyng fmt --spacing --wrap src/file.lyng
+```
+
+
+#### Notes
+
+- Both native and JVM distributions expose the same CLI interface. Use whichever best fits your environment.
+- When executing scripts, all positional arguments after the script name are available in Lyng as `ARGV`.
+- The interpreter recognizes shebang lines (`#!`) at the beginning of a script file and ignores them at runtime, so you can make Lyng scripts directly executable on Unix-like systems.

docs/lyngio.md

@@ -0,0 +1,87 @@
+### lyngio — Extended I/O and System Library for Lyng
+
+`lyngio` is a separate library that extends the Lyng core (`lynglib`) with powerful, multiplatform, and secure I/O capabilities.
+
+#### Why a separate module?
+
+1. **Security:** I/O and process execution are sensitive operations. By keeping them in a separate module, we ensure that the Lyng core remains 100% safe by default. You only enable what you explicitly need.
+2. **Footprint:** Not every script needs filesystem or process access. Keeping these as a separate module helps minimize the dependency footprint for small embedded projects.
+3. **Control:** `lyngio` provides fine-grained security policies (`FsAccessPolicy`, `ProcessAccessPolicy`) that allow you to control exactly what a script can do.
+
+#### Included Modules
+
+- **[lyng.io.fs](lyng.io.fs.md):** Async filesystem access. Provides the `Path` class for file/directory operations, streaming, and globbing.
+- **[lyng.io.process](lyng.io.process.md):** External process execution and shell commands. Provides `Process`, `RunningProcess`, and `Platform` information.
+
+---
+
+#### Quick Start: Embedding lyngio
+
+##### 1. Add Dependencies (Gradle)
+
+```kotlin
+repositories {
+    maven("https://gitea.sergeych.net/api/packages/SergeychWorks/maven")
+}
+
+dependencies {
+    // Both are required for full I/O support
+    implementation("net.sergeych:lynglib:0.0.1-SNAPSHOT")
+    implementation("net.sergeych:lyngio:0.0.1-SNAPSHOT")
+}
+```
+
+##### 2. Initialize in Kotlin (JVM or Native)
+
+To use `lyngio` modules in your scripts, you must install them into your Lyng scope and provide a security policy.
+
+```kotlin
+import net.sergeych.lyng.Script
+import net.sergeych.lyng.io.fs.createFs
+import net.sergeych.lyng.io.process.createProcessModule
+import net.sergeych.lyngio.fs.security.PermitAllAccessPolicy
+import net.sergeych.lyngio.process.security.PermitAllProcessAccessPolicy
+
+suspend fun runMyScript() {
+    val scope = Script.newScope()
+    
+    // Install modules with policies
+    createFs(PermitAllAccessPolicy, scope)
+    createProcessModule(PermitAllProcessAccessPolicy, scope)
+    
+    // Now scripts can import them
+    scope.eval("""
+        import lyng.io.fs
+        import lyng.io.process
+        
+        println("Working dir: " + Path(".").readUtf8())
+        println("OS: " + Platform.details().name)
+    """)
+}
+```
+
+---
+
+#### Security Tools
+
+`lyngio` is built with a "Secure by Default" philosophy. Every I/O or process operation is checked against a policy.
+
+- **Filesystem Security:** Implement `FsAccessPolicy` to restrict access to specific paths or operations (e.g., read-only access to a sandbox directory).
+- **Process Security:** Implement `ProcessAccessPolicy` to restrict which executables can be run or to disable shell execution entirely.
+
+For more details, see the specific module documentation:
+- [Filesystem Security Details](lyng.io.fs.md#access-policy-security)
+- [Process Security Details](lyng.io.process.md#security-policy)
+
+---
+
+#### Platform Support Overview
+
+| Platform | lyng.io.fs | lyng.io.process |
+| :--- | :---: | :---: |
+| **JVM** | ✅ | ✅ |
+| **Native (Linux/macOS)** | ✅ | ✅ |
+| **Native (Windows)** | ✅ | 🚧 (Planned) |
+| **Android** | ✅ | ❌ |
+| **NodeJS** | ✅ | ❌ |
+| **Browser / Wasm** | ✅ (In-memory) | ❌ |

docs/math.md

@@ -9,17 +9,37 @@ Same as in C++.
 | **Highest**<br>0 | power, not, calls, indexing, dot,... |
 |        1         | `%` `*` `/`                          |
 |        2         | `+` `-`                              |
-|        3         | bit shifts (NI)                      |
+|        3         | bit shifts `<<` `>>`                 |
 |        4         | `<=>` (1)                            |
 |        5         | `<=` `>=` `<` `>`                    |
 |        6         | `==` `!=`                            |
-|        7         | bitwise and `&` (NI)                 |
-|        9         | bitwise or `\|` (NI)                 |
+|        7         | bitwise and `&`                      |
+|        8         | bitwise xor `^`                      |
+|        9         | bitwise or `\|`                      |
 |        10        | `&&`                                 |
 |  11<br/>lowest   | `\|\|`                               |
 
-(NI)
-: not yet implemented.
+Bitwise operators
+: available only for `Int` values. For mixed `Int`/`Real` numeric expressions, bitwise operators are not defined.
+
+Bitwise NOT `~x`
+: unary operator that inverts all bits of a 64‑bit signed integer (`Int`). It follows two's‑complement rules, so
+  `~x` is numerically equal to `-(x + 1)`. Examples: `~0 == -1`, `~1 == -2`, `~(-1) == 0`.
+
+Examples:
+
+```
+5 & 3    // -> 1
+5 | 3    // -> 7
+5 ^ 3    // -> 6
+~0       // -> -1
+1 << 3   // -> 8
+8 >> 3   // -> 1
+```
+
+Notes:
+- Shifts operate on 64-bit signed integers (`Int` is 64-bit). Right shift `>>` is arithmetic (sign-propagating).
+- Shift count is masked to the range 0..63, similar to the JVM/Kotlin behavior (e.g., `1 << 65` equals `1 << 1`).
 
 (1)
 : Shuttle operator: `a <=> b` returns 0 if a == b, negative Int if a < b and positive Int otherwise. It is necessary to

docs/migrate_time_to_2_2.md

@@ -0,0 +1,25 @@
+# Migration of Instant and Clock
+
+## History
+
+Before kotlin 2.0, there was an excellent library, kotlinx.datetime, which was widely used everywhere, also in Lyng and its dependencies.
+
+When kotlin 2.0 was released, or soon after, JetBrains made an exptic decision to remove `Instant` and `Clock` from kotlinx.datetime and replace it with _yet experimental_ analogs in `kotlin.time`.
+
+The problem is, these were not quite the same (these weren't `@Serializable`!), so people didn't migrate with ease. Okay, then JetBrains decided to not only deprecate it but also make them unusable on Apple targets. It sort of split auditories of many published libraries to those who hate JetBrains and Apple and continue to use 1.9-2.0 compatible versions that no longer work with Kotlin 2.2 on Apple targets (but work pretty well with earlier Kotlin or on other platforms). 
+
+Later JetBrains added serializers for their new `Instant` and `Clock` types, but strangely not in the stdlib, but in newer versions of `kotlinx.serialization`. This means that plain upgrade of dependencies to 2.2 is not enough to make them work.
+
+## Solution
+
+We hereby publish a new version of Lyng, 1.0.8-SNAPSHOT, which uses `ktlin.time.Instant` and `kotlin.time.Clock` instead of `kotlinx.datetime.Instant` and `kotlinx.datetime.Clock; it is in other aspects compatible also with Lynon encoded binaries. Still you might need to migrate your code to use `kotlinx.datetime` types.
+
+So, if you are getting errors with new version, plase do:
+
+- upgrade to Kotlin 2.2
+- upgrade to Lyng 1.0.8-SNAPSHOT
+- replace in your code imports (or other uses) of`kotlinx.datetime.Clock` to `kotlin.time.Clock` and `kotlinx.datetime.Instant` to `kotlin.time.Instant`.
+
+This should solve the problem and hopefully we'll see no more suh a brillant ideas from IDEA ideologspersons.
+
+Sorry for inconvenicence and send a ray of hate to JetBrains ;)

docs/parallelism.md

@@ -1,4 +1,6 @@
-# Parallelism in Lyng
+# Multithreading/parallel execution
+
+[//]: # (topMenu)
 
 Lyng is built to me multithreaded where possible (e.g. all targets byt JS and wasmJS as for now)
 and cooperatively parallel (coroutine based) everywhere.
@@ -36,19 +38,19 @@ Launch has the only argument which should be a callable (lambda usually) that is
 
 ## Synchronization: Mutex
 
-Suppose we have a resource, that could be used concurrently, a coutner in our case. If we won'r protect it, concurrent usage cause RC, Race Condition, providing wrong result:
+Suppose we have a resource, that could be used concurrently, a counter in our case. If we won't protect it, concurrent usage cause RC, Race Condition, providing wrong result:
 
     var counter = 0
     
-    (1..4).map { 
+    (1..50).map { 
         launch {
             // slow increment:
             val c = counter
-            delay(10)
+            delay(100)
             counter = c + 1
         }
     }.forEach { it.await() }
-    assert(counter < 4)
+    assert(counter < 50) { "counter is "+counter }
     >>> void
 
 The obviously wrong result is not 4, as all coroutines capture the counter value, which is 1, then sleep for 5ms, then save 1 + 1 as result. May some coroutines will pass, so it will be 1 or 2, most likely.
@@ -205,3 +207,34 @@ Flows allow easy transforming of any [Iterable]. See how the standard Lyng libra
 
 
 [Iterable]: Iterable.md
+
+## Scope frame pooling (JVM)
+
+Lyng includes an optional optimization for function/method calls on JVM: scope frame pooling, toggled by the runtime flag `PerfFlags.SCOPE_POOL`.
+
+- Default: `SCOPE_POOL` is OFF on JVM.
+- Rationale: the current `ScopePool` implementation is not thread‑safe. Lyng targets multi‑threaded execution on most platforms, therefore we keep pooling disabled by default until a thread‑safe design is introduced.
+- When safe to enable: single‑threaded runs (e.g., micro‑benchmarks or scripts executed on a single worker) where no scopes are shared across threads.
+- How to toggle at runtime (Kotlin/JVM tests):
+  - `PerfFlags.SCOPE_POOL = true` to enable.
+  - `PerfFlags.SCOPE_POOL = false` to disable.
+- Expected effect (from our JVM micro‑benchmarks): in deep call loops, enabling pooling reduced total time by about 1.38× in a dedicated pooling benchmark; mileage may vary depending on workload.
+
+Future work: introduce thread‑safe pooling (e.g., per‑thread pools or confinement strategies) before considering enabling it by default in multi‑threaded environments.
+
+### Closures inside coroutine helpers (launch/flow)
+
+Closures executed by `launch { ... }` and `flow { ... }` resolve names using the `ClosureScope` rules:
+
+1. **Current frame locals and arguments**: Variables defined within the current closure execution.
+2. **Captured lexical ancestry**: Outer local variables captured at the site where the closure was defined (the "lexical environment").
+3. **Captured receiver members**: If the closure was defined within a class or explicitly bound to an object, it checks members of that object (`this`), following MRO and respecting visibility.
+4. **Caller environment**: Falls back to the calling context (e.g., the caller's `this` or local variables).
+5. **Global/Module fallbacks**: Final check for module-level constants and global functions.
+
+Implications:
+- Outer locals (e.g., `counter`) stay visible across suspension points.
+- Global helpers like `delay(ms)` and `yield()` are available from inside closures.
+- If you write your own async helpers, execute user lambdas under `ClosureScope(callScope, capturedCreatorScope)` and avoid manual ancestry walking.
+
+See also: [Scopes and Closures: resolution and safety](scopes_and_closures.md)

docs/perf_guide.md

@@ -0,0 +1,622 @@
+
+This document explains how to enable and measure the performance optimizations added to the Lyng interpreter. The focus is JVM‑first with safe, flag‑guarded rollouts and quick A/B testing. Other targets (JS/Wasm/Native) keep conservative defaults until validated.
+
+[//]: # (excludeFromIndex)
+
+## Overview
+
+Optimizations are controlled by runtime‑mutable flags in `net.sergeych.lyng.PerfFlags`, initialized from platform‑specific static defaults `net.sergeych.lyng.PerfDefaults` (KMP `expect/actual`).
+
+- JVM/Android defaults are aggressive (e.g. `RVAL_FASTPATH=true`).
+- Non‑JVM defaults are conservative (e.g. `RVAL_FASTPATH=false`).
+
+All flags are `var` and can be flipped at runtime (e.g., from tests or host apps) for A/B comparisons.
+
+### Workload presets (JVM‑first)
+
+To simplify switching between recommended flag sets for different workloads, use `net.sergeych.lyng.PerfProfiles`:
+
+```
+val snap = PerfProfiles.apply(PerfProfiles.Preset.BENCH)  // or BASELINE / BOOKS
+// ... run workload ...
+PerfProfiles.restore(snap)  // restore previous flags
+```
+
+- BASELINE: restores platform defaults from `PerfDefaults` (good rollback point).
+- BENCH: expression‑heavy micro‑bench focus (aggressive R‑value and PIC optimizations on JVM).
+- BOOKS: documentation workloads (prefers simpler paths; disables some PIC/arg builder features shown neutral/negative for this load in A/B).
+
+## Key flags
+
+- `LOCAL_SLOT_PIC` — Runtime cache in `LocalVarRef` to avoid repeated name→slot lookups per frame (ON JVM default).
+- `EMIT_FAST_LOCAL_REFS` — Compiler emits `FastLocalVarRef` for identifiers known to be locals/params (ON JVM default).
+- `ARG_BUILDER` — Efficient argument building: small‑arity no‑alloc and pooled builder on JVM (ON JVM default).
+- `ARG_SMALL_ARITY_12` — Extends small‑arity no‑alloc call paths from 0–8 to 0–12 arguments (JVM‑first exploration; OFF by default). Use for codebases with many 9–12 arg calls; A/B before enabling.
+- `SKIP_ARGS_ON_NULL_RECEIVER` — Early return on optional‑null receivers before building args (semantics‑compatible). A/B only.
+- `SCOPE_POOL` — Scope frame pooling for calls (per‑thread ThreadLocal pool on JVM/Android/Native; global deque on JS/Wasm). ON by default on all platforms; togglable at runtime.
+- `FIELD_PIC` — 2‑entry polymorphic inline cache for field reads/writes keyed by `(classId, layoutVersion)` (ON JVM default).
+- `METHOD_PIC` — 2‑entry PIC for instance method calls keyed by `(classId, layoutVersion)` (ON JVM default).
+- `FIELD_PIC_SIZE_4` — Increases Field PIC size from 2 to 4 entries (JVM-first tuning; OFF by default). Use for sites with >2 receiver shapes.
+- `METHOD_PIC_SIZE_4` — Increases Method PIC size from 2 to 4 entries (JVM-first tuning; OFF by default).
+- `PIC_ADAPTIVE_2_TO_4` — Adaptive growth of Field/Method PICs from 2→4 entries per-site when miss rate >20% over ≥256 accesses (JVM-first; OFF by default).
+- `INDEX_PIC` — Enables polymorphic inline cache for indexing (e.g., `a[i]`) and related fast paths. Defaults to follow `FIELD_PIC` on init; can be toggled independently.
+- `INDEX_PIC_SIZE_4` — Increases Index PIC size from 2 to 4 entries (JVM-first tuning). Default: ON for JVM; OFF elsewhere by default.
+- `PIC_DEBUG_COUNTERS` — Enable lightweight hit/miss counters via `PerfStats` (OFF by default).
+- `PRIMITIVE_FASTOPS` — Fast paths for `(ObjInt, ObjInt)` arithmetic/comparisons and `(ObjBool, ObjBool)` logic (ON JVM default).
+- `RVAL_FASTPATH` — Bypass `ObjRecord` in pure expression evaluation via `ObjRef.evalValue` (ON JVM default, OFF elsewhere).
+
+See `src/commonMain/kotlin/net/sergeych/lyng/PerfFlags.kt` and `PerfDefaults.*.kt` for details and platform defaults.
+
+## Where optimizations apply
+
+- Locals: `FastLocalVarRef`, `LocalVarRef` per‑frame cache (PIC).
+- Calls: small‑arity zero‑alloc paths (0–8 args; optionally 0–12 with `ARG_SMALL_ARITY_12`), pooled builder (JVM), and child frame pooling (optional).
+- Properties/methods: Field/Method PICs with receiver shape `(classId, layoutVersion)` and handle‑aware caches; configurable 2→4 entries under flags.
+- Expressions: R‑value fast paths in hot nodes (`UnaryOpRef`, `BinaryOpRef`, `ElvisRef`, logical ops, `RangeRef`, `IndexRef` read, `FieldRef` receiver eval, `ListLiteralRef` elements, `CallRef` callee, `MethodCallRef` receiver, assignment RHS).
+- Primitives: Direct boolean/int ops where safe.
+
+### Compiler constant folding (conservative)
+- The compiler folds a safe subset of literal‑only expressions at compile time to reduce runtime work:
+  - Integer arithmetic: `+ - * / %` (division/modulo only when divisor ≠ 0).
+  - Bitwise integer ops: `& ^ | << >>`.
+  - Comparisons and equality for ints/strings/chars: `== != < <= > >=`.
+  - Boolean logic for literal booleans: `|| &&` and unary `!`.
+  - String concatenation of literal strings: `"a" + "b"`.
+- Non‑literal operands or side‑effecting constructs are not folded.
+- Semantics remain unchanged; tests verify parity.
+
+## Running JVM micro‑benchmarks
+
+Each benchmark prints timings with `[DEBUG_LOG]` and includes correctness assertions to prevent dead‑code elimination.
+
+Run individual tests to avoid multiplatform matrices:
+
+```
+./gradlew :lynglib:jvmTest --tests LocalVarBenchmarkTest
+./gradlew :lynglib:jvmTest --tests CallBenchmarkTest
+./gradlew :lynglib:jvmTest --tests CallMixedArityBenchmarkTest
+./gradlew :lynglib:jvmTest --tests CallSplatBenchmarkTest
+./gradlew :lynglib:jvmTest --tests PicBenchmarkTest
+./gradlew :lynglib:jvmTest --tests PicInvalidationJvmTest
+./gradlew :lynglib:jvmTest --tests PicAdaptiveABTest
+./gradlew :lynglib:jvmTest --tests ArithmeticBenchmarkTest
+./gradlew :lynglib:jvmTest --tests ExpressionBenchmarkTest
+./gradlew :lynglib:jvmTest --tests IndexPicABTest
+./gradlew :lynglib:jvmTest --tests IndexWritePathABTest
+./gradlew :lynglib:jvmTest --tests CallPoolingBenchmarkTest
+./gradlew :lynglib:jvmTest --tests MethodPoolingBenchmarkTest
+./gradlew :lynglib:jvmTest --tests MixedBenchmarkTest
+./gradlew :lynglib:jvmTest --tests DeepPoolingStressJvmTest
+```
+
+Typical output (example):
+
+```
+[DEBUG_LOG] [BENCH] mixed-arity x200000 [ARG_BUILDER=ON]: 85.7 ms
+```
+
+Lower time is better. Run the same bench with a flag OFF vs ON to compare.
+
+### Optional JFR allocation profiling (JVM)
+
+When running end‑to‑end “book” workloads or heavier benches, you can enable JFR to capture allocation and GC details:
+
+```
+./gradlew :lynglib:jvmTest --tests BookAllocationProfileTest -Dlyng.jfr=true \
+  -Dlyng.profile.warmup=1 -Dlyng.profile.repeats=3 -Dlyng.profile.shuffle=true
+```
+
+- Dumps are saved to `lynglib/build/jfr_*.jfr` if the JVM supports Flight Recorder.
+- The test also records GC counts/time and median time/heap deltas to `lynglib/build/book_alloc_profile.txt`.
+
+## Toggling flags in tests
+
+Flags are mutable at runtime, e.g.:
+
+```kotlin
+PerfFlags.ARG_BUILDER = false
+val r1 = (Scope().eval(script) as ObjInt).value
+PerfFlags.ARG_BUILDER = true
+val r2 = (Scope().eval(script) as ObjInt).value
+```
+
+Reset flags at the end of a test to avoid impacting other tests.
+
+## PIC diagnostics (optional)
+
+Enable counters:
+
+```kotlin
+PerfFlags.PIC_DEBUG_COUNTERS = true
+PerfStats.resetAll()
+```
+
+Available counters in `PerfStats`:
+
+- Field PIC: `fieldPicHit`, `fieldPicMiss`, `fieldPicSetHit`, `fieldPicSetMiss`
+- Method PIC: `methodPicHit`, `methodPicMiss`
+- Index PIC: `indexPicHit`, `indexPicMiss`
+- Locals: `localVarPicHit`, `localVarPicMiss`, `fastLocalHit`, `fastLocalMiss`
+- Primitive ops: `primitiveFastOpsHit`
+
+Print a summary at the end of a bench/test as needed. Remember to turn counters OFF after the test.
+
+## A/B scenarios and guidance (JVM)
+
+### Adaptive PIC (fields/methods)
+- Flags: `FIELD_PIC=true`, `METHOD_PIC=true`, `FIELD_PIC_SIZE_4=false`, `METHOD_PIC_SIZE_4=false`, toggle `PIC_ADAPTIVE_2_TO_4` OFF vs ON.
+- Benchmarks: `PicBenchmarkTest`, `MixedBenchmarkTest`, `PicAdaptiveABTest`.
+- Expect wins at sites with >2 receiver shapes; counters should show fewer misses with adaptivity ON.
+
+### Index PIC and size
+- Flags: toggle `INDEX_PIC` OFF vs ON; then `INDEX_PIC_SIZE_4` OFF vs ON.
+- Benchmarks: `ExpressionBenchmarkTest` (list indexing) and `IndexPicABTest` (string/map indexing).
+- Expect wins when the same index shape recurs; counters should show higher `indexPicHit`.
+
+### Index WRITE paths (Map and List)
+- Flags: toggle `INDEX_PIC` OFF vs ON; then `INDEX_PIC_SIZE_4` OFF vs ON.
+- Benchmark: `IndexWritePathABTest` (Map[String] put, List[Int] set) — writes results to `lynglib/build/index_write_ab_results.txt`.
+- Direct fast‑paths are used on R‑value paths where safe and semantics‑preserving (e.g., optional‑chaining no‑ops on null receivers; bounds exceptions unchanged).
+
+## Guidance per flag (JVM)
+
+- Keep `RVAL_FASTPATH = true` unless debugging a suspected expression‑semantics issue.
+- Use `SCOPE_POOL = true` only for benchmarks or once pooling passes the deep stress tests and broader validation; currently OFF by default.
+- `FIELD_PIC` and `METHOD_PIC` should remain ON; they are validated with invalidation tests.
+- Consider enabling `FIELD_PIC_SIZE_4`/`METHOD_PIC_SIZE_4` for sites with 3–4 receiver shapes; measure first.
+- `PIC_ADAPTIVE_2_TO_4` is useful on polymorphic sites and may outperform fixed size 2 on mixed-shape workloads. Validate with `PicAdaptiveABTest`.
+- `INDEX_PIC` is generally beneficial on JVM; leave ON when measuring index‑heavy workloads.
+- `INDEX_PIC_SIZE_4` is ON by default on JVM as A/B showed consistent wins on String[Int] and Map[String] workloads. You can disable it by setting `PerfFlags.INDEX_PIC_SIZE_4 = false` if needed.
+- `ARG_BUILDER` should remain ON; switch OFF only to get a baseline.
+- `ARG_SMALL_ARITY_12` is experimental and OFF by default. Enable it only if your workload frequently calls functions with 9–12 arguments and A/B shows consistent wins.
+
+### Workload‑specific recommendations (JVM)
+
+- “Books”/documentation loads (BookTest): prefer simpler paths; in A/B these often benefit from the BOOKS preset (e.g., `ARG_BUILDER=false`, `SCOPE_POOL=false`, `INDEX_PIC=false`). Use `PerfProfiles.apply(PerfProfiles.Preset.BOOKS)` before the run and `restore(...)` after.
+- Expression‑heavy benches: use the BENCH preset (PICs and R‑value fast‑paths enabled, `INDEX_PIC_SIZE_4=true`).
+- Always verify with local A/B on your environment; rollback is a flag flip or applying BASELINE.
+
+## Notes on correctness & safety
+
+- Optional chaining semantics are preserved across fast paths.
+- Visibility/mutability checks are enforced even on PIC fast‑paths.
+- `frameId` is regenerated on each pooled frame borrow; stress tests verify no leakage under deep nesting/recursion.
+
+## Cross‑platform
+
+- Non‑JVM defaults keep `RVAL_FASTPATH=false` for now; other low‑risk flags may be ON.
+- Once JVM path is fully validated and measured, add lightweight benches for JS/Wasm/Native and enable flags incrementally.
+
+## Range fast iteration (experimental)
+
+- Flag: `RANGE_FAST_ITER` (default OFF).
+- When enabled and applicable, simple ascending integer ranges (`0..n`, `0..<n`) use a specialized non‑allocating iterator (`ObjFastIntRangeIterator`).
+- Benchmark: `RangeIterationBenchmarkTest` records OFF/ON timings for inclusive, exclusive, reversed, negative, and empty ranges. Semantics are preserved; non‑int or complex ranges fall back to the generic iterator.
+
+## Troubleshooting
+
+- If a benchmark shows regressions, flip related flags OFF to isolate the source (e.g., `ARG_BUILDER`, `RVAL_FASTPATH`, `FIELD_PIC`, `METHOD_PIC`).
+- Use `PIC_DEBUG_COUNTERS` to observe inline cache effectiveness.
+- Ensure tests do not accidentally keep flags ON for subsequent tests; reset after each test.
+
+
+## JVM micro-benchmark results (3× medians; OFF → ON)
+
+Date: 2025-11-10 23:04 (local)
+
+| Flag               | Benchmark/Test                              | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|--------------------|----------------------------------------------|-----------------:|----------------:|:-------:|-------|
+| ARG_BUILDER        | CallMixedArityBenchmarkTest                   |           788.02 |          668.79 |  1.18×  | Clear win on mixed arity |
+| ARG_BUILDER        | CallBenchmarkTest (simple calls)              |           423.87 |          425.47 |  1.00×  | Neutral on repeated simple calls |
+| FIELD_PIC          | PicBenchmarkTest::benchmarkFieldGetSetPic     |           113.575 |          106.017 |  1.07×  | Small but consistent win |
+| METHOD_PIC         | PicBenchmarkTest::benchmarkMethodPic          |           251.068 |          149.439 |  1.68×  | Large consistent win |
+| RVAL_FASTPATH      | ExpressionBenchmarkTest                       |           514.491 |          426.800 |  1.21×  | Consistent win in expression chains |
+| PRIMITIVE_FASTOPS  | ArithmeticBenchmarkTest (int-sum)             |           243.420 |          128.146 |  1.90×  | Big win for integer addition |
+| PRIMITIVE_FASTOPS  | ArithmeticBenchmarkTest (int-cmp)             |           210.385 |          168.534 |  1.25×  | Moderate win for comparisons |
+| SCOPE_POOL         | CallPoolingBenchmarkTest                      |           505.778 |          366.737 |  1.38×  | Single-threaded bench; per-thread ThreadLocal pool; default ON on JVM |
+
+Notes:
+- All results obtained from `[DEBUG_LOG] [BENCH]` outputs with three repeated Gradle test invocations per configuration; medians reported.
+- JVM defaults (current): `ARG_BUILDER=true`, `PRIMITIVE_FASTOPS=true`, `RVAL_FASTPATH=true`, `FIELD_PIC=true`, `METHOD_PIC=true`, `SCOPE_POOL=true` (per‑thread ThreadLocal pool), `REGEX_CACHE=true`.
+
+
+## Concurrency (multi‑core) pooling results (3× medians; OFF → ON)
+
+Date: 2025-11-10 22:56 (local)
+
+| Flag       | Benchmark/Test                      | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|------------|--------------------------------------|-----------------:|----------------:|:-------:|-------|
+| SCOPE_POOL | ConcurrencyCallBenchmarkTest (JVM)   |           521.102 |          201.374 |  2.59×  | Multithreaded workload on `Dispatchers.Default` with per‑thread ThreadLocal pool; workers=8, iters=15000/worker. |
+
+Methodology:
+- The test toggles `PerfFlags.SCOPE_POOL` within a single run and executes the same script across N worker coroutines scheduled on `Dispatchers.Default`.
+- We executed the test three times via Gradle and computed medians from the printed `[DEBUG_LOG]` timings:
+  - OFF runs (ms): 532.442 | 521.102 | 474.386 → median 521.102
+  - ON runs (ms):  218.683 | 201.374 | 198.737 → median 201.374
+- Speedup = OFF/ON.
+
+Reproduce:
+```
+./gradlew :lynglib:jvmTest --tests "ConcurrencyCallBenchmarkTest" --rerun-tasks
+```
+
+
+## Next optimization steps (JVM)
+
+Date: 2025-11-10 23:04 (local)
+
+- PICs
+  - Widen METHOD_PIC to 3–4 entries with tiny LRU; keep invalidation on layout change; re-run `PicInvalidationJvmTest`.
+  - Micro fast-path for FIELD_PIC read-then-write pairs (`x = x + 1`) to reuse the resolved slot within one step.
+- Locals and slots
+  - Pre-size `Scope` slot structures when compiler knows local/param counts; audit `EMIT_FAST_LOCAL_REFS` coverage.
+  - Re-run `LocalVarBenchmarkTest` to quantify gains.
+- RVAL_FASTPATH coverage
+  - Cover primitive `ObjList` index reads, pure receivers in `FieldRef`, and assignment RHS where safe; add micro-benches to `ExpressionBenchmarkTest`.
+- Collections and ranges
+  - Specialize `(Int..Int)` loops into tight counted loops (no intermediary objects).
+  - Add primitive-specialized `ObjList` ops (`map`, `filter`, `sum`, `contains`) under `PRIMITIVE_FASTOPS`.
+- Regex and strings
+  - Cache compiled regex for string literals at compile time; add a tiny LRU for dynamic patterns behind `REGEX_CACHE`.
+  - Add `RegexBenchmarkTest` for repeated matches.
+- JIT friendliness (Kotlin/JVM)
+  - Inline tiny helpers in hot paths, prefer arrays for internal buffers, finalize hot data structures where safe.
+
+Validation matrix
+- Always re-run: `CallBenchmarkTest`, `CallMixedArityBenchmarkTest`, `PicBenchmarkTest`, `ExpressionBenchmarkTest`, `ArithmeticBenchmarkTest`, `CallPoolingBenchmarkTest`, `DeepPoolingStressJvmTest`, `ConcurrencyCallBenchmarkTest` (3× medians when comparing).
+- Keep full `:lynglib:jvmTest` green after each change.
+
+
+
+## PIC update (4‑way METHOD_PIC) — JVM (3× medians; OFF → ON)
+
+Date: 2025-11-11 00:16 (local)
+
+| Flag      | Benchmark/Test                               | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|-----------|-----------------------------------------------|-----------------:|----------------:|:-------:|-------|
+| FIELD_PIC | PicBenchmarkTest::benchmarkFieldGetSetPic      |          207.578 |         106.481 |  1.95×  | Read→write loop; micro fast‑path groundwork present |
+| METHOD_PIC| PicBenchmarkTest::benchmarkMethodPic           |          273.478 |         182.226 |  1.50×  | 4‑way PIC with move‑to‑front (was 2‑way before) |
+
+Medians computed from three Gradle runs in this session; see `[DEBUG_LOG] [BENCH]` lines in test output.
+
+
+## Locals/slots capacity (pre‑sizing hints) — JVM (3× medians; OFF → ON)
+
+Date: 2025-11-11 13:19 (local)
+
+| Optimization            | Benchmark/Test              | OFF config                         | ON config                          | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|-------------------------|-----------------------------|------------------------------------|------------------------------------|-----------------:|----------------:|:-------:|-------|
+| Locals pre‑sizing + PIC | LocalVarBenchmarkTest       | LOCAL_SLOT_PIC=OFF, FAST_LOCAL=OFF | LOCAL_SLOT_PIC=ON, FAST_LOCAL=ON   |          472.129 |         370.871 |  1.27×  | Compiler hint `params+4`; slot pre‑size; semantics unchanged |
+
+Methodology:
+- Each configuration executed three times via `:lynglib:jvmTest --tests "…" --rerun-tasks`; medians reported.
+- Locals improvement stacks with per‑thread `SCOPE_POOL` and ARG fast paths.
+
+
+
+
+## RVAL fast paths update — JVM (IndexRef and FieldRef) [3× medians; OFF → ON]
+
+Date: 2025-11-11 13:19 (local)
+
+New micro-benchmarks have been added to quantify the latest `RVAL_FASTPATH` extensions:
+- Primitive `ObjList` index-read fast path in `IndexRef`.
+- Conservative “pure receiver” evaluation in `FieldRef` (monomorphic, immutable receiver), preserving visibility/mutability checks and optional chaining semantics.
+
+Benchmarks to run (each 3× OFF → ON):
+- `ExpressionBenchmarkTest::benchmarkListIndexReads`
+- `ExpressionBenchmarkTest::benchmarkFieldReadPureReceiver`
+
+Reproduce (3× each; collect `[DEBUG_LOG] [BENCH]` lines and compute medians):
+```
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkListIndexReads" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkListIndexReads" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkListIndexReads" --rerun-tasks
+
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkFieldReadPureReceiver" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkFieldReadPureReceiver" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkFieldReadPureReceiver" --rerun-tasks
+```
+
+Once collected, add medians and speedups to the table below:
+
+| Flag          | Benchmark/Test                                  | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|---------------|---------------------------------------------------|-----------------:|----------------:|:-------:|-------|
+| RVAL_FASTPATH | ExpressionBenchmarkTest::benchmarkListIndexReads  |           305.243 |          230.942 |  1.32×  | Fast path in `IndexRef` for `ObjList` + `ObjInt` index |
+| RVAL_FASTPATH | ExpressionBenchmarkTest::benchmarkFieldReadPureReceiver |           266.222 |          190.720 |  1.40×  | Pure-receiver evaluation in `FieldRef` (monomorphic, immutable) |
+
+Notes:
+- Both benches toggle `PerfFlags.RVAL_FASTPATH` within a single run to produce OFF and ON timings under identical conditions.
+- Correctness assertions ensure the loops are not optimized away.
+- All semantics (visibility/mutability checks, optional chaining) remain intact; fast paths only skip interim `ObjRecord` traffic when safe.
+
+
+## ARG_BUILDER — splat fast‑path (3× medians; OFF → ON)
+
+Date: 2025-11-11 13:12 (local)
+
+Environment: Gradle 8.7; JVM (JDK as configured by toolchain); single‑threaded test execution; stdout enabled.
+
+| Flag        | Benchmark/Test                    | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|-------------|-----------------------------------|-----------------:|----------------:|:-------:|-------|
+| ARG_BUILDER | CallSplatBenchmarkTest (splat)    |          613.689 |         463.593 |  1.32×  | Single‑splat fast‑path returns underlying list directly; avoids intermediate copies |
+
+Inputs (3×):
+- OFF runs (ms): 613.689 | 629.604 | 612.361 → median 613.689
+- ON runs (ms):  453.752 | 463.593 | 468.844 → median 463.593
+
+Reproduce (3×):
+```
+./gradlew :lynglib:jvmTest --tests "CallSplatBenchmarkTest" --rerun-tasks
+```
+
+
+
+## Phase A consolidation (JVM) — 3× medians updated
+
+Date: 2025-11-11 13:48 (local)
+Environment:
+- JDK: OpenJDK 20.0.2.1 (Amazon Corretto 20.0.2.1+10-FR)
+- Gradle: 8.7
+- OS/Arch: macOS 14.8.1 (aarch64)
+
+### ARG_BUILDER
+
+| Benchmark/Test                   | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|----------------------------------|-----------------:|----------------:|:-------:|-------|
+| CallMixedArityBenchmarkTest      |          866.681 |         717.439 |  1.21×  | Small-arity 0–8 fast path + builder; correctness preserved |
+| CallSplatBenchmarkTest (splat)   |          600.880 |         459.706 |  1.31×  | Single-splat fast path returns underlying list; avoids copies |
+
+Inputs (3×):
+- Mixed arity OFF: 874.088291 | 866.680959 | 858.577125 → median 866.680959
+- Mixed arity ON:  731.308625 | 706.440125 | 717.438542 → median 717.438542
+- Splat OFF: 600.268625 | 607.849416 | 600.879666 → median 600.879666
+- Splat ON:  459.706375 | 449.950166 | 461.815167 → median 459.706375
+
+### RVAL_FASTPATH (new coverage)
+
+| Benchmark/Test                                   | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|--------------------------------------------------|-----------------:|----------------:|:-------:|-------|
+| ExpressionBenchmarkTest::benchmarkListIndexReads |          299.366 |         218.812 |  1.37×  | IndexRef fast path for ObjList + ObjInt |
+| ExpressionBenchmarkTest::benchmarkFieldReadPureReceiver |          268.315 |         186.032 |  1.44×  | Pure-receiver evaluation in FieldRef (monomorphic, immutable) |
+
+Inputs (3×):
+- ListIndex OFF: 291.344 | 310.717167 | 299.365709 → median 299.365709
+- ListIndex ON:  217.795375 | 221.504166 | 218.812042 → median 218.812042
+- FieldRead OFF: 267.2775 | 274.355208 | 268.315125 → median 268.315125
+- FieldRead ON:  189.599333 | 186.031791 | 182.069167 → median 186.031791
+
+### Locals/slots capacity (precise hints)
+
+| Benchmark/Test             | OFF config                         | ON config                          | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|---------------------------|------------------------------------|------------------------------------|-----------------:|----------------:|:-------:|-------|
+| LocalVarBenchmarkTest     | LOCAL_SLOT_PIC=OFF, FAST_LOCAL=OFF | LOCAL_SLOT_PIC=ON, FAST_LOCAL=ON   |          446.018 |         347.964 |  1.28×  | Precise capacity hints + fast-locals coverage |
+
+Inputs (3×):
+- Locals OFF: 470.575041 | 441.89625 | 446.017833 → median 446.017833
+- Locals ON:  370.664208 | 345.615541 | 347.964291 → median 347.964291
+
+Methodology:
+- Each test executed three times via Gradle with stdout enabled; medians computed from `[DEBUG_LOG] [BENCH]` lines.
+- Full JVM tests and stress benches remain green in this cycle.
+
+
+
+## Phase B — List ops specialization (PRIMITIVE_FASTOPS) — 3× medians (OFF → ON)
+
+Date: 2025-11-11 13:48 (local)
+Environment:
+- JDK: OpenJDK 20.0.2.1 (Amazon Corretto 20.0.2.1+10-FR)
+- Gradle: 8.7
+- OS/Arch: macOS 14.8.1 (aarch64)
+
+| Optimization        | Benchmark/Test                          | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|---------------------|------------------------------------------|-----------------:|----------------:|:-------:|-------|
+| PRIMITIVE_FASTOPS   | ListOpsBenchmarkTest::benchmarkSumInts   |          324.805 |         144.908 |  2.24×  | ObjList.sum fast path for int lists; generic fallback preserved |
+| PRIMITIVE_FASTOPS   | ListOpsBenchmarkTest::benchmarkContainsInts |          440.414 |         415.476 |  1.06×  | ObjList.contains fast path when searching ObjInt in int list |
+
+Inputs (3×):
+- list-sum OFF: 332.863417 | 323.491625 | 324.804083 → median 324.804083
+- list-sum ON:  144.907833 | 148.870792 | 126.418542 → median 144.907833
+- list-contains OFF: 440.413709 | 440.368333 | 441.4365 → median 440.413709
+- list-contains ON:  416.465292 | 412.283291 | 415.475833 → median 415.475833
+
+Methodology:
+- Each test executed three times via Gradle; medians computed from `[DEBUG_LOG] [BENCH]` lines.
+- Changes are fully guarded by `PerfFlags.PRIMITIVE_FASTOPS`; semantics preserved (null on empty sum; generic fallback on mixed types).
+
+
+
+### Phase B — Ranges for-in lowering (PRIMITIVE_FASTOPS) — 3× medians (OFF → ON)
+
+Date: 2025-11-11 13:48 (local)
+Environment:
+- JDK: OpenJDK 20.0.2.1 (Amazon Corretto 20.0.2.1+10-FR)
+- Gradle: 8.7
+- OS/Arch: macOS 14.8.1 (aarch64)
+
+| Optimization        | Benchmark/Test                          | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|---------------------|------------------------------------------|-----------------:|----------------:|:-------:|-------|
+| PRIMITIVE_FASTOPS   | RangeBenchmarkTest::benchmarkIntRangeForIn |         1705.299 |         788.974 |  2.16×  | Tight counted loop for (Int..Int) for-in; preserves semantics |
+
+Inputs (3×):
+- range-for-in OFF: 1705.298958 | 1684.357708 | 1735.880917 → median 1705.298958
+- range-for-in ON:  794.178458 | 778.741834 | 788.973625 → median 788.973625
+
+Methodology:
+- Each configuration executed three times via Gradle; medians computed from `[DEBUG_LOG] [BENCH]` lines.
+- Lowering is guarded by `PerfFlags.PRIMITIVE_FASTOPS` and applies only when the source is an `ObjRange` with int bounds; otherwise falls back to generic iteration.
+
+
+
+## Phase B — Regex caching (REGEX_CACHE) — 3× medians (OFF → ON)
+
+Date: 2025-11-11 13:48 (local)
+Environment:
+- JDK: OpenJDK 20.0.2.1 (Amazon Corretto 20.0.2.1+10-FR)
+- Gradle: 8.7
+- OS/Arch: macOS 14.8.1 (aarch64)
+
+| Flag         | Benchmark/Test                                  | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|--------------|---------------------------------------------------|-----------------:|----------------:|:-------:|-------|
+| REGEX_CACHE  | RegexBenchmarkTest::benchmarkLiteralPatternMatches |          378.246 |         275.890 |  1.37×  | Caches compiled regex for identical literal pattern per iteration |
+| REGEX_CACHE  | RegexBenchmarkTest::benchmarkDynamicPatternMatches |          514.944 |         229.006 |  2.25×  | Two dynamic patterns alternate; cache size sufficient to retain both |
+
+Inputs (1× here; can extend to 3× on request):
+- regex-literal OFF: 378.245916; ON: 275.889541
+- regex-dynamic OFF: 514.944167; ON: 229.005834
+
+Methodology:
+- Each benchmark toggles `PerfFlags.REGEX_CACHE` inside a single test and prints `[DEBUG_LOG]` timings for OFF and ON runs under identical conditions. We recorded one set of OFF/ON timings here; we can extend to 3× medians if required for publication.
+- The cache is a tiny size-bounded map (64 entries) activated only when `PerfFlags.REGEX_CACHE` is true. Defaults remain OFF.
+
+
+
+
+## JIT tweaks (Round 1) — quick gains snapshot (locals, ranges, list ops)
+
+Date: 2025-11-11 21:05 (local)
+
+Scope: fast confirmation of overall gain using current configuration; focused on locals, ranges, and list ops. Each test prints OFF → ON timings in a single run. We executed the benches via Gradle with stdout enabled and single test fork.
+
+Environment:
+- Gradle: 8.7 (stdout enabled, maxParallelForks=1)
+- JVM: as configured by toolchain for this project
+- OS/Arch: per developer machine (unchanged from prior sections)
+
+Reproduce:
+```
+./gradlew :lynglib:jvmTest --tests LocalVarBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests RangeBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests ListOpsBenchmarkTest --rerun-tasks
+```
+
+Results (representative runs; OFF → ON):
+- Local variables — LOCAL_SLOT_PIC + EMIT_FAST_LOCAL_REFS
+  - Run 1: 468.407 ms → 367.277 ms (≈ 1.28×)
+  - Run 2: 447.031 ms → 346.126 ms (≈ 1.29×)
+- Ranges for‑in — PRIMITIVE_FASTOPS (tight counted loop for (Int..Int))
+  - 1731.780 ms → 799.023 ms (≈ 2.17×)
+- List ops — PRIMITIVE_FASTOPS
+  - sum(int list): 318.943 ms → 148.571 ms (≈ 2.15×)
+  - contains(int in int list): 440.013 ms → 412.450 ms (≈ 1.07×)
+
+Summary: All three areas improved with optimizations ON; no regressions observed in these runs. For publication‑grade stability, run each test 3× and report medians (see sections below for methodology and previous median tables).
+
+
+## Additional tweaks — verification snapshot (Index write fast‑path, List literal pre‑size, Regex LRU)
+
+Date: 2025-11-11 21:31 (local)
+
+Scope: Implemented three semantics‑neutral optimizations and verified they are green across targeted and broader JVM benches.
+
+What changed (guarded by flags where applicable):
+- RVAL_FASTPATH: Index write fast‑path
+  - `IndexRef.setAt`: direct path for `ObjList` + `ObjInt` (`list[i] = value`) mirrors the read fast‑path. Optional chaining semantics preserved; bounds exceptions propagate unchanged.
+- RVAL_FASTPATH: List literal pre‑sizing
+  - `ListLiteralRef.get`: pre‑counts element entries and uses `ArrayList` with capacity hint; for spreads of `ObjList`, uses `ensureCapacity` before bulk add. Evaluation order unchanged.
+- REGEX_CACHE: LRU‑like behavior
+  - `RegexCache`: emulates access‑order LRU within a tiny bounded map (`MAX=64`) by moving accessed entries to the tail; improves alternating‑pattern scenarios. Only active when `PerfFlags.REGEX_CACHE` is true.
+
+Reproduce quick verification (1× runs):
+```
+./gradlew :lynglib:jvmTest --tests ExpressionBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests ListOpsBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests RegexBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests PicBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests PicInvalidationJvmTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests LocalVarBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests ConcurrencyCallBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests DeepPoolingStressJvmTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests MultiThreadPoolingStressJvmTest --rerun-tasks
+```
+
+Observation: All listed tests green in this cycle; no behavioral regressions observed. For the new paths (index write, list literal), performance was neutral‑to‑positive in smoke runs; Regex benches remained positive or neutral with the LRU behavior. For publication‑grade medians, extend to 3× per test as in earlier sections.
+
+
+## Sanity matrix (JVM) — quick OFF→ON runs
+
+Date: 2025-11-11 21:59 (local)
+
+Scope: Final Round 1 sanity sweep across JVM micro‑benches and stress tests to confirm that optimizations ON do not regress performance vs OFF in representative scenarios. Each benchmark prints `[DEBUG_LOG] [BENCH]` timings for OFF → ON within a single run. This section records a quick pass confirmation (not 3× medians) and reproduction commands.
+
+Environment:
+- Gradle: 8.7 (stdout enabled, maxParallelForks=1)
+- JVM: as configured by the project toolchain
+- OS/Arch: macOS 14.x (aarch64)
+
+Benches covered (all green; no regressions observed in these runs):
+- Calls/Args: `CallBenchmarkTest`, `CallMixedArityBenchmarkTest` (ARG_BUILDER)
+- PICs: `PicBenchmarkTest` (field/method); `PicInvalidationJvmTest` correctness reconfirmed
+- Expressions/Arithmetic: `ExpressionBenchmarkTest`, `ArithmeticBenchmarkTest` (RVAL_FASTPATH, PRIMITIVE_FASTOPS)
+- Ranges: `RangeBenchmarkTest` (PRIMITIVE_FASTOPS counted loop)
+- List ops: `ListOpsBenchmarkTest` (PRIMITIVE_FASTOPS specializations)
+- Regex: `RegexBenchmarkTest` (REGEX_CACHE with LRU behavior)
+- Locals: `LocalVarBenchmarkTest` (LOCAL_SLOT_PIC + FAST_LOCAL)
+- Concurrency/Pooling: `ConcurrencyCallBenchmarkTest`, `DeepPoolingStressJvmTest`, `MultiThreadPoolingStressJvmTest` (SCOPE_POOL per‑thread)
+
+Reproduce (examples):
+```
+./gradlew :lynglib:jvmTest --tests CallBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests CallMixedArityBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests PicBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests PicInvalidationJvmTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests ExpressionBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests ArithmeticBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests RangeBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests ListOpsBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests RegexBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests LocalVarBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests ConcurrencyCallBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests DeepPoolingStressJvmTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests MultiThreadPoolingStressJvmTest --rerun-tasks
+```
+
+  Summary:
+  - All listed tests passed in this sanity sweep.
+  - For each benchmark’s OFF → ON printouts examined during this pass, ON was equal or faster than OFF; no ON<OFF regressions were observed.
+  - For publication‑grade numbers, use the 3× medians methodology outlined earlier in this document. The existing median tables in previous sections remain representative, and the additional tweaks (Index write, List literal pre‑size, Regex LRU, Field PIC 4‑way + read→write reuse, mixed Int/Real fast‑ops) remained neutral‑to‑positive.
+  
+
+## Quick snapshot — IndexRef PIC + negative miss cache (JVM) — 3× medians (OFF → ON)
+
+Date: 2025-11-11 22:32 (local)
+
+Scope
+- Confirm that the latest changes — IndexRef read/write PIC (stacked on RVAL_FASTPATH) and safe catch‑and‑cache negative entries for Field/Method PICs — do not regress performance. We collected 3× medians for the two expression sub‑benches that are most sensitive to RVAL paths and cross‑checked PICs and ranges.
+
+Environment
+- Gradle: 8.7 (stdout enabled, maxParallelForks=1)
+- JVM: project toolchain default
+- OS/Arch: macOS 14.x (aarch64)
+
+Results (3× medians)
+
+| Area | Benchmark/Test | OFF median (ms) | ON median (ms) | Speedup | Notes |
+|------|-----------------|-----------------:|----------------:|:-------:|-------|
+| RVAL_FASTPATH | ExpressionBenchmarkTest::benchmarkListIndexReads | 304.282 | 229.168 | 1.33× | IndexRef direct fast‑path for ObjList+ObjInt; 4‑way Index PIC handles polymorphic cases |
+| RVAL_FASTPATH | ExpressionBenchmarkTest::benchmarkFieldReadPureReceiver | 275.122 | 194.876 | 1.41× | Monomorphic, immutable receiver path; preserves visibility/optional semantics |
+
+Cross‑checks (from the same session, 1× quick)
+- PicBenchmarkTest::benchmarkFieldGetSetPic — OFF 203.701 ms → ON 117.129 ms (≈1.74×)
+- PicBenchmarkTest::benchmarkMethodPic — OFF 280.806 ms → ON 202.613 ms (≈1.39×)
+- RangeBenchmarkTest::benchmarkIntRangeForIn — OFF 1762.425 ms → ON 806.898 ms (≈2.18×)
+
+Reproduce
+```
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkListIndexReads" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkListIndexReads" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkListIndexReads" --rerun-tasks
+
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkFieldReadPureReceiver" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkFieldReadPureReceiver" --rerun-tasks
+./gradlew :lynglib:jvmTest --tests "ExpressionBenchmarkTest.benchmarkFieldReadPureReceiver" --rerun-tasks
+
+./gradlew :lynglib:jvmTest --tests PicBenchmarkTest --rerun-tasks
+./gradlew :lynglib:jvmTest --tests RangeBenchmarkTest --rerun-tasks
+```
+
+Notes
+- Negative caches are installed only after a real miss throws (cache‑after‑miss), preserving error semantics and invalidation on `layoutVersion` changes.
+- IndexRef PIC augments the existing direct path and uses move‑to‑front promotion; it is keyed on `(classId, layoutVersion)` like other PICs.
+

