Add decimal module and operator interop registry

docs/Decimal.md

@@ -0,0 +1,250 @@
+# Decimal (`lyng.decimal`)
+
+`lyng.decimal` adds an arbitrary-precision decimal type to Lyng as a normal library module.
+
+Import it when you need decimal arithmetic that should not inherit `Real`'s binary floating-point behavior:
+
+```lyng
+import lyng.decimal
+```
+
+## What `BigDecimal` Is For
+
+Use `BigDecimal` when values are fundamentally decimal:
+
+- money
+- human-entered quantities
+- exact decimal text
+- predictable decimal rounding
+- user-facing formatting and tests
+
+Do not use it just because a number has a fractional part. `Real` is still the right type for ordinary double-precision numeric work.
+
+## Creating Decimal Values
+
+There are three supported conversions:
+
+```lyng
+import lyng.decimal
+
+val a = 1.d
+val b = 2.2.d
+val c = "2.2".d
+
+assertEquals("1", a.toStringExpanded())
+assertEquals("2.2", b.toStringExpanded())
+assertEquals("2.2", c.toStringExpanded())
+```
+
+The three forms mean different things:
+
+- `1.d`: convert `Int -> BigDecimal`
+- `2.2.d`: convert `Real -> BigDecimal`
+- `"2.2".d`: parse exact decimal text
+
+That distinction is intentional.
+
+### `Real.d` vs `"..." .d`
+
+`Real.d` preserves the current `Real` value. It does not pretend the source code was exact decimal text.
+
+```lyng
+import lyng.decimal
+
+assertEquals("0.30000000000000004", (0.1 + 0.2).d.toStringExpanded())
+assertEquals("0.3", "0.3".d.toStringExpanded())
+```
+
+This follows the "minimal confusion" rule:
+
+- if you start from a `Real`, you get a decimal representation of that `Real`
+- if you want exact decimal source text, use a `String`
+
+## Factory Functions
+
+The explicit factory methods are:
+
+```lyng
+import lyng.decimal
+
+BigDecimal.fromInt(10)
+BigDecimal.fromReal(2.5)
+BigDecimal.fromString("12.34")
+```
+
+These are equivalent to the conversion-property forms, but sometimes clearer in APIs or generated code.
+
+## Core Operations
+
+`BigDecimal` supports:
+
+- `+`
+- `-`
+- `*`
+- `/`
+- `%`
+- unary `-`
+- comparison operators
+- equality operators
+
+Examples:
+
+```lyng
+import lyng.decimal
+
+assertEquals("3.75", ("1.5".d + "2.25".d).toStringExpanded())
+assertEquals("1.25", ("2.5".d - "1.25".d).toStringExpanded())
+assertEquals("3.0", ("1.5".d * 2.d).toStringExpanded())
+assertEquals("0.5", (1.d / 2.d).toStringExpanded())
+assert("2.0".d > "1.5".d)
+assert("2.0".d == 2.d)
+```
+
+## Interoperability With `Int` and `Real`
+
+The decimal module registers mixed-operand operator bridges so both sides read naturally:
+
+```lyng
+import lyng.decimal
+
+assertEquals(3.d, 1 + 2.d)
+assertEquals(3.d, 2.d + 1)
+assertEquals(1.5.d, 1.d + 0.5)
+assertEquals(1.5.d, 0.5 + 1.d)
+assert(2 == 2.d)
+assert(3 > 2.d)
+```
+
+Without this registration mechanism, only the cases directly implemented on the left-hand class would work. The bridge fills the gap for expressions such as `Int + BigDecimal` and `Real + BigDecimal`.
+
+See [OperatorInterop.md](OperatorInterop.md) for the generic mechanism behind that.
+
+## String Representation
+
+Use `toStringExpanded()` when you want plain decimal output without scientific notation:
+
+```lyng
+import lyng.decimal
+
+assertEquals("12.34", "12.34".d.toStringExpanded())
+```
+
+This is the recommended representation for:
+
+- tests
+- user-visible diagnostics
+- decimal formatting checks
+
+## Conversions Back To Built-ins
+
+```lyng
+import lyng.decimal
+
+assertEquals(2, "2.9".d.toInt())
+assertEquals(2.9, "2.9".d.toReal())
+```
+
+Use `toReal()` only when you are willing to return to binary floating-point semantics.
+
+## Division Context
+
+Division is the operation where precision and rounding matter most.
+
+By default, decimal division uses:
+
+- precision: `34` significant digits
+- rounding: `HalfEven`
+
+Example:
+
+```lyng
+import lyng.decimal
+
+assertEquals("0.3333333333333333333333333333333333", (1.d / 3.d).toStringExpanded())
+assertEquals("0.6666666666666666666666666666666667", ("2".d / 3.d).toStringExpanded())
+```
+
+## `withDecimalContext(...)`
+
+Use `withDecimalContext(...)` to override decimal division rules inside a block:
+
+```lyng
+import lyng.decimal
+
+assertEquals(
+    "0.3333333333",
+    withDecimalContext(10) { (1.d / 3.d).toStringExpanded() }
+)
+```
+
+You can also pass an explicit context object:
+
+```lyng
+import lyng.decimal
+
+val ctx = DecimalContext(6, DecimalRounding.HalfAwayFromZero)
+assertEquals("0.666667", withDecimalContext(ctx) { ("2".d / 3.d).toStringExpanded() })
+```
+
+The context is dynamic and local to the block. After the block exits, the previous context is restored.
+
+## Rounding Modes
+
+Available rounding modes:
+
+- `HalfEven`
+- `HalfAwayFromZero`
+- `HalfTowardsZero`
+- `Ceiling`
+- `Floor`
+- `AwayFromZero`
+- `TowardsZero`
+
+Tie example at precision `2`:
+
+```lyng
+import lyng.decimal
+
+assertEquals("0.12", withDecimalContext(2, DecimalRounding.HalfEven) { (1.d / 8.d).toStringExpanded() })
+assertEquals("0.13", withDecimalContext(2, DecimalRounding.HalfAwayFromZero) { (1.d / 8.d).toStringExpanded() })
+assertEquals("0.12", withDecimalContext(2, DecimalRounding.HalfTowardsZero) { (1.d / 8.d).toStringExpanded() })
+assertEquals("0.13", withDecimalContext(2, DecimalRounding.Ceiling) { (1.d / 8.d).toStringExpanded() })
+assertEquals("0.12", withDecimalContext(2, DecimalRounding.Floor) { (1.d / 8.d).toStringExpanded() })
+```
+
+Negative values follow the same named policy in the obvious direction:
+
+```lyng
+import lyng.decimal
+
+assertEquals("-0.13", withDecimalContext(2, DecimalRounding.HalfAwayFromZero) { (-1.d / 8.d).toStringExpanded() })
+assertEquals("-0.12", withDecimalContext(2, DecimalRounding.HalfTowardsZero) { (-1.d / 8.d).toStringExpanded() })
+```
+
+## Recommended Usage Rules
+
+If you care about exact decimal source text:
+
+```lyng
+"12.34".d
+```
+
+If you intentionally convert an existing binary floating-point value:
+
+```lyng
+someReal.d
+```
+
+If you want local control over division:
+
+```lyng
+withDecimalContext(precision, rounding) { ... }
+```
+
+If you want custom mixed operators for your own type, follow the same pattern as Decimal and use the operator registry:
+
+- define the operators on your own class
+- choose a common class
+- register mixed operand bridges
+
+See [OperatorInterop.md](OperatorInterop.md).

docs/OperatorInterop.md

@@ -0,0 +1,309 @@
+# Operator Interop Registry
+
+`lyng.operators` provides a runtime registry for mixed-class binary operators.
+
+Import it when you want expressions such as:
+
+- `1 + MyType(...)`
+- `2 < MyType(...)`
+- `3 == MyType(...)`
+
+to work without modifying the built-in `Int` or `Real` classes.
+
+```lyng
+import lyng.operators
+```
+
+## Why This Exists
+
+If your class defines:
+
+```lyng
+class Amount(val value: Int) {
+    fun plus(other: Amount) = Amount(value + other.value)
+}
+```
+
+then:
+
+```lyng
+Amount(1) + Amount(2)
+```
+
+works, because the left operand already knows how to add another `Amount`.
+
+But:
+
+```lyng
+1 + Amount(2)
+```
+
+does not naturally work, because `Int` has not been rewritten to know about `Amount`.
+
+The operator interop registry solves exactly that problem.
+
+## Mental Model
+
+Registration describes a mixed pair:
+
+- left class `L`
+- right class `R`
+- common class `C`
+
+When Lyng sees `L op R`, it:
+
+1. converts `L -> C`
+2. converts `R -> C`
+3. evaluates the operator as `C op C`
+
+So the registry is a bridge, not a separate arithmetic engine.
+
+## API
+
+```lyng
+OperatorInterop.register(
+    leftClass,
+    rightClass,
+    commonClass,
+    operators,
+    leftToCommon,
+    rightToCommon
+)
+```
+
+Parameters:
+
+- `leftClass`: original left operand class
+- `rightClass`: original right operand class
+- `commonClass`: class that will actually execute the operator methods
+- `operators`: list of operators enabled for this pair
+- `leftToCommon`: conversion from left operand to common class
+- `rightToCommon`: conversion from right operand to common class
+
+## Supported Operators
+
+`BinaryOperator` values:
+
+- `Plus`
+- `Minus`
+- `Mul`
+- `Div`
+- `Mod`
+- `Compare`
+- `Equals`
+
+Meaning:
+
+- `Compare` enables `<`, `<=`, `>`, `>=`, and `<=>`
+- `Equals` enables `==` and `!=`
+
+## Minimal Working Example
+
+```lyng
+package test.decimalbox
+import lyng.operators
+
+class DecimalBox(val value: Int) {
+    fun plus(other: DecimalBox) = DecimalBox(value + other.value)
+    fun minus(other: DecimalBox) = DecimalBox(value - other.value)
+    fun mul(other: DecimalBox) = DecimalBox(value * other.value)
+    fun div(other: DecimalBox) = DecimalBox(value / other.value)
+    fun mod(other: DecimalBox) = DecimalBox(value % other.value)
+    fun compareTo(other: DecimalBox) = value <=> other.value
+}
+
+OperatorInterop.register(
+    Int,
+    DecimalBox,
+    DecimalBox,
+    [
+        BinaryOperator.Plus,
+        BinaryOperator.Minus,
+        BinaryOperator.Mul,
+        BinaryOperator.Div,
+        BinaryOperator.Mod,
+        BinaryOperator.Compare,
+        BinaryOperator.Equals
+    ],
+    { x: Int -> DecimalBox(x) },
+    { x: DecimalBox -> x }
+)
+```
+
+Then:
+
+```lyng
+import test.decimalbox
+
+assertEquals(DecimalBox(3), 1 + DecimalBox(2))
+assertEquals(DecimalBox(1), 3 - DecimalBox(2))
+assertEquals(DecimalBox(8), 4 * DecimalBox(2))
+assertEquals(DecimalBox(4), 8 / DecimalBox(2))
+assertEquals(DecimalBox(1), 7 % DecimalBox(2))
+assert(1 < DecimalBox(2))
+assert(2 <= DecimalBox(2))
+assert(3 > DecimalBox(2))
+assert(2 == DecimalBox(2))
+assert(2 != DecimalBox(3))
+```
+
+## How Decimal Uses It
+
+`lyng.decimal` uses this same mechanism so that:
+
+```lyng
+import lyng.decimal
+
+1 + 2.d
+0.5 + 1.d
+2 == 2.d
+3 > 2.d
+```
+
+work naturally even though `Int` and `Real` themselves were not edited to know `BigDecimal`.
+
+The shape is:
+
+- `leftClass = Int` or `Real`
+- `rightClass = BigDecimal`
+- `commonClass = BigDecimal`
+- convert built-ins into `BigDecimal`
+- leave `BigDecimal` values unchanged
+
+## Step-By-Step Pattern For Your Own Type
+
+### 1. Pick the common class
+
+Choose one class that will be the actual arithmetic domain.
+
+For numeric-like types, that is usually your own class:
+
+```lyng
+class Rational(...)
+```
+
+### 2. Implement operators on that class
+
+The common class should define the operations you plan to register.
+
+Example:
+
+```lyng
+class Rational(val num: Int, val den: Int) {
+    fun plus(other: Rational) = Rational(num * other.den + other.num * den, den * other.den)
+    fun minus(other: Rational) = Rational(num * other.den - other.num * den, den * other.den)
+    fun mul(other: Rational) = Rational(num * other.num, den * other.den)
+    fun div(other: Rational) = Rational(num * other.den, den * other.num)
+    fun compareTo(other: Rational) = (num * other.den) <=> (other.num * den)
+
+    static fun fromInt(value: Int) = Rational(value, 1)
+}
+```
+
+### 3. Register the mixed pair
+
+```lyng
+import lyng.operators
+
+OperatorInterop.register(
+    Int,
+    Rational,
+    Rational,
+    [
+        BinaryOperator.Plus,
+        BinaryOperator.Minus,
+        BinaryOperator.Mul,
+        BinaryOperator.Div,
+        BinaryOperator.Compare,
+        BinaryOperator.Equals
+    ],
+    { x: Int -> Rational.fromInt(x) },
+    { x: Rational -> x }
+)
+```
+
+### 4. Use it
+
+```lyng
+assertEquals(Rational(3, 2), 1 + Rational(1, 2))
+assert(Rational(3, 2) == Rational(3, 2))
+assert(2 > Rational(3, 2))
+```
+
+## Registering More Than One Built-in Type
+
+If you want both `Int + MyType` and `Real + MyType`, register both pairs explicitly:
+
+```lyng
+OperatorInterop.register(
+    Int,
+    MyType,
+    MyType,
+    [BinaryOperator.Plus, BinaryOperator.Compare, BinaryOperator.Equals],
+    { x: Int -> MyType.fromInt(x) },
+    { x: MyType -> x }
+)
+
+OperatorInterop.register(
+    Real,
+    MyType,
+    MyType,
+    [BinaryOperator.Plus, BinaryOperator.Compare, BinaryOperator.Equals],
+    { x: Real -> MyType.fromReal(x) },
+    { x: MyType -> x }
+)
+```
+
+Each mixed pair is independent.
+
+## Pure Lyng Registration
+
+This mechanism is intentionally useful from pure Lyng code, not only from Kotlin-backed modules.
+
+That means you can:
+
+- declare a class in Lyng
+- define its operators in Lyng
+- register mixed operand bridges in Lyng
+
+without touching compiler internals.
+
+## Where To Register
+
+Register once during module initialization.
+
+Top-level module code is a good place:
+
+```lyng
+package my.rational
+import lyng.operators
+
+class Rational(...)
+
+OperatorInterop.register(...)
+```
+
+That keeps registration close to the type declaration and makes importing the module enough to activate the interop.
+
+## What Registration Does Not Do
+
+The registry does not:
+
+- invent operators your common class does not implement
+- change the original `Int`, `Real`, or other built-ins
+- automatically cover every class pair
+- replace normal method overload resolution when the left-hand class already knows what to do
+
+It only teaches Lyng how to bridge a specific mixed pair into a common class for the listed operators.
+
+## Recommended Design Rules
+
+If you want interop to feel natural:
+
+- choose one obvious common class
+- make conversions explicit and unsurprising
+- implement `compareTo` if you want ordering operators
+- register `Equals` whenever mixed equality should work
+- keep the registered operator list minimal and accurate
+
+For decimal-like semantics, also read [Decimal.md](Decimal.md).

docs/embedding.md

@@ -72,6 +72,14 @@ For module-level APIs, the default workflow is:
 1. declare globals in Lyng using `extern fun` / `extern val` / `extern var`;
 2. bind Kotlin implementation via `ModuleScope.globalBinder()`.
 
+This is also the recommended way to expose a Kotlin-backed value that should behave like a true
+Lyng global variable/property. If you need `x` to read/write through Kotlin on every access, use
+`extern var` / `extern val` plus `bindGlobalVar(...)`.
+
+Do not use `addConst(...)` for this case: `addConst(...)` installs a value, not a Kotlin-backed
+property accessor. It is appropriate for fixed values and objects, but not for a global that should
+delegate reads/writes back into Kotlin state.
+
 ```kotlin
 import net.sergeych.lyng.bridge.*
 import net.sergeych.lyng.obj.ObjInt
@@ -117,6 +125,12 @@ assertEquals("changed", globalProp)
 assertEquals("1.0.0", globalVersion)
 ```
 
+Minimal rule of thumb:
+
+- use `bindGlobalFun(...)` for global functions
+- use `bindGlobalVar(...)` for Kotlin-backed global variables/properties
+- use `addConst(...)` only for fixed values/objects that do not need getter/setter behavior
+
 For custom argument handling and full runtime access:
 
 ```kotlin
@@ -462,14 +476,21 @@ im.addPackage("my.tools") { module: ModuleScope ->
     module.eval(
         """
         extern val version: String
+        extern var status: String
         extern fun triple(x: Int): Int
         """.trimIndent()
     )
     val binder = module.globalBinder()
+    var status = "ready"
     binder.bindGlobalVar(
         name = "version",
         get = { "1.0" }
     )
+    binder.bindGlobalVar(
+        name = "status",
+        get = { status },
+        set = { status = it }
+    )
     binder.bindGlobalFun1<Int>("triple") { x ->
         ObjInt.of((x * 3).toLong())
     }
@@ -479,6 +500,7 @@ im.addPackage("my.tools") { module: ModuleScope ->
 scope.eval("""
     import my.tools.*
     val v = triple(14)
+    status = "busy"
 """)
 val v = scope.eval("v").toKotlin(scope) // -> 42
 ```

docs/whats_new.md

@@ -5,6 +5,73 @@ For a programmer-focused migration summary, see `docs/whats_new_1_5.md`.
 
 ## Language Features
 
+### Decimal Arithmetic Module (`lyng.decimal`)
+Lyng now ships a first-class decimal module built as a regular extension library rather than a deep core special case.
+
+It provides:
+
+- `BigDecimal`
+- convenient `.d` conversions from `Int`, `Real`, and `String`
+- mixed arithmetic with `Int` and `Real`
+- local division precision and rounding control via `withDecimalContext(...)`
+
+```lyng
+import lyng.decimal
+
+assertEquals("3", (1 + 2.d).toStringExpanded())
+assertEquals("0.30000000000000004", (0.1 + 0.2).d.toStringExpanded())
+assertEquals("0.3", "0.3".d.toStringExpanded())
+
+assertEquals(
+    "0.3333333333",
+    withDecimalContext(10) { (1.d / 3.d).toStringExpanded() }
+)
+```
+
+The distinction between `Real -> Decimal` and exact decimal parsing is explicit by design:
+
+- `2.2.d` converts the current `Real` value
+- `"2.2".d` parses exact decimal text
+
+See [Decimal](Decimal.md).
+
+### Binary Operator Interop Registry
+Lyng now provides a general mechanism for mixed binary operators through `lyng.operators`.
+
+This solves cases like:
+
+- `Int + MyType`
+- `Real < MyType`
+- `Int == MyType`
+
+without requiring changes to built-in classes.
+
+```lyng
+import lyng.operators
+
+class DecimalBox(val value: Int) {
+    fun plus(other: DecimalBox) = DecimalBox(value + other.value)
+    fun compareTo(other: DecimalBox) = value <=> other.value
+}
+
+OperatorInterop.register(
+    Int,
+    DecimalBox,
+    DecimalBox,
+    [BinaryOperator.Plus, BinaryOperator.Compare, BinaryOperator.Equals],
+    { x: Int -> DecimalBox(x) },
+    { x: DecimalBox -> x }
+)
+
+assertEquals(DecimalBox(3), 1 + DecimalBox(2))
+assert(1 < DecimalBox(2))
+assert(2 == DecimalBox(2))
+```
+
+`lyng.decimal` uses this same mechanism internally to interoperate with `Int` and `Real`.
+
+See [Operator Interop Registry](OperatorInterop.md).
+
 ### 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.
 

gradle/libs.versions.toml

@@ -8,6 +8,7 @@ android-compileSdk = "34"
 kotlinx-coroutines = "1.10.2"
 kotlinx-datetime = "0.6.1"
 mp_bintools = "0.3.2"
+ionspin-bignum = "0.3.10"
 firebaseCrashlyticsBuildtools = "3.0.3"
 okioVersion = "3.10.2"
 compiler = "3.2.0-alpha11"
@@ -22,6 +23,7 @@ kotlinx-coroutines-test = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-t
 kotlinx-coroutines-core = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-core", version.ref = "kotlinx-coroutines" }
 kotlinx-datetime = { module = "org.jetbrains.kotlinx:kotlinx-datetime", version.ref = "kotlinx-datetime" }
 mp_bintools = { module = "net.sergeych:mp_bintools", version.ref = "mp_bintools" }
+ionspin-bignum = { module = "com.ionspin.kotlin:bignum", version.ref = "ionspin-bignum" }
 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" }

lynglib/build.gradle.kts

@@ -101,6 +101,7 @@ kotlin {
                 //put your multiplatform dependencies here
                 api(libs.kotlinx.coroutines.core)
                 api(libs.mp.bintools)
+                implementation(libs.ionspin.bignum)
             }
         }
         val commonTest by getting {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt

@@ -184,6 +184,7 @@ class Compiler(
     private val encodedPayloadTypeByName: MutableMap<String, ObjClass> = mutableMapOf()
     private val objectDeclNames: MutableSet<String> = mutableSetOf()
     private val externCallableNames: MutableSet<String> = mutableSetOf()
+    private val externBindingNames: MutableSet<String> = mutableSetOf()
     private val moduleDeclaredNames: MutableSet<String> = mutableSetOf()
     private var seedingSlotPlan: Boolean = false
 
@@ -192,6 +193,7 @@ class Compiler(
         if (plan.slots.isEmpty()) return emptyMap()
         val result = LinkedHashMap<String, ForcedLocalSlotInfo>(plan.slots.size)
         for ((name, entry) in plan.slots) {
+            if (externBindingNames.contains(name)) continue
             result[name] = ForcedLocalSlotInfo(
                 index = entry.index,
                 isMutable = entry.isMutable,
@@ -581,7 +583,7 @@ class Compiler(
         val baseNames = cls.directParents.map { it.className }
         val nextFieldId = (fieldIds.values.maxOrNull() ?: -1) + 1
         val nextMethodId = (methodIds.values.maxOrNull() ?: -1) + 1
-        return CompileClassInfo(name, fieldIds, methodIds, nextFieldId, nextMethodId, baseNames)
+        return CompileClassInfo(name, cls.logicalPackageName, fieldIds, methodIds, nextFieldId, nextMethodId, baseNames)
     }
 
     private data class BaseMemberIds(
@@ -885,6 +887,7 @@ class Compiler(
             name = declaredName,
             isMutable = false,
             visibility = Visibility.Public,
+            actualExtern = false,
             initializer = initStmt,
             isTransient = false,
             typeDecl = null,
@@ -1550,6 +1553,7 @@ class Compiler(
 
     private data class CompileClassInfo(
         val name: String,
+        val packageName: String?,
         val fieldIds: Map<String, Int>,
         val methodIds: Map<String, Int>,
         val nextFieldId: Int,
@@ -1751,6 +1755,7 @@ class Compiler(
                         enumEntriesByName = enumEntriesByName,
                         callableReturnTypeByScopeId = callableReturnTypeByScopeId,
                         callableReturnTypeByName = callableReturnTypeByName,
+                        externBindingNames = externBindingNames,
                         lambdaCaptureEntriesByRef = lambdaCaptureEntriesByRef
                     ) as BytecodeStatement
                     unwrapped to bytecodeStmt.bytecodeFunction()
@@ -1957,6 +1962,9 @@ class Compiler(
         val scopeIndex = slotPlanStack.indexOfLast { it.id == slotLoc.scopeId }
         if (functionIndex >= 0 && scopeIndex >= functionIndex) return null
         val modulePlan = moduleSlotPlan()
+        if (modulePlan != null && slotLoc.scopeId == modulePlan.id && externBindingNames.contains(name)) {
+            return null
+        }
         if (useScopeSlots && modulePlan != null && slotLoc.scopeId == modulePlan.id) {
             return null
         }
@@ -2075,6 +2083,7 @@ class Compiler(
             callableReturnTypeByScopeId = callableReturnTypeByScopeId,
             callableReturnTypeByName = callableReturnTypeByName,
             externCallableNames = externCallableNames,
+            externBindingNames = externBindingNames,
             lambdaCaptureEntriesByRef = lambdaCaptureEntriesByRef
         )
     }
@@ -2105,6 +2114,7 @@ class Compiler(
             callableReturnTypeByScopeId = callableReturnTypeByScopeId,
             callableReturnTypeByName = callableReturnTypeByName,
             externCallableNames = externCallableNames,
+            externBindingNames = externBindingNames,
             lambdaCaptureEntriesByRef = lambdaCaptureEntriesByRef
         )
     }
@@ -2160,6 +2170,7 @@ class Compiler(
             callableReturnTypeByScopeId = callableReturnTypeByScopeId,
             callableReturnTypeByName = callableReturnTypeByName,
             externCallableNames = externCallableNames,
+            externBindingNames = externBindingNames,
             lambdaCaptureEntriesByRef = lambdaCaptureEntriesByRef
         )
     }
@@ -2343,6 +2354,7 @@ class Compiler(
                     stmt.name,
                     stmt.isMutable,
                     stmt.visibility,
+                    stmt.actualExtern,
                     init,
                     stmt.isTransient,
                     stmt.typeDecl,
@@ -4655,6 +4667,7 @@ class Compiler(
             }
             is MethodCallRef -> methodReturnTypeDeclByRef[ref]
             is CallRef -> callReturnTypeDeclByRef[ref]
+            is BinaryOpRef -> inferBinaryOpReturnTypeDecl(ref)
             is StatementRef -> (ref.statement as? ExpressionStatement)?.let { resolveReceiverTypeDecl(it.ref) }
             else -> null
         }
@@ -4718,6 +4731,7 @@ class Compiler(
             is ThisMethodSlotCallRef -> inferMethodCallReturnClass(ref.methodName())
             is QualifiedThisMethodSlotCallRef -> inferMethodCallReturnClass(ref.methodName())
             is CallRef -> inferCallReturnClass(ref)
+            is BinaryOpRef -> inferBinaryOpReturnClass(ref)
             is FieldRef -> {
                 val targetClass = resolveReceiverClassForMember(ref.target)
                 inferFieldReturnClass(targetClass, ref.name)
@@ -4732,10 +4746,105 @@ class Compiler(
         }
     }
 