docs/perf_plan_jvm.md

@@ -0,0 +1,58 @@
+# JVM-only Performance Optimization Plan (Saved)
+
+[//]: # (excludeFromIndex)
+
+Date: 2025-11-10 22:14 (local)
+
+This document captures the agreed next optimization steps so we can restore the plan later if needed.
+
+## Objectives
+- Reduce overhead on the call/argument path.
+- Extend and harden PIC performance (fields/methods/locals).
+- Improve R-value fast paths and interpreter hot nodes (loops, ranges, lists).
+- Make scope frame pooling thread-safe on JVM so it can be enabled by default later.
+- Keep semantics correct and all JVM tests green.
+
+## Prioritized tasks (now)
+1) Call/argument path: fewer allocs, tighter fast paths
+- Extend small-arity zero-alloc path to 6–8 args; benchmark with `CallMixedArityBenchmarkTest`.
+- Splat handling: fast-path single-list splats; benchmark with `CallSplatBenchmarkTest`.
+- Arg builder micro-optimizations: capacity hints, avoid redundant copies, inline simple branches.
+- Optional-chaining fast return (`SKIP_ARGS_ON_NULL_RECEIVER`) coverage audit, add A/B bench.
+
+2) Scope frame pooling: per-thread safety on JVM
+- Replace global deque with ThreadLocal pool on JVM (and Android) actuals.
+- Keep `frameId` uniqueness and pool size cap.
+- Verify with `DeepPoolingStressJvmTest`, `CallPoolingBenchmarkTest`, and spot benches.
+- Do NOT flip default yet; keep `SCOPE_POOL=false` unless explicitly approved.
+
+## Next tasks (queued)
+3) PICs: cheaper misses, broader hits
+- Method PIC 2→3/4 entries (tiny LRU); validate with `PicInvalidationJvmTest`.
+- Field PIC micro-fast path for read-then-write pairs.
+
+4) Locals and slots
+- Ensure `EMIT_FAST_LOCAL_REFS` coverage across compiler sites.
+- Pre-size `slots`/`nameToSlot` when local counts are known; re-run `LocalVarBenchmarkTest`.
+
+5) R-value fast path coverage
+- Cover index reads on primitive lists, pure receivers, assignment RHS where safe.
+- Add benches in `ExpressionBenchmarkTest`.
+
+6) Collections & ranges
+- Tight counted loop for `(Int..Int)` in `for`.
+- Primitive-specialized `ObjList` ops (`map`, `filter`, `sum`, `contains`) under `PRIMITIVE_FASTOPS`.
+
+7) Regex and string ops
+- Cache compiled regex for string literals at compile time; tiny LRU for dynamic patterns under a new `REGEX_CACHE` flag.
+
+8) JIT micro-tweaks
+- Inline tiny helpers; prefer arrays for hot buffers; finalize hot classes where safe.
+
+## Validation matrix
+- Always re-run: `CallBenchmarkTest`, `CallMixedArityBenchmarkTest`, `PicBenchmarkTest`, `ExpressionBenchmarkTest`, `ArithmeticBenchmarkTest`, `CallPoolingBenchmarkTest`, `DeepPoolingStressJvmTest`.
+- Use 3× medians where comparing flags; keep `:lynglib:jvmTest` green.
+
+## Notes
+- All risky changes remain flag-guarded and JVM-only where applicable.
+- Documentation and perf tables updated after each cycle.

docs/return_statement.md

@@ -0,0 +1,86 @@
+# The `return` statement
+
+The `return` statement is used to terminate the execution of the innermost enclosing callable (a function or a lambda) and optionally return a value to the caller.
+
+## Basic Usage
+
+By default, Lyng functions and blocks return the value of their last expression. However, `return` allows you to exit early, which is particularly useful for guard clauses.
+
+```lyng
+fun divide(a, b) {
+    if (b == 0) return null // Guard clause: early exit
+    a / b
+}
+```
+
+If no expression is provided, `return` returns `void`:
+
+```lyng
+fun logIfDebug(msg) {
+    if (!DEBUG) return
+    println("[DEBUG] " + msg)
+}
+```
+
+## Scoping Rules
+
+In Lyng, `return` always exits the **innermost enclosing callable**. Callables include:
+*   Named functions (`fun` or `fn`)
+*   Anonymous functions/lambdas (`{ ... }`)
+
+Standard control flow blocks like `if`, `while`, `do`, and `for` are **not** callables; `return` inside these blocks will return from the function or lambda that contains them.
+
+```lyng
+fun findFirstPositive(list) {
+    list.forEach { 
+        if (it > 0) return it // ERROR: This returns from the lambda, not findFirstPositive!
+    }
+    null
+}
+```
+*Note: To return from an outer scope, use [Non-local Returns](#non-local-returns).*
+
+## Non-local Returns
+
+Lyng supports returning from outer scopes using labels. This is a powerful feature for a closure-intensive language.
+
+### Named Functions as Labels
+Every named function automatically provides its name as a label.
+
+```lyng
+fun findFirstPositive(list) {
+    list.forEach { 
+        if (it > 0) return@findFirstPositive it // Returns from findFirstPositive
+    }
+    null
+}
+```
+
+### Labeled Lambdas
+You can explicitly label a lambda using the `@label` syntax to return from it specifically when nested.
+
+```lyng
+val process = @outer { x ->
+    val result = {
+        if (x < 0) return@outer "negative" // Returns from the outer lambda
+        x * 2
+    }()
+    "Result: " + result
+}
+```
+
+## Restriction on Shorthand Functions
+
+To maintain Lyng's clean, expression-oriented style, the `return` keyword is **forbidden** in shorthand function definitions (those using `=`).
+
+```lyng
+fun square(x) = x * x          // Correct
+fun square(x) = return x * x   // Syntax Error: 'return' not allowed here
+```
+
+## Summary
+*   `return [expression]` exits the innermost `fun` or `{}`.
+*   Use `return@label` for non-local returns.
+*   Named functions provide automatic labels.
+*   Cannot be used in `=` shorthand functions.
+*   Consistency: Mirrors the syntax and behavior of `break@label expression`.

docs/samples/fs_sample.lyng

@@ -0,0 +1,25 @@
+#!/bin/env lyng
+
+import lyng.io.fs
+import lyng.stdlib
+
+val files = Path("../..").list().toList()
+// most long is longest?
+val longestNameLength = files.maxOf { it.name.length }
+
+// testdoc
+fun test() {
+    22
+}
+
+
+val format = "%"+(longestNameLength+1) +"s %d"
+for( f in files )
+{
+    var name = f.name
+    if( f.isDirectory() )
+        name += "/"
+    println( format(name, f.size()) )
+}
+
+

docs/samples/happy_numbers.lyng.bad

@@ -19,12 +19,13 @@ fun naiveCountHappyNumbers() {
 import lyng.time
 
 //
-// After all optimizations it takes ~120ms.
+// After all optimizations it took ~120ms - before.
 //
-//for( r in 1..100 ) {
-//    val start = Instant.now()
+for( r in 1..900 ) {
+    val start = Instant.now()
     val found = naiveCountHappyNumbers()
-//    println("Found happy numbers: %d time %s"(found, Instant.now() - start))
+    println("Found happy numbers: %d time %s"(found, Instant.now() - start))
     assert( found == 55252 )
-//    delay(0.01)
-//}
+    delay(0.05)
+}
+

docs/samples/new_literals_utf8.lyng

@@ -0,0 +1,10 @@
+#!/bin/env lyng
+
+val переменная = "значение"
+
+val data = { greeting: "привет", переменная:, поле: "содержимое" }
+
+assertEquals(data["переменная"], "значение")
+assertEquals(data["поле"], "содержимое")
+
+println(data)

docs/samples/operator_overloading.lyng

@@ -0,0 +1,63 @@
+// Sample: Operator Overloading in Lyng
+
+class Vector(val x, val y) {
+    // Overload +
+    fun plus(other) = Vector(x + other.x, y + other.y)
+    
+    // Overload -
+    fun minus(other) = Vector(x - other.x, y - other.y)
+    
+    // Overload unary -
+    fun negate() = Vector(-x, -y)
+    
+    // Overload ==
+    fun equals(other) {
+        if (other is Vector) x == other.x && y == other.y
+        else false
+    }
+    
+    // Overload * (scalar multiplication)
+    fun mul(scalar) = Vector(x * scalar, y * scalar)
+    
+    override fun toString() = "Vector(${x}, ${y})"
+}
+
+val v1 = Vector(10, 20)
+val v2 = Vector(5, 5)
+
+println("v1: " + v1)
+println("v2: " + v2)
+
+// Test binary +
+val v3 = v1 + v2
+println("v1 + v2 = " + v3)
+assertEquals(Vector(15, 25), v3)
+
+// Test unary -
+val v4 = -v1
+println("-v1 = " + v4)
+assertEquals(Vector(-10, -20), v4)
+
+// Test scalar multiplication
+val v5 = v1 * 2
+println("v1 * 2 = " + v5)
+assertEquals(Vector(20, 40), v5)
+
+// Test += (falls back to plus)
+var v6 = Vector(1, 1)
+v6 += Vector(2, 2)
+println("v6 += (2,2) -> " + v6)
+assertEquals(Vector(3, 3), v6)
+
+// Test in-place mutation with plusAssign
+class Counter(var count) {
+    fun plusAssign(n) {
+        count = count + n
+    }
+}
+
+val c = Counter(0)
+c += 10
+c += 5
+println("Counter: " + c.count)
+assertEquals(15, c.count)

docs/samples/sum.lyng

@@ -1,7 +1,7 @@
+#!/bin/env lyng
 /*
     Calculate the limit of Sum( f(n) )
     until it reaches asymptotic limit 0.00001% change
-
     return null or found limit
 */
 fun findSumLimit(f) {

docs/scopes_and_closures.md

@@ -0,0 +1,92 @@
+# Scopes and Closures: resolution and safety
+
+This page documents how name resolution works with `ClosureScope`, how to avoid recursion pitfalls, and how to safely capture and execute callbacks that need access to outer locals.
+
+## Why this matters
+Name lookup across nested scopes and closures can accidentally form recursive resolution paths or hide expected symbols (outer locals, module/global functions). The rules below ensure predictable resolution and prevent infinite recursion.
+
+## Resolution order in ClosureScope
+When evaluating an identifier `name` inside a closure, `ClosureScope.get(name)` resolves in this order:
+
+1. **Current frame locals and arguments**: Variables defined within the current closure execution.
+2. **Captured lexical ancestry**: Outer local variables captured at the site where the closure was defined (the "lexical environment").
+3. **Captured receiver members**: If the closure was defined within a class or explicitly bound to an object, it checks members of that object (`this`). This includes both instance fields/methods and class-level static members, following the MRO (C3) and respecting visibility rules (private members are only visible if the closure was defined in their class).
+4. **Caller environment**: If not found lexically, it falls back to the calling context (e.g., the DSL's `this` or the caller's local variables).
+5. **Global/Module fallbacks**: Final check for module-level constants and global functions.
+
+This ensures that closures primarily interact with their defining environment (lexical capture) while still being able to participate in DSL-style calling contexts.
+
+## Use raw‑chain helpers for ancestry walks
+When authoring new scope types or advanced lookups, avoid calling virtual `get` while walking parents. Instead, use the non‑dispatch helpers on `Scope`:
+
+- `chainLookupIgnoreClosure(name)`
+  - Walk raw `parent` chain and check only per‑frame locals/bindings/slots.
+  - Ignores overridden `get` (e.g., in `ClosureScope`). Cycle‑safe.
+- `chainLookupWithMembers(name)`
+  - Like above, but after locals/bindings it also checks each frame’s `thisObj` members.
+  - Ignores overridden `get`. Cycle‑safe.
+- `baseGetIgnoreClosure(name)`
+  - For the current frame only: check locals/bindings, then walk raw parents (locals/bindings), then fallback to this frame’s `thisObj` members.
+
+These helpers avoid ping‑pong recursion and make structural cycles harmless (lookups terminate).
+
+## Preventing structural cycles
+- Don’t construct parent chains that can point back to a descendant.
+- A debug‑time guard throws if assigning a parent would create a cycle; keep it enabled for development builds.
+- Even with a cycle, chain helpers break out via a small `visited` set keyed by `frameId`.
+
+## Capturing lexical environments for callbacks
+For dynamic objects or custom builders, capture the creator’s lexical scope so callbacks can see outer locals/parameters:
+
+1. Use `snapshotForClosure()` on the caller scope to capture locals/bindings/slots and parent.
+2. Store this snapshot and run callbacks under `ClosureScope(callScope, captured)`.
+
+Kotlin sketch:
+```kotlin
+val captured = scope.snapshotForClosure()
+val execScope = ClosureScope(currentCallScope, captured)
+callback.execute(execScope)
+```
+
+This ensures expressions like `contractName` used inside dynamic `get { name -> ... }` resolve to outer variables defined at the creation site.
+
+## Closures in coroutines (launch/flow)
+- The closure frame still prioritizes its own locals/args.
+- Outer locals declared before suspension points remain visible through slot‑aware ancestry lookups.
+- Global functions like `delay(ms)` and `yield()` are resolved via module/root fallbacks from within closures.
+
+Tip: If a closure unexpectedly cannot see an outer local, check whether an intermediate runtime helper introduced an extra call frame; the built‑in lookup already traverses caller ancestry, so prefer the standard helpers rather than custom dispatch.
+
+## Local variable references and missing symbols
+- Unqualified identifier resolution first prefers locals/bindings/slots before falling back to `this` members.
+- If neither locals nor members contain the symbol, missing field lookups map to `SymbolNotFound` (compatibility alias for `SymbolNotDefinedException`).
+
+## Performance notes
+- The `visited` sets used for cycle detection are tiny and short‑lived; in typical scripts the overhead is negligible.
+- If profiling shows hotspots, consider limiting ancestry depth in your custom helpers or using small fixed arrays instead of hash sets—only for extremely hot code paths.
+
+## Practical Example: `cached`
+
+The `cached` function (defined in `lyng.stdlib`) is a classic example of using closures to maintain state. It wraps a builder into a zero-argument function that computes once and remembers the result:
+
+```lyng
+fun cached(builder) {
+    var calculated = false
+    var value = null
+    { // This lambda captures `calculated`, `value`, and `builder`
+        if( !calculated ) {
+            value = builder()
+            calculated = true
+        }
+        value
+    }
+}
+```
+
+Because Lyng now correctly isolates closures for each evaluation of a lambda literal, using `cached` inside a class instance works as expected: each instance maintains its own private `calculated` and `value` state, even if they share the same property declaration.
+
+## Dos and Don’ts
+- Do use `chainLookupIgnoreClosure` / `chainLookupWithMembers` for ancestry traversals.
+- Do maintain the resolution order above for predictable behavior.
+- Don’t call virtual `get` while walking parents; it risks recursion across scope types.
+- Don’t attach instance scopes to transient/pool frames; bind to a stable parent scope instead.

docs/textmate_bundle.md

@@ -0,0 +1,77 @@
+# TextMate bundle
+
+[//]: # (excludeFromIndex)
+
+The TextMate-format bundle contains a syntax definition for initial language support in
+popular editors that understand TextMate grammars: TextMate, Visual Studio Code, Sublime Text, etc.
+
+- [Download TextMate Bundle for Lyng](https://lynglang.com/distributables/lyng-textmate.zip)
+
+> Note for IntelliJ-based IDEs (IntelliJ IDEA, Fleet, etc.): although you can import TextMate
+> bundles there (Settings/Preferences → Editor → TextMate Bundles), we strongly recommend using the
+> dedicated plugin instead — it provides much better support (formatting, smart enter, background
+> analysis, etc.). See: [IDEA Plugin](#/docs/idea_plugin.md).
+
+## Visual Studio Code
+
+VS Code uses TextMate grammars packaged as extensions. A minimal local extension is easy to set up:
+
+1) Download and unzip the bundle above. Inside you will find the grammar file (usually
+   `*.tmLanguage.json` or `*.tmLanguage` plist).
+2) Create a new folder somewhere, e.g. `lyng-textmate-vscode/` with the following structure:
+
+```
+lyng-textmate-vscode/
+  package.json
+  syntaxes/
+    lyng.tmLanguage.json   # copy the grammar file here (rename if needed)
+```
+
+3) Put this minimal `package.json` into that folder (adjust file names if needed):
+
+```
+{
+  "name": "lyng-textmate",
+  "displayName": "Lyng (TextMate grammar)",
+  "publisher": "local",
+  "version": "0.0.1",
+  "engines": { "vscode": "^1.70.0" },
+  "contributes": {
+    "languages": [
+      { "id": "lyng", "aliases": ["Lyng"], "extensions": [".lyng"] }
+    ],
+    "grammars": [
+      {
+        "language": "lyng",
+        "scopeName": "source.lyng",
+        "path": "./syntaxes/lyng.tmLanguage.json"
+      }
+    ]
+  }
+}
+```
+
+4) Open a terminal in `lyng-textmate-vscode/` and run:
+
+```
+code --install-extension .
+```
+
+   Alternatively, open the folder in VS Code and press F5 to run an Extension Development Host.
+5) Reload VS Code. Files with the `.lyng` extension should now get Lyng highlighting.
+
+## Sublime Text 3/4
+
+1) Download and unzip the bundle.
+2) In Sublime Text, use “Preferences → Browse Packages…”, then copy the unzipped bundle
+   to a folder like `Packages/Lyng/`.
+3) Open a `.lyng` file; Sublime should pick up the syntax automatically. If not, use
+   “View → Syntax → Lyng”.
+
+## TextMate 2
+
+1) Download and unzip the bundle.
+2) Double‑click the `.tmBundle`/grammar package or drag it onto TextMate to install, or place
+   it into `~/Library/Application Support/TextMate/Bundles/`.
+3) Restart TextMate if needed and open a `.lyng` file.
+

docs/tutorial.md

@@ -1,8 +1,3 @@
----
-gitea: none
-include_toc: true
----
-
 # Lyng tutorial
 
 Lyng is a very simple language, where we take only most important and popular features from
@@ -11,9 +6,10 @@ In other word, the code usually works as expected when you see it. So, nothing u
 
 __Other documents to read__ maybe after this one:
 
-- [Advanced topics](advanced_topics.md), [declaring arguments](declaring_arguments.md)
+- [Advanced topics](advanced_topics.md), [declaring arguments](declaring_arguments.md), [Scopes and Closures](scopes_and_closures.md)
 - [OOP notes](OOP.md), [exception handling](exceptions_handling.md)
-- [math in Lyng](math.md)
+- [math in Lyng](math.md), [the `when` statement](when.md), [return statement](return_statement.md)
+- [Testing and Assertions](Testing.md)
 - [time](time.md) and [parallelism](parallelism.md)
 - [parallelism] - multithreaded code, coroutines, etc.
 - Some class
@@ -36,6 +32,15 @@ any block also returns it's last expression:
     }
     >>> 6
 
+If you want to exit a function or lambda earlier, use the `return` statement:
+
+    fn divide(a, b) {
+        if( b == 0 ) return null
+        a / b
+    }
+
+See [return statement](return_statement.md) for more details on scoping and non-local returns.
+
 If you don't want block to return anything, use `void`:
 
     fn voidFunction() {
@@ -71,6 +76,47 @@ You can use blocks in if statement, as expected:
     limited
     >>> 120.0
 
+## Enums (quick intro)
+
+Lyng supports simple enums for a fixed set of named constants. Declare with `enum Name { ... }` and use entries as `Name.ENTRY`.
+
+    enum Color {
+        RED, GREEN, BLUE
+    }
+
+    assert( Color.RED is Color )
+    assertEquals( 0, Color.RED.ordinal )
+    assertEquals( "BLUE", Color.BLUE.name )
+
+    // All entries as a list, in order:
+    assertEquals( [Color.RED, Color.GREEN, Color.BLUE], Color.entries )
+
+    // Lookup by name:
+    assertEquals( Color.GREEN, Color.valueOf("GREEN") )
+
+For more details (usage patterns, `when` switching, serialization), see OOP notes: [Enums in detail](OOP.md#enums).
+
+## Singleton Objects
+
+Singleton objects are declared using the `object` keyword. They define a class and create its single instance immediately.
+
+    object Logger {
+        fun log(msg) { println("[LOG] " + msg) }
+    }
+    
+    Logger.log("Hello singleton!")
+
+## Delegation (briefly)
+
+You can delegate properties and functions to other objects using the `by` keyword. This is perfect for patterns like `lazy` initialization.
+
+    val expensiveData by lazy {
+        // computed only once on demand
+        "computed"
+    }
+
+For more details on these features, see [Delegation in Lyng](delegation.md) and [OOP notes](OOP.md).
+
 When putting multiple statments in the same line it is convenient and recommended to use `;`:
 
     var from; var to
@@ -91,6 +137,41 @@ Assignemnt is an expression that changes its lvalue and return assigned value:
     >>> 11
     >>> 6
 
+### Destructuring assignments
+
+Lyng supports destructuring assignments for lists. This allows you to unpack list elements into multiple variables at once:
+
+    val [a, b, c] = [1, 2, 3]
+    assertEquals(1, a)
+    assertEquals(2, b)
+    assertEquals(3, c)
+
+It also supports *splats* (ellipsis) to capture multiple elements into a list:
+
+    val [head, rest...] = [1, 2, 3]
+    assertEquals(1, head)
+    assertEquals([2, 3], rest)
+
+    val [first, middle..., last] = [1, 2, 3, 4, 5]
+    assertEquals(1, first)
+    assertEquals([2, 3, 4], middle)
+    assertEquals(5, last)
+
+Destructuring can be nested:
+
+    val [x, [y, z...]] = [1, [2, 3, 4]]
+    assertEquals(1, x)
+    assertEquals(2, y)
+    assertEquals([3, 4], z)
+
+And it can be used for reassigning existing variables, for example, to swap values:
+
+    var x = 5
+    var y = 10
+    [x, y] = [y, x]
+    assertEquals(10, x)
+    assertEquals(5, y)
+
 As the assignment itself is an expression, you can use it in strange ways. Just remember
 to use parentheses as assignment operation insofar is left-associated and will not
 allow chained assignments (we might fix it later). Use parentheses insofar:
@@ -107,14 +188,13 @@ Note that assignment operator returns rvalue, it can't be assigned.
 ## Modifying arithmetics
 
 There is a set of assigning operations: `+=`, `-=`, `*=`, `/=` and even `%=`.
+There is also a special null-aware assignment operator `?=`: it performs the assignment only if the lvalue is `null`.
 
-    var x = 5
-    assert( 25 == (x*=5) )
-    assert( 25 == x)
-    assert( 24 == (x-=1) )
-    assert( 12 == (x/=2) )
-    x
-    >>> 12
+    var x = null
+    x ?= 10
+    assertEquals(10, x)
+    x ?= 20
+    assertEquals(10, x)
 
 Notice the parentheses here: the assignment has low priority!
 
@@ -167,6 +247,13 @@ There is also "elvis operator", null-coalesce infix operator '?:' that returns r
     null ?: "nothing"
     >>> "nothing"
 
+There is also a null-aware assignment operator `?=`, which assigns a value only if the target is `null`:
+
+    var config = null
+    config ?= { port: 8080 }
+    config ?= { port: 9000 } // no-op, config is already not null
+    assertEquals(8080, config.port)
+
 ## Utility functions
 
 The following functions simplify nullable values processing and
@@ -210,7 +297,7 @@ Much like let, but it does not alter returned value:
     >>> void
 
 While it is not altering return value, the source object could be changed:
-
+also
     class Point(x,y)
     val p = Point(1,2).also { it.x++ }
     assertEquals(p.x, 2)
@@ -226,6 +313,16 @@ It works much like `also`, but is executed in the context of the source object:
     assertEquals(p, Point(2,3))
     >>> void
 
+## with
+
+Sets `this` to the first argument and executes the block. Returns the value returned by the block:
+
+    class Point(x,y)
+    val p = Point(1,2)
+    val sum = with(p) { x + y }
+    assertEquals(3, sum)
+    >>> void
+
 ## run
 
 Executes a block after it returning the value passed by the block. for example, can be used with elvis operator:
@@ -275,6 +372,8 @@ Logical operation could be used the same
 |   ===    |     | Any               | (2)      |
 |   !==    |     | Any               | (2)      |
 |    !=    |     | Any               | (1)      |
+|    =~    |     |                   | (3)      |
+|    !~    |     |                   | (3)      |
 | ++a, a++ |     | Int               |          |
 | --a, a-- |     | Int               |          |
 
@@ -286,13 +385,14 @@ Logical operation could be used the same
 singleton object, like `null`, are referentially equal too, while string different literals even being equal are most
 likely referentially not equal
 
+(3)
+: Implemented now in String and Regex as regular expression match and not match, see [Regex].
+
 Reference quality and object equality example:
 
     assert( null == null)  // singletons
     assert( null === null)
     // but, for non-singletons:
-    assert( 5 == 5)
-    assert( 5 !== 5)
     assert( "foo" !== "foo" )
     >>> void
 
@@ -309,7 +409,7 @@ will be thrown:
     // WRONG! Exception will be thrown at next line:
     foo + "bar"
 
-Correct pattern is:
+The correct pattern is:
 
     foo = "foo"
     // now is OK:
@@ -383,6 +483,19 @@ It is possible to define also vararg using ellipsis:
 
 See the [arguments reference](declaring_arguments.md) for more details.
 
+## Named arguments
+
+When calling functions, you can use named arguments with the colon syntax `name: value`. This is particularly useful when you have many parameters with default values.
+
+```lyng
+    fun test(a="foo", b="bar", c="bazz") { [a, b, c] }
+
+    assertEquals(["foo", "b", "bazz"], test(b: "b"))
+    assertEquals(["a", "bar", "c"], test("a", c: "c"))
+```
+
+**Note for Kotlin users:** Lyng uses `:` instead of `=` for named arguments at call sites. This is because in Lyng, `=` is an expression that returns the assigned value, and using it in an argument list would create ambiguity.
+
 ## Closures
 
 Each __block has an isolated context that can be accessed from closures__. For example:
@@ -458,6 +571,8 @@ one could be with ellipsis that means "the rest pf arguments as List":
 
 ### Using lambda as the parameter
 
+See also: [Testing and Assertions](Testing.md)
+
     // note that fun returns its last calculated value,
     // in our case, result after in-place addition:
     fun mapValues(iterable, transform) {
@@ -676,14 +791,63 @@ Please see [Set] for detailed description.
 
 # Maps
 
-Maps are unordered collection of key-value pairs, where keys are unique. See [Map] for details. Map also
-are [Iterable]:
+Maps are unordered collections of key-value pairs, where keys are unique. Maps are also [Iterable].
 
-    val m = Map( "foo" => 77, "bar" => "buzz" )
-    assertEquals( m["foo"], 77 )
+You can create them either with the classic constructor (still supported):
+
+    val old = Map( "foo" => 77, "bar" => "buzz" )
+    assertEquals( old["foo"], 77 )
     >>> void
 
-Please see [Map] reference for detailed description on using Maps.
+…or with map literals, which are often more convenient:
+
+    val x = 10
+    val y = 10
+    val m = { "a": 1, x: x * 2, y: }
+    // identifier keys become strings; `y:` is shorthand for y: y
+    assertEquals(1, m["a"])      // string-literal key
+    assertEquals(20, m["x"])     // identifier key
+    assertEquals(10, m["y"])     // shorthand
+    >>> void
+
+Map literals support trailing commas for nicer diffs:
+
+    val m2 = {
+        "a": 1,
+        b: 2,
+    }
+    assertEquals(1, m2["a"]) 
+    assertEquals(2, m2["b"]) 
+    >>> void
+
+You can spread other maps inside a literal with `...`. Items merge left-to-right and the rightmost value wins:
+
+    val base = { a: 1, b: 2 }
+    val merged = { a: 0, ...base, b: 3, c: 4 }
+    assertEquals(1, merged["a"])  // base overwrites a:0
+    assertEquals(3, merged["b"])  // literal overwrites spread
+    assertEquals(4, merged["c"])  // new key
+    >>> void
+
+Merging also works with `+` and `+=`, and you can combine maps and entries conveniently:
+
+    val m3 = { "a": 10 } + ("b" => 20)
+    assertEquals(10, m3["a"]) 
+    assertEquals(20, m3["b"]) 
+
+    var m4 = ("x" => 1) + ("y" => 2)      // entry + entry → Map
+    m4 += { z: 3 }                          // merge literal
+    assertEquals(1, m4["x"]) 
+    assertEquals(2, m4["y"]) 
+    assertEquals(3, m4["z"]) 
+    >>> void
+
+Notes:
+- Access keys with brackets: `m["key"]`. There is no `m.key` sugar.
+- Empty `{}` remains a block/lambda; use `Map()` to create an empty map.
+- When you need computed (expression) keys or non-string keys, use `Map(...)` constructor with entries, e.g. `Map( ("a" + "b") => 1 )`, then merge with a literal if needed: `{ base: } + (computedKey => 42)`.
+
+Please see the [Map] reference for a deeper guide.
 
 # Flow control operators
 
@@ -712,6 +876,8 @@ Or, more neat:
 
 ## When
 
+See also: [Comprehensive guide to `when`](when.md)
+
 It is very much like the kotlin's:
 
     fun type(x) {
@@ -1086,7 +1252,7 @@ The same with `--`:
     sum
     >>> 5050
 
-There are self-assigning version for operators too:
+There is a self-assigning version for operators too:
 
     var count = 100
     var sum = 0
@@ -1184,13 +1350,38 @@ See also [math operations](math.md)
 
 The type for the character objects is `Char`.
 
+### String literal escapes
+
+| escape | ASCII value           |
+|--------|-----------------------|
+| \n     | 0x10, newline         |
+| \r     | 0x13, carriage return |
+| \t     | 0x07, tabulation      |
+| \\     | \ slash character     |
+| \"     | " double quote        |
+
+Other `\c` combinations, where c is any char except mentioned above, are left intact, e.g.:
+
+    val s = "\a"
+    assert(s[0] == '\')
+    assert(s[1] == 'a')
+    >>> void
+
+same as:
+
+    val s = "\\a"
+    assert(s[0] == '\')
+    assert(s[1] == 'a')
+    >>> void
+
 ### Char literal escapes
 
 Are the same as in string literals with little difference:
 
 | escape | ASCII value           |
-|--------|-------------------|
+|--------|-----------------------|
 | \n     | 0x10, newline         |
+| \r     | 0x13, carriage return |
 | \t     | 0x07, tabulation      |
 | \\     | \ slash character     |
 | \'     | ' apostrophe          |
@@ -1262,17 +1453,40 @@ Open-ended ranges could be used to get start and end too:
 
 ### String operations
 
-Concatenation is a `+`: `"hello " + name` works as expected. No confusion.
+Concatenation is a `+`: `"hello " + name` works as expected. No confusion. There is also
+[Regex] support for strings, see the link, for example, whole string match:
 
-Typical set of String functions includes:
+    assert( !"123".matches( "\d\d".re ) )
+    assert( "123".matches( "\d\d\d".re ) )
+    >>> void
+
+Extraction:
+
+    "abcd42def"[ "\d+".re ].value
+    >>> "42"
+
+Part match:
+
+    assert( "abc foo def" =~ "f[oO]+".re )
+    assert( "foo" == $~.value )
+    >>> void
+
+Repeating the fragment:
+
+    assertEquals("hellohello", "hello"*2)
+    assertEquals("", "hello"*0)
+    >>> void
+
+A typical set of String functions includes:
 
 | fun/prop             | description / notes                                        |
-|--------------------|------------------------------------------------------------|
-| lower()            | change case to unicode upper                               |
-| upper()            | change case to unicode lower                               |
+|----------------------|------------------------------------------------------------|
+| lower(), lowercase() | change case to unicode upper                               |
+| upper(), uppercase() | change case to unicode lower                               |
 | trim()               | trim space chars from both ends                            |
 | startsWith(prefix)   | true if starts with a prefix                               |
 | endsWith(prefix)     | true if ends with a prefix                                 |
+| last()               | get last character of a string or throw                    |
 | take(n)              | get a new string from up to n first characters             |
 | takeLast(n)          | get a new string from up to n last characters              |
 | drop(n)              | get a new string dropping n first chars, or empty string   |
@@ -1280,17 +1494,23 @@ Typical set of String functions includes:
 | size                 | size in characters like `length` because String is [Array] |
 | (args...)            | sprintf-like formatting, see [string formatting]           |
 | [index]              | character at index                                         | 
-| [Range]            | substring at range                                         |
+| [Range]              | substring at range (2)                                     |
+| [Regex]              | find first match of regex, like [Regex.find] (2)           |
 | s1 + s2              | concatenation                                              |
 | s1 += s2             | self-modifying concatenation                               |
 | toReal()             | attempts to parse string as a Real value                   |
 | toInt()              | parse string to Int value                                  |
-| characters()       | create [List] of characters (1)                            |
+| characters           | create [List] of characters (1)                            |
 | encodeUtf8()         | returns [Buffer] with characters encoded to utf8           |
+| matches(re)          | matches the regular expression (2)                         |
+|                      |                                                            |
 
 (1)
 : List is mutable therefore a new copy is created on each call.
 
+(2)
+: See [Regex]
+
 ### Literals
 
 String literal could be multiline:
@@ -1318,8 +1538,8 @@ if blank, will be removed too, for example:
 See [math functions](math.md). Other general purpose functions are:
 
 | name                                  | description                                                |
-|----------------------------------------------|------------------------------------------------------------|
-| assert(condition,message="assertion failed") | runtime code check. There will be an option to skip them   |
+|---------------------------------------|------------------------------------------------------------|
+| assert(condition, fn)                 | (1) runtime code check with generic or custom nessage `fn` |
 | assertEquals(a,b)                     |                                                            |
 | assertNotEquals(a,b)                  |                                                            |
 | assertTrows { /* block */ }           |                                                            |
@@ -1329,8 +1549,14 @@ See [math functions](math.md). Other general purpose functions are:
 | print(args...)                        | Open for overriding, it prints to stdout without newline.  |
 | flow {}                               | create flow sequence, see [parallelism]                    |
 | delay, launch, yield                  | see [parallelism]                                          |
-| cached(builder)                              | remembers builder() on first invocation and return it then |
-| let, also, apply, run                        | see above, flow controls                                   |
+| cached(builder)                       | [Lazy evaluation with `cached`](#lazy-evaluation-with-cached) |
+| let, also, apply, run, with       | see above, flow controls                                   |
+
+(1)
+: `fn` is optional lambda returning string message to add to exception string. 
+Lambda avoid unnecessary execution if assertion is not failed. for example:
+
+    assert( x < 10 ) { "x=%s should be < 10"(x) } 
 
 # Built-in constants
 
@@ -1341,6 +1567,8 @@ See [math functions](math.md). Other general purpose functions are:
 
 [List]: List.md
 
+[Testing]: Testing.md
+
 [Iterable]: Iterable.md
 
 [Iterator]: Iterator.md
@@ -1349,7 +1577,7 @@ See [math functions](math.md). Other general purpose functions are:
 
 [Range]: Range.md
 
-[String]: String.md
+[String]: ../archived/development/String.md
 
 [string formatting]: https://github.com/sergeych/mp_stools?tab=readme-ov-file#sprintf-syntax-summary
 
@@ -1364,3 +1592,140 @@ See [math functions](math.md). Other general purpose functions are:
 [RingBuffer]: RingBuffer.md
 
 [Collection]: Collection.md
+
+[Array]: Array.md
+
+[Regex]: Regex.md
+
+## Lazy evaluation with `cached`
+
+Sometimes you have an expensive computation that you only want to perform if and when it is actually needed, and then remember (cache) the result for all future calls. Lyng provides the `cached(builder)` function for this purpose.
+
+It is extremely simple to use: you pass it a block (lambda) that performs the computation, and it returns a zero-argument function that manages the caching for you.
+
+### Basic Example
+
+```lyng
+val expensive = cached {
+    println("Performing expensive calculation...")
+    2 + 2
+}
+
+println(expensive()) // Prints "Performing expensive calculation...") then "4"
+println(expensive()) // Prints only "4" (result is cached)
+```
+
+### Benefits and Simplicity
+
+1.  **Lazy Execution:** The code inside the `cached` block doesn't run until you actually call the resulting function.
+2.  **Automatic State Management:** You don't need to manually check if a value has been computed or store it in a separate variable.
+3.  **Closures and Class Support:** `cached` works perfectly with closures. If you use it inside a class, it will correctly capture the instance variables, and each instance will have its own independent cache.
+
+### Use Case: Lazy Properties in Classes
+
+This is the most common use case for `cached`. It allows you to define expensive "fields" that are only computed if someone actually uses them:
+
+```lyng
+class User(val id: Int) {
+    // The details will be fetched only once, on demand
+    val details = cached {
+        println("Fetching details for user " + id)
+        // Db.query is a hypothetical example
+        Db.query("SELECT * FROM users WHERE id = " + id)
+    }
+}
+
+val u = User(101)
+// ... nothing happens yet ...
+val d = u.details() // Computation happens here
+val sameD = u.details() // Returns the same result immediately
+```
+
+## Multiple Inheritance (quick start)
+
+Lyng supports multiple inheritance (MI) with simple, predictable rules. For a full reference see OOP notes, this is a quick, copy‑paste friendly overview.
+
+Declare a class with multiple bases and pass constructor arguments to each base in the header:
+
+```
+class Foo(val a) {
+    var tag = "F"
+    fun runA() { "ResultA:" + a }
+    fun common() { "CommonA" }
+    private fun privateInFoo() {}
+    protected fun protectedInFoo() {}
+}
+
+class Bar(val b) {
+    var tag = "B"
+    fun runB() { "ResultB:" + b }
+    fun common() { "CommonB" }
+}
+
+class FooBar(a, b) : Foo(a), Bar(b) {
+    // Inside class bodies you can qualify with this@Type
+    fun fromFoo() { this@Foo.common() }
+    fun fromBar() { this@Bar.common() }
+}
+
+val fb = FooBar(1, 2)
+assertEquals("ResultA:1", fb.runA())
+assertEquals("ResultB:2", fb.runB())
+
+// Unqualified ambiguous member uses the first base (leftmost)
+assertEquals("CommonA", fb.common())
+
+// Disambiguate with casts
+assertEquals("CommonB", (fb as Bar).common())
+assertEquals("CommonA", (fb as Foo).common())
+
+// Field collisions: unqualified read/write uses the first in order
+assertEquals("F", fb.tag)
+fb.tag = "X"
+assertEquals("X", fb.tag)          // Foo.tag updated
+assertEquals("X", (fb as Foo).tag) // qualified read: Foo.tag
+assertEquals("B", (fb as Bar).tag) // qualified read: Bar.tag
+
+// Qualified write targets the chosen base storage
+(fb as Bar).tag = "Y"
+assertEquals("X", (fb as Foo).tag)
+assertEquals("Y", (fb as Bar).tag)
+
+// Optional casts with safe call
+class Buzz : Bar(3)
+val buzz = Buzz()
+assertEquals("ResultB:3", buzz.runB())
+assertEquals("ResultB:3", (buzz as? Bar)?.runB())
+assertEquals(null, (buzz as? Foo)?.runA())
+```
+
+Notes:
+- Resolution order uses C3 MRO (active): deterministic, monotonic order suitable for diamonds and complex hierarchies. Example: for `class D() : B(), C()` where both `B()` and `C()` derive from `A()`, the C3 order is `D → B → C → A`. The first visible match wins.
+- `private` is visible only inside the declaring class; `protected` is visible from the declaring class and any of its transitive subclasses. Qualialsofication (`this@Type`) or casts do not bypass visibility.
+- Safe‑call `?.` works with `as?` for optional dispatch.
+
+## Extension members
+
+You can add new methods and properties to existing classes without modifying them.
+
+### Extension functions
+
+    fun String.shout() = this.upper() + "!!!"
+    "hello".shout()
+    >>> "HELLO!!!"
+
+### Extension properties
+
+    val Int.isEven = this % 2 == 0
+    4.isEven
+    >>> true
+
+Example with custom accessors:
+
+    val String.firstChar get() = this[0]
+    "abc".firstChar
+    >>> 'a'
+
+Extension members are **scope-isolated**: they are visible only in the scope where they are defined and its children. This prevents name collisions and improves security.
+
+To get details on OOP in Lyng, see [OOP notes](OOP.md).

docs/whats_new.md

@@ -0,0 +1,188 @@
+# What's New in Lyng
+
+This document highlights the latest additions and improvements to the Lyng language and its ecosystem.
+
+## Language Features
+
+### Class Properties with Accessors
+Classes now support properties with custom `get()` and `set()` accessors. Properties in Lyng do **not** have automatic backing fields; they are pure accessors.
+
+```lyng
+class Person(private var _age: Int) {
+    // Read-only property
+    val ageCategory get() = if (_age < 18) "Minor" else "Adult"
+
+    // Read-write property
+    var age: Int
+        get() = _age
+        set(v) {
+            if (v >= 0) _age = v
+        }
+}
+```
+
+### Private and Protected Setters
+You can now restrict the visibility of a property's or field's setter using `private set` or `protected set`. This allows members to be publicly readable but only writable from within the declaring class or its subclasses.
+
+```lyng
+class Counter {
+    var count = 0
+        private set  // Field with private setter
+        
+    fun increment() { count++ }
+}
+
+class AdvancedCounter : Counter {
+    var totalOperations = 0
+        protected set // Settable here and in further subclasses
+}
+
+let c = Counter()
+c.increment() // OK
+// c.count = 10 // Error: setter is private
+```
+
+### Late-initialized `val` Fields
+`val` fields in classes can be declared without an immediate initializer, provided they are assigned exactly once. If accessed before initialization, they hold the special `Unset` singleton.
+
+```lyng
+class Service {
+    val logger
+    
+    fun check() {
+        if (logger == Unset) println("Not initialized yet")
+    }
+
+    init {
+        logger = Logger("Service")
+    }
+}
+```
+
+### Named Arguments and Named Splats
+Function calls now support named arguments using the `name: value` syntax. If the variable name matches the parameter name, you can use the `name:` shorthand.
+
+```lyng
+fun greet(name, greeting = "Hello") {
+    println("$greeting, $name!")
+}
+
+val name = "Alice"
+greet(name:)                  // Shorthand for greet(name: name)
+greet(greeting: "Hi", name: "Bob")
+
+let params = { name: "Charlie", greeting: "Hey")
+greet(...params)              // Named splat expansion
+```
+
+### Multiple Inheritance (MI)
+Lyng now supports multiple inheritance using the C3 Method Resolution Order (MRO). Use `this@Type` or casts for disambiguation.
+
+```lyng
+class A { fun foo() = "A" }
+class B { fun foo() = "B" }
+
+class Derived : A, B {
+    fun test() {
+        println(foo())              // Resolves to A.foo (leftmost)
+        println(this@B.foo())       // Qualified dispatch to B.foo
+    }
+}
+
+let d = Derived()
+println((d as B).foo())             // Disambiguation via cast
+```
+
+### Singleton Objects
+Singleton objects are declared using the `object` keyword. They provide a convenient way to define a class and its single instance in one go.
+
+```lyng
+object Config {
+    val version = "1.2.3"
+    fun show() = println("Config version: " + version)
+}
+
+Config.show()
+```
+
+### Object Expressions
+You can now create anonymous objects that inherit from classes or interfaces using the `object : Base { ... }` syntax. These expressions capture their lexical scope and support multiple inheritance.
+
+```lyng
+val worker = object : Runnable {
+    override fun run() = println("Working...")
+}
+
+val x = object : Base(arg1), Interface1 {
+    val property = 42
+    override fun method() = this@object.property * 2
+}
+```
+
+Use `this@object` to refer to the innermost anonymous object instance when `this` is rebound.
+
+### Unified Delegation Model
+A powerful new delegation system allows `val`, `var`, and `fun` members to delegate their logic to other objects using the `by` keyword.
+
+```lyng
+// Property delegation
+val lazyValue by lazy { "expensive" }
+
+// Function delegation
+fun remoteAction by myProxy
+
+// Observable properties
+var name by Observable("initial") { n, old, new -> 
+    println("Changed!") 
+}
+```
+
+The system features a unified interface (`getValue`, `setValue`, `invoke`) and a `bind` hook for initialization-time validation and configuration. See the [Delegation Guide](delegation.md) for more.
+
+### User-Defined Exception Classes
+You can now create custom exception types by inheriting from the built-in `Exception` class. Custom exceptions are real classes that can have their own fields and methods, and they work seamlessly with `throw` and `try-catch` blocks.
+
+```lyng
+class ValidationException(val field, m) : Exception(m)
+
+try {
+    throw ValidationException("email", "Invalid format")
+}
+catch(e: ValidationException) {
+    println("Error in " + e.field + ": " + e.message)
+}
+```
+
+### Assign-if-null Operator (`?=`)
+The new `?=` operator provides a concise way to assign a value only if the target is `null`. It is especially useful for setting default values or lazy initialization.
+
+```lyng
+var x = null
+x ?= 42          // x is now 42
+x ?= 100         // x remains 42 (not null)
+
+// Works with properties and index access
+config.port ?= 8080
+settings["theme"] ?= "dark"
+```
+
+The operator returns the final value of the receiver (the original value if it was not `null`, or the new value if the assignment occurred).
+
+## Tooling and Infrastructure
+
+### CLI: Formatting Command
+A new `fmt` subcommand has been added to the Lyng CLI.
+
+```bash
+lyng fmt MyFile.lyng             # Print formatted code to stdout
+lyng fmt --in-place MyFile.lyng  # Format file in-place
+lyng fmt --check MyFile.lyng     # Check if file needs formatting
+```
+
+### IDEA Plugin: Autocompletion
+Experimental lightweight autocompletion is now available in the IntelliJ plugin. It features type-aware member suggestions and inheritance-aware completion.
+
+You can enable it in **Settings | Lyng Formatter | Enable Lyng autocompletion**.
+
+### Kotlin API: Exception Handling
+The `Obj.getLyngExceptionMessageWithStackTrace()` extension method has been added to simplify retrieving detailed error information from Lyng exception objects in Kotlin. Additionally, `getLyngExceptionMessage()` and `raiseAsExecutionError()` now accept an optional `Scope`, making it easier to use them when a scope is not immediately available.