+    private fun typeDeclOfClass(objClass: ObjClass): TypeDecl = TypeDecl.Simple(objClass.className, false)
+
+    private fun binaryOpMethodName(op: BinOp): String? = when (op) {
+        BinOp.PLUS -> "plus"
+        BinOp.MINUS -> "minus"
+        BinOp.STAR -> "mul"
+        BinOp.SLASH -> "div"
+        BinOp.PERCENT -> "mod"
+        else -> null
+    }
+
+    private fun interopOperatorFor(op: BinOp): InteropOperator? = when (op) {
+        BinOp.PLUS -> InteropOperator.Plus
+        BinOp.MINUS -> InteropOperator.Minus
+        BinOp.STAR -> InteropOperator.Mul
+        BinOp.SLASH -> InteropOperator.Div
+        BinOp.PERCENT -> InteropOperator.Mod
+        BinOp.LT, BinOp.LTE, BinOp.GT, BinOp.GTE -> InteropOperator.Compare
+        BinOp.EQ, BinOp.NEQ -> InteropOperator.Equals
+        else -> null
+    }
+
+    private fun sameClassArithmeticFallback(leftClass: ObjClass, rightClass: ObjClass, op: BinOp): TypeDecl? {
+        if (leftClass !== rightClass) return null
+        val methodName = binaryOpMethodName(op) ?: return null
+        if (leftClass.getInstanceMemberOrNull(methodName, includeAbstract = true) == null) return null
+        return typeDeclOfClass(leftClass)
+    }
+
+    private fun inferBinaryOpReturnTypeDecl(ref: BinaryOpRef): TypeDecl? {
+        val leftClass = resolveReceiverClassForMember(ref.left) ?: inferObjClassFromRef(ref.left)
+        val rightClass = resolveReceiverClassForMember(ref.right) ?: inferObjClassFromRef(ref.right)
+        val boolType = typeDeclOfClass(ObjBool.type)
+        val intType = typeDeclOfClass(ObjInt.type)
+        val realType = typeDeclOfClass(ObjReal.type)
+        val stringType = typeDeclOfClass(ObjString.type)
+
+        when (ref.op) {
+            BinOp.OR, BinOp.AND,
+            BinOp.EQARROW, BinOp.EQ, BinOp.NEQ, BinOp.REF_EQ, BinOp.REF_NEQ, BinOp.MATCH, BinOp.NOTMATCH,
+            BinOp.LTE, BinOp.LT, BinOp.GTE, BinOp.GT,
+            BinOp.IN, BinOp.NOTIN,
+            BinOp.IS, BinOp.NOTIS -> return boolType
+            else -> {}
+        }
+
+        if (leftClass == null || rightClass == null) return null
+
+        val leftIsInt = leftClass == ObjInt.type
+        val rightIsInt = rightClass == ObjInt.type
+        val leftIsReal = leftClass == ObjReal.type
+        val rightIsReal = rightClass == ObjReal.type
+        val leftIsNumeric = leftIsInt || leftIsReal
+        val rightIsNumeric = rightIsInt || rightIsReal
+
+        return when (ref.op) {
+            BinOp.PLUS -> when {
+                leftIsInt && rightIsInt -> intType
+                leftIsNumeric && rightIsNumeric -> realType
+                leftClass == ObjString.type -> stringType
+                interopOperatorFor(ref.op)?.let {
+                    OperatorInteropRegistry.commonClassFor(leftClass, rightClass, it)
+                } != null -> typeDeclOfClass(
+                    OperatorInteropRegistry.commonClassFor(leftClass, rightClass, interopOperatorFor(ref.op)!!)!!
+                )
+                else -> binaryOpMethodName(ref.op)?.let { classMethodReturnTypeDecl(leftClass, it) }
+                    ?: sameClassArithmeticFallback(leftClass, rightClass, ref.op)
+            }
+            BinOp.MINUS, BinOp.STAR, BinOp.SLASH, BinOp.PERCENT -> when {
+                leftIsInt && rightIsInt -> intType
+                leftIsNumeric && rightIsNumeric -> realType
+                ref.op == BinOp.STAR && leftClass == ObjString.type && rightIsNumeric -> stringType
+                interopOperatorFor(ref.op)?.let {
+                    OperatorInteropRegistry.commonClassFor(leftClass, rightClass, it)
+                } != null -> typeDeclOfClass(
+                    OperatorInteropRegistry.commonClassFor(leftClass, rightClass, interopOperatorFor(ref.op)!!)!!
+                )
+                else -> binaryOpMethodName(ref.op)?.let { classMethodReturnTypeDecl(leftClass, it) }
+                    ?: sameClassArithmeticFallback(leftClass, rightClass, ref.op)
+            }
+            BinOp.BAND, BinOp.BOR, BinOp.BXOR, BinOp.SHL, BinOp.SHR ->
+                if (leftIsInt && rightIsInt) intType else null
+            else -> null
+        }
+    }
+
     private fun inferBinaryOpReturnClass(ref: BinaryOpRef): ObjClass? {
+        inferBinaryOpReturnTypeDecl(ref)?.let { declared ->
+            resolveTypeDeclObjClass(declared)?.let { return it }
+        }
         val leftClass = resolveReceiverClassForMember(ref.left) ?: inferObjClassFromRef(ref.left)
         val rightClass = resolveReceiverClassForMember(ref.right) ?: inferObjClassFromRef(ref.right)
         if (leftClass == null || rightClass == null) return null
+        interopOperatorFor(ref.op)?.let { op ->
+            OperatorInteropRegistry.commonClassFor(leftClass, rightClass, op)?.let { return it }
+        }
+        sameClassArithmeticFallback(leftClass, rightClass, ref.op)?.let { declared ->
+            resolveTypeDeclObjClass(declared)?.let { return it }
+        }
         return when (ref.op) {
             BinOp.PLUS, BinOp.MINUS -> when {
                 leftClass == ObjInstant.type && rightClass == ObjInstant.type && ref.op == BinOp.MINUS -> ObjDuration.type
@@ -6446,7 +6555,7 @@ class Compiler(
             WhenStatement(value, cases, elseCase, whenPos)
         } else {
             // when { cond -> ... }
-            TODO("when without object is not yet implemented")
+            throw ScriptError(t.pos, "when without subject is not implemented")
         }
         return wrapBytecode(stmt)
     }
@@ -6699,6 +6808,7 @@ class Compiler(
         )
         compileClassInfos[qualifiedName] = CompileClassInfo(
             name = qualifiedName,
+            packageName = packageName,
             fieldIds = fieldIds,
             methodIds = methodIds,
             nextFieldId = fieldIds.size,
@@ -6821,6 +6931,7 @@ class Compiler(
                         classCtx?.let { ctx ->
                             compileClassInfos[className] = CompileClassInfo(
                                 name = className,
+                                packageName = packageName,
                                 fieldIds = ctx.memberFieldIds.toMap(),
                                 methodIds = ctx.memberMethodIds.toMap(),
                                 nextFieldId = ctx.nextFieldId,
@@ -6862,6 +6973,7 @@ class Compiler(
                     val baseIds = collectBaseMemberIds(baseSpecs.map { it.name })
                     compileClassInfos[className] = CompileClassInfo(
                         name = className,
+                        packageName = packageName,
                         fieldIds = baseIds.fieldIds,
                         methodIds = baseIds.methodIds,
                         nextFieldId = baseIds.nextFieldId,
@@ -7110,6 +7222,7 @@ class Compiler(
                                 }
                                 compileClassInfos[qualifiedName] = CompileClassInfo(
                                     name = qualifiedName,
+                                    packageName = packageName,
                                     fieldIds = ctx.memberFieldIds.toMap(),
                                     methodIds = ctx.memberMethodIds.toMap(),
                                     nextFieldId = ctx.nextFieldId,
@@ -7125,6 +7238,7 @@ class Compiler(
                             classCtx?.let { ctx ->
                                 compileClassInfos[qualifiedName] = CompileClassInfo(
                                     name = qualifiedName,
+                                    packageName = packageName,
                                     fieldIds = ctx.memberFieldIds.toMap(),
                                     methodIds = ctx.memberMethodIds.toMap(),
                                     nextFieldId = ctx.nextFieldId,
@@ -7211,6 +7325,7 @@ class Compiler(
                                 }
                                 compileClassInfos[qualifiedName] = CompileClassInfo(
                                     name = qualifiedName,
+                                    packageName = packageName,
                                     fieldIds = ctx.memberFieldIds.toMap(),
                                     methodIds = ctx.memberMethodIds.toMap(),
                                     nextFieldId = ctx.nextFieldId,
@@ -8390,7 +8505,7 @@ class Compiler(
             is ImplicitThisMethodCallRef -> {
                 when (directRef.methodName()) {
                     "iterator" -> ObjIterator
-                    "lazy" -> ObjLazyDelegate.type
+                    "lazy" -> resolveClassByName("lazy") ?: inferMethodCallReturnClass(directRef.methodName())
                     else -> inferMethodCallReturnClass(directRef.methodName())
                 }
             }
@@ -8409,7 +8524,7 @@ class Compiler(
                 when {
                     target is LocalSlotRef -> {
                         when (target.name) {
-                            "lazy" -> ObjLazyDelegate.type
+                            "lazy" -> resolveClassByName("lazy")
                             "iterator" -> ObjIterator
                             "flow" -> ObjFlow.type
                             "launch" -> ObjDeferred.type
@@ -8420,7 +8535,7 @@ class Compiler(
                     }
                     target is LocalVarRef -> {
                         when (target.name) {
-                            "lazy" -> ObjLazyDelegate.type
+                            "lazy" -> resolveClassByName("lazy")
                             "iterator" -> ObjIterator
                             "flow" -> ObjFlow.type
                             "launch" -> ObjDeferred.type
@@ -8459,7 +8574,9 @@ class Compiler(
             ?: unwrapDirectRef(initializer)?.let { inferObjClassFromRef(it) }
             ?: throw ScriptError(initializer.pos, "Delegate type must be known at compile time")
         if (initClass !== delegateClass &&
+            initClass.logicalName != delegateClass.logicalName &&
             !initClass.allParentsSet.contains(delegateClass) &&
+            !initClass.allParentsSet.any { it.logicalName == delegateClass.logicalName } &&
             !initClass.allImplementingNames.contains(delegateClass.className)
         ) {
             throw ScriptError(
@@ -8549,7 +8666,9 @@ class Compiler(
             if (closedParent != null) {
                 throw ScriptError(Pos.builtIn, "can't inherit from closed class ${closedParent.className}")
             }
-            ObjInstanceClass(info.name, *parents.toTypedArray())
+            ObjInstanceClass(info.name, *parents.toTypedArray()).apply {
+                logicalPackageNameOverride = info.packageName
+            }
         }
         if (stub is ObjInstanceClass) {
             for ((fieldName, fieldId) in info.fieldIds) {
@@ -8893,7 +9012,7 @@ class Compiler(
         val effectiveEqToken = if (isProperty) null else eqToken
 
         // Register the local name at compile time so that subsequent identifiers can be emitted as fast locals
-        if (!isStatic && declaringClassNameCaptured == null) declareLocalName(name, isMutable)
+        if (!isStatic && declaringClassNameCaptured == null && !actualExtern) declareLocalName(name, isMutable)
         val declKind = if (codeContexts.lastOrNull() is CodeContext.ClassBody) {
             SymbolKind.MEMBER
         } else {
@@ -8902,6 +9021,8 @@ class Compiler(
         resolutionSink?.declareSymbol(name, declKind, isMutable, nameStartPos, isOverride = isOverride)
         if (declKind == SymbolKind.MEMBER && extTypeName == null) {
             (codeContexts.lastOrNull() as? CodeContext.ClassBody)?.declaredMembers?.add(name)
+        } else if (actualExtern) {
+            externBindingNames.add(name)
         }
 
         val isDelegate = if (isAbstract || actualExtern) {
@@ -8967,7 +9088,11 @@ class Compiler(
 
         if (isDelegate && initialExpression != null) {
             ensureDelegateType(initialExpression)
-            if (isMutable && resolveInitializerObjClass(initialExpression) == ObjLazyDelegate.type) {
+            val lazyClass = resolveClassByName("lazy")
+            if (isMutable &&
+                lazyClass != null &&
+                resolveInitializerObjClass(initialExpression)?.logicalName == lazyClass.logicalName
+            ) {
                 throw ScriptError(initialExpression.pos, "lazy delegate is read-only")
             }
         }
@@ -9059,6 +9184,7 @@ class Compiler(
                 name,
                 isMutable,
                 visibility,
+                actualExtern,
                 initialExpression,
                 isTransient,
                 declaredType,

lynglib/src/commonMain/kotlin/net/sergeych/lyng/OperatorInteropRegistry.kt

@@ -0,0 +1,109 @@
+/*
+ * 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
+
+import net.sergeych.lyng.obj.Obj
+import net.sergeych.lyng.obj.ObjClass
+import net.sergeych.lyng.obj.ObjInt
+import net.sergeych.lyng.obj.ObjVoid
+
+internal enum class InteropOperator(val memberName: String?) {
+    Plus("plus"),
+    Minus("minus"),
+    Mul("mul"),
+    Div("div"),
+    Mod("mod"),
+    Compare("compareTo"),
+    Equals("equals");
+
+    companion object {
+        fun fromName(name: String): InteropOperator =
+            entries.firstOrNull { it.name == name }
+                ?: throw IllegalArgumentException("unknown interop operator: $name")
+    }
+}
+
+private data class InteropRule(
+    val commonClass: ObjClass,
+    val operators: Set<InteropOperator>,
+    val leftToCommon: Obj,
+    val rightToCommon: Obj
+)
+
+internal data class PromotedOperands(val left: Obj, val right: Obj)
+
+internal object OperatorInteropRegistry {
+    private val rules = mutableMapOf<Pair<ObjClass, ObjClass>, InteropRule>()
+
+    fun register(
+        leftClass: ObjClass,
+        rightClass: ObjClass,
+        commonClass: ObjClass,
+        operatorNames: List<String>,
+        leftToCommon: Obj,
+        rightToCommon: Obj
+    ) {
+        val operators = operatorNames.mapTo(linkedSetOf(), InteropOperator::fromName)
+        rules[leftClass to rightClass] = InteropRule(commonClass, operators, leftToCommon, rightToCommon)
+        if (leftClass !== rightClass) {
+            rules[rightClass to leftClass] = InteropRule(commonClass, operators, rightToCommon, leftToCommon)
+        }
+    }
+
+    suspend fun promote(scope: Scope, left: Obj, right: Obj, operator: InteropOperator): PromotedOperands? {
+        val leftValue = unwrap(left)
+        val rightValue = unwrap(right)
+        val rule = rules[leftValue.objClass to rightValue.objClass] ?: return null
+        if (operator !in rule.operators) return null
+        val promotedLeft = rule.leftToCommon.invoke(scope, ObjVoid, Arguments(leftValue))
+        val promotedRight = rule.rightToCommon.invoke(scope, ObjVoid, Arguments(rightValue))
+        if (promotedLeft.objClass !== rule.commonClass || promotedRight.objClass !== rule.commonClass) {
+            scope.raiseIllegalState(
+                "Operator interop promotion must return ${rule.commonClass.className}, " +
+                    "got ${promotedLeft.objClass.className} and ${promotedRight.objClass.className}"
+            )
+        }
+        return PromotedOperands(promotedLeft, promotedRight)
+    }
+
+    suspend fun invokeBinary(scope: Scope, left: Obj, right: Obj, operator: InteropOperator): Obj? {
+        val promoted = promote(scope, left, right, operator) ?: return null
+        val memberName = operator.memberName ?: return null
+        return promoted.left.invokeInstanceMethod(scope, memberName, Arguments(promoted.right))
+    }
+
+    suspend fun invokeCompare(scope: Scope, left: Obj, right: Obj): Int? {
+        val promoted = promote(scope, left, right, InteropOperator.Compare) ?: return null
+        return promoted.left.invokeInstanceMethod(scope, "compareTo", Arguments(promoted.right))
+            .cast<ObjInt>(scope)
+            .value
+            .toInt()
+    }
+
+    fun commonClassFor(leftClass: ObjClass, rightClass: ObjClass, operator: InteropOperator): ObjClass? {
+        val rule = rules[leftClass to rightClass] ?: return null
+        if (operator !in rule.operators) return null
+        return rule.commonClass
+    }
+
+    private suspend fun unwrap(obj: Obj): Obj = when (obj) {
+        is FrameSlotRef -> obj.read()
+        is RecordSlotRef -> obj.read()
+        else -> obj
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt

@@ -27,7 +27,9 @@ import net.sergeych.lyng.bytecode.CmdVm
 import net.sergeych.lyng.miniast.*
 import net.sergeych.lyng.obj.*
 import net.sergeych.lyng.pacman.ImportManager
+import net.sergeych.lyng.stdlib_included.decimalLyng
 import net.sergeych.lyng.stdlib_included.observableLyng
+import net.sergeych.lyng.stdlib_included.operatorsLyng
 import net.sergeych.lyng.stdlib_included.rootLyng
 import net.sergeych.lynon.ObjLynonClass
 import net.sergeych.mp_tools.globalDefer
@@ -46,6 +48,28 @@ class Script(
 //    private val catchReturn: Boolean = false,
 ) : Statement() {
     fun statements(): List<Statement> = statements
+
+    /**
+     * Explicitly apply this script's import/module bindings to [scope] without executing the script.
+     * This is intended for embedding scenarios where the host owns scope lifecycle and wants
+     * script-specific imports to be a separate, opt-in preparation step.
+     */
+    suspend fun importInto(scope: Scope, seedScope: Scope = scope): Scope {
+        prepareScriptScope(scope, seedScope)
+        return scope
+    }
+
+    /**
+     * Create a fresh raw module scope and apply this script's import/module bindings to it.
+     * If [seedScope] is provided, its import provider is reused and seed-bound imports resolve from it.
+     */
+    suspend fun instantiateModule(seedScope: Scope? = null, pos: Pos = this.pos): ModuleScope {
+        val provider = seedScope?.currentImportProvider ?: defaultImportManager
+        val module = provider.newModuleAt(pos)
+        prepareScriptScope(module, seedScope ?: module)
+        return module
+    }
+
     override suspend fun execute(scope: Scope): Obj {
         scope.pos = pos
         val execScope = resolveModuleScope(scope) ?: scope
@@ -75,6 +99,19 @@ class Script(
         return ObjVoid
     }
 