docs/when.md

@@ -0,0 +1,241 @@
+# The `when` statement (expression)
+
+[//]: # (topMenu)
+
+Lyng provides a concise multi-branch selection with `when`, heavily inspired by Kotlin. In Lyng, `when` is an expression: it evaluates to a value. If the selected branch contains no value (e.g., it ends with `void` or calls a void function like `println`), the whole `when` expression evaluates to `void`.
+
+Currently, Lyng implements the "subject" form: `when(value) { ... }`. The subject-less form `when { condition -> ... }` is not implemented yet.
+
+## Quick examples
+
+    val r1 = when("a") {
+        "a" -> "ok"
+        else -> "nope"
+    }
+    assertEquals("ok", r1)
+    
+    val r2 = when(5) {
+        3 -> "no"
+        4 -> "no"
+        else -> "five"
+    }
+    assertEquals("five", r2)
+    
+    val r3 = when(5) {
+        3 -> "no"
+        4 -> "no"
+    }
+    // no matching case and no else → `void`
+    assert(r3 == void)
+    >>> void
+
+## Syntax
+
+    when(subject) {
+        condition1 [, condition2, ...] -> resultExpressionOrBlock
+        conditionN -> result
+        else -> fallback
+    }
+
+- Commas group multiple conditions for one branch.
+- First matching branch wins; there is no fall‑through.
+- `else` is optional. If omitted and nothing matches, the result is `void`.
+
+## Matching rules (conditions)
+
+Within `when(subject)`, each condition is evaluated against the already evaluated `subject`. Lyng supports:
+
+1) Equality match (default)
+- Any expression value can be used as a condition. It matches if it is equal to `subject`.
+- Equality relies on Lyng’s comparison (`compareTo(...) == 0`). For user types, implement comparison accordingly.
+
+    when(x) {
+        0 -> "zero"
+        "EUR" -> "currency"
+    }
+    >>> void
+
+2) Type checks: `is` and `!is`
+- Check whether the subject is an instance of a class.
+- Works with built‑in classes and user classes.
+
+    fun typeOf(x) {
+        when(x) {
+            is Real, is Int -> "number"
+            is String -> "string"
+            else -> "other"
+        }
+    }
+    assertEquals("number", typeOf(5))
+    assertEquals("string", typeOf("hi"))
+    >>> void
+
+3) Containment checks: `in` and `!in`
+- `in container` matches if `container.contains(subject)` is true.
+- `!in container` matches if `contains(subject)` is false.
+- Any object that provides `contains(item)` can act as a container.
+
+Common containers:
+- Ranges (e.g., `'a'..'z'`, `1..10`, `1..<10`, `..5`, `5..`)
+- Lists, Sets, Arrays, Buffers
+- Strings (character or substring containment)
+
+Examples:
+
+    when('e') {
+        in 'a'..'c' -> "small"
+        in 'a'..'z' -> "letter"
+        else -> "other"
+    }
+    >>> "letter"
+    
+    when(5) {
+        in [1,2,3,4,6] -> "no"
+        in [7,0,9] -> "no"
+        else -> "ok"
+    }
+    >>> "ok"
+    
+    when(5) {
+        in [1,2,3,4,6] -> "no"
+        in [7,0,9] -> "no"
+        in [-1,5,11] -> "yes"
+        else -> "no"
+    }
+    >>> "yes"
+    
+    when(5) {
+        !in [1,2,3,4,6,5] -> "no"
+        !in [7,0,9,5] -> "no"
+        !in [-1,15,11] -> "ok"
+        else -> "no"
+    }
+    >>> "ok"
+    
+    // String containment
+    "foo" in "foobar"   // true (substring)
+    'o' in "foobar"      // true (character)
+    >>> true
+
+Notes on mixed String/Char ranges:
+- Prefer character ranges for characters: `'a'..'z'`.
+- `"a".."z"` is a String range and may not behave as you expect with `Char` subjects.
+
+    assert( "more" in "a".."z")
+    assert( 'x' !in "a".."z")  // Char vs String range: often not what you want
+    assert( 'x' in 'a'..'z')     // OK
+    assert( "x" !in 'a'..'z')   // String in Char range: likely not intended
+    >>> void
+
+## Grouping multiple conditions with commas
+
+You can group values and/or `is`/`in` checks for a single result:
+
+    fun classify(x) {
+        when(x) {
+            "42", 42 -> "answer"
+            is Real, is Int -> "number"
+            in ['@', '#', '^'] -> "punct1"
+            in "*&.," -> "punct2"
+            else -> "unknown"
+        }
+    }
+    assertEquals("number", classify(π/2))
+    assertEquals("answer", classify(42))
+    assertEquals("answer", classify("42"))
+    >>> void
+
+## Return value and blocks
+
+- `when` returns the value of the matched branch result expression/block.
+- Branch bodies can be single expressions or blocks `{ ... }`.
+- If a matched branch produces `void` (e.g., only prints), the `when` result is `void`.
+
+    val res = when(2) {
+        1 -> 10
+        2 -> { println("two"); 20 }
+        else -> 0
+    }
+    assertEquals(20, res)
+    >>> void
+
+## Else branch
+
+- Optional but recommended when non‑exhaustive.
+- If omitted and nothing matches, `when` result is `void` (see r3 in the Quick examples).
+- Only one `else` is allowed.
+
+## Subject‑less `when`
+
+The Kotlin‑style subject‑less form `when { condition -> ... }` is not implemented yet in Lyng. Use `if/else` chains or structure your checks around a subject with `when(subject) { ... }`.
+
+## Extending `when` for your own types
+
+### Equality matches
+- Equality checks in `when(subject)` use Lyng comparison (`compareTo` semantics under the hood). For your own Lyng classes, implement comparison appropriately so that `subject == value` works as intended.
+
+### `in` / `!in` containment
+- Provide a `contains(item)` method on your class to participate in `in` conditions.
+- Example: a custom `Box` that contains one specific item:
+
+    class Box(val item)
+    fun Box.contains(x) { x == item }
+    
+    val b = Box(10)
+    when(10) { in b -> "hit" }
+    >>> "hit"
+
+Any built‑in collection (`List`, `Set`, `Array`), `Range`, `Buffer`, and other containers already implement `contains`.
+
+### Type checks (`is` / `!is`)
+- Every value has a `::class` that yields its Lyng class object, e.g. `[1,2,3]::class` → `List`.
+- `is ClassName` in `when` uses Lyng’s class hierarchy. Ensure your class is declared and can be referenced by name.
+
+    []::class == List
+    >>> true
+    
+    fun f(x) { when(x) { is List -> "list" else -> "other" } }
+    assertEquals("list", f([1]))
+    >>> void
+
+## Kotlin‑backed classes (embedding)
+
+When embedding Lyng in Kotlin, you may expose Kotlin‑backed objects and classes. Interactions inside `when` work as follows:
+- `is` checks use the Lyng class object you expose for your Kotlin type. Ensure your exposed class participates in the Lyng class hierarchy (see Embedding docs).
+- `in` checks call `contains(subject)`; if your Kotlin‑backed object wants to support `in`, expose a `contains(item)` method (mapped to Lyng) or implement the corresponding Lyng container wrapper.
+- Equality follows Lyng comparison rules. Ensure your Kotlin‑backed object’s Lyng adapter implements equality/compare correctly.
+
+For details on exposing classes/methods from Kotlin, see: [Embedding Lyng in your Kotlin project](embedding.md).
+
+## Gotchas and tips
+
+- First match wins; there is no fall‑through. Order branches carefully.
+- Group related conditions with commas for readability and performance (a single branch evaluation).
+- Prefer character ranges for character tests; avoid mixing `String` and `Char` ranges.
+- If you rely on `in`, check that your container implements `contains(item)`.
+- Remember: `when` is an expression — you can assign its result to a variable or return it from a function.
+
+## Additional examples
+
+    fun label(ch) {
+        when(ch) {
+            in '0'..'9' -> "digit"
+            in 'a'..'z', in 'A'..'Z' -> "letter"
+            '$' -> "dollar"
+            else -> "other"
+        }
+    }
+    assertEquals("digit", label('3'))
+    assertEquals("dollar", label('$'))
+    >>> void
+
+    fun normalize(x) {
+        when(x) {
+            is Int -> x
+            is Real -> x.round()
+            else -> 0
+        }
+    }
+    assertEquals(12, normalize(12))
+    assertEquals(3,  normalize(2.6))
+    >>> void

editors/lyng-textmate/README.md

@@ -0,0 +1,68 @@
+Lyng TextMate grammar
+======================
+
+This folder contains a TextMate grammar for the Lyng language so you can get syntax highlighting quickly in:
+
+- JetBrains IDEs (IntelliJ IDEA, Fleet, etc.) via “TextMate Bundles”
+- VS Code (via “Install from VSIX” or by adding as an extension folder)
+
+Files
+-----
+- `package.json` — VS Code–style wrapper that JetBrains IDEs can import as a TextMate bundle.
+- `syntaxes/lyng.tmLanguage.json` — the grammar. It highlights:
+  - Line and block comments (`//`, `/* */`)
+  - Shebang line at file start (`#!...`)
+  - Strings: single and double quotes with escapes
+  - Char literals `'x'` with escapes
+  - Numbers: decimal with underscores and exponents, and hex (`0x...`)
+  - Keywords (control and declarations), boolean operator words (`and`, `or`, `not`, `in`, `is`, `as`, `as?`)
+  - Composite textual operators: `not in`, `not is`
+  - Constants: `true`, `false`, `null`, `this`
+  - Annotations: `@name` (Unicode identifiers supported)
+  - Labels: `name:` (Unicode identifiers supported)
+  - Declarations: highlights declared names in `fun|fn name`, `class|enum|interface Name`, `val|var name`
+  - Types: built-ins (`Int|Real|String|Bool|Char|Regex`) and Capitalized identifiers (heuristic)
+  - Operators including ranges (`..`, `..<`, `...`), null-safe (`?.`, `?[`, `?(`, `?{`, `?:`, `??`), arrows (`->`, `=>`, `::`), match operators (`=~`, `!~`), bitwise, arithmetic, etc.
+  - Shuttle operator `<=>`
+  - Division operator `/` (note: Lyng has no regex literal syntax; `/` is always division)
+  - Named arguments at call sites `name: value` (the `name` part is highlighted as `variable.parameter.named.lyng` and the `:` as punctuation). The rule is anchored to `(` or `,` and excludes `::` to avoid conflicts.
+
+Install in IntelliJ IDEA (and other JetBrains IDEs)
+---------------------------------------------------
+1. Open Settings / Preferences → Editor → TextMate Bundles.
+2. Click “+” and select this folder `editors/lyng-textmate/` (the folder that contains `package.json`).
+3. Ensure `*.lyng` is associated with the Lyng grammar (IntelliJ usually picks this up from `fileTypes`).
+4. Optional: customize colors with Settings → Editor → Color Scheme → TextMate.
+
+Enable Markdown code-fence highlighting in IntelliJ
+--------------------------------------------------
+1. Settings / Preferences → Languages & Frameworks → Markdown → Code style → Code fences → Languages.
+2. Add mapping: language id `lyng` → “Lyng (TextMate)”.
+3. Now blocks like
+   ```
+   ```lyng
+   // Lyng code here
+   ```
+   ```
+   will be highlighted.
+
+Install in VS Code
+------------------
+Fastest local install without packaging:
+1. Copy or symlink this folder somewhere stable (or keep it in your workspace).
+2. Use “Developer: Install Extension from Location…” (Insiders) or package with `vsce package` and install the resulting `.vsix`.
+3. VS Code will auto-associate `*.lyng` via this extension; if needed, check File Associations.
+
+Notes and limitations
+---------------------
+- Type highlighting is heuristic (Capitalized identifiers). The IntelliJ plugin will use language semantics and avoid false positives.
+- If your language adds or changes tokens, please update patterns in `lyng.tmLanguage.json`. The Kotlin sources in `lynglib/src/commonMain/kotlin/net/sergeych/lyng/highlight/` are a good reference for token kinds.
+- Labels `name:` at statement level remain supported and are kept distinct from named call arguments by context. The grammar prefers named-argument matching when a `name:` appears right after `(` or `,`.
+
+Lyng specifics
+--------------
+- There are no regex literal tokens in Lyng at the moment; the slash character `/` is always treated as the division operator. The grammar intentionally does not define a `/.../` regex rule to avoid mis-highlighting lines like `a / b`.
+
+Contributing
+------------
+Pull requests to refine patterns and add tests/samples are welcome. You can place test snippets in `sample_texts/` and visually verify.

editors/lyng-textmate/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "lyng-textmate",
+  "displayName": "Lyng",
+  "description": "TextMate grammar for the Lyng language (for JetBrains IDEs via TextMate Bundles and VS Code).",
+  "version": "0.1.0",
+  "publisher": "lyng",
+  "license": "Apache-2.0",
+  "engines": { "vscode": "^1.0.0" },
+  "contributes": {
+    "languages": [
+      {
+        "id": "lyng",
+        "aliases": ["Lyng", "lyng"],
+        "extensions": [".lyng"]
+      }
+    ],
+    "grammars": [
+      {
+        "language": "lyng",
+        "scopeName": "source.lyng",
+        "path": "./syntaxes/lyng.tmLanguage.json"
+      }
+    ]
+  }
+}

editors/lyng-textmate/syntaxes/lyng.tmLanguage.json

@@ -0,0 +1,86 @@
+{
+  "$schema": "https://raw.githubusercontent.com/martinring/tmlanguage/master/tmlanguage.json",
+  "name": "Lyng",
+  "scopeName": "source.lyng",
+  "fileTypes": ["lyng"],
+  "patterns": [
+    { "include": "#shebang" },
+    { "include": "#comments" },
+    { "include": "#strings" },
+    { "include": "#char" },
+    { "include": "#numbers" },
+    { "include": "#declarations" },
+    { "include": "#keywords" },
+    { "include": "#constants" },
+    { "include": "#types" },
+    { "include": "#mapLiterals" },
+    { "include": "#namedArgs" },
+    { "include": "#annotations" },
+    { "include": "#labels" },
+    { "include": "#directives" },
+    { "include": "#operators" },
+    { "include": "#punctuation" }
+  ],
+  "repository": {
+    "shebang": { "patterns": [ { "name": "comment.line.shebang.lyng", "match": "^#!.*$" } ] },
+    "comments": {
+      "patterns": [
+        { "name": "comment.line.double-slash.lyng", "match": "//.*$" },
+        { "name": "comment.block.lyng", "begin": "/\\*", "end": "\\*/" }
+      ]
+    },
+    "strings": {
+      "patterns": [
+        { "name": "string.quoted.double.lyng", "begin": "\"", "end": "\"", "patterns": [ { "match": "\\\\.", "name": "constant.character.escape.lyng" } ] },
+        { "name": "string.quoted.single.lyng", "begin": "'", "end": "'", "patterns": [ { "match": "\\\\.", "name": "constant.character.escape.lyng" } ] }
+      ]
+    },
+    "char": { "patterns": [ { "name": "constant.character.lyng", "match": "'(?:[^\\\\']|\\\\.)'" } ] },
+    "numbers": {
+      "patterns": [
+        { "name": "constant.numeric.hex.lyng", "match": "0x[0-9A-Fa-f_]+" },
+        { "name": "constant.numeric.decimal.lyng", "match": "(?<![A-Za-z_])(?:[0-9][0-9_]*)\\.(?:[0-9_]+)(?:[eE][+-]?[0-9_]+)?|(?<![A-Za-z_])(?:[0-9][0-9_]*)(?:[eE][+-]?[0-9_]+)?" }
+      ]
+    },
+    "annotations": { "patterns": [ { "name": "entity.name.label.at.lyng", "match": "@[\\p{L}_][\\p{L}\\p{N}_]*" } ] },
+    "mapLiterals": {
+      "patterns": [
+        {
+          "name": "meta.map.entry.lyng",
+          "match": "(?:(?<=\\{|,))\\s*(\"[^\"]*\"|[\\p{L}_][\\p{L}\\p{N}_]*)\\s*(:)(?!:)",
+          "captures": {
+            "1": { "name": "variable.other.property.key.lyng" },
+            "2": { "name": "punctuation.separator.colon.lyng" }
+          }
+        },
+        {
+          "name": "meta.map.spread.lyng",
+          "match": "(?:(?<=\\{|,))\\s*(\\.\\.\\.)",
+          "captures": {
+            "1": { "name": "keyword.operator.spread.lyng" }
+          }
+        }
+      ]
+    },
+    "namedArgs": {
+      "patterns": [
+        {
+          "name": "meta.argument.named.lyng",
+          "match": "(?:(?<=\\()|(?<=,))\\s*([\\p{L}_][\\p{L}\\p{N}_]*)\\s*(:)(?!:)",
+          "captures": {
+            "1": { "name": "variable.parameter.named.lyng" },
+            "2": { "name": "punctuation.separator.colon.lyng" }
+          }
+        }
+      ]
+    },
+    "labels": { "patterns": [ { "name": "entity.name.label.lyng", "match": "[\\p{L}_][\\p{L}\\p{N}_]*@" } ] },
+    "directives": { "patterns": [ { "name": "meta.directive.lyng", "match": "^\\s*#[_A-Za-z][_A-Za-z0-9]*" } ] },
+    "declarations": { "patterns": [ { "name": "meta.function.declaration.lyng", "match": "\\b(fun|fn)\\s+(?:([\\p{L}_][\\p{L}\\p{N}_]*)\\.)?([\\p{L}_][\\p{L}\\p{N}_]*)", "captures": { "1": { "name": "keyword.declaration.lyng" }, "2": { "name": "entity.name.type.lyng" }, "3": { "name": "entity.name.function.lyng" } } }, { "name": "meta.type.declaration.lyng", "match": "\\b(?:class|enum|interface|object)(?:\\s+([\\p{L}_][\\p{L}\\p{N}_]*))?", "captures": { "1": { "name": "entity.name.type.lyng" } } }, { "name": "meta.variable.declaration.lyng", "match": "\\b(val|var)\\s+(?:([\\p{L}_][\\p{L}\\p{N}_]*)\\.)?([\\p{L}_][\\p{L}\\p{N}_]*)", "captures": { "1": { "name": "keyword.declaration.lyng" }, "2": { "name": "entity.name.type.lyng" }, "3": { "name": "variable.other.declaration.lyng" } } } ] },
+    "keywords": { "patterns": [ { "name": "keyword.control.lyng", "match": "\\b(?:if|else|when|while|do|for|try|catch|finally|throw|return|break|continue)\\b" }, { "name": "keyword.declaration.lyng", "match": "\\b(?:fun|fn|class|enum|interface|val|var|import|package|constructor|property|abstract|override|open|closed|extern|private|protected|static|get|set|object|init|by)\\b" }, { "name": "keyword.operator.word.lyng", "match": "\\bnot\\s+(?:in|is)\\b" }, { "name": "keyword.operator.word.lyng", "match": "\\b(?:and|or|not|in|is|as|as\\?)\\b" } ] },
+    "constants": { "patterns": [ { "name": "constant.language.lyng", "match": "(?:\\b(?:true|false|null|this(?:@[\\p{L}_][\\p{L}\\p{N}_]*)?)\\b|π)" } ] },
+    "types": { "patterns": [ { "name": "storage.type.lyng", "match": "\\b(?:Int|Real|String|Bool|Char|Regex)\\b" }, { "name": "entity.name.type.lyng", "match": "\\b[A-Z][A-Za-z0-9_]*\\b(?!\\s*\\()" } ] },
+    "operators": { "patterns": [ { "name": "keyword.operator.comparison.lyng", "match": "===|!==|==|!=|<=|>=|<|>" }, { "name": "keyword.operator.shuttle.lyng", "match": "<=>" }, { "name": "keyword.operator.arrow.lyng", "match": "=>|->|::" }, { "name": "keyword.operator.range.lyng", "match": "\\.\\.\\.|\\.\\.<|\\.\\." }, { "name": "keyword.operator.nullsafe.lyng", "match": "\\?\\.|\\?\\[|\\?\\(|\\?\\{|\\?:|\\?\\?" }, { "name": "keyword.operator.assignment.lyng", "match": "(?:\\+=|-=|\\*=|/=|%=|=)" }, { "name": "keyword.operator.logical.lyng", "match": "&&|\\|\\|" }, { "name": "keyword.operator.bitwise.lyng", "match": "<<|>>|&|\\||\\^|~" }, { "name": "keyword.operator.match.lyng", "match": "=~|!~" }, { "name": "keyword.operator.arithmetic.lyng", "match": "\\+\\+|--|[+\\-*/%]" }, { "name": "keyword.operator.other.lyng", "match": "[!?]" } ] },
+    "punctuation": { "patterns": [ { "name": "punctuation.separator.comma.lyng", "match": "," }, { "name": "punctuation.terminator.statement.lyng", "match": ";" }, { "name": "punctuation.section.block.begin.lyng", "match": "[(]{1}|[{]{1}|\\[" }, { "name": "punctuation.section.block.end.lyng", "match": "[)]{1}|[}]{1}|\\]" }, { "name": "punctuation.accessor.dot.lyng", "match": "\\." }, { "name": "punctuation.separator.colon.lyng", "match": ":" } ] }
+  }
+}

gradle.properties

@@ -29,3 +29,12 @@ android.nonTransitiveRClass=true
 
 # other
 kotlin.native.cacheKind.linuxX64=none
+
+# Workaround: Ensure Gradle uses a JDK with `jlink` available for AGP's JDK image transform.
+# On this environment, the system JDK 21 installation lacks `jlink`, causing
+# :lynglib:androidJdkImage to fail. Point Gradle to a JDK that includes `jlink`.
+# This affects only the JDK Gradle runs with; Kotlin/JVM target remains compatible.
+#org.gradle.java.home=/home/sergeych/.jdks/corretto-21.0.9
+android.experimental.lint.migrateToK2=false
+android.lint.useK2Uast=false
+kotlin.mpp.applyDefaultHierarchyTemplate=true

gradle/libs.versions.toml

@@ -1,11 +1,11 @@
 [versions]
 agp = "8.5.2"
 clikt = "5.0.3"
-kotlin = "2.1.21"
+kotlin = "2.3.0"
 android-minSdk = "24"
 android-compileSdk = "34"
-kotlinx-coroutines = "1.9.0"
-mp_bintools = "0.1.12"
+kotlinx-coroutines = "1.10.2"
+mp_bintools = "0.3.2"
 firebaseCrashlyticsBuildtools = "3.0.3"
 okioVersion = "3.10.2"
 compiler = "3.2.0-alpha11"
@@ -20,6 +20,7 @@ mp_bintools = { module = "net.sergeych:mp_bintools", version.ref = "mp_bintools"
 firebase-crashlytics-buildtools = { group = "com.google.firebase", name = "firebase-crashlytics-buildtools", version.ref = "firebaseCrashlyticsBuildtools" }
 okio = { module = "com.squareup.okio:okio", version.ref = "okioVersion" }
 okio-fakefilesystem = { module = "com.squareup.okio:okio-fakefilesystem", version.ref = "okioVersion" }
+okio-nodefilesystem = { module = "com.squareup.okio:okio-nodefilesystem", version.ref = "okioVersion" }
 compiler = { group = "androidx.databinding", name = "compiler", version.ref = "compiler" }
 
 [plugins]

images/lyng-icons/lyng_file.svg

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  - Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+  -
+  - Licensed under the Apache License, Version 2.0 (the "License");
+  - you may not use this file except in compliance with the License.
+  - You may obtain a copy of the License at
+  -
+  -     http://www.apache.org/licenses/LICENSE-2.0
+  -
+  - Unless required by applicable law or agreed to in writing, software
+  - distributed under the License is distributed on an "AS IS" BASIS,
+  - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  - See the License for the specific language governing permissions and
+  - limitations under the License.
+  -
+  -->
+
+<svg width="16" height="16" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg" aria-labelledby="title" role="img">
+  <title>Lyng File Icon (temporary λ)</title>
+  <defs>
+    <style>
+      .g { fill: none; stroke: currentColor; stroke-width: 1.6; stroke-linecap: round; stroke-linejoin: round; }
+    </style>
+  </defs>
+  <!-- Keep shapes crisp on small canvas; slight inset to avoid clipping -->
+  <g transform="translate(0.5,0.5)">
+    <!-- Stylized lambda fitted to 14x14 -->
+    <path class="g" d="M4.5 2.5 L7 9.5 C7.6 11.2 9.0 12.5 11.0 12.5 L14.5 12.5"/>
+    <path class="g" d="M7 9.5 L2.5 14.5"/>
+  </g>
+</svg>

images/lyng-icons/pluginIcon.svg

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  - Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+  -
+  - Licensed under the Apache License, Version 2.0 (the "License");
+  - you may not use this file except in compliance with the License.
+  - You may obtain a copy of the License at
+  -
+  -     http://www.apache.org/licenses/LICENSE-2.0
+  -
+  - Unless required by applicable law or agreed to in writing, software
+  - distributed under the License is distributed on an "AS IS" BASIS,
+  - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  - See the License for the specific language governing permissions and
+  - limitations under the License.
+  -
+  -->
+
+<svg width="40" height="40" viewBox="0 0 40 40" xmlns="http://www.w3.org/2000/svg" aria-labelledby="title" role="img">
+  <title>Lyng Plugin Icon (temporary λ)</title>
+  <defs>
+    <!-- Monochrome, theme-friendly -->
+    <style>
+      .glyph { fill: none; stroke: currentColor; stroke-width: 3; stroke-linecap: round; stroke-linejoin: round; }
+    </style>
+  </defs>
+  <!-- Safe inset to avoid edge clipping in 40x40 canvas -->
+  <g transform="translate(2,2)">
+    <!-- Stylized lambda: rising stem + curved tail -->
+    <path class="glyph" d="M12 6 L18 22 C19.2 25.5 22.2 28 26 28 L32 28"/>
+    <path class="glyph" d="M18 22 L8 34"/>
+  </g>
+</svg>

lyng-idea/build.gradle.kts

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+plugins {
+    kotlin("jvm")
+    id("org.jetbrains.intellij") version "1.17.4"
+}
+
+group = "net.sergeych.lyng"
+version = "0.0.5-SNAPSHOT"
+
+kotlin {
+    jvmToolchain(17)
+}
+
+repositories {
+    mavenCentral()
+    // Use the same repositories as the rest of the project so plugin runtime deps resolve
+    maven("https://maven.universablockchain.com/")
+    maven("https://gitea.sergeych.net/api/packages/SergeychWorks/maven")
+    mavenLocal()
+}
+
+dependencies {
+    implementation(project(":lynglib"))
+    // Include lyngio so Quick Docs can reflectively load fs docs registrar (FsBuiltinDocs)
+    implementation(project(":lyngio"))
+    // Rich Markdown renderer for Quick Docs
+    implementation("com.vladsch.flexmark:flexmark-all:0.64.8")
+
+    // Tests for IntelliJ Platform fixtures rely on JUnit 3/4 API (junit.framework.TestCase)
+    // Add JUnit 4 which contains the JUnit 3 compatibility classes used by BasePlatformTestCase/UsefulTestCase
+    testImplementation("junit:junit:4.13.2")
+    testRuntimeOnly("org.junit.vintage:junit-vintage-engine:5.10.2")
+    testImplementation("org.opentest4j:opentest4j:1.3.0")
+}
+
+intellij {
+    type.set("IC")
+    // Build against a modern baseline. Install range is controlled by since/until below.
+    version.set("2024.1.6")
+    // We manage <idea-version> ourselves in plugin.xml to keep it open-ended (no upper cap)
+    updateSinceUntilBuild.set(false)
+    // Include only available bundled plugins for this IDE build
+    plugins.set(listOf(
+        "com.intellij.java",
+        // Provide Grazie API on compile classpath (bundled in 2024.3+, but add here for compilation)
+        "tanvd.grazi"
+        // Do not list com.intellij.spellchecker here: it is expected to be bundled with the IDE.
+        // Listing it causes Gradle to search for a separate plugin artifact and fail on IC 2024.3.
+    ))
+}
+
+tasks {
+    patchPluginXml {
+        // Keep version and other metadata patched by Gradle, but since/until are controlled in plugin.xml.
+        // (intellij.updateSinceUntilBuild=false prevents Gradle from injecting an until-build cap)
+    }
+
+    // Build an installable plugin zip and copy it to $PROJECT_ROOT/distributables
+    // Usage: ./gradlew :lyng-idea:buildInstallablePlugin
+    // It depends on buildPlugin and overwrites any existing file with the same name
+    register<Copy>("buildInstallablePlugin") {
+        dependsOn("buildPlugin")
+
+        // The Gradle IntelliJ Plugin produces: build/distributions/<project.name>-<version>.zip
+        val zipName = "${project.name}-${project.version}.zip"
+        val sourceZip = layout.buildDirectory.file("distributions/$zipName")
+
+        from(sourceZip)
+        into(rootProject.layout.projectDirectory.dir("distributables"))
+
+        // Overwrite if a file with the same name exists
+        duplicatesStrategy = DuplicatesStrategy.INCLUDE
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/LyngFileType.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea
+
+import com.intellij.openapi.fileTypes.LanguageFileType
+import javax.swing.Icon
+
+object LyngFileType : LanguageFileType(LyngLanguage) {
+    override fun getName(): String = "Lyng"
+    override fun getDescription(): String = "Lyng language file"
+    override fun getDefaultExtension(): String = "lyng"
+    override fun getIcon(): Icon? = LyngIcons.FILE
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/LyngFileTypeFactory.kt

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea
+
+import com.intellij.openapi.fileTypes.FileTypeConsumer
+import com.intellij.openapi.fileTypes.FileTypeFactory
+import com.intellij.openapi.fileTypes.WildcardFileNameMatcher
+
+/**
+ * Legacy way to register file type matchers, used here to robustly match *.lyng.d
+ * without conflicting with standard .d extensions from other plugins.
+ */
+@Suppress("DEPRECATION")
+class LyngFileTypeFactory : FileTypeFactory() {
+    override fun createFileTypes(consumer: FileTypeConsumer) {
+        // Register the multi-dot pattern explicitly
+        consumer.consume(LyngFileType, WildcardFileNameMatcher("*.lyng.d"))
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/LyngIcons.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea
+
+import com.intellij.openapi.util.IconLoader
+import javax.swing.Icon
+
+object LyngIcons {
+    val FILE: Icon = IconLoader.getIcon("/icons/lyng_file.svg", LyngIcons::class.java)
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/LyngLanguage.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea
+
+import com.intellij.lang.Language
+
+object LyngLanguage : Language("Lyng")

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/actions/RunLyngScriptAction.kt

@@ -0,0 +1,144 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyng.idea.actions
+
+import com.intellij.execution.filters.TextConsoleBuilderFactory
+import com.intellij.execution.ui.ConsoleView
+import com.intellij.execution.ui.ConsoleViewContentType
+import com.intellij.openapi.actionSystem.AnAction
+import com.intellij.openapi.actionSystem.AnActionEvent
+import com.intellij.openapi.actionSystem.CommonDataKeys
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.wm.ToolWindow
+import com.intellij.openapi.wm.ToolWindowAnchor
+import com.intellij.openapi.wm.ToolWindowId
+import com.intellij.openapi.wm.ToolWindowManager
+import com.intellij.psi.PsiFile
+import com.intellij.psi.PsiManager
+import com.intellij.ui.content.ContentFactory
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.launch
+import net.sergeych.lyng.ExecutionError
+import net.sergeych.lyng.Script
+import net.sergeych.lyng.Source
+import net.sergeych.lyng.idea.LyngIcons
+import net.sergeych.lyng.obj.ObjVoid
+import net.sergeych.lyng.obj.getLyngExceptionMessageWithStackTrace
+
+class RunLyngScriptAction : AnAction(LyngIcons.FILE) {
+    private val scope = CoroutineScope(Dispatchers.Default + SupervisorJob())
+
+    private fun getPsiFile(e: AnActionEvent): PsiFile? {
+        val project = e.project ?: return null
+        return e.getData(CommonDataKeys.PSI_FILE) ?: run {
+            val vf = e.getData(CommonDataKeys.VIRTUAL_FILE)
+            if (vf != null) PsiManager.getInstance(project).findFile(vf) else null
+        }
+    }
+
+    override fun update(e: AnActionEvent) {
+        val psiFile = getPsiFile(e)
+        val isLyng = psiFile?.name?.endsWith(".lyng") == true
+        e.presentation.isEnabledAndVisible = isLyng
+        if (isLyng) {
+            e.presentation.text = "Run '${psiFile.name}'"
+        } else {
+            e.presentation.text = "Run Lyng Script"
+        }
+    }
+
+    override fun actionPerformed(e: AnActionEvent) {
+        val project = e.project ?: return
+        val psiFile = getPsiFile(e) ?: return
+        val text = psiFile.text
+        val fileName = psiFile.name
+
+        val (console, toolWindow) = getConsoleAndToolWindow(project)
+        console.clear()
+
+        toolWindow.show {
+            scope.launch {
+                try {
+                    val lyngScope = Script.newScope()
+                    lyngScope.addFn("print") {
+                        val sb = StringBuilder()
+                        for ((i, arg) in args.list.withIndex()) {
+                            if (i > 0) sb.append(" ")
+                            sb.append(arg.toString(this).value)
+                        }
+                        console.print(sb.toString(), ConsoleViewContentType.NORMAL_OUTPUT)
+                        ObjVoid
+                    }
+                    lyngScope.addFn("println") {
+                        val sb = StringBuilder()
+                        for ((i, arg) in args.list.withIndex()) {
+                            if (i > 0) sb.append(" ")
+                            sb.append(arg.toString(this).value)
+                        }
+                        console.print(sb.toString() + "\n", ConsoleViewContentType.NORMAL_OUTPUT)
+                        ObjVoid
+                    }
+
+                    console.print("--- Running $fileName ---\n", ConsoleViewContentType.SYSTEM_OUTPUT)
+                    val result = lyngScope.eval(Source(fileName, text))
+                    console.print("\n--- Finished with result: ${result.inspect(lyngScope)} ---\n", ConsoleViewContentType.SYSTEM_OUTPUT)
+                } catch (t: Throwable) {
+                    console.print("\n--- Error ---\n", ConsoleViewContentType.ERROR_OUTPUT)
+                    if( t is ExecutionError ) {
+                        val m = t.errorObject.getLyngExceptionMessageWithStackTrace()
+                        console.print(m, ConsoleViewContentType.ERROR_OUTPUT)
+                    }
+                    else
+                        console.print(t.message ?: t.toString(), ConsoleViewContentType.ERROR_OUTPUT)
+                    console.print("\n", ConsoleViewContentType.ERROR_OUTPUT)
+                }
+            }
+        }
+    }
+
+    private fun getConsoleAndToolWindow(project: Project): Pair<ConsoleView, ToolWindow> {
+        val toolWindowManager = ToolWindowManager.getInstance(project)
+        var toolWindow = toolWindowManager.getToolWindow(ToolWindowId.RUN)
+        if (toolWindow == null) {
+            toolWindow = toolWindowManager.getToolWindow(ToolWindowId.MESSAGES_WINDOW)
+        }
+        if (toolWindow == null) {
+            toolWindow = toolWindowManager.getToolWindow("Lyng")
+        }
+        val actualToolWindow = toolWindow ?: run {
+            @Suppress("DEPRECATION")
+            toolWindowManager.registerToolWindow("Lyng", true, ToolWindowAnchor.BOTTOM)
+        }
+
+        val contentManager = actualToolWindow.contentManager
+        val existingContent = contentManager.findContent("Lyng Run")
+        if (existingContent != null) {
+            val console = existingContent.component as ConsoleView
+            contentManager.setSelectedContent(existingContent)
+            return console to actualToolWindow
+        }
+
+        val console = TextConsoleBuilderFactory.getInstance().createBuilder(project).console
+        val content = ContentFactory.getInstance().createContent(console.component, "Lyng Run", false)
+        contentManager.addContent(content)
+        contentManager.setSelectedContent(content)
+        return console to actualToolWindow
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/annotators/LyngExternalAnnotator.kt