+    private suspend fun prepareScriptScope(scope: Scope, seedScope: Scope) {
+        if (importBindings.isNotEmpty() || importedModules.isNotEmpty()) {
+            seedImportBindings(scope, seedScope)
+        }
+        if (moduleSlotPlan.isNotEmpty()) {
+            scope.applySlotPlan(moduleSlotPlan)
+            for (name in moduleSlotPlan.keys) {
+                val record = scope.objects[name] ?: scope.localBindings[name] ?: continue
+                scope.updateSlotFor(name, record)
+            }
+        }
+    }
+
     private suspend fun seedModuleSlots(scope: Scope, seedScope: Scope) {
         if (importBindings.isEmpty() && importedModules.isEmpty()) return
         seedImportBindings(scope, seedScope)
@@ -505,10 +542,6 @@ class Script(
                     cachedValue
                 }
             }
-            addFn("lazy") {
-                val builder = requireOnlyArg<Obj>()
-                ObjLazyDelegate(builder, requireScope())
-            }
             addVoidFn("delay") {
                 val a = args.firstAndOnly()
                 when (a) {
@@ -696,6 +729,36 @@ class Script(
                     module.addConst("ChangeRejectionException", ObjChangeRejectionExceptionClass)
                     module.eval(Source("lyng.observable", observableLyng))
                 }
+                addPackage("lyng.operators") { module ->
+                    module.eval(Source("lyng.operators", operatorsLyng))
+                    module.bindObject("OperatorInterop") {
+                        addFun("register") {
+                            val leftClass = requiredArg<ObjClass>(0)
+                            val rightClass = requiredArg<ObjClass>(1)
+                            val commonClass = requiredArg<ObjClass>(2)
+                            val operators = requiredArg<ObjList>(3).list.map { value ->
+                                val entry = value as? ObjEnumEntry
+                                    ?: requireScope().raiseIllegalArgument(
+                                        "OperatorInterop.register expects BinaryOperator enum entries"
+                                    )
+                                entry.name.value
+                            }
+                            OperatorInteropRegistry.register(
+                                leftClass = leftClass,
+                                rightClass = rightClass,
+                                commonClass = commonClass,
+                                operatorNames = operators,
+                                leftToCommon = args[4],
+                                rightToCommon = args[5]
+                            )
+                            ObjVoid
+                        }
+                    }
+                }
+                addPackage("lyng.decimal") { module ->
+                    module.eval(Source("lyng.decimal", decimalLyng))
+                    ObjBigDecimalSupport.bindTo(module)
+                }
                 addPackage("lyng.buffer") {
                     it.addConstDoc(
                         name = "Buffer",

lynglib/src/commonMain/kotlin/net/sergeych/lyng/VarDeclStatement.kt

@@ -24,6 +24,7 @@ class VarDeclStatement(
     val name: String,
     val isMutable: Boolean,
     val visibility: Visibility,
+    val actualExtern: Boolean,
     val initializer: Statement?,
     val isTransient: Boolean,
     val typeDecl: TypeDecl?,

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt

@@ -42,6 +42,7 @@ class BytecodeCompiler(
     private val callableReturnTypeByScopeId: Map<Int, Map<Int, ObjClass>> = emptyMap(),
     private val callableReturnTypeByName: Map<String, ObjClass> = emptyMap(),
     private val externCallableNames: Set<String> = emptySet(),
+    private val externBindingNames: Set<String> = emptySet(),
     private val lambdaCaptureEntriesByRef: Map<ValueFnRef, List<LambdaCaptureEntry>> = emptyMap(),
 ) {
     private val useScopeSlots: Boolean = allowedScopeNames != null || scopeSlotNameSet != null
@@ -1088,7 +1089,6 @@ class BytecodeCompiler(
 
     private fun isDelegateClass(receiverClass: ObjClass): Boolean =
         receiverClass.className == "Delegate" ||
-            receiverClass.className == "LazyDelegate" ||
             receiverClass.implementingNames.contains("Delegate")
 
     private fun operatorMemberName(op: BinOp): String? = when (op) {
@@ -4508,7 +4508,7 @@ class BytecodeCompiler(
             val resolved = slotTypes[slot] ?: SlotType.UNKNOWN
             return CompiledValue(slot, resolved)
         }
-        if (useScopeSlots && allowedScopeNames?.contains(name) == true) {
+        if (useScopeSlots && isPreparedScopeName(name)) {
             scopeSlotIndexByName[name]?.let { slot ->
                 val resolved = slotTypes[slot] ?: SlotType.UNKNOWN
                 return CompiledValue(slot, resolved)
@@ -8073,7 +8073,7 @@ class BytecodeCompiler(
                         slotInitClassByKey[ScopeSlotKey(scopeId, slotIndex)] = cls
                     }
                 }
-                if (allowLocalSlots && slotIndex != null && !shouldUseScopeSlotFor(scopeId)) {
+                if (allowLocalSlots && slotIndex != null && (stmt.actualExtern || !shouldUseScopeSlotFor(scopeId, stmt.name, isDelegated = false))) {
                     val key = ScopeSlotKey(scopeId, slotIndex)
                     declaredLocalKeys.add(key)
                     if (!localSlotInfoMap.containsKey(key)) {
@@ -8100,7 +8100,7 @@ class BytecodeCompiler(
                 val scopeId = stmt.spec.scopeId ?: 0
                 if (slotIndex != null) {
                     val key = ScopeSlotKey(scopeId, slotIndex)
-                    if (allowLocalSlots && !shouldUseScopeSlotFor(scopeId)) {
+                    if (allowLocalSlots && !shouldUseScopeSlotFor(scopeId, stmt.spec.name, isDelegated = false)) {
                         if (!localSlotInfoMap.containsKey(key)) {
                             localSlotInfoMap[key] = LocalSlotInfo(stmt.spec.name, isMutable = false, isDelegated = false)
                         }
@@ -8117,7 +8117,7 @@ class BytecodeCompiler(
             is DelegatedVarDeclStatement -> {
                 val slotIndex = stmt.slotIndex
                 val scopeId = stmt.scopeId ?: 0
-                if (allowLocalSlots && slotIndex != null && !shouldUseScopeSlotFor(scopeId)) {
+                if (allowLocalSlots && slotIndex != null && !shouldUseScopeSlotFor(scopeId, stmt.name, isDelegated = true)) {
                     val key = ScopeSlotKey(scopeId, slotIndex)
                     declaredLocalKeys.add(key)
                     if (!localSlotInfoMap.containsKey(key)) {
@@ -8283,15 +8283,26 @@ class BytecodeCompiler(
 
     private fun isModuleSlot(scopeId: Int, name: String?): Boolean {
         if (moduleScopeId != null && scopeId != moduleScopeId) return false
-        val scopeNames = allowedScopeNames ?: scopeSlotNameSet
-        if (scopeNames == null || name == null) return false
-        return scopeNames.contains(name)
+        return isPreparedScopeName(name)
     }
 
     private fun shouldUseScopeSlotFor(scopeId: Int): Boolean {
         return useScopeSlots && moduleScopeId != null && scopeId == moduleScopeId
     }
 
+    private fun shouldUseScopeSlotFor(scopeId: Int, name: String, isDelegated: Boolean): Boolean {
+        if (moduleScopeId == null || scopeId != moduleScopeId) return false
+        if (isDelegated) return false
+        if (externBindingNames.contains(name)) return true
+        return useScopeSlots && isPreparedScopeName(name)
+    }
+
+    private fun isPreparedScopeName(name: String?): Boolean {
+        if (name == null) return false
+        if (scopeSlotNameSet?.contains(name) == true) return true
+        return allowedScopeNames?.contains(name) == true
+    }
+
     private fun collectLoopVarNames(stmt: Statement) {
         if (stmt is BytecodeStatement) {
             collectLoopVarNames(stmt.original)
@@ -8400,8 +8411,9 @@ class BytecodeCompiler(
                     captureSlotKeys.add(key)
                     return
                 }
+                val forceScopeSlot = shouldUseScopeSlotFor(scopeId, ref.name, ref.isDelegated)
                 val isModuleSlot = if (ref.isDelegated) false else isModuleSlot(scopeId, ref.name)
-                if (allowLocalSlots && !isModuleSlot) {
+                if (allowLocalSlots && !isModuleSlot && !forceScopeSlot) {
                     if (!localSlotInfoMap.containsKey(key)) {
                         localSlotInfoMap[key] = LocalSlotInfo(ref.name, ref.isMutable, ref.isDelegated)
                     }
@@ -8448,8 +8460,9 @@ class BytecodeCompiler(
                         }
                         captureSlotKeys.add(key)
                     } else {
+                        val forceScopeSlot = shouldUseScopeSlotFor(scopeId, target.name, target.isDelegated)
                         val isModuleSlot = if (target.isDelegated) false else isModuleSlot(scopeId, target.name)
-                        if (allowLocalSlots && !isModuleSlot) {
+                        if (allowLocalSlots && !isModuleSlot && !forceScopeSlot) {
                             if (!localSlotInfoMap.containsKey(key)) {
                                 localSlotInfoMap[key] = LocalSlotInfo(target.name, target.isMutable, target.isDelegated)
                             }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeStatement.kt

@@ -87,6 +87,7 @@ class BytecodeStatement private constructor(
             callableReturnTypeByScopeId: Map<Int, Map<Int, ObjClass>> = emptyMap(),
             callableReturnTypeByName: Map<String, ObjClass> = emptyMap(),
             externCallableNames: Set<String> = emptySet(),
+            externBindingNames: Set<String> = emptySet(),
             lambdaCaptureEntriesByRef: Map<ValueFnRef, List<LambdaCaptureEntry>> = emptyMap(),
             slotTypeDeclByScopeId: Map<Int, Map<Int, TypeDecl>> = emptyMap(),
         ): Statement {
@@ -122,6 +123,7 @@ class BytecodeStatement private constructor(
                 callableReturnTypeByScopeId = callableReturnTypeByScopeId,
                 callableReturnTypeByName = callableReturnTypeByName,
                 externCallableNames = externCallableNames,
+                externBindingNames = externBindingNames,
                 lambdaCaptureEntriesByRef = lambdaCaptureEntriesByRef
             )
             val compiled = compiler.compileStatement(nameHint, statement)
@@ -236,6 +238,7 @@ class BytecodeStatement private constructor(
                         stmt.name,
                         stmt.isMutable,
                         stmt.visibility,
+                        stmt.actualExtern,
                         stmt.initializer?.let { unwrapDeep(it) },
                         stmt.isTransient,
                         stmt.typeDecl,

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/CmdRuntime.kt

@@ -2392,8 +2392,13 @@ class CmdDeclLocal(internal val constId: Int, internal val slot: Int) : Cmd() {
             ?: error("DECL_LOCAL expects LocalDecl at $constId")
         if (slot < frame.fn.scopeSlotCount) {
             val target = frame.scopeTarget(slot)
-            frame.ensureScopeSlot(target, slot)
-            val value = frame.slotToObj(slot).byValueCopy()
+            val index = frame.ensureScopeSlot(target, slot)
+            val raw = target.getSlotRecord(index).value
+            val value = when (raw) {
+                is FrameSlotRef -> raw.read()
+                is RecordSlotRef -> raw.read()
+                else -> raw
+            }.byValueCopy()
             target.updateSlotFor(
                 decl.name,
                 ObjRecord(
@@ -3930,7 +3935,7 @@ class CmdFrame(
                     } else {
                         val raw = frame.getRawObj(localIndex)
                         if (raw == null && name != null) {
-                            val record = scope.get(name)
+                            val record = findNamedExistingRecord(scope, name)
                             if (record != null) {
                                 val value = record.value
                                 return@mapIndexed when (value) {
@@ -3939,6 +3944,12 @@ class CmdFrame(
                                     else -> ObjRecord(value, isMutable)
                                 }
                             }
+                            if (hasNamedScopeBinding(scope, name)) {
+                                throw ScriptError(
+                                    ensureScope().pos,
+                                    "captured binding '$name' is not available in the execution scope; prepare the script imports/module bindings explicitly"
+                                )
+                            }
                         }
                         when (raw) {
                             is FrameSlotRef -> ObjRecord(raw, isMutable)
@@ -3952,22 +3963,27 @@ class CmdFrame(
                     val target = moduleScope
                     val name = captureNames?.getOrNull(index)
                     if (name != null) {
-                        target.tryGetLocalRecord(target, name, target.currentClassCtx)?.let { return@mapIndexed it }
-                        target.getSlotIndexOf(name)?.let { return@mapIndexed target.getSlotRecord(it) }
-                        target.get(name)?.let { return@mapIndexed it }
+                        findNamedExistingRecord(target, name)?.let { return@mapIndexed it }
                         // Fallback to current scope in case the module scope isn't in the parent chain
                         // or doesn't carry the imported symbol yet.
-                        scope.tryGetLocalRecord(scope, name, scope.currentClassCtx)?.let { return@mapIndexed it }
-                        scope.get(name)?.let { return@mapIndexed it }
+                        findNamedExistingRecord(scope, name)?.let { return@mapIndexed it }
                     }
                     if (slotId < target.slotCount) {
-                        return@mapIndexed target.getSlotRecord(slotId)
+                        val existing = target.getSlotRecord(slotId)
+                        if (name == null || existing.value !== ObjUnset || hasResolvedNamedScopeBinding(target, name)) {
+                            return@mapIndexed existing
+                        }
                     }
                     if (name != null) {
-                        target.applySlotPlan(mapOf(name to slotId))
-                        return@mapIndexed target.getSlotRecord(slotId)
+                        throw ScriptError(
+                            ensureScope().pos,
+                            "module capture '$name' is not available in the execution scope; prepare the script imports/module bindings explicitly"
+                        )
                     }
-                    error("Missing module capture slot $slotId")
+                    throw ScriptError(
+                        ensureScope().pos,
+                        "missing module capture slot $slotId"
+                    )
                 }
             }
         }
@@ -4546,7 +4562,7 @@ class CmdFrame(
         return getScopeSlotValueAtAddr(addrSlot)
     }
 
-    fun setAddrObj(addrSlot: Int, value: Obj) {
+    suspend fun setAddrObj(addrSlot: Int, value: Obj) {
         setScopeSlotValueAtAddr(addrSlot, value)
     }
 
@@ -4554,7 +4570,7 @@ class CmdFrame(
         return getScopeSlotValueAtAddr(addrSlot).toLong()
     }
 
-    fun setAddrInt(addrSlot: Int, value: Long) {
+    suspend fun setAddrInt(addrSlot: Int, value: Long) {
         setScopeSlotValueAtAddr(addrSlot, ObjInt.of(value))
     }
 
@@ -4562,7 +4578,7 @@ class CmdFrame(
         return getScopeSlotValueAtAddr(addrSlot).toDouble()
     }
 
-    fun setAddrReal(addrSlot: Int, value: Double) {
+    suspend fun setAddrReal(addrSlot: Int, value: Double) {
         setScopeSlotValueAtAddr(addrSlot, ObjReal.of(value))
     }
 