@@ -0,0 +1,402 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyng.idea.annotators
+
+import com.intellij.lang.annotation.AnnotationHolder
+import com.intellij.lang.annotation.ExternalAnnotator
+import com.intellij.lang.annotation.HighlightSeverity
+import com.intellij.openapi.editor.Document
+import com.intellij.openapi.progress.ProgressManager
+import com.intellij.openapi.util.Key
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiFile
+import net.sergeych.lyng.Source
+import net.sergeych.lyng.binding.Binder
+import net.sergeych.lyng.binding.SymbolKind
+import net.sergeych.lyng.highlight.HighlightKind
+import net.sergeych.lyng.highlight.SimpleLyngHighlighter
+import net.sergeych.lyng.highlight.offsetOf
+import net.sergeych.lyng.idea.highlight.LyngHighlighterColors
+import net.sergeych.lyng.idea.util.LyngAstManager
+import net.sergeych.lyng.miniast.*
+
+/**
+ * ExternalAnnotator that runs Lyng MiniAst on the document text in background
+ * and applies semantic highlighting comparable with the web highlighter.
+ */
+class LyngExternalAnnotator : ExternalAnnotator<LyngExternalAnnotator.Input, LyngExternalAnnotator.Result>() {
+    data class Input(val text: String, val modStamp: Long, val previousSpans: List<Span>?, val file: PsiFile)
+
+    data class Span(val start: Int, val end: Int, val key: com.intellij.openapi.editor.colors.TextAttributesKey)
+    data class Error(val start: Int, val end: Int, val message: String)
+    data class Result(val modStamp: Long, val spans: List<Span>, val error: Error? = null)
+
+    override fun collectInformation(file: PsiFile): Input? {
+        val doc: Document = file.viewProvider.document ?: return null
+        val cached = file.getUserData(CACHE_KEY)
+        val combinedStamp = LyngAstManager.getCombinedStamp(file)
+
+        val prev = if (cached != null && cached.modStamp == combinedStamp) cached.spans else null
+        return Input(doc.text, combinedStamp, prev, file)
+    }
+
+    override fun doAnnotate(collectedInfo: Input?): Result? {
+        if (collectedInfo == null) return null
+        ProgressManager.checkCanceled()
+        val text = collectedInfo.text
+        val tokens = try { SimpleLyngHighlighter().highlight(text) } catch (_: Throwable) { emptyList() }
+        
+        // Use LyngAstManager to get the (potentially merged) Mini-AST
+        val mini = LyngAstManager.getMiniAst(collectedInfo.file) 
+            ?: return Result(collectedInfo.modStamp, collectedInfo.previousSpans ?: emptyList())
+        
+        ProgressManager.checkCanceled()
+        val source = Source(collectedInfo.file.name, text)
+        
+        val out = ArrayList<Span>(256)
+
+        fun isFollowedByParenOrBlock(rangeEnd: Int): Boolean {
+            var i = rangeEnd
+            while (i < text.length) {
+                val ch = text[i]
+                if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n') { i++; continue }
+                return ch == '(' || ch == '{'
+            }
+            return false
+        }
+
+        fun putRange(start: Int, end: Int, key: com.intellij.openapi.editor.colors.TextAttributesKey) {
+            if (start in 0..end && end <= text.length && start < end) out += Span(start, end, key)
+        }
+        fun putName(startPos: net.sergeych.lyng.Pos, name: String, key: com.intellij.openapi.editor.colors.TextAttributesKey) {
+            val s = source.offsetOf(startPos)
+            putRange(s, (s + name.length).coerceAtMost(text.length), key)
+        }
+        fun putMiniRange(r: MiniRange, key: com.intellij.openapi.editor.colors.TextAttributesKey) {
+            val s = source.offsetOf(r.start)
+            val e = source.offsetOf(r.end)
+            putRange(s, e, key)
+        }
+
+        // Declarations
+        mini.declarations.forEach { d ->
+            if (d.nameStart.source != source) return@forEach
+            when (d) {
+                is MiniFunDecl -> putName(d.nameStart, d.name, LyngHighlighterColors.FUNCTION_DECLARATION)
+                is MiniClassDecl -> putName(d.nameStart, d.name, LyngHighlighterColors.TYPE)
+                is MiniValDecl -> putName(
+                    d.nameStart,
+                    d.name,
+                    if (d.mutable) LyngHighlighterColors.VARIABLE else LyngHighlighterColors.VALUE
+                )
+                is MiniEnumDecl -> putName(d.nameStart, d.name, LyngHighlighterColors.TYPE)
+            }
+        }
+
+        // Imports: each segment as namespace/path
+        mini.imports.forEach { imp ->
+            if (imp.range.start.source != source) return@forEach
+            imp.segments.forEach { seg -> putMiniRange(seg.range, LyngHighlighterColors.NAMESPACE) }
+        }
+
+        // Parameters
+        fun addParams(params: List<MiniParam>) {
+            params.forEach { p ->
+                if (p.nameStart.source == source)
+                    putName(p.nameStart, p.name, LyngHighlighterColors.PARAMETER)
+            }
+        }
+        mini.declarations.forEach { d ->
+            when (d) {
+                is MiniFunDecl -> addParams(d.params)
+                is MiniClassDecl -> d.members.filterIsInstance<MiniMemberFunDecl>().forEach { addParams(it.params) }
+                else -> {}
+            }
+        }
+
+        // Type name segments (including generics base & args)
+        fun addTypeSegments(t: MiniTypeRef?) {
+            when (t) {
+                is MiniTypeName -> t.segments.forEach { seg ->
+                    if (seg.range.start.source != source) return@forEach
+                    val s = source.offsetOf(seg.range.start)
+                    putRange(s, (s + seg.name.length).coerceAtMost(text.length), LyngHighlighterColors.TYPE)
+                }
+                is MiniGenericType -> {
+                    addTypeSegments(t.base)
+                    t.args.forEach { addTypeSegments(it) }
+                }
+                is MiniFunctionType -> {
+                    t.receiver?.let { addTypeSegments(it) }
+                    t.params.forEach { addTypeSegments(it) }
+                    addTypeSegments(t.returnType)
+                }
+                is MiniTypeVar -> { /* name is in range; could be highlighted as TYPE as well */
+                    if (t.range.start.source == source)
+                        putMiniRange(t.range, LyngHighlighterColors.TYPE)
+                }
+                null -> {}
+            }
+        }
+        fun addDeclTypeSegments(d: MiniDecl) {
+            if (d.nameStart.source != source) return
+            when (d) {
+                is MiniFunDecl -> {
+                    addTypeSegments(d.returnType)
+                    d.params.forEach { addTypeSegments(it.type) }
+                    addTypeSegments(d.receiver)
+                }
+                is MiniValDecl -> {
+                    addTypeSegments(d.type)
+                    addTypeSegments(d.receiver)
+                }
+                is MiniClassDecl -> {
+                    d.ctorFields.forEach { addTypeSegments(it.type) }
+                    d.classFields.forEach { addTypeSegments(it.type) }
+                    for (m in d.members) {
+                        when (m) {
+                            is MiniMemberFunDecl -> {
+                                addTypeSegments(m.returnType)
+                                m.params.forEach { addTypeSegments(it.type) }
+                            }
+                            is MiniMemberValDecl -> {
+                                addTypeSegments(m.type)
+                            }
+                            else -> {}
+                        }
+                    }
+                }
+                is MiniEnumDecl -> {}
+            }
+        }
+        mini.declarations.forEach { d -> addDeclTypeSegments(d) }
+
+        ProgressManager.checkCanceled()
+
+        // Semantic usages via Binder (best-effort)
+        try {
+            val binding = Binder.bind(text, mini)
+
+            // Map declaration ranges to avoid duplicating them as usages
+            val declKeys = HashSet<Pair<Int, Int>>(binding.symbols.size * 2)
+            binding.symbols.forEach { sym -> declKeys += (sym.declStart to sym.declEnd) }
+
+            fun keyForKind(k: SymbolKind) = when (k) {
+                SymbolKind.Function -> LyngHighlighterColors.FUNCTION
+                SymbolKind.Class, SymbolKind.Enum -> LyngHighlighterColors.TYPE
+                SymbolKind.Parameter -> LyngHighlighterColors.PARAMETER
+                SymbolKind.Value -> LyngHighlighterColors.VALUE
+                SymbolKind.Variable -> LyngHighlighterColors.VARIABLE
+            }
+
+            // Track covered ranges to not override later heuristics
+            val covered = HashSet<Pair<Int, Int>>()
+
+            binding.references.forEach { ref ->
+                val key = ref.start to ref.end
+                if (!declKeys.contains(key)) {
+                    val sym = binding.symbols.firstOrNull { it.id == ref.symbolId }
+                    if (sym != null) {
+                        val color = keyForKind(sym.kind)
+                        putRange(ref.start, ref.end, color)
+                        covered += key
+                    }
+                }
+            }
+
+            // Heuristics on top of binder: function call-sites and simple name-based roles
+            ProgressManager.checkCanceled()
+
+            // Build simple name -> role map for top-level vals/vars and parameters
+            val nameRole = HashMap<String, com.intellij.openapi.editor.colors.TextAttributesKey>(8)
+            mini.declarations.forEach { d ->
+                when (d) {
+                    is MiniValDecl -> nameRole[d.name] =
+                        if (d.mutable) LyngHighlighterColors.VARIABLE else LyngHighlighterColors.VALUE
+
+                    is MiniFunDecl -> d.params.forEach { p -> nameRole[p.name] = LyngHighlighterColors.PARAMETER }
+                    is MiniClassDecl -> {
+                        d.members.forEach { m ->
+                            if (m is MiniMemberFunDecl) {
+                                m.params.forEach { p -> nameRole[p.name] = LyngHighlighterColors.PARAMETER }
+                            }
+                        }
+                    }
+                    else -> {}
+                }
+            }
+
+            tokens.forEach { s ->
+                if (s.kind == HighlightKind.Identifier) {
+                    val start = s.range.start
+                    val end = s.range.endExclusive
+                    val key = start to end
+                    if (key !in covered && key !in declKeys) {
+                        // Call-site detection first so it wins over var/param role
+                        if (isFollowedByParenOrBlock(end)) {
+                            putRange(start, end, LyngHighlighterColors.FUNCTION)
+                            covered += key
+                        } else {
+                            // Simple role by known names
+                            val ident = try {
+                                text.substring(start, end)
+                            } catch (_: Throwable) {
+                                null
+                            }
+                            if (ident != null) {
+                                val roleKey = nameRole[ident]
+                                if (roleKey != null) {
+                                    putRange(start, end, roleKey)
+                                    covered += key
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        } catch (e: Throwable) {
+            // Must rethrow cancellation; otherwise ignore binder failures (best-effort)
+            if (e is com.intellij.openapi.progress.ProcessCanceledException) throw e
+        }
+
+        // Add annotation/label coloring using token highlighter
+        run {
+            tokens.forEach { s ->
+                if (s.kind == HighlightKind.Label) {
+                    val start = s.range.start
+                    val end = s.range.endExclusive
+                    if (start in 0..end && end <= text.length && start < end) {
+                        val lexeme = try {
+                            text.substring(start, end)
+                        } catch (_: Throwable) {
+                            null
+                        }
+                        if (lexeme != null) {
+                            // Heuristic: if it starts with @ and follows a control keyword, it's likely a label
+                            // Otherwise if it starts with @ it's an annotation.
+                            // If it ends with @ it's a loop label.
+                            when {
+                                lexeme.endsWith("@") -> putRange(start, end, LyngHighlighterColors.LABEL)
+                                lexeme.startsWith("@") -> {
+                                    // Try to see if it's an exit label
+                                    val prevNonWs = prevNonWs(text, start)
+                                    val prevWord = if (prevNonWs >= 0) {
+                                        var wEnd = prevNonWs + 1
+                                        var wStart = prevNonWs
+                                        while (wStart > 0 && text[wStart - 1].isLetter()) wStart--
+                                        text.substring(wStart, wEnd)
+                                    } else null
+
+                                    if (prevWord in setOf("return", "break", "continue") || isFollowedByParenOrBlock(end)) {
+                                        putRange(start, end, LyngHighlighterColors.LABEL)
+                                    } else {
+                                        putRange(start, end, LyngHighlighterColors.ANNOTATION)
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        tokens.forEach { s ->
+            if (s.kind == HighlightKind.EnumConstant) {
+                val start = s.range.start
+                val end = s.range.endExclusive
+                if (start in 0..end && end <= text.length && start < end) {
+                    putRange(start, end, LyngHighlighterColors.ENUM_CONSTANT)
+                }
+            }
+        }
+
+        return Result(collectedInfo.modStamp, out, null)
+    }
+
+
+    override fun apply(file: PsiFile, annotationResult: Result?, holder: AnnotationHolder) {
+        if (annotationResult == null) return
+        // Skip if cache is up-to-date
+        val combinedStamp = LyngAstManager.getCombinedStamp(file)
+        val cached = file.getUserData(CACHE_KEY)
+        val result = if (cached != null && cached.modStamp == combinedStamp) cached else annotationResult
+        file.putUserData(CACHE_KEY, result)
+
+        val doc = file.viewProvider.document
+
+        for (s in result.spans) {
+            holder.newSilentAnnotation(HighlightSeverity.INFORMATION)
+                .range(TextRange(s.start, s.end))
+                .textAttributes(s.key)
+                .create()
+        }
+
+        // Show syntax error if present
+        val err = result.error
+        if (err != null) {
+            val start = err.start.coerceIn(0, (doc?.textLength ?: 0))
+            val end = err.end.coerceIn(start, (doc?.textLength ?: start))
+            if (end > start) {
+                holder.newAnnotation(HighlightSeverity.ERROR, err.message)
+                    .range(TextRange(start, end))
+                    .create()
+            }
+        }
+    }
+
+    companion object {
+        private val CACHE_KEY: Key<Result> = Key.create("LYNG_SEMANTIC_CACHE")
+    }
+
+    private fun prevNonWs(text: String, idxExclusive: Int): Int {
+        var i = idxExclusive - 1
+        while (i >= 0) {
+            val ch = text[i]
+            if (ch != ' ' && ch != '\t' && ch != '\n' && ch != '\r') return i
+            i--
+        }
+        return -1
+    }
+
+    /**
+     * Make the error highlight a bit wider than a single character so it is easier to see and click.
+     * Strategy:
+     *  - If the offset points inside an identifier-like token (letters/digits/underscore), expand to the full token.
+     *  - Otherwise select a small range starting at the offset with a minimum width, but not crossing the line end.
+     */
+    private fun expandErrorRange(text: String, rawStart: Int): Pair<Int, Int> {
+        if (text.isEmpty()) return 0 to 0
+        val len = text.length
+        val start = rawStart.coerceIn(0, len)
+        fun isWord(ch: Char) = ch == '_' || ch.isLetterOrDigit()
+
+        if (start < len && isWord(text[start])) {
+            var s = start
+            var e = start
+            while (s > 0 && isWord(text[s - 1])) s--
+            while (e < len && isWord(text[e])) e++
+            return s to e
+        }
+
+        // Not inside a word: select a short, visible range up to EOL
+        val lineEnd = text.indexOf('\n', start).let { if (it == -1) len else it }
+        val minWidth = 4
+        val end = (start + minWidth).coerceAtMost(lineEnd).coerceAtLeast((start + 1).coerceAtMost(lineEnd))
+        return start to end
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/comment/LyngCommenter.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.comment
+
+import com.intellij.lang.Commenter
+
+class LyngCommenter : Commenter {
+    override fun getLineCommentPrefix(): String = "//"
+    override fun getBlockCommentPrefix(): String = "/*"
+    override fun getBlockCommentSuffix(): String = "*/"
+    override fun getCommentedBlockCommentPrefix(): String? = null
+    override fun getCommentedBlockCommentSuffix(): String? = null
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/completion/LyngCompletionContributor.kt

@@ -0,0 +1,617 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/*
+ * Lightweight BASIC completion for Lyng, MVP version.
+ * Uses MiniAst (best-effort) + BuiltinDocRegistry to suggest symbols.
+ */
+package net.sergeych.lyng.idea.completion
+
+import com.intellij.codeInsight.completion.*
+import com.intellij.codeInsight.lookup.LookupElementBuilder
+import com.intellij.icons.AllIcons
+import com.intellij.openapi.diagnostic.Logger
+import com.intellij.openapi.editor.Document
+import com.intellij.patterns.PlatformPatterns
+import com.intellij.psi.PsiFile
+import com.intellij.util.ProcessingContext
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.highlight.LyngTokenTypes
+import net.sergeych.lyng.idea.settings.LyngFormatterSettings
+import net.sergeych.lyng.idea.util.DocsBootstrap
+import net.sergeych.lyng.idea.util.LyngAstManager
+import net.sergeych.lyng.idea.util.TextCtx
+import net.sergeych.lyng.miniast.*
+
+class LyngCompletionContributor : CompletionContributor() {
+    init {
+        extend(
+            CompletionType.BASIC,
+            PlatformPatterns.psiElement().withLanguage(LyngLanguage),
+            Provider
+        )
+    }
+
+    private object Provider : CompletionProvider<CompletionParameters>() {
+        private val log = Logger.getInstance(LyngCompletionContributor::class.java)
+        private const val DEBUG_COMPLETION = false
+
+        override fun addCompletions(
+            parameters: CompletionParameters,
+            context: ProcessingContext,
+            result: CompletionResultSet
+        ) {
+            // Ensure external/bundled docs are registered (e.g., lyng.io.fs with Path)
+            DocsBootstrap.ensure()
+            // Ensure stdlib Obj*-defined docs (e.g., String methods via ObjString.addFnDoc) are initialized
+            StdlibDocsBootstrap.ensure()
+            val file: PsiFile = parameters.originalFile
+            if (file.language != LyngLanguage) return
+
+            // Disable completion inside comments
+            val pos = parameters.position
+            val et = pos.node.elementType
+            if (et == LyngTokenTypes.LINE_COMMENT || et == LyngTokenTypes.BLOCK_COMMENT) return
+
+            // Feature toggle: allow turning completion off from settings
+            val settings = LyngFormatterSettings.getInstance(file.project)
+            if (!settings.enableLyngCompletionExperimental) return
+            val document: Document = file.viewProvider.document ?: return
+            val text = document.text
+            val caret = parameters.offset.coerceIn(0, text.length)
+
+            val prefix = TextCtx.prefixAt(text, caret)
+            val withPrefix = result.withPrefixMatcher(prefix).caseInsensitive()
+
+            // Emission with cap
+            val cap = 200
+            var added = 0
+            val emit: (com.intellij.codeInsight.lookup.LookupElement) -> Unit = { le ->
+                if (added < cap) {
+                    withPrefix.addElement(le)
+                    added++
+                }
+            }
+
+            // Determine if we are in member context (dot before caret or before word start)
+            val wordRange = TextCtx.wordRangeAt(text, caret)
+            val memberDotPos = (wordRange?.let { TextCtx.findDotLeft(text, it.startOffset) })
+                ?: TextCtx.findDotLeft(text, caret)
+            if (DEBUG_COMPLETION) {
+                log.info("[LYNG_DEBUG] Completion: caret=$caret prefix='${prefix}' memberDotPos=${memberDotPos} file='${file.name}'")
+            }
+
+            // Build MiniAst (cached) for both global and member contexts to enable local class/val inference
+            val mini = LyngAstManager.getMiniAst(file)
+            val binding = LyngAstManager.getBinding(file)
+
+            // Delegate computation to the shared engine to keep behavior in sync with tests
+            val engineItems = try {
+                runBlocking { CompletionEngineLight.completeSuspend(text, caret, mini, binding) }
+            } catch (t: Throwable) {
+                if (DEBUG_COMPLETION) log.warn("[LYNG_DEBUG] Engine completion failed: ${t.message}")
+                emptyList()
+            }
+            if (DEBUG_COMPLETION) {
+                val preview = engineItems.take(10).joinToString { it.name }
+                log.info("[LYNG_DEBUG] Engine items: count=${engineItems.size} preview=[${preview}]")
+            }
+
+            // If we are in member context and the engine produced nothing, try a guarded local fallback
+            if (memberDotPos != null && engineItems.isEmpty()) {
+                if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Fallback: engine returned 0 in member context; trying local inference")
+                // Build imported modules from text (lenient) + stdlib; avoid heavy MiniAst here
+                val fromText = DocLookupUtils.extractImportsFromText(text)
+                val imported = LinkedHashSet<String>().apply {
+                    fromText.forEach { add(it) }
+                    add("lyng.stdlib")
+                }.toList()
+
+                // Try inferring return/receiver class around the dot
+                val inferred =
+                    // Prefer MiniAst-based inference (return type from member call or receiver type)
+                    DocLookupUtils.guessReturnClassFromMemberCallBeforeMini(mini, text, memberDotPos, imported, binding)
+                        ?: DocLookupUtils.guessReceiverClassViaMini(mini, text, memberDotPos, imported, binding)
+                        ?: 
+                    DocLookupUtils.guessReturnClassFromMemberCallBefore(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReturnClassFromTopLevelCallBefore(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReturnClassAcrossKnownCallees(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReceiverClass(text, memberDotPos, imported, mini)
+
+                if (inferred != null) {
+                    if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Fallback inferred receiver/return class='$inferred' — offering its members")
+                    offerMembers(emit, imported, inferred, sourceText = text, mini = mini)
+                    return
+                } else {
+                    if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Fallback could not infer class; keeping list empty (no globals after dot)")
+                    return
+                }
+            }
+
+            // Render engine items
+            for (ci in engineItems) {
+                val builder = when (ci.kind) {
+                    Kind.Function -> LookupElementBuilder.create(ci.name)
+                        .withIcon(AllIcons.Nodes.Function)
+                        .let { b -> if (!ci.tailText.isNullOrBlank()) b.withTailText(ci.tailText, true) else b }
+                        .let { b -> if (!ci.typeText.isNullOrBlank()) b.withTypeText(ci.typeText, true) else b }
+                        .withInsertHandler(ParenInsertHandler)
+                    Kind.Method -> LookupElementBuilder.create(ci.name)
+                        .withIcon(AllIcons.Nodes.Method)
+                        .let { b -> if (!ci.tailText.isNullOrBlank()) b.withTailText(ci.tailText, true) else b }
+                        .let { b -> if (!ci.typeText.isNullOrBlank()) b.withTypeText(ci.typeText, true) else b }
+                        .withInsertHandler(ParenInsertHandler)
+                    Kind.Class_ -> LookupElementBuilder.create(ci.name)
+                        .withIcon(AllIcons.Nodes.Class)
+                    Kind.Enum -> LookupElementBuilder.create(ci.name)
+                        .withIcon(AllIcons.Nodes.Enum)
+                    Kind.Value -> LookupElementBuilder.create(ci.name)
+                        .withIcon(AllIcons.Nodes.Variable)
+                        .let { b -> if (!ci.typeText.isNullOrBlank()) b.withTypeText(ci.typeText, true) else b }
+                    Kind.Field -> LookupElementBuilder.create(ci.name)
+                        .withIcon(AllIcons.Nodes.Field)
+                        .let { b -> if (!ci.typeText.isNullOrBlank()) b.withTypeText(ci.typeText, true) else b }
+                }
+                if (ci.priority != 0.0) {
+                    emit(PrioritizedLookupElement.withPriority(builder, ci.priority))
+                } else {
+                    emit(builder)
+                }
+            }
+            // In member context, ensure stdlib extension-like methods (e.g., String.re) are present
+            if (memberDotPos != null) {
+                val existing = engineItems.map { it.name }.toMutableSet()
+                val fromText = DocLookupUtils.extractImportsFromText(text)
+                val imported = LinkedHashSet<String>().apply {
+                    fromText.forEach { add(it) }
+                    add("lyng.stdlib")
+                }.toList()
+                val inferredClass =
+                    DocLookupUtils.guessReturnClassFromMemberCallBeforeMini(mini, text, memberDotPos, imported, binding)
+                        ?: DocLookupUtils.guessReceiverClassViaMini(mini, text, memberDotPos, imported, binding)
+                        ?: DocLookupUtils.guessReturnClassFromMemberCallBefore(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReturnClassFromTopLevelCallBefore(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReturnClassAcrossKnownCallees(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReceiverClass(text, memberDotPos, imported, mini)
+                if (!inferredClass.isNullOrBlank()) {
+                    val ext = DocLookupUtils.collectExtensionMemberNames(imported, inferredClass, mini)
+                    if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Post-engine extension check for $inferredClass: ${ext}")
+                    for (name in ext) {
+                        if (existing.contains(name)) continue
+                        val resolved = DocLookupUtils.resolveMemberWithInheritance(imported, inferredClass, name, mini)
+                        if (resolved != null) {
+                            val m = resolved.second
+                            val builder = when (m) {
+                                is MiniMemberFunDecl -> {
+                                    val params = m.params.joinToString(", ") { it.name }
+                                    val ret = typeOf(m.returnType)
+                                    LookupElementBuilder.create(name)
+                                        .withIcon(AllIcons.Nodes.Method)
+                                        .withTailText("($params)", true)
+                                        .withTypeText(ret, true)
+                                        .withInsertHandler(ParenInsertHandler)
+                                }
+                                is MiniFunDecl -> {
+                                    val params = m.params.joinToString(", ") { it.name }
+                                    val ret = typeOf(m.returnType)
+                                    LookupElementBuilder.create(name)
+                                        .withIcon(AllIcons.Nodes.Method)
+                                        .withTailText("($params)", true)
+                                        .withTypeText(ret, true)
+                                        .withInsertHandler(ParenInsertHandler)
+                                }
+                                is MiniMemberValDecl -> {
+                                    LookupElementBuilder.create(name)
+                                        .withIcon(if (m.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field)
+                                        .withTypeText(typeOf(m.type), true)
+                                }
+                                is MiniValDecl -> {
+                                    LookupElementBuilder.create(name)
+                                        .withIcon(if (m.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field)
+                                        .withTypeText(typeOf(m.type), true)
+                                }
+                                else -> {
+                                    LookupElementBuilder.create(name)
+                                        .withIcon(AllIcons.Nodes.Method)
+                                        .withTailText("()", true)
+                                        .withInsertHandler(ParenInsertHandler)
+                                }
+                            }
+                            emit(builder)
+                            existing.add(name)
+                        } else {
+                            // Fallback: emit simple method name without detailed types
+                            val builder = LookupElementBuilder.create(name)
+                                .withIcon(AllIcons.Nodes.Method)
+                                .withTailText("()", true)
+                                .withInsertHandler(ParenInsertHandler)
+                            emit(builder)
+                            existing.add(name)
+                        }
+                    }
+                }
+            }
+            // If in member context and engine items are suspiciously sparse, try to enrich via local inference + offerMembers
+            if (memberDotPos != null && engineItems.size < 3) {
+                if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Engine produced only ${engineItems.size} items in member context — trying enrichment")
+                val fromText = DocLookupUtils.extractImportsFromText(text)
+                val imported = LinkedHashSet<String>().apply {
+                    fromText.forEach { add(it) }
+                    add("lyng.stdlib")
+                }.toList()
+                val inferred =
+                    DocLookupUtils.guessReturnClassFromMemberCallBeforeMini(mini, text, memberDotPos, imported, binding)
+                        ?: DocLookupUtils.guessReceiverClassViaMini(mini, text, memberDotPos, imported, binding)
+                        ?: DocLookupUtils.guessReturnClassFromMemberCallBefore(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReturnClassFromTopLevelCallBefore(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReturnClassAcrossKnownCallees(text, memberDotPos, imported, mini)
+                        ?: DocLookupUtils.guessReceiverClass(text, memberDotPos, imported, mini)
+                if (inferred != null) {
+                    if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Enrichment inferred class='$inferred' — offering its members")
+                    offerMembers(emit, imported, inferred, sourceText = text, mini = mini)
+                }
+            }
+            return
+        }
+
+        private fun offerDecl(emit: (com.intellij.codeInsight.lookup.LookupElement) -> Unit, d: MiniDecl) {
+            val name = d.name
+            val builder = when (d) {
+                is MiniFunDecl -> {
+                    val params = d.params.joinToString(", ") { it.name }
+                    val ret = typeOf(d.returnType)
+                    val tail = "(${params})"
+                    LookupElementBuilder.create(name)
+                        .withIcon(AllIcons.Nodes.Function)
+                        .withTailText(tail, true)
+                        .withTypeText(ret, true)
+                        .withInsertHandler(ParenInsertHandler)
+                }
+                is MiniClassDecl -> LookupElementBuilder.create(name)
+                    .withIcon(AllIcons.Nodes.Class)
+                is MiniValDecl -> {
+                    val kindIcon = if (d.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field
+                    LookupElementBuilder.create(name)
+                        .withIcon(kindIcon)
+                        .withTypeText(typeOf(d.type), true)
+                }
+                is MiniEnumDecl -> LookupElementBuilder.create(name)
+                    .withIcon(AllIcons.Nodes.Enum)
+            }
+            emit(builder)
+        }
+
+        private object ParenInsertHandler : InsertHandler<com.intellij.codeInsight.lookup.LookupElement> {
+            override fun handleInsert(context: InsertionContext, item: com.intellij.codeInsight.lookup.LookupElement) {
+                val doc = context.document
+                val tailOffset = context.tailOffset
+                val nextChar = doc.charsSequence.getOrNull(tailOffset)
+                if (nextChar != '(') {
+                    doc.insertString(tailOffset, "()")
+                    context.editor.caretModel.moveToOffset(tailOffset + 1)
+                }
+            }
+        }
+
+        // --- Member completion helpers ---
+
+        private fun offerMembers(
+            emit: (com.intellij.codeInsight.lookup.LookupElement) -> Unit,
+            imported: List<String>,
+            className: String,
+            staticOnly: Boolean = false
+        , sourceText: String,
+        mini: MiniScript? = null
+        ) {
+            val classes = DocLookupUtils.aggregateClasses(imported, mini)
+            if (DEBUG_COMPLETION) {
+                val keys = classes.keys.joinToString(", ")
+                log.info("[LYNG_DEBUG] offerMembers: imported=${imported} classes=[${keys}] target=${className}")
+            }
+            val visited = mutableSetOf<String>()
+            // Collect separated to keep tiers: direct first, then inherited
+            val directMap = LinkedHashMap<String, MutableList<MiniMemberDecl>>()
+            val inheritedMap = LinkedHashMap<String, MutableList<MiniMemberDecl>>()
+
+            // 0) Prefer locally-declared class members (same-file) when available
+            val localClass = mini?.declarations?.filterIsInstance<MiniClassDecl>()?.firstOrNull { it.name == className }
+            if (localClass != null) {
+                for (m in localClass.members) {
+                    val list = directMap.getOrPut(m.name) { mutableListOf() }
+                    list.add(m)
+                }
+                // If MiniAst didn't populate members (empty), try to scan class body text for member signatures
+                if (localClass.members.isEmpty()) {
+                    val scanned = DocLookupUtils.scanLocalClassMembersFromText(mini, text = sourceText, cls = localClass)
+                    if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Local scan for class ${localClass.name}: found ${scanned.size} members -> ${scanned.keys}")
+                    for ((name, sig) in scanned) {
+                        when (sig.kind) {
+                            "fun" -> {
+                                val builder = LookupElementBuilder.create(name)
+                                    .withIcon(AllIcons.Nodes.Method)
+                                    .withTailText("(" + (sig.params?.joinToString(", ") ?: "") + ")", true)
+                                    .let { b -> sig.typeText?.let { b.withTypeText(": $it", true) } ?: b }
+                                    .withInsertHandler(ParenInsertHandler)
+                                emit(builder)
+                            }
+                            "val", "var" -> {
+                                val builder = LookupElementBuilder.create(name)
+                                    .withIcon(if (sig.kind == "var") AllIcons.Nodes.Variable else AllIcons.Nodes.Field)
+                                    .let { b -> sig.typeText?.let { b.withTypeText(": $it", true) } ?: b }
+                                emit(builder)
+                            }
+                        }
+                    }
+                }
+            }
+
+            fun addMembersOf(clsName: String, tierDirect: Boolean) {
+                val cls = classes[clsName] ?: return
+                val target = if (tierDirect) directMap else inheritedMap
+                for (m in cls.members) {
+                    if (staticOnly) {
+                        // Filter only static members in namespace/static context
+                        when (m) {
+                            is MiniMemberFunDecl -> if (!m.isStatic) continue
+                            is MiniMemberValDecl -> if (!m.isStatic) continue
+                            is MiniInitDecl -> continue
+                        }
+                    }
+                    val list = target.getOrPut(m.name) { mutableListOf() }
+                    list.add(m)
+                }
+                // Then inherited
+                for (base in cls.bases) {
+                    if (visited.add(base)) addMembersOf(base, false)
+                }
+            }
+
+            visited.add(className)
+            addMembersOf(className, true)
+            if (DEBUG_COMPLETION) {
+                log.info("[LYNG_DEBUG] offerMembers: direct=${directMap.size} inherited=${inheritedMap.size} for ${className}")
+            }
+
+            // If the docs model lacks explicit bases for some core container classes,
+            // conservatively supplement with preferred parents to expose common ops.
+            fun supplementPreferredBases(receiver: String) {
+                // Preference/known lineage map kept tiny and safe
+                val extras = when (receiver) {
+                    "List" -> listOf("Collection", "Iterable")
+                    "Array" -> listOf("Collection", "Iterable")
+                    // In practice, many high-level ops users expect on iteration live on Iterable.
+                    // For editor assistance, expose Iterable ops for Iterator receivers too.
+                    "Iterator" -> listOf("Iterable")
+                    else -> emptyList()
+                }
+                for (base in extras) {
+                    if (visited.add(base)) addMembersOf(base, false)
+                }
+            }
+            supplementPreferredBases(className)
+
+            fun emitGroup(map: LinkedHashMap<String, MutableList<MiniMemberDecl>>, groupPriority: Double) {
+                val keys = map.keys.sortedBy { it.lowercase() }
+                for (name in keys) {
+                    val list = map[name] ?: continue
+                    // Choose a representative for display:
+                    // 1) Prefer a method with return type AND parameters
+                    // 2) Prefer a method with parameters
+                    // 3) Prefer a method with return type
+                    // 4) Else any method
+                    // 5) Else the first variant
+                    val rep =
+                        list.asSequence().filterIsInstance<MiniMemberFunDecl>()
+                            .firstOrNull { it.returnType != null && it.params.isNotEmpty() }
+                            ?: list.asSequence().filterIsInstance<MiniMemberFunDecl>()
+                                .firstOrNull { it.params.isNotEmpty() }
+                            ?: list.asSequence().filterIsInstance<MiniMemberFunDecl>()
+                                .firstOrNull { it.returnType != null }
+                            ?: list.firstOrNull { it is MiniMemberFunDecl }
+                            ?: list.first()
+                    when (rep) {
+                        is MiniMemberFunDecl -> {
+                            val params = rep.params.joinToString(", ") { it.name }
+                            val ret = typeOf(rep.returnType)
+                            val extra = list.count { it is MiniMemberFunDecl } - 1
+                            val overloads = if (extra > 0) " (+$extra overloads)" else ""
+                            val tail = "(${params})$overloads"
+                            val icon = AllIcons.Nodes.Method
+                            val builder = LookupElementBuilder.create(name)
+                                .withIcon(icon)
+                                .withTailText(tail, true)
+                                .withTypeText(ret, true)
+                                .withInsertHandler(ParenInsertHandler)
+                            if (groupPriority != 0.0) {
+                                emit(PrioritizedLookupElement.withPriority(builder, groupPriority))
+                            } else {
+                                emit(builder)
+                            }
+                        }
+                        is MiniMemberValDecl -> {
+                            val icon = if (rep.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field
+                            // Prefer a field variant with known type if available
+                            val chosen = list.asSequence()
+                                .filterIsInstance<MiniMemberValDecl>()
+                                .firstOrNull { it.type != null } ?: rep
+                            val builder = LookupElementBuilder.create(name)
+                                .withIcon(icon)
+                                .withTypeText(typeOf(chosen.type), true)
+                            if (groupPriority != 0.0) {
+                                emit(PrioritizedLookupElement.withPriority(builder, groupPriority))
+                            } else {
+                                emit(builder)
+                            }
+                        }
+                        is MiniInitDecl -> {}
+                    }
+                }
+            }
+
+            // Emit what we have first
+            emitGroup(directMap, 100.0)
+            emitGroup(inheritedMap, 0.0)
+
+            // If suggestions are suspiciously sparse for known container classes,
+            // try to conservatively supplement using a curated list resolved via docs registry.
+            val totalSuggested = directMap.size + inheritedMap.size
+            val isContainer = className in setOf("Iterator", "Iterable", "Collection", "List", "Array")
+            if (isContainer && totalSuggested < 3) {
+                if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Supplementing members for $className; had=$totalSuggested")
+                val common = when (className) {
+                    "Iterator" -> listOf(
+                        "hasNext", "next", "forEach", "map", "filter", "take", "drop", "toList", "count", "any", "all"
+                    )
+                    else -> listOf(
+                        // Iterable/Collection/List/Array common ops
+                        "size", "isEmpty", "map", "flatMap", "filter", "first", "last", "contains",
+                        "any", "all", "count", "forEach", "toList", "toSet"
+                    )
+                }
+                val already = (directMap.keys + inheritedMap.keys).toMutableSet()
+                for (name in common) {
+                    if (name in already) continue
+                    // Try resolve across classes first to get types/params; if it fails, emit a synthetic safe suggestion.
+                    val resolved = DocLookupUtils.findMemberAcrossClasses(imported, name, mini)
+                    if (resolved != null) {
+                        val member = resolved.second
+                        val builder = when (member) {
+                            is MiniMemberFunDecl -> {
+                                val params = member.params.joinToString(", ") { it.name }
+                                val ret = typeOf(member.returnType)
+                                LookupElementBuilder.create(name)
+                                    .withIcon(AllIcons.Nodes.Method)
+                                    .withTailText("($params)", true)
+                                    .withTypeText(ret, true)
+                                    .withInsertHandler(ParenInsertHandler)
+                            }
+                            is MiniFunDecl -> {
+                                val params = member.params.joinToString(", ") { it.name }
+                                val ret = typeOf(member.returnType)
+                                LookupElementBuilder.create(name)
+                                    .withIcon(AllIcons.Nodes.Method)
+                                    .withTailText("($params)", true)
+                                    .withTypeText(ret, true)
+                                    .withInsertHandler(ParenInsertHandler)
+                            }
+                            is MiniMemberValDecl -> {
+                                LookupElementBuilder.create(name)
+                                    .withIcon(if (member.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field)
+                                    .withTypeText(typeOf(member.type), true)
+                            }
+                            is MiniValDecl -> {
+                                LookupElementBuilder.create(name)
+                                    .withIcon(if (member.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field)
+                                    .withTypeText(typeOf(member.type), true)
+                            }
+                            else -> {
+                                LookupElementBuilder.create(name)
+                                    .withIcon(AllIcons.Nodes.Method)
+                                    .withTailText("()", true)
+                                    .withInsertHandler(ParenInsertHandler)
+                            }
+                        }
+                        emit(PrioritizedLookupElement.withPriority(builder, 50.0))
+                        already.add(name)
+                    } else {
+                        // Synthetic fallback: method without detailed params/types to improve UX in absence of docs
+                        val isProperty = name in setOf("size", "length")
+                        val builder = if (isProperty) {
+                            LookupElementBuilder.create(name)
+                                .withIcon(AllIcons.Nodes.Field)
+                        } else {
+                            LookupElementBuilder.create(name)
+                                .withIcon(AllIcons.Nodes.Method)
+                                .withTailText("()", true)
+                                .withInsertHandler(ParenInsertHandler)
+                        }
+                        emit(PrioritizedLookupElement.withPriority(builder, 50.0))
+                        already.add(name)
+                    }
+                }
+            }
+
+            // Supplement with stdlib extension members defined in root.lyng (e.g., fun String.trim(...))
+            run {
+                val already = (directMap.keys + inheritedMap.keys).toMutableSet()
+                val ext = BuiltinDocRegistry.extensionMemberNamesFor(className)
+                if (DEBUG_COMPLETION) log.info("[LYNG_DEBUG] Extensions for $className: count=${ext.size} -> ${ext}")
+                for (name in ext) {
+                    if (already.contains(name)) continue
+                    // Try to resolve full signature via registry first to get params and return type
+                    val resolved = DocLookupUtils.resolveMemberWithInheritance(imported, className, name, mini)
+                    if (resolved != null) {
+                        val m = resolved.second
+                        val builder = when (m) {
+                            is MiniMemberFunDecl -> {
+                                val params = m.params.joinToString(", ") { it.name }
+                                val ret = typeOf(m.returnType)
+                                LookupElementBuilder.create(name)
+                                    .withIcon(AllIcons.Nodes.Method)
+                                    .withTailText("($params)", true)
+                                    .withTypeText(ret, true)
+                                    .withInsertHandler(ParenInsertHandler)
+                            }
+                            is MiniFunDecl -> {
+                                val params = m.params.joinToString(", ") { it.name }
+                                val ret = typeOf(m.returnType)
+                                LookupElementBuilder.create(name)
+                                    .withIcon(AllIcons.Nodes.Method)
+                                    .withTailText("($params)", true)
+                                    .withTypeText(ret, true)
+                                    .withInsertHandler(ParenInsertHandler)
+                            }
+                            is MiniMemberValDecl -> {
+                                LookupElementBuilder.create(name)
+                                    .withIcon(if (m.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field)
+                                    .withTypeText(typeOf(m.type), true)
+                            }
+                            is MiniValDecl -> {
+                                LookupElementBuilder.create(name)
+                                    .withIcon(if (m.mutable) AllIcons.Nodes.Variable else AllIcons.Nodes.Field)
+                                    .withTypeText(typeOf(m.type), true)
+                            }
+                            else -> {
+                                LookupElementBuilder.create(name)
+                                    .withIcon(AllIcons.Nodes.Method)
+                                    .withTailText("()", true)
+                                    .withInsertHandler(ParenInsertHandler)
+                            }
+                        }
+                        emit(PrioritizedLookupElement.withPriority(builder, 50.0))
+                        already.add(name)
+                        continue
+                    }
+                    // Fallback: emit without detailed types if we couldn't resolve
+                    val builder = LookupElementBuilder.create(name)
+                        .withIcon(AllIcons.Nodes.Method)
+                        .withTailText("()", true)
+                        .withInsertHandler(ParenInsertHandler)
+                    emit(PrioritizedLookupElement.withPriority(builder, 50.0))
+                    already.add(name)
+                }
+            }
+        }
+
+
+        private fun typeOf(t: MiniTypeRef?): String {
+            val s = DocLookupUtils.typeOf(t)
+            return if (s.isEmpty()) "" else ": $s"
+        }
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/docs/FsDocsFallback.kt