@@ -4570,7 +4586,7 @@ class CmdFrame(
         return getScopeSlotValueAtAddr(addrSlot).toBool()
     }
 
-    fun setAddrBool(addrSlot: Int, value: Boolean) {
+    suspend fun setAddrBool(addrSlot: Int, value: Boolean) {
         setScopeSlotValueAtAddr(addrSlot, if (value) ObjTrue else ObjFalse)
     }
 
@@ -4776,12 +4792,13 @@ class CmdFrame(
 
     private suspend fun getScopeSlotValue(slot: Int): Obj {
         val target = scopeTarget(slot)
+        val name = fn.scopeSlotNames[slot]
+        val hadNamedBinding = name != null && hasResolvedNamedScopeBinding(target, name)
         val index = ensureScopeSlot(target, slot)
         val record = target.getSlotRecord(index)
         val direct = record.value
         if (direct is FrameSlotRef) return direct.read()
         if (direct is RecordSlotRef) return direct.read()
-        val name = fn.scopeSlotNames[slot]
         if (name != null && record.memberName != null && record.memberName != name) {
             val resolved = target.get(name)
             if (resolved != null) {
@@ -4802,9 +4819,15 @@ class CmdFrame(
             return direct
         }
         if (name == null) return record.value
-        val resolved = target.get(name) ?: return record.value
+        val resolved = target.get(name)
+        if (resolved == null) {
+            failMissingPreparedModuleBinding(slot, name, hadNamedBinding, record)
+            return record.value
+        }
         if (resolved.value !== ObjUnset) {
             target.updateSlotFor(name, resolved)
+        } else {
+            failMissingPreparedModuleBinding(slot, name, hadNamedBinding, resolved)
         }
         return resolved.value
     }
@@ -4812,12 +4835,13 @@ class CmdFrame(
     private suspend fun getScopeSlotValueAtAddr(addrSlot: Int): Obj {
         val target = addrScopes[addrSlot] ?: error("Address slot $addrSlot is not resolved")
         val index = addrIndices[addrSlot]
+        val slotId = addrScopeSlots[addrSlot]
+        val name = fn.scopeSlotNames.getOrNull(slotId)
+        val hadNamedBinding = name != null && hasResolvedNamedScopeBinding(target, name)
         val record = target.getSlotRecord(index)
         val direct = record.value
         if (direct is FrameSlotRef) return direct.read()
         if (direct is RecordSlotRef) return direct.read()
-        val slotId = addrScopeSlots[addrSlot]
-        val name = fn.scopeSlotNames.getOrNull(slotId)
         if (name != null && record.memberName != null && record.memberName != name) {
             val resolved = target.get(name)
             if (resolved != null) {
@@ -4838,16 +4862,29 @@ class CmdFrame(
             return direct
         }
         if (name == null) return record.value
-        val resolved = target.get(name) ?: return record.value
+        val resolved = target.get(name)
+        if (resolved == null) {
+            failMissingPreparedModuleBinding(slotId, name, hadNamedBinding, record)
+            return record.value
+        }
         if (resolved.value !== ObjUnset) {
             target.updateSlotFor(name, resolved)
+        } else {
+            failMissingPreparedModuleBinding(slotId, name, hadNamedBinding, resolved)
         }
         return resolved.value
     }
 
-    private fun setScopeSlotValueAtAddr(addrSlot: Int, value: Obj) {
+    private suspend fun setScopeSlotValueAtAddr(addrSlot: Int, value: Obj) {
         val target = addrScopes[addrSlot] ?: error("Address slot $addrSlot is not resolved")
         val index = addrIndices[addrSlot]
+        val record = target.getSlotRecord(index)
+        val slotId = addrScopeSlots[addrSlot]
+        val name = fn.scopeSlotNames.getOrNull(slotId)
+        if (name != null && (record.type == ObjRecord.Type.Delegated || record.type == ObjRecord.Type.Property || record.value is ObjProperty)) {
+            target.assign(record, name, value)
+            return
+        }
         target.setSlotValue(index, value)
     }
 
@@ -4875,6 +4912,41 @@ class CmdFrame(
         return index
     }
 
+    private fun hasNamedScopeBinding(target: Scope, name: String): Boolean {
+        if (target.tryGetLocalRecord(target, name, target.currentClassCtx) != null) return true
+        if (target.getSlotIndexOf(name) != null) return true
+        if (target.get(name) != null) return true
+        return false
+    }
+
+    private fun hasResolvedNamedScopeBinding(target: Scope, name: String): Boolean =
+        findNamedExistingRecord(target, name) != null
+
+    private fun findNamedExistingRecord(target: Scope, name: String): ObjRecord? {
+        target.tryGetLocalRecord(target, name, target.currentClassCtx)?.let { return it }
+        target.get(name)?.let { record ->
+            if (record.value !== ObjUnset || record.type == ObjRecord.Type.Delegated || record.type == ObjRecord.Type.Property) {
+                return record
+            }
+        }
+        return null
+    }
+
+    private fun failMissingPreparedModuleBinding(
+        slot: Int,
+        name: String,
+        hadNamedBinding: Boolean,
+        record: ObjRecord
+    ) {
+        if (hadNamedBinding) return
+        if (record.value !== ObjUnset) return
+        if (fn.scopeSlotIsModule.getOrNull(slot) != true) return
+        throw ScriptError(
+            ensureScope().pos,
+            "module binding '$name' is not available in the execution scope; prepare the script imports/module bindings explicitly"
+        )
+    }
+
     private fun ensureLocalMutable(localIndex: Int) {
         val name = fn.localSlotNames.getOrNull(localIndex) ?: return
         val isMutable = fn.localSlotMutables.getOrNull(localIndex) ?: true

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/SeedLocals.kt

@@ -36,7 +36,7 @@ internal suspend fun seedFrameLocalsFromScope(frame: CmdFrame, scope: Scope) {
         } else {
             record.value
         }
-        if (value is net.sergeych.lyng.FrameSlotRef && value.refersTo(frame.frame, base + i)) {
+        if (value is net.sergeych.lyng.FrameSlotRef && value.refersTo(frame.frame, i)) {
             continue
         }
         frame.setObjUnchecked(base + i, value)

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/Obj.kt

@@ -25,6 +25,8 @@ import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonNull
 import kotlinx.serialization.serializer
 import net.sergeych.lyng.*
+import net.sergeych.lyng.InteropOperator
+import net.sergeych.lyng.OperatorInteropRegistry
 import net.sergeych.lyng.miniast.ParamDoc
 import net.sergeych.lyng.miniast.addFnDoc
 import net.sergeych.lyng.miniast.type
@@ -175,7 +177,8 @@ open class Obj {
         if (other === this) return 0
         if (other === ObjNull || other === ObjUnset || other === ObjVoid) return 2
         return invokeInstanceMethod(scope, "compareTo", Arguments(other)) {
-            scope.raiseNotImplemented("compareTo for ${objClass.className}")
+            OperatorInteropRegistry.invokeCompare(scope, this, other)?.let { ObjInt.of(it.toLong()) }
+                ?: scope.raiseNotImplemented("compareTo for ${objClass.className}")
         }.cast<ObjInt>(scope).toInt()
     }
 
@@ -284,7 +287,8 @@ open class Obj {
         }
         if (self !== this) return self.plus(scope, otherValue)
         return invokeInstanceMethod(scope, "plus", Arguments(otherValue)) {
-            scope.raiseNotImplemented("plus for ${objClass.className}")
+            OperatorInteropRegistry.invokeBinary(scope, self, otherValue, InteropOperator.Plus)
+                ?: scope.raiseNotImplemented("plus for ${objClass.className}")
         }
     }
 
@@ -301,7 +305,8 @@ open class Obj {
         }
         if (self !== this) return self.minus(scope, otherValue)
         return invokeInstanceMethod(scope, "minus", Arguments(otherValue)) {
-            scope.raiseNotImplemented("minus for ${objClass.className}")
+            OperatorInteropRegistry.invokeBinary(scope, self, otherValue, InteropOperator.Minus)
+                ?: scope.raiseNotImplemented("minus for ${objClass.className}")
         }
     }
 
@@ -324,7 +329,8 @@ open class Obj {
         }
         if (self !== this) return self.mul(scope, otherValue)
         return invokeInstanceMethod(scope, "mul", Arguments(otherValue)) {
-            scope.raiseNotImplemented("mul for ${objClass.className}")
+            OperatorInteropRegistry.invokeBinary(scope, self, otherValue, InteropOperator.Mul)
+                ?: scope.raiseNotImplemented("mul for ${objClass.className}")
         }
     }
 
@@ -341,7 +347,8 @@ open class Obj {
         }
         if (self !== this) return self.div(scope, otherValue)
         return invokeInstanceMethod(scope, "div", Arguments(otherValue)) {
-            scope.raiseNotImplemented("div for ${objClass.className}")
+            OperatorInteropRegistry.invokeBinary(scope, self, otherValue, InteropOperator.Div)
+                ?: scope.raiseNotImplemented("div for ${objClass.className}")
         }
     }
 
@@ -358,7 +365,8 @@ open class Obj {
         }
         if (self !== this) return self.mod(scope, otherValue)
         return invokeInstanceMethod(scope, "mod", Arguments(otherValue)) {
-            scope.raiseNotImplemented("mod for ${objClass.className}")
+            OperatorInteropRegistry.invokeBinary(scope, self, otherValue, InteropOperator.Mod)
+                ?: scope.raiseNotImplemented("mod for ${objClass.className}")
         }
     }
 