@@ -0,0 +1,55 @@
+/*
+ * Minimal fallback docs seeding for `lyng.io.fs` used only inside the IDEA plugin
+ * when external docs module (lyngio) is not present on the classpath.
+ *
+ * We keep it tiny and plugin-local to avoid coupling core library to external packages.
+ */
+package net.sergeych.lyng.idea.docs
+
+import net.sergeych.lyng.miniast.BuiltinDocRegistry
+import net.sergeych.lyng.miniast.ParamDoc
+import net.sergeych.lyng.miniast.TypeGenericDoc
+import net.sergeych.lyng.miniast.type
+
+internal object FsDocsFallback {
+    @Volatile
+    private var seeded = false
+
+    fun ensureOnce(): Boolean {
+        if (seeded) return true
+        synchronized(this) {
+            if (seeded) return true
+            BuiltinDocRegistry.module("lyng.io.fs") {
+                // Class Path summary and a few commonly used methods
+                classDoc(name = "Path", doc = "Filesystem path class. Construct with a string: `Path(\"/tmp\")`.") {
+                    method(name = "exists", doc = "Whether the path exists on the filesystem.", returns = type("lyng.Bool"))
+                    method(name = "isFile", doc = "Whether the path exists and is a file.", returns = type("lyng.Bool"))
+                    method(name = "isDir", doc = "Whether the path exists and is a directory.", returns = type("lyng.Bool"))
+                    method(name = "readUtf8", doc = "Read the entire file as UTF-8 string.", returns = type("lyng.String"))
+                    method(
+                        name = "writeUtf8",
+                        doc = "Write UTF-8 string to the file (overwrite).",
+                        params = listOf(ParamDoc("text", type("lyng.String")))
+                    )
+                    method(
+                        name = "bytes",
+                        doc = "Iterate file content as `Buffer` chunks.",
+                        params = listOf(ParamDoc("size", type("lyng.Int"))),
+                        returns = TypeGenericDoc(type("lyng.Iterator"), listOf(type("lyng.Buffer")))
+                    )
+                    method(
+                        name = "lines",
+                        doc = "Iterate file as lines of text.",
+                        returns = TypeGenericDoc(type("lyng.Iterator"), listOf(type("lyng.String")))
+                    )
+                }
+
+                // Top-level exported constants
+                valDoc(name = "Path", doc = "Filesystem path class. Construct with a string: `Path(\"/tmp\")`.", type = type("Path"))
+                valDoc(name = "Paths", doc = "Alias of `Path` for those who prefer plural form.", type = type("Path"))
+            }
+            seeded = true
+            return true
+        }
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/docs/LyngDocumentationProvider.kt

@@ -0,0 +1,782 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyng.idea.docs
+
+import com.intellij.lang.documentation.AbstractDocumentationProvider
+import com.intellij.openapi.diagnostic.Logger
+import com.intellij.openapi.editor.Document
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiElement
+import com.intellij.psi.PsiFile
+import net.sergeych.lyng.highlight.offsetOf
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.util.LyngAstManager
+import net.sergeych.lyng.idea.util.TextCtx
+import net.sergeych.lyng.miniast.*
+
+/**
+ * Quick Docs backed by MiniAst: when caret is on an identifier that corresponds
+ * to a declaration name or parameter, render a simple HTML with kind, signature,
+ * and doc summary if present.
+ */
+class LyngDocumentationProvider : AbstractDocumentationProvider() {
+    private val log = Logger.getInstance(LyngDocumentationProvider::class.java)
+    // Toggle to trace inheritance-based resolutions in Quick Docs. Keep false for normal use.
+    private val DEBUG_INHERITANCE = false
+    // Global Quick Doc debug toggle (OFF by default). When false, [LYNG_DEBUG] logs are suppressed.
+    private val DEBUG_LOG = false
+    override fun generateDoc(element: PsiElement?, originalElement: PsiElement?): String? {
+        // Try load external docs registrars (e.g., lyngio) if present on classpath
+        ensureExternalDocsRegistered()
+        // Ensure stdlib Obj*-defined docs (e.g., String methods via ObjString.addFnDoc) are initialized
+        try {
+            net.sergeych.lyng.miniast.StdlibDocsBootstrap.ensure()
+        } catch (_: Throwable) {
+            // best-effort; absence must not break Quick Doc
+        }
+        if (element == null) return null
+        val file: PsiFile = element.containingFile ?: return null
+        val document: Document = file.viewProvider.document ?: return null
+        val text = document.text
+
+        // Determine caret/lookup offset from the element range
+        val offset = originalElement?.textRange?.startOffset ?: element.textRange.startOffset
+        val idRange = TextCtx.wordRangeAt(text, offset) ?: run {
+            if (DEBUG_LOG) log.info("[LYNG_DEBUG] QuickDoc: no word at offset=$offset in ${file.name}")
+            return null
+        }
+        if (idRange.isEmpty) return null
+        val ident = text.substring(idRange.startOffset, idRange.endOffset)
+        if (DEBUG_LOG) log.info("[LYNG_DEBUG] QuickDoc: ident='$ident' at ${idRange.startOffset}..${idRange.endOffset} in ${file.name}")
+
+        // 1. Get merged mini-AST from Manager (handles local + .lyng.d merged declarations)
+        val mini = LyngAstManager.getMiniAst(file) ?: return null
+        val miniSource = mini.range.start.source
+        val imported = DocLookupUtils.canonicalImportedModules(mini, text)
+
+        // Try resolve to: function param at position, function/class/val declaration at position
+        // 1) Use unified declaration detection
+        DocLookupUtils.findDeclarationAt(mini, offset, ident)?.let { (name, kind) ->
+            if (DEBUG_LOG) log.info("[LYNG_DEBUG] QuickDoc: matched declaration '$name' kind=$kind")
+            // Find the actual declaration object to render
+            mini.declarations.forEach { d ->
+                if (d.name == name) {
+                    val s: Int = miniSource.offsetOf(d.nameStart)
+                    if (s <= offset && s + d.name.length > offset) {
+                        return renderDeclDoc(d, text, mini, imported)
+                    }
+                }
+                // Handle members if it was a member
+                if (d is MiniClassDecl) {
+                    d.members.forEach { m ->
+                        if (m.name == name) {
+                            val s: Int = miniSource.offsetOf(m.nameStart)
+                            if (s <= offset && s + m.name.length > offset) {
+                                return when (m) {
+                                    is MiniMemberFunDecl -> renderMemberFunDoc(d.name, m)
+                                    is MiniMemberValDecl -> renderMemberValDoc(d.name, m)
+                                    else -> null
+                                }
+                            }
+                        }
+                    }
+                    d.ctorFields.forEach { cf ->
+                        if (cf.name == name) {
+                            val s: Int = miniSource.offsetOf(cf.nameStart)
+                            if (s <= offset && s + cf.name.length > offset) {
+                                // Render as a member val
+                                val mv = MiniMemberValDecl(
+                                    range = MiniRange(cf.nameStart, cf.nameStart), // dummy
+                                    name = cf.name,
+                                    mutable = cf.mutable,
+                                    type = cf.type,
+                                    initRange = null,
+                                    doc = null,
+                                    nameStart = cf.nameStart
+                                )
+                                return renderMemberValDoc(d.name, mv)
+                            }
+                        }
+                    }
+                    d.classFields.forEach { cf ->
+                        if (cf.name == name) {
+                            val s: Int = miniSource.offsetOf(cf.nameStart)
+                            if (s <= offset && s + cf.name.length > offset) {
+                                // Render as a member val
+                                val mv = MiniMemberValDecl(
+                                    range = MiniRange(cf.nameStart, cf.nameStart), // dummy
+                                    name = cf.name,
+                                    mutable = cf.mutable,
+                                    type = cf.type,
+                                    initRange = null,
+                                    doc = null,
+                                    nameStart = cf.nameStart
+                                )
+                                return renderMemberValDoc(d.name, mv)
+                            }
+                        }
+                    }
+                }
+                if (d is MiniEnumDecl) {
+                    if (d.entries.contains(name)) {
+                        val s: Int = miniSource.offsetOf(d.range.start)
+                        val e: Int = miniSource.offsetOf(d.range.end)
+                        if (offset >= s && offset <= e) {
+                            // For enum constant, we don't have detailed docs in MiniAst yet, but we can render a title
+                            return "<div class='doc-title'>enum constant ${d.name}.${name}</div>"
+                        }
+                    }
+                }
+            }
+            // Check parameters
+            mini.declarations.filterIsInstance<MiniFunDecl>().forEach { fn ->
+                fn.params.forEach { p ->
+                    if (p.name == name) {
+                        val s: Int = miniSource.offsetOf(p.nameStart)
+                        if (s <= offset && s + p.name.length > offset) {
+                            return renderParamDoc(fn, p)
+                        }
+                    }
+                }
+            }
+        }
+
+        // 3) usages in current file via Binder (resolves local variables, parameters, and classes)
+        try {
+            val binding = net.sergeych.lyng.binding.Binder.bind(text, mini)
+            val ref = binding.references.firstOrNull { offset in it.start until it.end }
+            if (ref != null) {
+                val sym = binding.symbols.firstOrNull { it.id == ref.symbolId }
+                if (sym != null) {
+                    // Find local declaration that matches this symbol
+                    var dsFound: MiniDecl? = null
+                    mini.declarations.forEach { decl ->
+                        if (decl.name == sym.name) {
+                            val sOffset: Int = miniSource.offsetOf(decl.nameStart)
+                            if (sOffset == sym.declStart) {
+                                dsFound = decl
+                            }
+                        }
+                    }
+                    if (dsFound != null) return renderDeclDoc(dsFound, text, mini, imported)
+
+                    // Check parameters
+                    mini.declarations.filterIsInstance<MiniFunDecl>().forEach { fn ->
+                        fn.params.forEach { p ->
+                            if (p.name == sym.name) {
+                                val sOffset: Int = miniSource.offsetOf(p.nameStart)
+                                if (sOffset == sym.declStart) {
+                                    return renderParamDoc(fn, p)
+                                }
+                            }
+                        }
+                    }
+
+                    // Check class members (fields/functions)
+                    mini.declarations.filterIsInstance<MiniClassDecl>().forEach { cls ->
+                        cls.members.forEach { m ->
+                            if (m.name == sym.name) {
+                                val sOffset: Int = miniSource.offsetOf(m.nameStart)
+                                if (sOffset == sym.declStart) {
+                                    return when (m) {
+                                        is MiniMemberFunDecl -> renderMemberFunDoc(cls.name, m)
+                                        is MiniMemberValDecl -> renderMemberValDoc(cls.name, m)
+                                        else -> null
+                                    }
+                                }
+                            }
+                        }
+                        cls.ctorFields.forEach { cf ->
+                            if (cf.name == sym.name) {
+                                val sOffset: Int = miniSource.offsetOf(cf.nameStart)
+                                if (sOffset == sym.declStart) {
+                                    // Render as a member val
+                                    val mv = MiniMemberValDecl(
+                                        range = MiniRange(cf.nameStart, cf.nameStart), // dummy
+                                        name = cf.name,
+                                        mutable = cf.mutable,
+                                        type = cf.type,
+                                        initRange = null,
+                                        doc = null,
+                                        nameStart = cf.nameStart
+                                    )
+                                    return renderMemberValDoc(cls.name, mv)
+                                }
+                            }
+                        }
+                        cls.classFields.forEach { cf ->
+                            if (cf.name == sym.name) {
+                                val sOffset: Int = miniSource.offsetOf(cf.nameStart)
+                                if (sOffset == sym.declStart) {
+                                    // Render as a member val
+                                    val mv = MiniMemberValDecl(
+                                        range = MiniRange(cf.nameStart, cf.nameStart), // dummy
+                                        name = cf.name,
+                                        mutable = cf.mutable,
+                                        type = cf.type,
+                                        initRange = null,
+                                        doc = null,
+                                        nameStart = cf.nameStart
+                                    )
+                                    return renderMemberValDoc(cls.name, mv)
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        } catch (e: Throwable) {
+            if (DEBUG_LOG) log.warn("[LYNG_DEBUG] QuickDoc: local binder resolution failed: ${e.message}")
+        }
+        // 4) Member-context resolution first (dot immediately before identifier): handle literals and calls
+        run {
+            val dotPos = TextCtx.findDotLeft(text, idRange.startOffset)
+                ?: TextCtx.findDotLeft(text, offset)
+            if (dotPos != null) {
+                // Build imported modules (MiniAst-derived if available, else lenient from text) and ensure stdlib is present
+                val importedModules = DocLookupUtils.canonicalImportedModules(mini, text)
+
+                // Try literal and call-based receiver inference around the dot
+                val i = TextCtx.prevNonWs(text, dotPos - 1)
+                val className: String? = when {
+                    i >= 0 && text[i] == '"' -> "String"
+                    i >= 0 && text[i] == ']' -> "List"
+                    i >= 0 && text[i] == '}' -> "Dict"
+                    i >= 0 && text[i] == ')' -> {
+                        // Parenthesized expression: walk back to matching '(' and inspect the inner expression
+                        var j = i - 1
+                        var depth = 0
+                        while (j >= 0) {
+                            when (text[j]) {
+                                ')' -> depth++
+                                '(' -> if (depth == 0) break else depth--
+                            }
+                            j--
+                        }
+                        if (j >= 0 && text[j] == '(') {
+                            val innerS = (j + 1).coerceAtLeast(0)
+                            val innerE = i.coerceAtMost(text.length)
+                            if (innerS < innerE) {
+                                val inner = text.substring(innerS, innerE).trim()
+                                when {
+                                    inner.startsWith('"') && inner.endsWith('"') -> "String"
+                                    inner.startsWith('[') && inner.endsWith(']') -> "List"
+                                    inner.startsWith('{') && inner.endsWith('}') -> "Dict"
+                                    else -> null
+                                }
+                            } else null
+                        } else null
+                    }
+                    else -> {
+                        DocLookupUtils.guessReceiverClassViaMini(mini, text, dotPos, importedModules)
+                            ?: DocLookupUtils.guessClassFromCallBefore(text, dotPos, importedModules, mini)
+                            ?: run {
+                                // handle this@Type or as Type
+                                val i2 = TextCtx.prevNonWs(text, dotPos - 1)
+                                if (i2 >= 0) {
+                                    val identRange = TextCtx.wordRangeAt(text, i2 + 1)
+                                    if (identRange != null) {
+                                        val id = text.substring(identRange.startOffset, identRange.endOffset)
+                                        val k = TextCtx.prevNonWs(text, identRange.startOffset - 1)
+                                        if (k >= 1 && text[k] == 's' && text[k - 1] == 'a' && (k - 1 == 0 || !text[k - 2].isLetterOrDigit())) {
+                                            id
+                                        } else if (k >= 0 && text[k] == '@') {
+                                            val k2 = TextCtx.prevNonWs(text, k - 1)
+                                            if (k2 >= 3 && text.substring(k2 - 3, k2 + 1) == "this") id else null
+                                        } else null
+                                    } else null
+                                } else null
+                            }
+                    }
+                }
+                if (DEBUG_LOG) log.info("[LYNG_DEBUG] QuickDoc: memberCtx dotPos=${dotPos} chBeforeDot='${if (dotPos > 0) text[dotPos - 1] else ' '}' classGuess=${className} imports=${importedModules}")
+                if (className != null) {
+                    DocLookupUtils.resolveMemberWithInheritance(importedModules, className, ident, mini)?.let { (owner, member) ->
+                        if (DEBUG_INHERITANCE) log.info("[LYNG_DEBUG] QuickDoc: literal/call '$ident' resolved to $owner.${member.name}")
+                        return when (member) {
+                            is MiniMemberFunDecl -> renderMemberFunDoc(owner, member)
+                            is MiniMemberValDecl -> renderMemberValDoc(owner, member)
+                            is MiniInitDecl -> null
+                            is MiniFunDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniValDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniClassDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniEnumDecl -> renderDeclDoc(member, text, mini, importedModules)
+                        }
+                    }
+                    log.info("[LYNG_DEBUG] QuickDoc: resolve failed for ${className}.${ident}")
+                }
+            }
+        }
+
+        // 4) As a fallback, if the caret is on an identifier text that matches any declaration name, show that
+        mini.declarations.firstOrNull { it.name == ident }?.let {
+            log.info("[LYNG_DEBUG] QuickDoc: fallback by name '${it.name}' kind=${it::class.simpleName}")
+            return renderDeclDoc(it, text, mini, imported)
+        }
+
+        // 4) Consult BuiltinDocRegistry for imported modules (top-level and class members)
+        // Canonicalize import names using ImportManager, as users may write shortened names (e.g., "io.fs")
+        var importedModules = DocLookupUtils.canonicalImportedModules(mini, text)
+        // Always include stdlib as a fallback context
+        if (!importedModules.contains("lyng.stdlib")) importedModules = importedModules + "lyng.stdlib"
+        // 4a) try top-level decls
+        importedModules.forEach { mod ->
+            val docs = BuiltinDocRegistry.docsForModule(mod)
+            val matches = docs.filterIsInstance<MiniFunDecl>().filter { it.name == ident }
+            if (matches.isNotEmpty()) {
+                // Prefer overload by arity when caret is in a call position; otherwise show first
+                val arity = callArity(text, idRange.endOffset)
+                val chosen = arity?.let { a -> matches.firstOrNull { it.params.size == a } } ?: matches.first()
+                // If multiple and none matched arity, consider showing an overloads list
+                if (arity != null && chosen.params.size != arity && matches.size > 1) {
+                    return renderOverloads(ident, matches)
+                }
+                return renderDeclDoc(chosen, text, mini, imported)
+            }
+            // Also allow values/consts
+            docs.filterIsInstance<MiniValDecl>().firstOrNull { it.name == ident }?.let { return renderDeclDoc(it, text, mini, imported) }
+            // And classes/enums
+            docs.filterIsInstance<MiniClassDecl>().firstOrNull { it.name == ident }?.let { return renderDeclDoc(it, text, mini, imported) }
+            docs.filterIsInstance<MiniEnumDecl>().firstOrNull { it.name == ident }?.let { return renderDeclDoc(it, text, mini, imported) }
+        }
+        // Defensive fallback: if nothing found and it's a well-known stdlib function, render minimal inline docs
+        if (ident == "println" || ident == "print") {
+            val fallback = if (ident == "println")
+                "Print values to the standard output and append a newline. Accepts any number of arguments." else
+                "Print values to the standard output without a trailing newline. Accepts any number of arguments."
+            val title = "function $ident(values)"
+            return "<div class='doc-title'>${htmlEscape(title)}</div>" + styledMarkdown(htmlEscape(fallback))
+        }
+        // 4b) try class members like ClassName.member with inheritance fallback
+        val lhs = previousWordBefore(text, idRange.startOffset)
+        if (lhs != null && hasDotBetween(text, lhs.endOffset, idRange.startOffset)) {
+            val className = text.substring(lhs.startOffset, lhs.endOffset)
+            DocLookupUtils.resolveMemberWithInheritance(importedModules, className, ident, mini)?.let { (owner, member) ->
+                if (DEBUG_INHERITANCE) log.info("[LYNG_DEBUG] Inheritance resolved $className.$ident to $owner.${member.name}")
+                return when (member) {
+                    is MiniMemberFunDecl -> renderMemberFunDoc(owner, member)
+                    is MiniMemberValDecl -> renderMemberValDoc(owner, member)
+                    is MiniInitDecl -> null
+                    is MiniFunDecl -> renderDeclDoc(member, text, mini, importedModules)
+                    is MiniValDecl -> renderDeclDoc(member, text, mini, importedModules)
+                    is MiniClassDecl -> renderDeclDoc(member, text, mini, importedModules)
+                    is MiniEnumDecl -> renderDeclDoc(member, text, mini, importedModules)
+                }
+            }
+        } else {
+            // Heuristics when LHS is not an identifier (literals or call results):
+            //  - List literal like [..].member → assume class List
+            //  - Otherwise, try to find a unique class across imported modules that defines this member
+            val dotPos = findDotLeft(text, idRange.startOffset)
+            if (dotPos != null) {
+                val guessed = when {
+                    looksLikeListLiteralBefore(text, dotPos) -> "List"
+                    else -> DocLookupUtils.guessClassFromCallBefore(text, dotPos, importedModules, mini)
+                }
+                if (guessed != null) {
+                    DocLookupUtils.resolveMemberWithInheritance(importedModules, guessed, ident, mini)?.let { (owner, member) ->
+                        if (DEBUG_INHERITANCE) log.info("[LYNG_DEBUG] Heuristic '$guessed.$ident' resolved via inheritance to $owner.${member.name}")
+                        return when (member) {
+                            is MiniMemberFunDecl -> renderMemberFunDoc(owner, member)
+                            is MiniMemberValDecl -> renderMemberValDoc(owner, member)
+                            is MiniInitDecl -> null
+                            is MiniFunDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniValDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniClassDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniEnumDecl -> renderDeclDoc(member, text, mini, importedModules)
+                        }
+                    }
+                } else {
+                    // Extra fallback: try a small set of known receiver classes (covers literals when guess failed)
+                    run {
+                        val candidates = listOf("String", "Iterable", "Iterator", "List", "Collection", "Array", "Dict", "Regex")
+                        for (c in candidates) {
+                            DocLookupUtils.resolveMemberWithInheritance(importedModules, c, ident, mini)?.let { (owner, member) ->
+                                if (DEBUG_INHERITANCE) log.info("[LYNG_DEBUG] Candidate '$c.$ident' resolved via inheritance to $owner.${member.name}")
+                                return when (member) {
+                                    is MiniMemberFunDecl -> renderMemberFunDoc(owner, member)
+                                    is MiniMemberValDecl -> renderMemberValDoc(owner, member)
+                                    is MiniInitDecl -> null
+                                    is MiniFunDecl -> renderDeclDoc(member, text, mini, importedModules)
+                                    is MiniValDecl -> renderDeclDoc(member, text, mini, importedModules)
+                                    is MiniClassDecl -> renderDeclDoc(member, text, mini, importedModules)
+                                    is MiniEnumDecl -> renderDeclDoc(member, text, mini, importedModules)
+                                }
+                            }
+                        }
+                    }
+                    // As a last resort try aggregated String members (extensions from stdlib text)
+                    run {
+                        val classes = DocLookupUtils.aggregateClasses(importedModules, mini)
+                        val stringCls = classes["String"]
+                        val m = stringCls?.members?.firstOrNull { it.name == ident }
+                        if (m != null) {
+                            if (DEBUG_INHERITANCE) log.info("[LYNG_DEBUG] Aggregated fallback resolved String.$ident")
+                            return when (m) {
+                                is MiniMemberFunDecl -> renderMemberFunDoc("String", m)
+                                is MiniMemberValDecl -> renderMemberValDoc("String", m)
+                                is MiniInitDecl -> null
+                            }
+                        }
+                    }
+                    // Search across classes; prefer Iterable, then Iterator, then List for common ops
+                    DocLookupUtils.findMemberAcrossClasses(importedModules, ident, mini)?.let { (owner, member) ->
+                        if (DEBUG_INHERITANCE) log.info("[LYNG_DEBUG] Cross-class '$ident' resolved to $owner.${member.name}")
+                        return when (member) {
+                            is MiniMemberFunDecl -> renderMemberFunDoc(owner, member)
+                            is MiniMemberValDecl -> renderMemberValDoc(owner, member)
+                            is MiniInitDecl -> null
+                            is MiniFunDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniValDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniClassDecl -> renderDeclDoc(member, text, mini, importedModules)
+                            is MiniEnumDecl -> renderDeclDoc(member, text, mini, importedModules)
+                        }
+                    }
+                }
+            }
+        }
+
+        if (DEBUG_LOG) log.info("[LYNG_DEBUG] QuickDoc: nothing found for ident='$ident'")
+        return null
+    }
+
+    private val externalDocsLoaded: Boolean by lazy { tryLoadExternalDocs() }
+
+    private fun ensureExternalDocsRegistered() { @Suppress("UNUSED_EXPRESSION") externalDocsLoaded }
+
+    private fun tryLoadExternalDocs(): Boolean {
+        var anyLoaded = false
+        try {
+            // Try known registrars; ignore failures if module is absent
+            val cls = Class.forName("net.sergeych.lyngio.docs.FsBuiltinDocs")
+            val m = cls.getMethod("ensure")
+            m.invoke(null)
+            log.info("[LYNG_DEBUG] QuickDoc: external docs loaded: net.sergeych.lyngio.docs.FsBuiltinDocs.ensure() OK")
+            anyLoaded = true
+        } catch (_: Throwable) {}
+
+        try {
+            val cls = Class.forName("net.sergeych.lyngio.docs.ProcessBuiltinDocs")
+            val m = cls.getMethod("ensure")
+            m.invoke(null)
+            log.info("[LYNG_DEBUG] QuickDoc: external docs loaded: net.sergeych.lyngio.docs.ProcessBuiltinDocs.ensure() OK")
+            anyLoaded = true
+        } catch (_: Throwable) {}
+
+        if (!anyLoaded) {
+            // Seed a minimal plugin-local fallback so Path docs still work without lyngio
+            val seeded = try {
+                FsDocsFallback.ensureOnce()
+                ProcessDocsFallback.ensureOnce()
+                true
+            } catch (_: Throwable) { false }
+            if (seeded) {
+                log.info("[LYNG_DEBUG] QuickDoc: external docs NOT found; seeded plugin fallbacks")
+            } else {
+                log.info("[LYNG_DEBUG] QuickDoc: external docs NOT found (lyngio absent on classpath)")
+            }
+            return seeded
+        }
+        return true
+    }
+
+    override fun getCustomDocumentationElement(
+        editor: Editor,
+        file: PsiFile,
+        contextElement: PsiElement?,
+        targetOffset: Int
+    ): PsiElement? {
+        // Ensure our provider gets a chance for Lyng files regardless of PSI sophistication
+        if (file.language != LyngLanguage) return null
+        return contextElement ?: file.findElementAt(targetOffset)
+    }
+
+    private fun renderDeclDoc(d: MiniDecl, text: String, mini: MiniScript, imported: List<String>): String {
+        val title = when (d) {
+            is MiniFunDecl -> "function ${d.name}${signatureOf(d)}"
+            is MiniClassDecl -> "class ${d.name}"
+            is MiniEnumDecl -> "enum ${d.name} { ${d.entries.joinToString(", ")} }"
+            is MiniValDecl -> {
+                val t = d.type ?: DocLookupUtils.inferTypeRefForVal(d, text, imported, mini)
+                val typeStr = if (t == null) ": Object?" else typeOf(t)
+                if (d.mutable) "var ${d.name}${typeStr}" else "val ${d.name}${typeStr}"
+            }
+        }
+        val sb = StringBuilder()
+        sb.append("<div class='doc-title'>").append(htmlEscape(title)).append("</div>")
+        sb.append(renderDocBody(d.doc))
+        return sb.toString()
+    }
+
+    private fun renderParamDoc(fn: MiniFunDecl, p: MiniParam): String {
+        val title = "parameter ${p.name}${typeOf(p.type)} in ${fn.name}${signatureOf(fn)}"
+        val sb = StringBuilder()
+        sb.append("<div class='doc-title'>").append(htmlEscape(title)).append("</div>")
+
+        // Find matching @param tag
+        fn.doc?.tags?.get("param")?.forEach { tag ->
+            val parts = tag.split(Regex("\\s+"), 2)
+            if (parts.getOrNull(0) == p.name && parts.size > 1) {
+                sb.append(styledMarkdown(MarkdownRenderer.render(parts[1])))
+            }
+        }
+
+        return sb.toString()
+    }
+
+    private fun renderMemberFunDoc(className: String, m: MiniMemberFunDecl): String {
+        val params = m.params.joinToString(", ") { p ->
+            val ts = typeOf(p.type)
+            if (ts.isNotBlank()) "${p.name}${ts}" else p.name
+        }
+        val ret = typeOf(m.returnType)
+        val staticStr = if (m.isStatic) "static " else ""
+        val title = "${staticStr}method $className.${m.name}(${params})${ret}"
+        val sb = StringBuilder()
+        sb.append("<div class='doc-title'>").append(htmlEscape(title)).append("</div>")
+        sb.append(renderDocBody(m.doc))
+        return sb.toString()
+    }
+
+    private fun renderMemberValDoc(className: String, m: MiniMemberValDecl): String {
+        val ts = if (m.type == null) ": Object?" else typeOf(m.type)
+        val kind = if (m.mutable) "var" else "val"
+        val staticStr = if (m.isStatic) "static " else ""
+        val title = "${staticStr}${kind} $className.${m.name}${ts}"
+        val sb = StringBuilder()
+        sb.append("<div class='doc-title'>").append(htmlEscape(title)).append("</div>")
+        sb.append(renderDocBody(m.doc))
+        return sb.toString()
+    }
+
+    private fun typeOf(t: MiniTypeRef?): String {
+        val s = DocLookupUtils.typeOf(t)
+        return if (s.isEmpty()) (if (t == null) ": Object?" else "") else ": $s"
+    }
+
+    private fun signatureOf(fn: MiniFunDecl): String {
+        val params = fn.params.joinToString(", ") { p ->
+            val ts = typeOf(p.type)
+            if (ts.isNotBlank()) "${p.name}${ts}" else p.name
+        }
+        val ret = typeOf(fn.returnType)
+        return "(${params})${ret}"
+    }
+
+    private fun htmlEscape(s: String): String = buildString(s.length) {
+        for (ch in s) append(
+            when (ch) {
+                '<' -> "&lt;"
+                '>' -> "&gt;"
+                '&' -> "&amp;"
+                '"' -> "&quot;"
+                else -> ch
+            }
+        )
+    }
+
+    private fun styledMarkdown(html: String): String {
+        // IntelliJ doc renderer sanitizes and may surface <style> content as text.
+        // Strip any style tags defensively and keep markup lean; rely on platform defaults.
+        val safe = stripStyleTags(html)
+        return """
+            <div class="lyng-doc-md" style="max-width:72ch; line-height:1.4; font-size:0.96em;">
+              $safe
+            </div>
+        """.trimIndent()
+    }
+
+    private fun stripStyleTags(src: String): String {
+        // Remove any <style>...</style> blocks (case-insensitive, dotall)
+        val styleRegex = Regex("(?is)<style[^>]*>.*?</style>")
+        return src.replace(styleRegex, "")
+    }
+
+    // --- Simple helpers to support overload selection and heuristics ---
+    /**
+     * If identifier at [rightAfterIdent] is followed by a call like `(a, b)`,
+     * return the argument count; otherwise return null. Nested parentheses are
+     * handled conservatively to skip commas inside lambdas/parentheses.
+     */
+    private fun callArity(text: String, rightAfterIdent: Int): Int? {
+        var i = rightAfterIdent
+        // Skip whitespace
+        while (i < text.length && text[i].isWhitespace()) i++
+        if (i >= text.length || text[i] != '(') return null
+        i++
+        var depth = 0
+        var commas = 0
+        var hasToken = false
+        while (i < text.length) {
+            val ch = text[i]
+            when (ch) {
+                '(' -> { depth++; hasToken = true }
+                ')' -> {
+                    if (depth == 0) {
+                        // Empty parentheses => arity 0 if no token and no commas
+                        if (!hasToken && commas == 0) return 0
+                        return commas + 1
+                    } else depth--
+                }
+                ',' -> if (depth == 0) { commas++; hasToken = false }
+                '\n' -> {}
+                else -> if (!ch.isWhitespace()) hasToken = true
+            }
+            i++
+        }
+        return null
+    }
+
+    private fun renderOverloads(name: String, overloads: List<MiniFunDecl>): String {
+        val sb = StringBuilder()
+        sb.append("<div class='doc-title'>Overloads for ").append(htmlEscape(name)).append("</div>")
+        sb.append("<ul>")
+        overloads.forEach { fn ->
+            sb.append("<li><code>")
+                .append(htmlEscape("fun ${fn.name}${signatureOf(fn)}"))
+                .append("</code>")
+            fn.doc?.summary?.let { sum -> sb.append(" — ").append(htmlEscape(sum)) }
+            sb.append("</li>")
+        }
+        sb.append("</ul>")
+        return sb.toString()
+    }
+
+    private fun wordRangeAt(text: String, offset: Int): TextRange? {
+        if (text.isEmpty()) return null
+        var s = offset.coerceIn(0, text.length)
+        var e = s
+        while (s > 0 && isIdentChar(text[s - 1])) s--
+        while (e < text.length && isIdentChar(text[e])) e++
+        return if (e > s) TextRange(s, e) else null
+    }
+
+    private fun renderDocBody(doc: MiniDoc?): String {
+        if (doc == null) return ""
+        val sb = StringBuilder()
+        if (doc.raw.isNotBlank()) {
+            sb.append(styledMarkdown(MarkdownRenderer.render(doc.raw)))
+        }
+        if (doc.tags.isNotEmpty()) {
+            sb.append(renderTags(doc.tags))
+        }
+        return sb.toString()
+    }
+
+    private fun renderTags(tags: Map<String, List<String>>): String {
+        if (tags.isEmpty()) return ""
+        val sb = StringBuilder()
+        sb.append("<table class='sections'>")
+
+        fun section(title: String, list: List<String>, isKeyValue: Boolean = false) {
+            if (list.isEmpty()) return
+            sb.append("<tr><td valign='top' class='section'><p>").append(htmlEscape(title)).append(":</p></td><td valign='top'>")
+            list.forEachIndexed { index, item ->
+                if (index > 0) sb.append("<p>")
+                if (isKeyValue) {
+                    val parts = item.split(Regex("\\s+"), 2)
+                    sb.append("<code>").append(htmlEscape(parts[0])).append("</code>")
+                    if (parts.size > 1) {
+                        sb.append(" — ").append(MarkdownRenderer.render(parts[1]).removePrefix("<p>").removeSuffix("</p>"))
+                    }
+                } else {
+                    sb.append(MarkdownRenderer.render(item).removePrefix("<p>").removeSuffix("</p>"))
+                }
+            }
+            sb.append("</td></tr>")
+        }
+
+        section("Parameters", tags["param"] ?: emptyList(), isKeyValue = true)
+        section("Returns", tags["return"] ?: emptyList())
+        section("Throws", tags["throws"] ?: emptyList(), isKeyValue = true)
+
+        tags.forEach { (name, list) ->
+            if (name !in listOf("param", "return", "throws")) {
+                section(name.replaceFirstChar { if (it.isLowerCase()) it.titlecase() else it.toString() }, list)
+            }
+        }
+
+        sb.append("</table>")
+        return sb.toString()
+    }
+
+    private fun previousWordBefore(text: String, offset: Int): TextRange? {
+        // skip spaces and the dot to the left, but stop after hitting a non-identifier boundary
+        var i = (offset - 1).coerceAtLeast(0)
+        // skip trailing spaces
+        while (i >= 0 && text[i].isWhitespace()) i--
+        // skip the dot if present
+        if (i >= 0 && text[i] == '.') i--
+        // skip spaces before the dot
+        while (i >= 0 && text[i].isWhitespace()) i--
+        // remember position to check for dot between words
+        val end = i + 1
+        // now find the start of the identifier
+        while (i >= 0 && isIdentChar(text[i])) i--
+        val start = (i + 1)
+        return if (start < end && start >= 0) TextRange(start, end) else null
+    }
+
+    private fun hasDotBetween(text: String, leftEnd: Int, rightStart: Int): Boolean {
+        val s = leftEnd.coerceAtLeast(0)
+        val e = rightStart.coerceAtMost(text.length)
+        if (e <= s) return false
+        for (i in s until e) if (text[i] == '.') return true
+        return false
+    }
+
+    private fun isIdentChar(c: Char): Boolean = c == '_' || c.isLetterOrDigit()
+
+    // --- Helpers for inheritance-aware and heuristic member lookup ---
+
+    // Removed: member/class resolution helpers moved to lynglib DocLookupUtils for reuse
+
+    private fun findDotLeft(text: String, rightStart: Int): Int? {
+        var i = (rightStart - 1).coerceAtLeast(0)
+        while (i >= 0 && text[i].isWhitespace()) i--
+        while (i >= 0) {
+            val ch = text[i]
+            if (ch == '.') return i
+            if (ch == '\n') return null
+            i--
+        }
+        return null
+    }
+
+    private fun looksLikeListLiteralBefore(text: String, dotPos: Int): Boolean {
+        // Look left for a closing ']' possibly with spaces, then a matching '[' before a comma or assignment
+        var i = (dotPos - 1).coerceAtLeast(0)
+        while (i >= 0 && text[i].isWhitespace()) i--
+        if (i < 0 || text[i] != ']') return false
+        var depth = 0
+        i--
+        while (i >= 0) {
+            val ch = text[i]
+            when (ch) {
+                ']' -> depth++
+                '[' -> if (depth == 0) return true else depth--
+                '\n' -> return false
+            }
+            i--
+        }
+        return false
+    }
+
+    // Removed: guessClassFromCallBefore moved to DocLookupUtils
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/docs/LyngDocumentationTargets.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.docs
+
+// 243: We do not use DocumentationTarget API here. Quick Docs works via
+// AbstractDocumentationProvider registered as lang.documentationProvider.
+internal object LyngDocumentationTargetsPlaceholder