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjBigDecimalSupport.kt

@@ -0,0 +1,313 @@
+/*
+ * 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.obj
+
+import com.ionspin.kotlin.bignum.decimal.BigDecimal as IonBigDecimal
+import com.ionspin.kotlin.bignum.decimal.DecimalMode
+import com.ionspin.kotlin.bignum.decimal.RoundingMode
+import com.ionspin.kotlin.bignum.integer.BigInteger
+import net.sergeych.lyng.Arguments
+import net.sergeych.lyng.FrameSlotRef
+import net.sergeych.lyng.InteropOperator
+import net.sergeych.lyng.ModuleScope
+import net.sergeych.lyng.OperatorInteropRegistry
+import net.sergeych.lyng.RecordSlotRef
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.ScopeFacade
+import net.sergeych.lyng.TypeDecl
+import net.sergeych.lyng.miniast.addPropertyDoc
+import net.sergeych.lyng.miniast.type
+import net.sergeych.lyng.requiredArg
+
+object ObjBigDecimalSupport {
+    private const val decimalContextVar = "__lyng_decimal_context__"
+    // For Real -> BigDecimal, preserve the actual IEEE-754 Double value using a
+    // round-trip-safe precision. This intentionally does not try to recover source text.
+    private val realConversionMode = DecimalMode(17L, RoundingMode.ROUND_HALF_TO_EVEN)
+    // Division needs an explicit stopping rule for non-terminating results. Use a
+    // decimal128-like default context until Lyng exposes per-operation contexts.
+    private val defaultDivisionMode = DecimalMode(34L, RoundingMode.ROUND_HALF_TO_EVEN)
+    private val zero: IonBigDecimal = IonBigDecimal.ZERO
+    private val decimalTypeDecl = TypeDecl.Simple("lyng.decimal.BigDecimal", false)
+    private object BoundMarker
+    private data class DecimalRuntimeContext(
+        val precision: Long,
+        val rounding: RoundingMode
+    ) : Obj()
+
+    suspend fun bindTo(module: ModuleScope) {
+        val decimalClass = module.requireClass("BigDecimal")
+        if (decimalClass.kotlinClassData === BoundMarker) return
+        decimalClass.kotlinClassData = BoundMarker
+        decimalClass.isAbstract = false
+        val hooks = decimalClass.bridgeInitHooks ?: mutableListOf<suspend (ScopeFacade, ObjInstance) -> Unit>().also {
+            decimalClass.bridgeInitHooks = it
+        }
+        hooks += { _, instance ->
+            instance.kotlinInstanceData = zero
+        }
+        decimalClass.addFn("plus") {
+            newInstance(decimalClass, valueOf(thisObj).plus(coerceArg(requireScope(), args.firstAndOnly())))
+        }
+        decimalClass.addFn("minus") {
+            newInstance(decimalClass, valueOf(thisObj).minus(coerceArg(requireScope(), args.firstAndOnly())))
+        }
+        decimalClass.addFn("mul") {
+            newInstance(decimalClass, valueOf(thisObj).times(coerceArg(requireScope(), args.firstAndOnly())))
+        }
+        decimalClass.addFn("div") {
+            newInstance(decimalClass, divideWithContext(valueOf(thisObj), coerceArg(requireScope(), args.firstAndOnly()), currentDivisionMode(requireScope())))
+        }
+        decimalClass.addFn("mod") {
+            newInstance(decimalClass, valueOf(thisObj).rem(coerceArg(requireScope(), args.firstAndOnly())))
+        }
+        decimalClass.addFn("compareTo") {
+            ObjInt.of(valueOf(thisObj).compareTo(coerceArg(requireScope(), args.firstAndOnly())).toLong())
+        }
+        decimalClass.addFn("negate") {
+            newInstance(decimalClass, valueOf(thisObj).unaryMinus())
+        }
+        decimalClass.addFn("toInt") {
+            ObjInt.of(valueOf(thisObj).longValue(false))
+        }
+        decimalClass.addFn("toReal") {
+            ObjReal.of(valueOf(thisObj).doubleValue(false))
+        }
+        decimalClass.addFn("toStringExpanded") {
+            ObjString(valueOf(thisObj).toStringExpanded())
+        }
+        decimalClass.addClassFn("fromInt") {
+            val value = requiredArg<ObjInt>(0).value
+            newInstance(decimalClass, IonBigDecimal.fromLongAsSignificand(value))
+        }
+        decimalClass.addClassFn("fromReal") {
+            val value = requiredArg<ObjReal>(0).value
+            newInstance(decimalClass, IonBigDecimal.fromDouble(value, realConversionMode))
+        }
+        decimalClass.addClassFn("fromString") {
+            val value = requiredArg<ObjString>(0).value
+            try {
+                newInstance(decimalClass, IonBigDecimal.parseStringWithMode(value))
+            } catch (e: Throwable) {
+                requireScope().raiseIllegalArgument("invalid BigDecimal string: $value")
+            }
+        }
+        module.addFn("withDecimalContext") {
+            val (context, block) = when (args.list.size) {
+                2 -> {
+                    val first = args[0]
+                    val block = args[1]
+                    if (first is ObjInt) {
+                        DecimalRuntimeContext(first.value, RoundingMode.ROUND_HALF_TO_EVEN) to block
+                    } else {
+                        normalizeContext(requireScope(), first) to block
+                    }
+                }
+                3 -> {
+                    val precision = requiredArg<ObjInt>(0).value
+                    val rounding = roundingModeFromObj(requireScope(), args[1])
+                    DecimalRuntimeContext(precision, rounding) to args[2]
+                }
+                else -> requireScope().raiseIllegalArgument("withDecimalContext expects (context, block), (precision, block), or (precision, rounding, block)")
+            }
+            val child = requireScope().createChildScope()
+            child.addConst(decimalContextVar, context)
+            block.callOn(child)
+        }
+        registerBuiltinConversions(decimalClass)
+        registerInterop(decimalClass)
+    }
+
+    private fun valueOf(obj: Obj): IonBigDecimal {
+        val instance = obj as? ObjInstance ?: error("BigDecimal receiver must be an object instance")
+        return instance.kotlinInstanceData as? IonBigDecimal ?: zero
+    }
+
+    private suspend fun currentDivisionMode(scope: Scope): DecimalMode {
+        val context = findContextObject(scope) ?: return defaultDivisionMode
+        return DecimalMode(context.precision, context.rounding)
+    }
+
+    private fun divideWithContext(left: IonBigDecimal, right: IonBigDecimal, mode: DecimalMode): IonBigDecimal {
+        if (mode.decimalPrecision <= 0L) {
+            return stripMode(left.divide(right, mode))
+        }
+        val exactLeft = stripMode(left)
+        val exactRight = stripMode(right)
+        val guardMode = DecimalMode(mode.decimalPrecision + 2, RoundingMode.TOWARDS_ZERO)
+        var guarded = stripMode(exactLeft.divide(exactRight, guardMode))
+        val hasMoreTail = !stripMode(exactLeft - stripMode(guarded * exactRight)).isZero()
+        if (hasMoreTail && isHalfRounding(mode.roundingMode) && looksLikeExactHalf(guarded, mode.decimalPrecision)) {
+            guarded = nudgeLastDigitAwayFromZero(guarded)
+        }
+        return stripMode(guarded.roundSignificand(mode))
+    }
+
+    private suspend fun ScopeFacade.newInstance(decimalClass: ObjClass, value: IonBigDecimal): ObjInstance {
+        val instance = call(decimalClass) as? ObjInstance
+            ?: raiseIllegalState("BigDecimal() did not return an object instance")
+        instance.kotlinInstanceData = value
+        return instance
+    }
+
+    private fun coerceArg(scope: Scope, value: Obj): IonBigDecimal = when (value) {
+        is ObjInt -> IonBigDecimal.fromLongAsSignificand(value.value)
+        is ObjReal -> IonBigDecimal.fromDouble(value.value, realConversionMode)
+        is ObjInstance -> {
+            if (value.objClass.className != "BigDecimal") {
+                scope.raiseIllegalArgument("expected BigDecimal-compatible value, got ${value.objClass.className}")
+            }
+            value.kotlinInstanceData as? IonBigDecimal ?: zero
+        }
+        else -> scope.raiseIllegalArgument("expected BigDecimal-compatible value, got ${value.objClass.className}")
+    }
+
+    private suspend fun normalizeContext(scope: Scope, value: Obj): DecimalRuntimeContext {
+        val instance = value as? ObjInstance
+            ?: scope.raiseClassCastError("withDecimalContext expects DecimalContext as the first argument")
+        if (instance.objClass.className != "DecimalContext") {
+            scope.raiseClassCastError("withDecimalContext expects DecimalContext as the first argument")
+        }
+        return decimalRuntimeContextFromInstance(scope, instance)
+    }
+
+    private fun findContextObject(scope: Scope): DecimalRuntimeContext? {
+        var current: Scope? = scope
+        while (current != null) {
+            val record = current.objects[decimalContextVar] ?: current.localBindings[decimalContextVar]
+            val value = when (val raw = record?.value) {
+                is FrameSlotRef -> raw.peekValue()
+                is RecordSlotRef -> raw.peekValue()
+                else -> raw
+            }
+            when (value) {
+                is DecimalRuntimeContext -> return value
+            }
+            current = current.parent
+        }
+        return null
+    }
+
+    private suspend fun decimalRuntimeContextFromInstance(scope: Scope, context: ObjInstance): DecimalRuntimeContext {
+        val precision = context.readField(scope, "precision").value as? ObjInt
+            ?: scope.raiseClassCastError("DecimalContext.precision must be Int")
+        if (precision.value <= 0L) {
+            scope.raiseIllegalArgument("DecimalContext precision must be positive")
+        }
+        val rounding = roundingModeFromObj(scope, context.readField(scope, "rounding").value)
+        return DecimalRuntimeContext(precision.value, rounding)
+    }
+
+    private fun stripMode(value: IonBigDecimal): IonBigDecimal =
+        IonBigDecimal.fromBigIntegerWithExponent(value.significand, value.exponent)
+
+    private fun isHalfRounding(mode: RoundingMode): Boolean = when (mode) {
+        RoundingMode.ROUND_HALF_TO_EVEN,
+        RoundingMode.ROUND_HALF_AWAY_FROM_ZERO,
+        RoundingMode.ROUND_HALF_TOWARDS_ZERO,
+        RoundingMode.ROUND_HALF_CEILING,
+        RoundingMode.ROUND_HALF_FLOOR,
+        RoundingMode.ROUND_HALF_TO_ODD -> true
+        else -> false
+    }
+
+    private fun looksLikeExactHalf(value: IonBigDecimal, targetPrecision: Long): Boolean {
+        val digits = value.significand.abs().toString(10)
+        if (digits.length <= targetPrecision) return false
+        val discarded = digits.substring(targetPrecision.toInt())
+        return discarded[0] == '5' && discarded.drop(1).all { it == '0' }
+    }
+
+    private fun nudgeLastDigitAwayFromZero(value: IonBigDecimal): IonBigDecimal {
+        val ulpExponent = value.exponent - value.precision + 1
+        val ulp = IonBigDecimal.fromBigIntegerWithExponent(BigInteger.ONE, ulpExponent)
+        return if (value.significand.signum() < 0) value - ulp else value + ulp
+    }
+
+    private fun roundingModeFromObj(scope: Scope, value: Obj): RoundingMode {
+        val entry = value as? ObjEnumEntry ?: scope.raiseClassCastError("DecimalContext.rounding must be DecimalRounding")
+        return when (entry.name.value) {
+            "HalfEven" -> RoundingMode.ROUND_HALF_TO_EVEN
+            "HalfAwayFromZero" -> RoundingMode.ROUND_HALF_AWAY_FROM_ZERO
+            "HalfTowardsZero" -> RoundingMode.ROUND_HALF_TOWARDS_ZERO
+            "Ceiling" -> RoundingMode.CEILING
+            "Floor" -> RoundingMode.FLOOR
+            "AwayFromZero" -> RoundingMode.AWAY_FROM_ZERO
+            "TowardsZero" -> RoundingMode.TOWARDS_ZERO
+            else -> scope.raiseIllegalArgument("unsupported DecimalRounding: ${entry.name.value}")
+        }
+    }
+
+    private fun registerBuiltinConversions(decimalClass: ObjClass) {
+        ObjInt.type.addPropertyDoc(
+            name = "d",
+            doc = "Convert this integer to a BigDecimal.",
+            type = type("lyng.decimal.BigDecimal"),
+            moduleName = "lyng.decimal",
+            getter = { newInstance(decimalClass, IonBigDecimal.fromLongAsSignificand(thisAs<ObjInt>().value)) }
+        )
+        ObjInt.type.members["d"] = ObjInt.type.members.getValue("d").copy(typeDecl = decimalTypeDecl)
+        ObjReal.type.addPropertyDoc(
+            name = "d",
+            doc = "Convert this real number to a BigDecimal by preserving the current IEEE-754 value with 17 significant digits and half-even rounding.",
+            type = type("lyng.decimal.BigDecimal"),
+            moduleName = "lyng.decimal",
+            getter = { newInstance(decimalClass, IonBigDecimal.fromDouble(thisAs<ObjReal>().value, realConversionMode)) }
+        )
+        ObjReal.type.members["d"] = ObjReal.type.members.getValue("d").copy(typeDecl = decimalTypeDecl)
+        ObjString.type.addPropertyDoc(
+            name = "d",
+            doc = "Parse this string as a BigDecimal.",
+            type = type("lyng.decimal.BigDecimal"),
+            moduleName = "lyng.decimal",
+            getter = {
+                val value = thisAs<ObjString>().value
+                try {
+                    newInstance(decimalClass, IonBigDecimal.parseStringWithMode(value))
+                } catch (e: Throwable) {
+                    requireScope().raiseIllegalArgument("invalid BigDecimal string: $value")
+                }
+            }
+        )
+        ObjString.type.members["d"] = ObjString.type.members.getValue("d").copy(typeDecl = decimalTypeDecl)
+    }
+
+    private fun registerInterop(decimalClass: ObjClass) {
+        OperatorInteropRegistry.register(
+            leftClass = ObjInt.type,
+            rightClass = decimalClass,
+            commonClass = decimalClass,
+            operatorNames = listOf(
+                InteropOperator.Plus.name,
+                InteropOperator.Minus.name,
+                InteropOperator.Mul.name,
+                InteropOperator.Div.name,
+                InteropOperator.Mod.name,
+                InteropOperator.Compare.name,
+                InteropOperator.Equals.name
+            ),
+            leftToCommon = ObjExternCallable.fromBridge {
+                val value = requiredArg<ObjInt>(0).value
+                newInstance(decimalClass, IonBigDecimal.fromLongAsSignificand(value))
+            },
+            rightToCommon = ObjExternCallable.fromBridge {
+                requiredArg<Obj>(0)
+            }
+        )
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjClass.kt

@@ -106,10 +106,20 @@ open class ObjClass(
     vararg parents: ObjClass,
 ) : Obj() {
 
+    private fun declaringModulePackageName(scope: Scope?): String? {
+        var current = scope
+        while (current != null) {
+            if (current is ModuleScope) return current.packageName
+            current = current.parent
+        }
+        return null
+    }
+
     var isAnonymous: Boolean = false
 
     var isAbstract: Boolean = false
     var isClosed: Boolean = false
+    var logicalPackageNameOverride: String? = null
 
     // Stable identity and simple structural version for PICs
     val classId: Long = ClassIdGen.nextId()
@@ -169,6 +179,16 @@ open class ObjClass(
      */
     var classScope: Scope? = null
 
+    /**
+     * Stable logical identity for class matching across separately instantiated modules.
+     * Uses declaring module package plus class name when available.
+     */
+    val logicalPackageName: String?
+        get() = logicalPackageNameOverride ?: declaringModulePackageName(classScope)
+
+    val logicalName: String
+        get() = logicalPackageName?.let { "$it::$className" } ?: className
+
     /** Direct parents in declaration order (kept deterministic). */
     val directParents: List<ObjClass> = parents.toList()
 

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjDynamic.kt

@@ -129,6 +129,7 @@ open class ObjDynamic(var readCallback: Obj? = null, var writeCallback: Obj? = n
         }
 
         val type = object : ObjClass("Delegate") {}.apply {
+            logicalPackageNameOverride = "lyng.stdlib"
             addFn("getValue") { raiseError("Delegate.getValue is not implemented") }
             addFn("setValue") { raiseError("Delegate.setValue is not implemented") }
             addFn("invoke") { raiseError("Delegate.invoke is not implemented") }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjInstance.kt

@@ -364,6 +364,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
         onNotFoundResult: (suspend () -> Obj?)?
     ): Obj {
         val caller = scope.currentClassCtx
+        val methodScope = scope.applyClosure(instanceScope)
         
         // Fast path for public members when outside any class context
         if (caller == null) {
@@ -373,7 +374,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                     if (rec.type == ObjRecord.Type.Property) {
                         if (args.isEmpty()) return (rec.value as ObjProperty).callGetter(scope, this, decl)
                     } else if (rec.type == ObjRecord.Type.Fun) {
-                        return rec.value.invoke(instanceScope, this, args, decl)
+                        return rec.value.invoke(methodScope, this, args, decl)
                     }
                 }
             }
@@ -384,7 +385,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                         if (rec.type == ObjRecord.Type.Property) {
                             if (args.isEmpty()) return (rec.value as ObjProperty).callGetter(scope, this, decl)
                         } else if (rec.type == ObjRecord.Type.Fun) {
-                            return rec.value.invoke(instanceScope, this, args, decl)
+                            return rec.value.invoke(methodScope, this, args, decl)
                         }
                     }
                 }
@@ -394,7 +395,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                         if (rec.type == ObjRecord.Type.Property) {
                             if (args.isEmpty()) return (rec.value as ObjProperty).callGetter(scope, this, decl)
                         } else if (rec.type == ObjRecord.Type.Fun) {
-                            return rec.value.invoke(instanceScope, this, args, decl)
+                            return rec.value.invoke(methodScope, this, args, decl)
                         }
                     }
                 }
@@ -409,7 +410,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                     if (rec.type == ObjRecord.Type.Property) {
                         if (args.isEmpty()) return (rec.value as ObjProperty).callGetter(scope, this, c)
                     } else if (rec.type == ObjRecord.Type.Fun) {
-                        return rec.value.invoke(instanceScope, this, args, c)
+                        return rec.value.invoke(methodScope, this, args, c)
                     }
                 }
             }
@@ -418,7 +419,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                     if (rec.type == ObjRecord.Type.Property) {
                         if (args.isEmpty()) return (rec.value as ObjProperty).callGetter(scope, this, c)
                     } else if (rec.type == ObjRecord.Type.Fun) {
-                        return rec.value.invoke(instanceScope, this, args, c)
+                        return rec.value.invoke(methodScope, this, args, c)
                     }
                 }
             }
@@ -427,7 +428,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                     if (rec.type == ObjRecord.Type.Property) {
                         if (args.isEmpty()) return (rec.value as ObjProperty).callGetter(scope, this, c)
                     } else if (rec.type == ObjRecord.Type.Fun) {
-                        return rec.value.invoke(instanceScope, this, args, c)
+                        return rec.value.invoke(methodScope, this, args, c)
                     }
                 }
             }
@@ -439,7 +440,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                 val decl = rec.declaringClass ?: objClass.findDeclaringClassOf(name) ?: objClass
                 val effectiveCaller = caller ?: if (scope.thisObj === this) objClass else null
                 if (canAccessMember(rec.visibility, decl, effectiveCaller, name)) {
-                    return rec.value.invoke(instanceScope, this, args, decl)
+                    return rec.value.invoke(methodScope, this, args, decl)
                 }
             }
         }
@@ -474,7 +475,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
                 if (args.isEmpty()) return (rec.value as ObjProperty).callGetter(scope, this, decl)
             } else if (rec.type == ObjRecord.Type.Fun) {
                 return rec.value.invoke(
-                    instanceScope,
+                    methodScope,
                     this,
                     args,
                     decl
@@ -586,8 +587,10 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
     }
 
     override suspend fun compareTo(scope: Scope, other: Obj): Int {
-        if (other !is ObjInstance) return -1
-        if (other.objClass != objClass) return -1
+        if (other !is ObjInstance || other.objClass != objClass) {
+            OperatorInteropRegistry.invokeCompare(scope, this, other)?.let { return it }
+            return -1
+        }
         for (f in comparableVars) {
             val a = f.value.value
             val b = other.instanceScope.objects[f.key]?.value ?: scope.raiseError("Internal error: field ${f.key} not found in other instance")

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjInt.kt

@@ -19,6 +19,8 @@ package net.sergeych.lyng.obj
 
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonPrimitive
+import net.sergeych.lyng.InteropOperator
+import net.sergeych.lyng.OperatorInteropRegistry
 import net.sergeych.lyng.Scope
 import net.sergeych.lyng.miniast.addFnDoc
 import net.sergeych.lynon.LynonDecoder
@@ -54,10 +56,11 @@ class ObjInt(val value: Long, override val isConst: Boolean = false) : Obj(), Nu
     }
 
     override suspend fun compareTo(scope: Scope, other: Obj): Int {
-        if (other !is Numeric) return -2
         return if (other is ObjInt) {
             value.compareTo(other.value)
         } else {
+            OperatorInteropRegistry.invokeCompare(scope, this, other)?.let { return it }
+            if (other !is Numeric) return -2
             doubleValue.compareTo(other.doubleValue)
         }
     }
@@ -70,28 +73,39 @@ class ObjInt(val value: Long, override val isConst: Boolean = false) : Obj(), Nu
         if (other is ObjInt)
             of(this.value + other.value)
         else
+            OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Plus)
+                ?:
             ObjReal.of(this.doubleValue + other.toDouble())
 
     override suspend fun minus(scope: Scope, other: Obj): Obj =
         if (other is ObjInt)
             of(this.value - other.value)
         else
+            OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Minus)
+                ?:
             ObjReal.of(this.doubleValue - other.toDouble())
 
     override suspend fun mul(scope: Scope, other: Obj): Obj =
         if (other is ObjInt) {
             of(this.value * other.value)
-        } else ObjReal.of(this.value * other.toDouble())
+        } else {
+            OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Mul)
+                ?: ObjReal.of(this.value * other.toDouble())
+        }
 
     override suspend fun div(scope: Scope, other: Obj): Obj =
         if (other is ObjInt)
             of(this.value / other.value)
-        else ObjReal.of(this.value / other.toDouble())
+        else
+            OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Div)
+                ?: ObjReal.of(this.value / other.toDouble())
 
     override suspend fun mod(scope: Scope, other: Obj): Obj =
         if (other is ObjInt)
             of(this.value % other.value)
-        else ObjReal.of(this.value.toDouble() % other.toDouble())
+        else
+            OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Mod)
+                ?: ObjReal.of(this.value.toDouble() % other.toDouble())
 
     /**
      * Numbers are now immutable, so we can't do in-place assignment.

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjLazyDelegate.kt

@@ -1,86 +0,0 @@
-/*
- * 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.obj
-
-import net.sergeych.lyng.Arguments
-import net.sergeych.lyng.Pos
-import net.sergeych.lyng.Scope
-import net.sergeych.lyng.Statement
-import net.sergeych.lyng.Visibility
-import net.sergeych.lyng.executeBytecodeWithSeed
-
-/**
- * Lazy delegate used by `val x by lazy { ... }`.
- */
-class ObjLazyDelegate(
-    private val builder: Obj,
-    private val capturedScope: Scope,
-) : Obj() {
-    override val objClass: ObjClass = type
-
-    private var calculated = false
-    private var cachedValue: Obj = ObjVoid
-
-    override suspend fun invokeInstanceMethod(
-        scope: Scope,
-        name: String,
-        args: Arguments,
-        onNotFoundResult: (suspend () -> Obj?)?,
-    ): Obj {
-        return when (name) {
-            "getValue" -> {
-                if (!calculated) {
-                    val callScope = capturedScope.createChildScope(capturedScope.pos, args = Arguments.EMPTY)
-                    cachedValue = if (builder is Statement) {
-                        executeBytecodeWithSeed(callScope, builder, "lazy delegate")
-                    } else {
-                        builder.callOn(callScope)
-                    }
-                    calculated = true
-                }
-                cachedValue
-            }
-            "setValue" -> scope.raiseIllegalAssignment("lazy delegate is read-only")
-            else -> super.invokeInstanceMethod(scope, name, args, onNotFoundResult)
-        }
-    }
-
-    companion object {
-        val type = ObjClass("LazyDelegate").apply {
-            implementingNames.add("Delegate")
-            createField(
-                "getValue",
-                ObjNull,
-                isMutable = false,
-                visibility = Visibility.Public,
-                pos = Pos.builtIn,
-                declaringClass = this,
-                type = ObjRecord.Type.Fun
-            )
-            createField(
-                "setValue",
-                ObjNull,
-                isMutable = false,
-                visibility = Visibility.Public,
-                pos = Pos.builtIn,
-                declaringClass = this,
-                type = ObjRecord.Type.Fun
-            )
-        }
-    }
-}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjReal.kt

@@ -19,6 +19,8 @@ package net.sergeych.lyng.obj
 
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonPrimitive
+import net.sergeych.lyng.InteropOperator
+import net.sergeych.lyng.OperatorInteropRegistry
 import net.sergeych.lyng.Scope
 import net.sergeych.lyng.miniast.addConstDoc
 import net.sergeych.lyng.miniast.addFnDoc
@@ -40,6 +42,8 @@ data class ObjReal(val value: Double) : Obj(), Numeric {
     override fun byValueCopy(): Obj = this
 
     override suspend fun compareTo(scope: Scope, other: Obj): Int {
+        if (other is ObjReal) return value.compareTo(other.value)
+        OperatorInteropRegistry.invokeCompare(scope, this, other)?.let { return it }
         if (other !is Numeric) return -2
         return value.compareTo(other.doubleValue)
     }
@@ -63,19 +67,24 @@ data class ObjReal(val value: Double) : Obj(), Numeric {
     }
 
     override suspend fun plus(scope: Scope, other: Obj): Obj =
-        of(this.value + other.toDouble())
+        OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Plus)
+            ?: of(this.value + other.toDouble())
 
     override suspend fun minus(scope: Scope, other: Obj): Obj =
-        of(this.value - other.toDouble())
+        OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Minus)
+            ?: of(this.value - other.toDouble())
 
     override suspend fun mul(scope: Scope, other: Obj): Obj =
-        of(this.value * other.toDouble())
+        OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Mul)
+            ?: of(this.value * other.toDouble())
 
     override suspend fun div(scope: Scope, other: Obj): Obj =
-        of(this.value / other.toDouble())
+        OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Div)
+            ?: of(this.value / other.toDouble())
 
     override suspend fun mod(scope: Scope, other: Obj): Obj =
-        of(this.value % other.toDouble())
+        OperatorInteropRegistry.invokeBinary(scope, this, other, InteropOperator.Mod)
+            ?: of(this.value % other.toDouble())
 
     /**
      * Returns unboxed Double value

lynglib/src/commonMain/kotlin/net/sergeych/lyng/stdlib_included/decimal_lyng.kt

@@ -0,0 +1,222 @@
+/*
+ * 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.stdlib_included
+
+@Suppress("Unused", "MemberVisibilityCanBePrivate")
+internal val decimalLyng = """
+package lyng.decimal
+
+/**
+ * Rounding policies used by [DecimalContext] and `withDecimalContext(...)`.
+ *
+ * These modes currently affect decimal division. They are designed to be explicit and readable in Lyng code.
+ *
+ * Common examples at precision `2`:
+ * - `HalfEven`: `1.d / 8.d -> 0.12`
+ * - `HalfAwayFromZero`: `1.d / 8.d -> 0.13`, `-1.d / 8.d -> -0.13`
+ * - `HalfTowardsZero`: `1.d / 8.d -> 0.12`, `-1.d / 8.d -> -0.12`
+ * - `Ceiling`: rounds toward positive infinity
+ * - `Floor`: rounds toward negative infinity
+ * - `AwayFromZero`: always increases magnitude when rounding is needed
+ * - `TowardsZero`: always truncates toward zero
+ */
+enum DecimalRounding {
+    HalfEven,
+    HalfAwayFromZero,
+    HalfTowardsZero,
+    Ceiling,
+    Floor,
+    AwayFromZero,
+    TowardsZero
+}
+
+/**
+ * Dynamic decimal arithmetic settings.
+ *
+ * A decimal context is not attached permanently to a `BigDecimal` value. Instead, it is applied dynamically
+ * inside `withDecimalContext(...)`, which makes the rule local to a block of code.
+ *
+ * Default context:
+ * - precision: `34` significant digits
+ * - rounding: `DecimalRounding.HalfEven`
+ *
+ * Example:
+ *
+ *     import lyng.decimal
+ *
+ *     (1.d / 3.d).toStringExpanded()
+ *     >>> "0.3333333333333333333333333333333333"
+ *
+ *     withDecimalContext(10) { (1.d / 3.d).toStringExpanded() }
+ *     >>> "0.3333333333"
+ *
+ *     withDecimalContext(2, DecimalRounding.HalfAwayFromZero) { (1.d / 8.d).toStringExpanded() }
+ *     >>> "0.13"
+ */
+class DecimalContext(
+    val precision: Int = 34,
+    val rounding: DecimalRounding = DecimalRounding.HalfEven
+)
+
+/**
+ * Arbitrary-precision decimal value.
+ *
+ * `BigDecimal` is intended for decimal arithmetic where binary floating-point (`Real`) is the wrong tool:
+ * - money
+ * - human-entered decimal values
+ * - ratios that should round in decimal, not in binary
+ * - reproducible decimal formatting
+ *
+ * Creating values:
+ *
+ * - `1.d` converts `Int -> BigDecimal`
+ * - `2.2.d` converts `Real -> BigDecimal` by preserving the current IEEE-754 value
+ * - `"2.2".d` parses exact decimal text
+ * - `BigDecimal.fromInt(...)`, `fromReal(...)`, `fromString(...)` are explicit factory forms
+ *
+ * Important distinction:
+ *
+ * - `2.2.d` means "take the current `Real` value and convert it"
+ * - `"2.2".d` means "parse this exact decimal literal text"
+ *
+ * Therefore:
+ *
+ *     import lyng.decimal
+ *
+ *     2.2.d.toStringExpanded()
+ *     >>> "2.2"
+ *
+ *     (0.1 + 0.2).d.toStringExpanded()
+ *     >>> "0.30000000000000004"
+ *
+ *     "0.3".d.toStringExpanded()
+ *     >>> "0.3"
+ *
+ * Mixed arithmetic:
+ *
+ * `BigDecimal` defines its own operators against decimal-compatible values, and the decimal module also registers
+ * interop bridges so built-in left-hand operands work naturally:
+ *
+ *     import lyng.decimal
+ *
+ *     1.d + 2
+ *     >>> 3.d
+ *
+ *     1 + 2.d
+ *     >>> 3.d
+ *
+ *     0.5 + 1.d
+ *     >>> 1.5.d
+ *
+ * Precision and rounding:
+ *
+ * - division uses the default decimal context unless overridden
+ * - use `withDecimalContext(...)` to apply a local precision/rounding policy
+ *
+ * Exact decimal literal style:
+ *
+ * If you want the source text itself to be the decimal value, use a string:
+ *
+ *     "2.2".d
+ *
+ * That is the precise form. `2.2.d` remains a `Real -> BigDecimal` conversion by design.
+ */
+extern class BigDecimal() {
+    /** Add another decimal-compatible value. */
+    extern fun plus(other: Object): BigDecimal
+    /** Subtract another decimal-compatible value. */
+    extern fun minus(other: Object): BigDecimal
+    /** Multiply by another decimal-compatible value. */
+    extern fun mul(other: Object): BigDecimal
+    /**
+     * Divide by another decimal-compatible value.
+     *
+     * Division uses the current decimal context:
+     * - by default: `34` significant digits, `HalfEven`
+     * - inside `withDecimalContext(...)`: the context active for the current block
+     */
+    extern fun div(other: Object): BigDecimal
+    /** Remainder with another decimal-compatible value. */
+    extern fun mod(other: Object): BigDecimal
+    /** Compare with another decimal-compatible value. */
+    extern fun compareTo(other: Object): Int
+    /** Unary minus. */
+    extern fun negate(): BigDecimal
+    /** Convert to `Int` by dropping the fractional part according to backend conversion rules. */
+    extern fun toInt(): Int
+    /** Convert to `Real`. */
+    extern fun toReal(): Real
+    /**
+     * Convert to a plain decimal string without scientific notation.
+     *
+     * This is the preferred representation for user-facing decimal tests and diagnostics.
+     */
+    extern fun toStringExpanded(): String
+
+    /** Create a decimal from an `Int`. */
+    static extern fun fromInt(value: Int): BigDecimal
+    /**
+     * Create a decimal from a `Real`.
+     *
+     * This preserves the current IEEE-754 value using a round-trip-safe decimal conversion.
+     * It does not try to recover the original source text.
+     */
+    static extern fun fromReal(value: Real): BigDecimal
+    /** Parse exact decimal text. */
+    static extern fun fromString(value: String): BigDecimal
+}
+
+/**
+ * Run [block] with the provided decimal context.
+ *
+ * This is the main way to control decimal division precision and rounding locally without changing global behavior.
+ *
+ * Example:
+ *
+ *     import lyng.decimal
+ *
+ *     withDecimalContext(10) {
+ *         (1.d / 3.d).toStringExpanded()
+ *     }
+ *     >>> "0.3333333333"
+ *
+ * Contexts are dynamic and block-local. After the block finishes, the previous context is restored.
+ */
+extern fun withDecimalContext<T>(context: DecimalContext, block: ()->T): T
+
+/**
+ * Convenience overload for changing only precision.
+ *
+ * Equivalent to `withDecimalContext(DecimalContext(precision, DecimalRounding.HalfEven), block)`.
+ */
+extern fun withDecimalContext<T>(precision: Int, block: ()->T): T
+
+/**
+ * Convenience overload for changing precision and rounding explicitly.
+ *
+ * Example:
+ *
+ *     import lyng.decimal
+ *
+ *     withDecimalContext(2, DecimalRounding.HalfAwayFromZero) {
+ *         (1.d / 8.d).toStringExpanded()
+ *     }
+ *     >>> "0.13"
+ */
+extern fun withDecimalContext<T>(precision: Int, rounding: DecimalRounding, block: ()->T): T
+""".trimIndent()

lynglib/src/commonMain/kotlin/net/sergeych/lyng/stdlib_included/operators_lyng.kt