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/docs/MarkdownRenderer.kt

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyng.idea.docs
+
+import com.vladsch.flexmark.ext.autolink.AutolinkExtension
+import com.vladsch.flexmark.ext.gfm.strikethrough.StrikethroughExtension
+import com.vladsch.flexmark.ext.tables.TablesExtension
+import com.vladsch.flexmark.html.HtmlRenderer
+import com.vladsch.flexmark.parser.Parser
+import com.vladsch.flexmark.util.data.MutableDataSet
+
+/**
+ * Rich Markdown renderer for the IDEA Quick Docs using Flexmark.
+ *
+ * - Supports fenced code blocks (with language class "language-xyz")
+ * - Autolinks, tables, strikethrough
+ * - Converts soft breaks to <br/>
+ * - Tiny in-memory cache to avoid repeated parsing of the same doc blocks
+ */
+object MarkdownRenderer {
+    private val options = MutableDataSet().apply {
+        set(Parser.EXTENSIONS, listOf(
+            AutolinkExtension.create(),
+            TablesExtension.create(),
+            StrikethroughExtension.create(),
+        ))
+        // Add CSS class for code fences like ```lyng → class="language-lyng"
+        set(HtmlRenderer.FENCED_CODE_LANGUAGE_CLASS_PREFIX, "language-")
+        // Treat single newlines as a space (soft break) so consecutive lines remain one paragraph.
+        // Real paragraph breaks require an empty line, hard breaks still work via Markdown (two spaces + \n).
+        set(HtmlRenderer.SOFT_BREAK, " ")
+    }
+
+    private val parser: Parser = Parser.builder(options).build()
+    private val renderer: HtmlRenderer = HtmlRenderer.builder(options).build()
+
+    private val cache = object : LinkedHashMap<String, String>(256, 0.75f, true) {
+        override fun removeEldestEntry(eldest: MutableMap.MutableEntry<String, String>?): Boolean = size > 256
+    }
+
+    fun render(markdown: String): String {
+        // Fast path: cache
+        synchronized(cache) { cache[markdown]?.let { return it } }
+        val node = parser.parse(markdown)
+        val html = renderer.render(node)
+        synchronized(cache) { cache[markdown] = html }
+        return html
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/docs/ProcessDocsFallback.kt

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/*
+ * Minimal fallback docs seeding for `lyng.io.process` used only inside the IDEA plugin
+ * when external docs module (lyngio) is not present on the classpath.
+ */
+package net.sergeych.lyng.idea.docs
+
+import net.sergeych.lyng.miniast.BuiltinDocRegistry
+import net.sergeych.lyng.miniast.ParamDoc
+import net.sergeych.lyng.miniast.type
+
+internal object ProcessDocsFallback {
+    @Volatile
+    private var seeded = false
+
+    fun ensureOnce(): Boolean {
+        if (seeded) return true
+        synchronized(this) {
+            if (seeded) return true
+            BuiltinDocRegistry.module("lyng.io.process") {
+                classDoc(name = "Process", doc = "Process execution and control.") {
+                    method(
+                        name = "execute",
+                        doc = "Execute a process with arguments.",
+                        params = listOf(ParamDoc("executable", type("lyng.String")), ParamDoc("args", type("lyng.List"))),
+                        returns = type("RunningProcess"),
+                        isStatic = true
+                    )
+                    method(
+                        name = "shell",
+                        doc = "Execute a command via system shell.",
+                        params = listOf(ParamDoc("command", type("lyng.String"))),
+                        returns = type("RunningProcess"),
+                        isStatic = true
+                    )
+                }
+
+                classDoc(name = "RunningProcess", doc = "Handle to a running process.") {
+                    method(name = "stdout", doc = "Get standard output stream as a Flow of lines.", returns = type("lyng.Flow"))
+                    method(name = "stderr", doc = "Get standard error stream as a Flow of lines.", returns = type("lyng.Flow"))
+                    method(name = "waitFor", doc = "Wait for the process to exit.", returns = type("lyng.Int"))
+                    method(name = "signal", doc = "Send a signal to the process.", params = listOf(ParamDoc("signal", type("lyng.String"))))
+                    method(name = "destroy", doc = "Forcefully terminate the process.")
+                }
+
+                valDoc(name = "Process", doc = "Process execution and control.", type = type("Process"))
+                valDoc(name = "RunningProcess", doc = "Handle to a running process.", type = type("RunningProcess"))
+            }
+            seeded = true
+            return true
+        }
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngBackspaceHandler.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+import com.intellij.codeInsight.editorActions.BackspaceHandlerDelegate
+import com.intellij.openapi.editor.Editor
+import com.intellij.psi.PsiFile
+
+/**
+ * Backspace handler (currently inactive, not registered). Minimal stub to keep build green.
+ * We will enable and implement smart behavior after API verification on the target IDE.
+ */
+class LyngBackspaceHandler : BackspaceHandlerDelegate() {
+    override fun beforeCharDeleted(c: Char, file: PsiFile, editor: Editor) {
+        // no-op
+    }
+
+    override fun charDeleted(c: Char, file: PsiFile, editor: Editor): Boolean {
+        // no-op; let default behavior stand
+        return false
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngCopyPastePreProcessor.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+/**
+ * Disabled placeholder. We currently use the EditorPaste action handler (LyngPasteHandler)
+ * which works across IDE builds without relying on RawText API.
+ */
+class LyngCopyPastePreProcessorDisabled

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngCopyPastePreProcessor243.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+/**
+ * Placeholder for 2024.3+ RawText-based CopyPastePreProcessor.
+ * Not compiled against current SDK classpath; kept for future activation.
+ */
+class LyngCopyPastePreProcessor243Disabled

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngEnterHandler.kt

@@ -0,0 +1,200 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+import com.intellij.application.options.CodeStyle
+import com.intellij.codeInsight.editorActions.enter.EnterHandlerDelegate
+import com.intellij.codeInsight.editorActions.enter.EnterHandlerDelegate.Result
+import com.intellij.openapi.actionSystem.DataContext
+import com.intellij.openapi.command.WriteCommandAction
+import com.intellij.openapi.diagnostic.Logger
+import com.intellij.openapi.editor.Caret
+import com.intellij.openapi.editor.Document
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.editor.actionSystem.EditorActionHandler
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.util.Ref
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiDocumentManager
+import com.intellij.psi.PsiFile
+import com.intellij.psi.codeStyle.CodeStyleManager
+import net.sergeych.lyng.format.LyngFormatConfig
+import net.sergeych.lyng.format.LyngFormatter
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.util.FormattingUtils.computeDesiredIndent
+import net.sergeych.lyng.idea.util.FormattingUtils.findFirstNonWs
+
+class LyngEnterHandler : EnterHandlerDelegate {
+    private val log = Logger.getInstance(LyngEnterHandler::class.java)
+    override fun preprocessEnter(
+        file: PsiFile,
+        editor: Editor,
+        caretOffset: Ref<Int>,
+        caretAdvance: Ref<Int>,
+        dataContext: DataContext,
+        originalHandler: EditorActionHandler?
+    ): Result {
+        if (file.language != LyngLanguage) return Result.Continue
+        if (log.isDebugEnabled) log.debug("[LyngEnter] preprocess in Lyng file at caretOffset=${caretOffset.get()}")
+        // Let the platform insert the newline; we will fix indentation in postProcessEnter.
+        return Result.Continue
+    }
+
+    override fun postProcessEnter(file: PsiFile, editor: Editor, dataContext: DataContext): Result {
+        if (file.language != LyngLanguage) return Result.Continue
+        val project = file.project
+        val doc = editor.document
+        val psiManager = PsiDocumentManager.getInstance(project)
+        psiManager.commitDocument(doc)
+
+        // Handle all carets independently to keep multi-caret scenarios sane
+        for (caret in editor.caretModel.allCarets) {
+            val line = doc.safeLineNumber(caret.offset)
+            if (line < 0) continue
+            if (log.isDebugEnabled) log.debug("[LyngEnter] postProcess at line=$line offset=${caret.offset}")
+            // Adjust previous '}' line if applicable, then indent the current line using our rules
+            adjustBraceAndCurrentIndent(project, file, doc, line)
+
+            // After indenting, ensure caret sits after the computed indent of this new line
+            moveCaretToIndentIfOnLeadingWs(editor, doc, file, line, caret)
+        }
+        return Result.Continue
+    }
+
+    private fun adjustBraceAndCurrentIndent(project: Project, file: PsiFile, doc: Document, currentLine: Int) {
+        val prevLine = currentLine - 1
+        if (prevLine >= 0) {
+            val prevText = doc.getLineText(prevLine)
+            val trimmed = prevText.trimStart()
+            // consider only code part before // comment
+            val code = trimmed.substringBefore("//").trim()
+            if (code == "}" || code == "*/") {
+                // Adjust indent for the previous line if it's a block or comment closer
+                val prevStart = doc.getLineStartOffset(prevLine)
+                if (file.context == null) {
+                    try {
+                        CodeStyleManager.getInstance(project).adjustLineIndent(file, prevStart)
+                    } catch (e: Exception) {
+                        log.warn("Failed to adjust line indent for previous line: ${e.message}")
+                    }
+                }
+
+                // Fallback for previous line: manual application
+                val desiredPrev = computeDesiredIndent(project, doc, prevLine)
+                val lineStartPrev = doc.getLineStartOffset(prevLine)
+                val lineEndPrev = doc.getLineEndOffset(prevLine)
+                val firstNonWsPrev = findFirstNonWs(doc, lineStartPrev, lineEndPrev)
+                val currentIndentLenPrev = firstNonWsPrev - lineStartPrev
+                if (doc.getText(TextRange(lineStartPrev, lineStartPrev + currentIndentLenPrev)) != desiredPrev) {
+                    WriteCommandAction.runWriteCommandAction(project) {
+                        doc.replaceString(lineStartPrev, lineStartPrev + currentIndentLenPrev, desiredPrev)
+                    }
+                }
+            }
+        }
+        // Adjust indent for the current (new) line
+        val currentStart = doc.getLineStartOffsetSafe(currentLine)
+        if (file.context == null) {
+            try {
+                CodeStyleManager.getInstance(project).adjustLineIndent(file, currentStart)
+            } catch (e: Exception) {
+                log.warn("Failed to adjust line indent for current line: ${e.message}")
+            }
+        }
+
+        // Fallback: if the platform didn't physically insert indentation, compute it from our formatter and apply
+        val lineStart = doc.getLineStartOffset(currentLine)
+        val lineEnd = doc.getLineEndOffset(currentLine)
+        val desiredIndent = computeDesiredIndent(project, doc, currentLine)
+        val firstNonWs = findFirstNonWs(doc, lineStart, lineEnd)
+        val currentIndentLen = firstNonWs - lineStart
+        if (desiredIndent.isNotEmpty() || currentIndentLen != 0) {
+            // Replace existing leading whitespace to match desired indent exactly
+            val replaceFrom = lineStart
+            val replaceTo = lineStart + currentIndentLen
+            if (doc.getText(TextRange(replaceFrom, replaceTo)) != desiredIndent) {
+                com.intellij.openapi.command.WriteCommandAction.runWriteCommandAction(project) {
+                    doc.replaceString(replaceFrom, replaceTo, desiredIndent)
+                }
+                PsiDocumentManager.getInstance(project).commitDocument(doc)
+                if (log.isDebugEnabled) {
+                    val dbg = desiredIndent.replace("\t", "\\t")
+                    log.debug("[LyngEnter] rewrote current line leading WS to '$dbg' at line=$currentLine")
+                }
+            }
+        }
+    }
+
+    private fun reindentClosedBlockAroundBrace(project: Project, file: PsiFile, doc: Document, braceLine: Int) {
+        // Find the absolute index of the '}' at or before end of braceLine
+        val braceLineStart = doc.getLineStartOffset(braceLine)
+        val braceLineEnd = doc.getLineEndOffset(braceLine)
+        val rawBraceLine = doc.getText(TextRange(braceLineStart, braceLineEnd))
+        val codeBraceLine = rawBraceLine.substringBefore("//")
+        val closeRel = codeBraceLine.lastIndexOf('}')
+        if (closeRel < 0) return
+        val closeAbs = braceLineStart + closeRel
+
+        // Compute the enclosing block range in raw text (document char sequence)
+        val blockRange = net.sergeych.lyng.format.BraceUtils.findEnclosingBlockRange(doc.charsSequence, closeAbs, includeTrailingNewline = true)
+            ?: return
+
+        val options = CodeStyle.getIndentOptions(project, doc)
+        val cfg = LyngFormatConfig(
+            indentSize = options.INDENT_SIZE.coerceAtLeast(1),
+            useTabs = options.USE_TAB_CHARACTER,
+            continuationIndentSize = options.CONTINUATION_INDENT_SIZE.coerceAtLeast(options.INDENT_SIZE.coerceAtLeast(1)),
+        )
+
+        // Run partial reindent over the slice and replace only if changed
+        val whole = doc.text
+        val updated = LyngFormatter.reindentRange(whole, blockRange, cfg, preserveBaseIndent = true)
+        if (updated != whole) {
+            WriteCommandAction.runWriteCommandAction(project) {
+                doc.replaceString(0, doc.textLength, updated)
+            }
+            PsiDocumentManager.getInstance(project).commitDocument(doc)
+            if (log.isDebugEnabled) log.debug("[LyngEnter] reindented closed block range=${'$'}blockRange")
+        }
+    }
+
+    private fun moveCaretToIndentIfOnLeadingWs(editor: Editor, doc: Document, file: PsiFile, line: Int, caret: Caret) {
+        if (line < 0 || line >= doc.lineCount) return
+        val lineStart = doc.getLineStartOffset(line)
+        val lineEnd = doc.getLineEndOffset(line)
+        val desiredIndent = computeDesiredIndent(file.project, doc, line)
+        val firstNonWs = (lineStart + desiredIndent.length).coerceAtMost(doc.textLength)
+        val caretOffset = caret.offset
+        // If caret is at beginning of the line or still within the leading whitespace, move it after indent
+        val target = firstNonWs.coerceIn(lineStart, lineEnd)
+        caret.moveToOffset(target)
+    }
+
+
+    private fun Document.safeLineNumber(offset: Int): Int =
+        getLineNumber(offset.coerceIn(0, textLength))
+
+    private fun Document.getLineText(line: Int): String {
+        if (line < 0 || line >= lineCount) return ""
+        val start = getLineStartOffset(line)
+        val end = getLineEndOffset(line)
+        return getText(TextRange(start, end))
+    }
+
+    private fun Document.getLineStartOffsetSafe(line: Int): Int =
+        if (line < 0) 0 else getLineStartOffset(line.coerceAtMost(lineCount - 1).coerceAtLeast(0))
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngOnPasteProcessor.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+/**
+ * Disabled placeholder: we rely on LyngPasteHandler (EditorPaste action handler).
+ */
+class LyngOnPasteProcessorDisabled

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngPasteHandler.kt

@@ -0,0 +1,166 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+import com.intellij.application.options.CodeStyle
+import com.intellij.openapi.actionSystem.DataContext
+import com.intellij.openapi.command.WriteCommandAction
+import com.intellij.openapi.editor.Caret
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.editor.actionSystem.EditorWriteActionHandler
+import com.intellij.openapi.ide.CopyPasteManager
+import com.intellij.psi.PsiDocumentManager
+import net.sergeych.lyng.format.LyngFormatConfig
+import net.sergeych.lyng.format.LyngFormatter
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.settings.LyngFormatterSettings
+import java.awt.datatransfer.DataFlavor
+
+/**
+ * Smart Paste using an editor action handler (avoids RawText API variance).
+ * Reindents pasted blocks when caret is in leading whitespace and the setting is enabled.
+ */
+class LyngPasteHandler : EditorWriteActionHandler(true) {
+    private val log = com.intellij.openapi.diagnostic.Logger.getInstance(LyngPasteHandler::class.java)
+    override fun doExecute(editor: Editor, caret: Caret?, dataContext: DataContext) {
+        val project = editor.project
+        if (project == null) return
+
+        val psiDocMgr = PsiDocumentManager.getInstance(project)
+        val file = psiDocMgr.getPsiFile(editor.document)
+        if (file == null || file.language != LyngLanguage) {
+            pasteAsIs(editor)
+            return
+        }
+
+        val settings = LyngFormatterSettings.getInstance(project)
+        if (!settings.reindentPastedBlocks) {
+            pasteAsIs(editor)
+            return
+        }
+
+        val text = CopyPasteManager.getInstance().getContents<String>(DataFlavor.stringFlavor)
+        if (text == null) {
+            pasteAsIs(editor)
+            return
+        }
+
+        val caretModel = editor.caretModel
+        val effectiveCaret = caret ?: caretModel.currentCaret
+        val doc = editor.document
+        PsiDocumentManager.getInstance(project).commitDocument(doc)
+
+        // Paste the text as-is first, then compute the inserted range and reindent that slice
+        val options = CodeStyle.getIndentOptions(project, doc)
+        val cfg = LyngFormatConfig(
+            indentSize = options.INDENT_SIZE.coerceAtLeast(1),
+            useTabs = options.USE_TAB_CHARACTER,
+            continuationIndentSize = options.CONTINUATION_INDENT_SIZE.coerceAtLeast(options.INDENT_SIZE.coerceAtLeast(1)),
+        )
+
+        // Replace selection (if any) or insert at caret with original clipboard text
+        val selModel = editor.selectionModel
+        val replaceStart = if (selModel.hasSelection()) selModel.selectionStart else effectiveCaret.offset
+        val replaceEnd = if (selModel.hasSelection()) selModel.selectionEnd else effectiveCaret.offset
+
+        WriteCommandAction.runWriteCommandAction(project) {
+            log.info("[LyngPaste] handler invoked for Lyng file; setting ON=${settings.reindentPastedBlocks}")
+            // Step 1: paste as-is
+            val beforeLen = doc.textLength
+            doc.replaceString(replaceStart, replaceEnd, text)
+            psiDocMgr.commitDocument(doc)
+
+            // Step 2: compute the freshly inserted range robustly (account for line-separator normalization)
+            val insertedStart = replaceStart
+            val delta = doc.textLength - beforeLen + (replaceEnd - replaceStart)
+            val insertedEndExclusive = (insertedStart + delta).coerceIn(insertedStart, doc.textLength)
+
+            // Expand to full lines to let the formatter compute proper base/closing alignment
+            val lineStart = run {
+                var i = (insertedStart - 1).coerceAtLeast(0)
+                while (i >= 0 && doc.charsSequence[i] != '\n') i--
+                i + 1
+            }
+            var lineEndInclusive = run {
+                var i = insertedEndExclusive
+                val seq = doc.charsSequence
+                while (i < seq.length && seq[i] != '\n') i++
+                // include trailing newline if present
+                if (i < seq.length && seq[i] == '\n') i + 1 else i
+            }
+
+            // If the next non-whitespace char right after the insertion is a closing brace '}',
+            // include that brace line into the formatting slice for better block alignment.
+            run {
+                val seq = doc.charsSequence
+                var j = insertedEndExclusive
+                while (j < seq.length && (seq[j] == ' ' || seq[j] == '\t' || seq[j] == '\n' || seq[j] == '\r')) j++
+                if (j < seq.length && seq[j] == '}') {
+                    var k = j
+                    while (k < seq.length && seq[k] != '\n') k++
+                    lineEndInclusive = if (k < seq.length && seq[k] == '\n') k + 1 else k
+                }
+            }
+
+            val fullTextBefore = doc.text
+            val expandedRange = (lineStart until lineEndInclusive)
+            log.info("[LyngPaste] inserted=[$insertedStart,$insertedEndExclusive) expanded=[$lineStart,$lineEndInclusive)")
+            val updatedFull = LyngFormatter.reindentRange(
+                fullTextBefore,
+                expandedRange,
+                cfg,
+                preserveBaseIndent = true,
+                baseIndentFrom = insertedStart
+            )
+
+            if (updatedFull != fullTextBefore) {
+                val delta = updatedFull.length - fullTextBefore.length
+                doc.replaceString(0, doc.textLength, updatedFull)
+                psiDocMgr.commitDocument(doc)
+                caretModel.moveToOffset((insertedEndExclusive + delta).coerceIn(0, doc.textLength))
+                log.info("[LyngPaste] applied reindent to expanded range")
+            } else {
+                // No changes after reindent — just move caret to end of the inserted text
+                caretModel.moveToOffset(insertedEndExclusive)
+                log.info("[LyngPaste] no changes after reindent")
+            }
+            selModel.removeSelection()
+        }
+    }
+
+    private fun pasteAsIs(editor: Editor) {
+        val text = CopyPasteManager.getInstance().getContents<String>(DataFlavor.stringFlavor) ?: return
+        pasteText(editor, text)
+    }
+
+    private fun pasteText(editor: Editor, text: String) {
+        val project = editor.project ?: return
+        val doc = editor.document
+        val caretModel = editor.caretModel
+        val selModel = editor.selectionModel
+        WriteCommandAction.runWriteCommandAction(project) {
+            val replaceStart = if (selModel.hasSelection()) selModel.selectionStart else caretModel.offset
+            val replaceEnd = if (selModel.hasSelection()) selModel.selectionEnd else caretModel.offset
+            doc.replaceString(replaceStart, replaceEnd, text)
+            PsiDocumentManager.getInstance(project).commitDocument(doc)
+            caretModel.moveToOffset(replaceStart + text.length)
+            selModel.removeSelection()
+        }
+    }
+
+    // no longer used
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngPastePreProcessor.kt

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+import com.intellij.application.options.CodeStyle
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.project.Project
+import com.intellij.psi.PsiDocumentManager
+import com.intellij.psi.PsiFile
+import net.sergeych.lyng.format.LyngFormatConfig
+import net.sergeych.lyng.format.LyngFormatter
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.settings.LyngFormatterSettings
+
+/**
+ * Helper for preparing reindented pasted text. EP wiring is deferred until API
+ * signature is finalized for the target IDE build.
+ */
+object LyngPastePreProcessor {
+    fun reindentForPaste(
+        project: Project,
+        editor: Editor,
+        file: PsiFile,
+        text: String
+    ): String {
+        if (file.language != LyngLanguage) return text
+        val settings = LyngFormatterSettings.getInstance(project)
+        if (!settings.reindentPastedBlocks) return text
+
+        val doc = editor.document
+        PsiDocumentManager.getInstance(project).commitDocument(doc)
+        val options = CodeStyle.getIndentOptions(project, doc)
+        val cfg = LyngFormatConfig(
+            indentSize = options.INDENT_SIZE.coerceAtLeast(1),
+            useTabs = options.USE_TAB_CHARACTER,
+            continuationIndentSize = options.CONTINUATION_INDENT_SIZE.coerceAtLeast(options.INDENT_SIZE.coerceAtLeast(1)),
+        )
+
+        // Only apply smart paste when caret is in leading whitespace position of its line
+        val caret = editor.caretModel.currentCaret
+        val line = doc.getLineNumber(caret.offset.coerceIn(0, doc.textLength))
+        if (line < 0 || line >= doc.lineCount) return text
+        val lineStart = doc.getLineStartOffset(line)
+        val firstNonWs = firstNonWhitespace(doc, lineStart, doc.getLineEndOffset(line))
+        if (caret.offset > firstNonWs) return text
+
+        val baseIndent = doc.charsSequence.subSequence(lineStart, caret.offset).toString()
+        val reindented = LyngFormatter.reindent(text, cfg)
+        // Prefix each non-empty line with base indent to preserve surrounding indentation
+        val lines = reindented.split('\n')
+        val sb = StringBuilder(reindented.length + lines.size * baseIndent.length)
+        for ((idx, ln) in lines.withIndex()) {
+            if (ln.isNotEmpty()) sb.append(baseIndent).append(ln) else sb.append(ln)
+            if (idx < lines.lastIndex) sb.append('\n')
+        }
+        return sb.toString()
+    }
+
+    private fun firstNonWhitespace(doc: com.intellij.openapi.editor.Document, from: Int, to: Int): Int {
+        val seq = doc.charsSequence
+        var i = from
+        while (i < to) {
+            val ch = seq[i]
+            if (ch != ' ' && ch != '\t') break
+            i++
+        }
+        return i
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngSmartPastePreProcessor.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.project.Project
+import com.intellij.psi.PsiDocumentManager
+import com.intellij.psi.PsiFile
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.settings.LyngFormatterSettings
+
+/**
+ * Smart Paste helper for Lyng. Not registered as EP yet to keep build stable across IDE SDKs.
+ * Use `processOnPasteIfEnabled` from a CopyPastePreProcessor adapter once API signature is finalized.
+ */
+object LyngSmartPastePreProcessorHelper {
+    fun processOnPasteIfEnabled(project: Project, file: PsiFile, editor: Editor, text: String): String {
+        if (file.language != LyngLanguage) return text
+        val settings = LyngFormatterSettings.getInstance(project)
+        if (!settings.reindentPastedBlocks) return text
+        PsiDocumentManager.getInstance(project).commitDocument(editor.document)
+        return LyngPastePreProcessor.reindentForPaste(project, editor, file, text)
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/editor/LyngTypedHandler.kt

@@ -0,0 +1,138 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.editor
+
+import com.intellij.application.options.CodeStyle
+import com.intellij.codeInsight.editorActions.TypedHandlerDelegate
+import com.intellij.openapi.command.WriteCommandAction
+import com.intellij.openapi.diagnostic.Logger
+import com.intellij.openapi.editor.Document
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiDocumentManager
+import com.intellij.psi.PsiFile
+import com.intellij.psi.codeStyle.CodeStyleManager
+import net.sergeych.lyng.format.BraceUtils
+import net.sergeych.lyng.format.LyngFormatConfig
+import net.sergeych.lyng.format.LyngFormatter
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.settings.LyngFormatterSettings
+import net.sergeych.lyng.idea.util.FormattingUtils.computeDesiredIndent
+import net.sergeych.lyng.idea.util.FormattingUtils.findFirstNonWs
+
+class LyngTypedHandler : TypedHandlerDelegate() {
+    private val log = Logger.getInstance(LyngTypedHandler::class.java)
+
+    override fun charTyped(c: Char, project: Project, editor: Editor, file: PsiFile): Result {
+        if (file.language != LyngLanguage) return Result.CONTINUE
+        
+        if (c == '}') {
+            val doc = editor.document
+            PsiDocumentManager.getInstance(project).commitDocument(doc)
+
+            val offset = editor.caretModel.offset
+            val line = doc.getLineNumber((offset - 1).coerceAtLeast(0))
+            if (line < 0) return Result.CONTINUE
+
+            val rawLine = doc.getLineText(line)
+            val code = rawLine.substringBefore("//").trim()
+            if (code == "}") {
+                val settings = LyngFormatterSettings.getInstance(project)
+                if (settings.reindentClosedBlockOnEnter) {
+                    reindentClosedBlockAroundBrace(project, file, doc, line)
+                }
+                // After block reindent, adjust line indent to what platform thinks (no-op in many cases)
+                val lineStart = doc.getLineStartOffset(line)
+                if (file.context == null) {
+                    try {
+                        CodeStyleManager.getInstance(project).adjustLineIndent(file, lineStart)
+                    } catch (e: Exception) {
+                        log.warn("Failed to adjust line indent for current line: ${e.message}")
+                    }
+                }
+            }
+        } else if (c == '/') {
+            val doc = editor.document
+            val offset = editor.caretModel.offset
+            if (offset >= 2 && doc.getText(TextRange(offset - 2, offset)) == "*/") {
+                PsiDocumentManager.getInstance(project).commitDocument(doc)
+                val line = doc.getLineNumber(offset - 1)
+                val lineStart = doc.getLineStartOffset(line)
+                if (file.context == null) {
+                    try {
+                        CodeStyleManager.getInstance(project).adjustLineIndent(file, lineStart)
+                    } catch (e: Exception) {
+                        log.warn("Failed to adjust line indent for comment: ${e.message}")
+                    }
+                }
+
+                // Manual application fallback
+                val desired = computeDesiredIndent(project, doc, line)
+                val lineEnd = doc.getLineEndOffset(line)
+                val firstNonWs = findFirstNonWs(doc, lineStart, lineEnd)
+                val currentIndentLen = firstNonWs - lineStart
+                if (doc.getText(TextRange(lineStart, lineStart + currentIndentLen)) != desired) {
+                    WriteCommandAction.runWriteCommandAction(project) {
+                        doc.replaceString(lineStart, lineStart + currentIndentLen, desired)
+                    }
+                }
+            }
+        }
+        return Result.CONTINUE
+    }
+
+    private fun reindentClosedBlockAroundBrace(project: Project, file: PsiFile, doc: Document, braceLine: Int) {
+        val braceLineStart = doc.getLineStartOffset(braceLine)
+        val braceLineEnd = doc.getLineEndOffset(braceLine)
+        val rawBraceLine = doc.getText(TextRange(braceLineStart, braceLineEnd))
+        val codeBraceLine = rawBraceLine.substringBefore("//")
+        val closeRel = codeBraceLine.lastIndexOf('}')
+        if (closeRel < 0) return
+        val closeAbs = braceLineStart + closeRel
+
+        val blockRange = BraceUtils.findEnclosingBlockRange(
+            doc.charsSequence,
+            closeAbs,
+            includeTrailingNewline = true
+        ) ?: return
+
+        val options = CodeStyle.getIndentOptions(project, doc)
+        val cfg = LyngFormatConfig(
+            indentSize = options.INDENT_SIZE.coerceAtLeast(1),
+            useTabs = options.USE_TAB_CHARACTER,
+            continuationIndentSize = options.CONTINUATION_INDENT_SIZE.coerceAtLeast(options.INDENT_SIZE.coerceAtLeast(1)),
+        )
+
+        val whole = doc.text
+        val updated = LyngFormatter.reindentRange(whole, blockRange, cfg, preserveBaseIndent = true)
+        if (updated != whole) {
+            WriteCommandAction.runWriteCommandAction(project) {
+                doc.replaceString(0, doc.textLength, updated)
+            }
+            PsiDocumentManager.getInstance(project).commitDocument(doc)
+            if (log.isDebugEnabled) log.debug("[LyngTyped] reindented closed block range=$blockRange")
+        }
+    }
+
+    private fun Document.getLineText(line: Int): String {
+        if (line < 0 || line >= lineCount) return ""
+        val start = getLineStartOffset(line)
+        val end = getLineEndOffset(line)
+        return getText(TextRange(start, end))
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/format/LyngFormattingModelBuilder.kt

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.format
+
+import com.intellij.formatting.*
+import com.intellij.lang.ASTNode
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiElement
+import com.intellij.psi.PsiFile
+import com.intellij.psi.codeStyle.CodeStyleSettings
+
+/**
+ * Minimal formatting model: enables Reformat Code to at least re-apply indentation via LineIndentProvider
+ * and normalize whitespace. We don’t implement a full PSI-based tree yet; this block treats the whole file
+ * as a single formatting region and lets platform query line indents.
+ */
+class LyngFormattingModelBuilder : FormattingModelBuilder {
+    override fun createModel(element: PsiElement, settings: CodeStyleSettings): FormattingModel {
+        val file = element.containingFile
+        val rootBlock = LineBlocksRootBlock(file, settings)
+        return FormattingModelProvider.createFormattingModelForPsiFile(file, rootBlock, settings)
+    }
+
+    override fun getRangeAffectingIndent(file: PsiFile, offset: Int, elementAtOffset: ASTNode?): TextRange? = null
+}
+
+private class LineBlocksRootBlock(
+    private val file: PsiFile,
+    private val settings: CodeStyleSettings
+) : Block {
+    override fun getTextRange(): TextRange = TextRange(0, file.textLength)
+
+    override fun getSubBlocks(): List<Block> = emptyList()
+
+    override fun getWrap(): Wrap? = null
+    override fun getIndent(): Indent? = Indent.getNoneIndent()
+    override fun getAlignment(): Alignment? = null
+    override fun getSpacing(child1: Block?, child2: Block): Spacing? = null
+    override fun getChildAttributes(newChildIndex: Int): ChildAttributes = ChildAttributes(Indent.getNoneIndent(), null)
+    override fun isIncomplete(): Boolean = false
+    override fun isLeaf(): Boolean = true
+}
+
+// Intentionally no sub-blocks/spacing: indentation is handled by PreFormatProcessor + LineIndentProvider

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/format/LyngLineIndentProvider.kt

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.format
+
+import com.intellij.application.options.CodeStyle
+import com.intellij.lang.Language
+import com.intellij.openapi.editor.Document
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiDocumentManager
+import com.intellij.psi.codeStyle.CommonCodeStyleSettings.IndentOptions
+import com.intellij.psi.codeStyle.lineIndent.LineIndentProvider
+import net.sergeych.lyng.idea.LyngLanguage
+import net.sergeych.lyng.idea.util.FormattingUtils
+
+/**
+ * Lightweight indentation provider for Lyng.
+ *
+ * Rules (heuristic, text-based):
+ * - New lines after an opening brace/paren increase indent level.
+ * - Lines starting with a closing brace/paren decrease indent level by one.
+ * - Keeps previous non-empty line's indent as baseline otherwise.
+ */
+class LyngLineIndentProvider : LineIndentProvider {
+    override fun getLineIndent(project: com.intellij.openapi.project.Project, editor: Editor, language: Language?, offset: Int): String? {
+        if (language != null && language != LyngLanguage) return null
+        val doc = editor.document
+        PsiDocumentManager.getInstance(project).commitDocument(doc)
+
+        val options = CodeStyle.getIndentOptions(project, doc)
+
+        val line = doc.getLineNumberSafe(offset)
+        return FormattingUtils.computeDesiredIndent(project, doc, line)
+    }
+
+    override fun isSuitableFor(language: Language?): Boolean = language == null || language == LyngLanguage
+
+    private fun Document.getLineNumberSafe(offset: Int): Int =
+        getLineNumber(offset.coerceIn(0, textLength))
+
+    private fun Document.getLineText(line: Int): String {
+        if (line < 0 || line >= lineCount) return ""
+        val start = getLineStartOffset(line)
+        val end = getLineEndOffset(line)
+        return getText(TextRange(start, end))
+    }
+
+    private fun indentUnit(options: IndentOptions): String =
+        if (options.USE_TAB_CHARACTER) "\t" else " ".repeat(options.INDENT_SIZE.coerceAtLeast(1))
+
+    private fun indentOfLine(doc: Document, line: Int): String {
+        val s = doc.getLineText(line)
+        val i = s.indexOfFirst { !it.isWhitespace() }
+        return if (i <= 0) s.takeWhile { it == ' ' || it == '\t' } else s.substring(0, i)
+    }
+
+    private fun countIndentUnits(indent: String, options: IndentOptions): Int {
+        if (indent.isEmpty()) return 0
+        if (options.USE_TAB_CHARACTER) return indent.count { it == '\t' }
+        val size = options.INDENT_SIZE.coerceAtLeast(1)
+        var spaces = 0
+        for (ch in indent) spaces += if (ch == '\t') size else 1
+        return spaces / size
+    }
+
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/format/LyngPostFormatProcessor.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.format
+
+// Placeholder: we planned a post-format processor fallback, but the 2024.3 platform
+// does not expose the older PostFormatProcessor API in our current dependency set.
+// Reformat Code will use the registered lang.formatter + LineIndentProvider.
+internal object LyngPostFormatProcessorPlaceholder

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/format/LyngPreFormatProcessor.kt

@@ -0,0 +1,208 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.format
+
+import com.intellij.application.options.CodeStyle
+import com.intellij.lang.ASTNode
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.codeStyle.CodeStyleManager
+import com.intellij.psi.impl.source.codeStyle.PreFormatProcessor
+import net.sergeych.lyng.format.LyngFormatConfig
+import net.sergeych.lyng.format.LyngFormatter
+import net.sergeych.lyng.idea.LyngLanguage
+
+/**
+ * Idempotent indentation fixer executed by Reformat Code before formatting.
+ * It walks all lines in the affected range and applies exact indentation using
+ * CodeStyleManager.adjustLineIndent(), which delegates to our LineIndentProvider.
+ */
+class LyngPreFormatProcessor : PreFormatProcessor {
+    override fun process(element: ASTNode, range: TextRange): TextRange {
+        val file = element.psi?.containingFile ?: return range
+        if (file.language != LyngLanguage) return range
+        val project: Project = file.project
+        val doc = file.viewProvider.document ?: return range
+        val psiDoc = com.intellij.psi.PsiDocumentManager.getInstance(project)
+        val options = CodeStyle.getIndentOptions(project, doc)
+
+        val settings = net.sergeych.lyng.idea.settings.LyngFormatterSettings.getInstance(project)
+        // When both spacing and wrapping are OFF, still fix indentation for the whole file to
+        // guarantee visible changes on Reformat Code.
+        val runFullFileIndent = !settings.enableSpacing && !settings.enableWrapping
+        var modified = false
+
+        val docW = doc as? com.intellij.injected.editor.DocumentWindow
+        // The host range of the entire injected fragment (or the whole file if not injected).
+        fun currentHostRange(): TextRange = if (docW != null) {
+            TextRange(docW.injectedToHost(0), docW.injectedToHost(doc.textLength))
+        } else {
+            file.textRange
+        }
+
+        // The range in 'doc' coordinate system (local 0..len for injections, host offsets for normal files).
+        fun currentLocalRange(): TextRange = if (docW != null) {
+            TextRange(0, doc.textLength)
+        } else {
+            file.textRange
+        }
+
+        val clr = currentLocalRange()
+        val chr = currentHostRange()
+
+        // Convert the input range to the coordinate system of 'doc'
+        var workingRangeLocal: TextRange = if (docW != null) {
+            val hostIntersection = range.intersection(chr)
+            if (hostIntersection != null) {
+                try {
+                    val start = docW.hostToInjected(hostIntersection.startOffset)
+                    val end = docW.hostToInjected(hostIntersection.endOffset)
+                    TextRange(start.coerceAtMost(end), end.coerceAtLeast(start))
+                } catch (e: Exception) {
+                    clr
+                }
+            } else {
+                range.intersection(clr) ?: clr
+            }
+        } else {
+            range.intersection(clr) ?: clr
+        }
+
+        val startLine = if (runFullFileIndent) {
+            doc.getLineNumber(currentLocalRange().startOffset)
+        } else {
+            doc.getLineNumber(workingRangeLocal.startOffset)
+        }
+        val endLine = if (runFullFileIndent) {
+            if (clr.endOffset <= clr.startOffset) doc.getLineNumber(clr.startOffset)
+            else doc.getLineNumber(clr.endOffset)
+        } else {
+            doc.getLineNumber(workingRangeLocal.endOffset.coerceAtMost(doc.textLength))
+        }
+
+        fun codePart(s: String): String {
+            val idx = s.indexOf("//")
+            return if (idx >= 0) s.substring(0, idx) else s
+        }
+
+        // Pre-scan to compute balances up to startLine.
+        val fragmentStartLine = doc.getLineNumber(currentLocalRange().startOffset)
+        var blockLevel = 0
+        var parenBalance = 0
+        var bracketBalance = 0
+        for (ln in fragmentStartLine until startLine) {
+            val text = doc.getText(TextRange(doc.getLineStartOffset(ln), doc.getLineEndOffset(ln)))
+            for (ch in codePart(text)) when (ch) {
+                '{' -> blockLevel++
+                '}' -> if (blockLevel > 0) blockLevel--
+                '(' -> parenBalance++
+                ')' -> if (parenBalance > 0) parenBalance--
+                '[' -> bracketBalance++
+                ']' -> if (bracketBalance > 0) bracketBalance--
+            }
+        }
+
+        // Re-indent each line deterministically (idempotent). We avoid any content
+        // rewriting here to prevent long-running passes or re-entrant formatting.
+        for (line in startLine..endLine) {
+            val lineStart = doc.getLineStartOffset(line)
+            // adjustLineIndent delegates to our LineIndentProvider which computes
+            // indentation from scratch; this is safe and idempotent
+            if (file.context == null) {
+                try {
+                    CodeStyleManager.getInstance(project).adjustLineIndent(file, lineStart)
+                } catch (e: Exception) {
+                    // Log as debug because this can be called many times during reformat
+                }
+            }
+
+            // After indentation, update block/paren/bracket balances using the current line text
+            val lineEnd = doc.getLineEndOffset(line)
+            val text = doc.getText(TextRange(lineStart, lineEnd))
+            val code = codePart(text)
+            for (ch in code) when (ch) {
+                '{' -> blockLevel++
+                '}' -> if (blockLevel > 0) blockLevel--
+                '(' -> parenBalance++
+                ')' -> if (parenBalance > 0) parenBalance--
+                '[' -> bracketBalance++
+                ']' -> if (bracketBalance > 0) bracketBalance--
+            }
+        }
+        // If both spacing and wrapping are OFF, explicitly reindent the text using core formatter to
+        // guarantee indentation is fixed even when the platform doesn't rewrite whitespace by itself.
+        if (!settings.enableSpacing && !settings.enableWrapping) {
+            val cfg = LyngFormatConfig(
+                indentSize = options.INDENT_SIZE.coerceAtLeast(1),
+                useTabs = options.USE_TAB_CHARACTER,
+                continuationIndentSize = options.CONTINUATION_INDENT_SIZE.coerceAtLeast(options.INDENT_SIZE.coerceAtLeast(1)),
+            )
+            val r = if (runFullFileIndent) currentLocalRange() else workingRangeLocal.intersection(currentLocalRange()) ?: currentLocalRange()
+            val text = doc.getText(r)
+            val formatted = LyngFormatter.reindent(text, cfg)
+            if (formatted != text) {
+                doc.replaceString(r.startOffset, r.endOffset, formatted)
+                modified = true
+                psiDoc.commitDocument(doc)
+                workingRangeLocal = currentLocalRange()
+            }
+        }
+
+        // Optionally apply spacing using the core formatter if enabled in settings (wrapping stays off)
+        if (settings.enableSpacing) {
+            val cfg = LyngFormatConfig(
+                indentSize = options.INDENT_SIZE.coerceAtLeast(1),
+                useTabs = options.USE_TAB_CHARACTER,
+                continuationIndentSize = options.CONTINUATION_INDENT_SIZE.coerceAtLeast(options.INDENT_SIZE.coerceAtLeast(1)),
+                applySpacing = true,
+                applyWrapping = false,
+            )
+            val r = if (runFullFileIndent) currentLocalRange() else workingRangeLocal.intersection(currentLocalRange()) ?: currentLocalRange()
+            val text = doc.getText(r)
+            val formatted = LyngFormatter.format(text, cfg)
+            if (formatted != text) {
+                doc.replaceString(r.startOffset, r.endOffset, formatted)
+                modified = true
+                psiDoc.commitDocument(doc)
+                workingRangeLocal = currentLocalRange()
+            }
+        }
+        // Optionally apply wrapping (after spacing) when enabled
+        if (settings.enableWrapping) {
+            val cfg = LyngFormatConfig(
+                indentSize = options.INDENT_SIZE.coerceAtLeast(1),
+                useTabs = options.USE_TAB_CHARACTER,
+                continuationIndentSize = options.CONTINUATION_INDENT_SIZE.coerceAtLeast(options.INDENT_SIZE.coerceAtLeast(1)),
+                applySpacing = settings.enableSpacing,
+                applyWrapping = true,
+            )
+            val r = if (runFullFileIndent) currentLocalRange() else workingRangeLocal.intersection(currentLocalRange()) ?: currentLocalRange()
+            val text = doc.getText(r)
+            val wrapped = LyngFormatter.format(text, cfg)
+            if (wrapped != text) {
+                doc.replaceString(r.startOffset, r.endOffset, wrapped)
+                modified = true
+                psiDoc.commitDocument(doc)
+                workingRangeLocal = currentLocalRange()
+            }
+        }
+        // Return a safe range for the formatter to continue with, preventing stale offsets.
+        // For injected files, ALWAYS return a range in local coordinates.
+        val finalRange = currentLocalRange()
+        return if (modified) finalRange else (range.intersection(finalRange) ?: finalRange)
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/grazie/LyngTextExtractor.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+package net.sergeych.lyng.idea.grazie
+
+import com.intellij.grazie.text.TextContent
+import com.intellij.grazie.text.TextContent.TextDomain
+import com.intellij.grazie.text.TextExtractor
+import com.intellij.psi.PsiElement
+import net.sergeych.lyng.idea.highlight.LyngTokenTypes
+import net.sergeych.lyng.idea.psi.LyngElementTypes
+
+/**
+ * Simplified TextExtractor for Lyng.
+ * Designates areas for Natural Languages (Grazie) to check.
+ */
+class LyngTextExtractor : TextExtractor() {
+    override fun buildTextContent(element: PsiElement, allowedDomains: Set<TextDomain>): TextContent? {
+        val type = element.node?.elementType ?: return null
+        
+        val domain = when (type) {
+            LyngTokenTypes.LINE_COMMENT, LyngTokenTypes.BLOCK_COMMENT -> TextDomain.COMMENTS
+            LyngTokenTypes.STRING -> TextDomain.LITERALS
+            LyngElementTypes.NAME_IDENTIFIER,
+            LyngElementTypes.PARAMETER_NAME,
+            LyngElementTypes.ENUM_CONSTANT_NAME -> TextDomain.COMMENTS
+            else -> return null
+        }
+        
+        if (!allowedDomains.contains(domain)) return null
+        
+        return TextContent.psiFragment(domain, element)
+    }
+}

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/highlight/LyngColorSettingsPage.kt

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyng.idea.highlight
+
+import com.intellij.openapi.editor.colors.TextAttributesKey
+import com.intellij.openapi.fileTypes.SyntaxHighlighter
+import com.intellij.openapi.options.colors.AttributesDescriptor
+import com.intellij.openapi.options.colors.ColorDescriptor
+import com.intellij.openapi.options.colors.ColorSettingsPage
+import javax.swing.Icon
+
+class LyngColorSettingsPage : ColorSettingsPage {
+    override fun getDisplayName(): String = "Lyng"
+
+    override fun getIcon(): Icon? = null
+
+    override fun getHighlighter(): SyntaxHighlighter = LyngSyntaxHighlighter()
+
+    override fun getDemoText(): String = """
+        // Lyng demo
+        import lyng.stdlib as std
+        
+        class Sample {
+          fun greet(name: String): String {
+            val message = "Hello, " + name
+            return message
+          }
+        }
+        
+        var counter = 0
+        outer@ while (counter < 10) {
+          if (counter == 5) return@outer
+          counter = counter + 1
+        }
+    """.trimIndent()
+
+    override fun getAdditionalHighlightingTagToDescriptorMap(): MutableMap<String, TextAttributesKey> = mutableMapOf(
+        "label" to LyngHighlighterColors.LABEL
+    )
+
+    override fun getAttributeDescriptors(): Array<AttributesDescriptor> = arrayOf(
+        AttributesDescriptor("Keyword", LyngHighlighterColors.KEYWORD),
+        AttributesDescriptor("String", LyngHighlighterColors.STRING),
+        AttributesDescriptor("Number", LyngHighlighterColors.NUMBER),
+        AttributesDescriptor("Line comment", LyngHighlighterColors.LINE_COMMENT),
+        AttributesDescriptor("Block comment", LyngHighlighterColors.BLOCK_COMMENT),
+        AttributesDescriptor("Identifier", LyngHighlighterColors.IDENTIFIER),
+        AttributesDescriptor("Punctuation", LyngHighlighterColors.PUNCT),
+        // Semantic
+        AttributesDescriptor("Annotation (semantic)", LyngHighlighterColors.ANNOTATION),
+        AttributesDescriptor("Label (semantic)", LyngHighlighterColors.LABEL),
+        AttributesDescriptor("Variable (semantic)", LyngHighlighterColors.VARIABLE),
+        AttributesDescriptor("Value (semantic)", LyngHighlighterColors.VALUE),
+        AttributesDescriptor("Function (semantic)", LyngHighlighterColors.FUNCTION),
+        AttributesDescriptor("Function declaration (semantic)", LyngHighlighterColors.FUNCTION_DECLARATION),
+        AttributesDescriptor("Type (semantic)", LyngHighlighterColors.TYPE),
+        AttributesDescriptor("Namespace (semantic)", LyngHighlighterColors.NAMESPACE),
+        AttributesDescriptor("Parameter (semantic)", LyngHighlighterColors.PARAMETER),
+        AttributesDescriptor("Enum constant (semantic)", LyngHighlighterColors.ENUM_CONSTANT),
+    )
+
+    override fun getColorDescriptors(): Array<ColorDescriptor> = ColorDescriptor.EMPTY_ARRAY
+}