@@ -0,0 +1,191 @@
+/*
+ * 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.stdlib_included
+
+@Suppress("Unused", "MemberVisibilityCanBePrivate")
+internal val operatorsLyng = """
+package lyng.operators
+
+/**
+ * Binary operators that can be bridged between two different operand classes.
+ *
+ * Registering a pair means:
+ * - the runtime can evaluate `left op right` when `left` has class `L` and `right` has class `R`
+ * - both operands are first converted to a shared "common" class `C`
+ * - the actual operator implementation is then looked up on `C`
+ *
+ * This is primarily useful when:
+ * - you add a new numeric-like type in a library or in pure Lyng code
+ * - your type already implements operators against itself
+ * - you also want existing left-hand types such as `Int` or `Real` to work when your type is on the right
+ *
+ * Example:
+ *
+ *     import lyng.operators
+ *
+ *     class DecimalBox(val value: Int) {
+ *         fun plus(other: DecimalBox) = DecimalBox(value + other.value)
+ *         fun compareTo(other: DecimalBox) = value <=> other.value
+ *     }
+ *
+ *     OperatorInterop.register(
+ *         Int,
+ *         DecimalBox,
+ *         DecimalBox,
+ *         [BinaryOperator.Plus, BinaryOperator.Compare, BinaryOperator.Equals],
+ *         { x: Int -> DecimalBox(x) },
+ *         { x: DecimalBox -> x }
+ *     )
+ *
+ * After registration:
+ * - `1 + DecimalBox(2)` works
+ * - `1 < DecimalBox(2)` works
+ * - `2 == DecimalBox(2)` works
+ *
+ * But this registration does not replace methods on the original classes. It only teaches
+ * Lyng how to bridge a mixed pair into a common class for the listed operators.
+ */
+enum BinaryOperator {
+    /** `a + b` */
+    Plus,
+    /** `a - b` */
+    Minus,
+    /** `a * b` */
+    Mul,
+    /** `a / b` */
+    Div,
+    /** `a % b` */
+    Mod,
+    /**
+     * Ordering comparisons.
+     *
+     * Registering `Compare` enables `<`, `<=`, `>`, `>=`, and the shuttle operator `<=>`
+     * for the mixed operand pair.
+     */
+    Compare,
+    /**
+     * Equality comparisons.
+     *
+     * Registering `Equals` enables `==` and `!=` for the mixed operand pair.
+     */
+    Equals
+}
+
+/**
+ * Runtime registry for mixed-class binary operators.
+ *
+ * `register(L, R, C, ...)` defines how Lyng should evaluate expressions where:
+ * - the left operand has class `L`
+ * - the right operand has class `R`
+ * - the actual operation should be executed as if both were values of class `C`
+ *
+ * The registry is symmetric for the converted values, but not for the original syntax.
+ * Its job is specifically to fill the gap where your custom type appears on the right:
+ *
+ * - `myDecimal + 1` usually already works if `BigDecimal.plus(Int)` exists
+ * - `1 + myDecimal` needs registration because `Int` itself is not rewritten
+ *
+ * Typical pattern for a custom type:
+ *
+ *     import lyng.operators
+ *
+ *     class Rational(val num: Int, val den: Int) {
+ *         fun plus(other: Rational) = Rational(num * other.den + other.num * den, den * other.den)
+ *         fun minus(other: Rational) = Rational(num * other.den - other.num * den, den * other.den)
+ *         fun mul(other: Rational) = Rational(num * other.num, den * other.den)
+ *         fun div(other: Rational) = Rational(num * other.den, den * other.num)
+ *         fun compareTo(other: Rational) = (num * other.den) <=> (other.num * den)
+ *
+ *         static fun fromInt(value: Int) = Rational(value, 1)
+ *     }
+ *
+ *     OperatorInterop.register(
+ *         Int,
+ *         Rational,
+ *         Rational,
+ *         [
+ *             BinaryOperator.Plus,
+ *             BinaryOperator.Minus,
+ *             BinaryOperator.Mul,
+ *             BinaryOperator.Div,
+ *             BinaryOperator.Compare,
+ *             BinaryOperator.Equals
+ *         ],
+ *         { x: Int -> Rational.fromInt(x) },
+ *         { x: Rational -> x }
+ *     )
+ *
+ * Then:
+ * - `1 + Rational(1, 2)` works
+ * - `3 > Rational(5, 2)` works
+ * - `2 == Rational(2, 1)` works
+ *
+ * Decimal uses the same mechanism internally to make `Int + BigDecimal` and `Real + BigDecimal`
+ * work without changing the built-in `Int` or `Real` classes.
+ */
+extern object OperatorInterop {
+    /**
+     * Register a mixed-operand operator bridge.
+     *
+     * @param leftClass class of the original left operand
+     * @param rightClass class of the original right operand
+     * @param commonClass class that will actually execute the operator methods
+     * @param operators operators supported for this mixed pair
+     * @param leftToCommon conversion from `L` to `C`
+     * @param rightToCommon conversion from `R` to `C`
+     *
+     * Requirements for `commonClass`:
+     * - if you register `Plus`, `C` should implement `fun plus(other: C): C` or equivalent accepted result type
+     * - if you register `Minus`, `C` should implement `fun minus(other: C): ...`
+     * - if you register `Mul`, `C` should implement `fun mul(other: C): ...`
+     * - if you register `Div`, `C` should implement `fun div(other: C): ...`
+     * - if you register `Mod`, `C` should implement `fun mod(other: C): ...`
+     * - if you register `Compare`, `C` should implement `fun compareTo(other: C): Int`
+     *
+     * `Equals` reuses comparison/equality semantics of the promoted values.
+     *
+     * Registration is usually done once at module initialization time:
+     *
+     *     package my.rational
+     *     import lyng.operators
+     *
+     *     class Rational(val num: Int, val den: Int) {
+     *         fun plus(other: Rational) = Rational(num * other.den + other.num * den, den * other.den)
+     *         fun compareTo(other: Rational) = (num * other.den) <=> (other.num * den)
+     *         static fun fromInt(value: Int) = Rational(value, 1)
+     *     }
+     *
+     *     OperatorInterop.register(
+     *         Int,
+     *         Rational,
+     *         Rational,
+     *         [BinaryOperator.Plus, BinaryOperator.Compare, BinaryOperator.Equals],
+     *         { x: Int -> Rational.fromInt(x) },
+     *         { x: Rational -> x }
+     *     )
+     */
+    extern fun register<L, R, C>(
+        leftClass: Class<L>,
+        rightClass: Class<R>,
+        commonClass: Class<C>,
+        operators: List<BinaryOperator>,
+        leftToCommon: (L)->C,
+        rightToCommon: (R)->C
+    ): Void
+}
+""".trimIndent()

lynglib/src/commonTest/kotlin/CompilerVmReviewRegressionTest.kt

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2026 Sergey S. Chernov
+ *
+ * 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.
+ */
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.Compiler
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.Script
+import net.sergeych.lyng.ScriptError
+import net.sergeych.lyng.Source
+import net.sergeych.lyng.asFacade
+import net.sergeych.lyng.obj.ObjString
+import net.sergeych.lyng.obj.toInt
+import net.sergeych.lyng.pacman.ImportManager
+import kotlin.test.Test
+import kotlin.test.assertContains
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+class CompilerVmReviewRegressionTest {
+
+    @Test
+    fun missingModuleCaptureFailsFastInsteadOfBecomingUnset() = runTest {
+        val manager = ImportManager()
+        manager.addTextPackages(
+            """
+            package foo
+
+            val answer = 42
+            """.trimIndent()
+        )
+        val script = Compiler.compile(
+            Source(
+                "<missing-module-capture>",
+                """
+                import foo
+                fun make() = { answer }
+                make()
+                """.trimIndent()
+            ),
+            manager
+        )
+
+        val prepared = manager.newModule()
+        script.importInto(prepared)
+        val preparedLambda = script.execute(prepared)
+        assertEquals(42, prepared.asFacade().call(preparedLambda).toInt())
+
+        val rawModule = manager.newModule()
+        val hostScope = Scope(parent = rawModule, thisObj = ObjString("receiver"))
+
+        val lambda = script.execute(hostScope)
+        val ex = assertFailsWith<ScriptError> {
+            hostScope.asFacade().call(lambda)
+        }
+        assertContains(ex.errorMessage, "module binding 'answer'")
+    }
+
+    @Test
+    fun subjectlessWhenReportsScriptError() = runTest {
+        val ex = assertFailsWith<ScriptError> {
+            Compiler.compile(
+                Source(
+                    "<when-without-subject>",
+                    """
+                    when {
+                        true -> 1
+                    }
+                    """.trimIndent()
+                ),
+                Script.defaultImportManager
+            )
+        }
+        assertContains(ex.errorMessage, "when without subject")
+    }
+}

lynglib/src/commonTest/kotlin/GlobalPropertyCaptureRegressionTest.kt

@@ -0,0 +1,52 @@
+/*
+ * 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
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.bridge.bindGlobalVar
+import net.sergeych.lyng.bridge.globalBinder
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class GlobalPropertyCaptureRegressionTest {
+    @Test
+    fun externGlobalVarAssignmentInsideFunctionShouldCallBoundSetter() = runTest {
+        val scope = Script.newScope()
+        var x = 1.0
+
+        scope.eval(
+            """
+            extern var X: Real
+
+            fun main() {
+                X = X + 1.0
+            }
+            """.trimIndent()
+        )
+
+        scope.globalBinder().bindGlobalVar(
+            name = "X",
+            get = { x },
+            set = { x = it }
+        )
+
+        scope.eval("main()")
+
+        assertEquals(2.0, x, "bound extern var should stay live inside function bodies")
+    }
+}

lynglib/src/commonTest/kotlin/ScriptImportPreparationTest.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2026 Sergey S. Chernov
+ *
+ * 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.
+ */
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.Compiler
+import net.sergeych.lyng.Script
+import net.sergeych.lyng.Source
+import net.sergeych.lyng.obj.toInt
+import net.sergeych.lyng.pacman.ImportManager
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import kotlin.test.assertNull
+
+class ScriptImportPreparationTest {
+
+    @Test
+    fun scriptImportIntoExplicitlyPreparesExistingScope() = runTest {
+        val manager = ImportManager()
+        manager.addTextPackages(
+            """
+            package foo
+
+            val answer = 42
+            """.trimIndent()
+        )
+        val script = Compiler.compile(
+            Source(
+                "<prepare-scope>",
+                """
+                import foo
+                answer
+                """.trimIndent()
+            ),
+            manager
+        )
+        val scope = manager.newModule()
+
+        assertNull(scope["answer"])
+
+        script.importInto(scope)
+
+        val record = assertNotNull(scope["answer"])
+        assertEquals(42, scope.resolve(record, "answer").toInt())
+    }
+
+    @Test
+    fun scriptInstantiateModuleUsesSeedScopeImportProvider() = runTest {
+        val manager = ImportManager()
+        manager.addTextPackages(
+            """
+            package foo
+
+            val answer = 42
+            """.trimIndent()
+        )
+        val script = Compiler.compile(
+            Source(
+                "<instantiate-module>",
+                """
+                import foo
+                answer
+                """.trimIndent()
+            ),
+            manager
+        )
+        val seedScope = manager.newModule()
+
+        val module = script.instantiateModule(seedScope)
+
+        val record = assertNotNull(module["answer"])
+        assertEquals(42, module.resolve(record, "answer").toInt())
+    }
+}

lynglib/src/commonTest/kotlin/SeedLocalsRegressionTest.kt

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2026 Sergey S. Chernov
+ *
+ * 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.
+ */
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.FrameSlotRef
+import net.sergeych.lyng.Pos
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.bytecode.BytecodeConst
+import net.sergeych.lyng.bytecode.CmdFrame
+import net.sergeych.lyng.bytecode.CmdFunction
+import net.sergeych.lyng.bytecode.CmdVm
+import net.sergeych.lyng.bytecode.seedFrameLocalsFromScope
+import kotlin.test.Test
+import kotlin.test.assertNull
+
+class SeedLocalsRegressionTest {
+
+    @Test
+    fun seedFrameLocalsSkipsSelfReferentialFrameSlotRef() = runTest {
+        val fn = CmdFunction(
+            name = "seed-self-ref",
+            localCount = 1,
+            addrCount = 0,
+            returnLabels = emptySet(),
+            scopeSlotCount = 1,
+            scopeSlotIndices = intArrayOf(0),
+            scopeSlotNames = arrayOf(null),
+            scopeSlotIsModule = booleanArrayOf(false),
+            localSlotNames = arrayOf("x"),
+            localSlotMutables = booleanArrayOf(true),
+            localSlotDelegated = booleanArrayOf(false),
+            localSlotCaptures = booleanArrayOf(false),
+            constants = listOf(BytecodeConst.IntVal(0)),
+            cmds = emptyArray(),
+            posByIp = emptyArray()
+        )
+        val scope = Scope(null, pos = Pos.builtIn)
+        val record = scope.addConst("x", net.sergeych.lyng.obj.ObjInt.of(1))
+        val frame = CmdFrame(CmdVm(), fn, scope, emptyList())
+        record.value = FrameSlotRef(frame.frame, 0)
+        scope.updateSlotFor("x", record)
+
+        seedFrameLocalsFromScope(frame, scope)
+
+        assertNull(frame.frame.getRawObj(0))
+    }
+}

lynglib/src/commonTest/kotlin/net/sergeych/lyng/BigDecimalModuleTest.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
+
+import kotlinx.coroutines.test.runTest
+import kotlin.test.Test
+
+class BigDecimalModuleTest {
+    @Test
+    fun testDecimalModuleFactoriesAndConversions() = runTest {
+        val scope = Script.newScope()
+        scope.eval(
+            """
+            import lyng.decimal
+
+            assertEquals("12.34", BigDecimal.fromString("12.34").toStringExpanded())
+            assertEquals("1", BigDecimal.fromInt(1).toStringExpanded())
+            assertEquals("2.5", "2.5".d.toStringExpanded())
+            assertEquals("1", 1.d.toStringExpanded())
+            assertEquals("2.2", 2.2.d.toStringExpanded())
+            assertEquals("3", (1 + 2).d.toStringExpanded())
+            assertEquals("1.5", (1 + 0.5).d.toStringExpanded())
+            assertEquals("3", (1 + 2.d).toStringExpanded())
+            assertEquals("3", (2.d + 1).toStringExpanded())
+            assertEquals(2.5, "2.5".d.toReal())
+            assertEquals(2, "2.5".d.toInt())
+            assertEquals(2.2, 2.2.d.toReal())
+            assertEquals("0.30000000000000004", (0.1 + 0.2).d.toStringExpanded())
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun testDecimalModuleMixedIntOperators() = runTest {
+        val scope = Script.newScope()
+        scope.eval(
+            """
+            import lyng.decimal
+
+            assertEquals(3.d, 1 + 2.d)
+            assertEquals(3.d, 2.d + 1)
+            assertEquals(1.d, 3 - 2.d)
+            assertEquals(1.d, 3.d - 2)
+            assertEquals(8.d, 4 * 2.d)
+            assertEquals(8.d, 4.d * 2)
+            assertEquals(4.d, 8 / 2.d)
+            assertEquals(4.d, 8.d / 2)
+            assertEquals(1.d, 7 % 2.d)
+            assertEquals(1.d, 7.d % 2)
+            assert(1 < 2.d)
+            assert(2 <= 2.d)
+            assert(3 > 2.d)
+            assert(3.d > 2)
+            assert(2 == 2.d)
+            assert(2.d == 2)
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun testDecimalDivisionUsesDefaultContext() = runTest {
+        val scope = Script.newScope()
+        scope.eval(
+            """
+            import lyng.decimal
+
+            assertEquals("0.125", (1.d / 8.d).toStringExpanded())
+            assertEquals("0.3333333333333333333333333333333333", (1.d / 3.d).toStringExpanded())
+            assertEquals("0.6666666666666666666666666666666667", ("2".d / 3.d).toStringExpanded())
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun testWithDecimalContextOverridesDivisionContext() = runTest {
+        val scope = Script.newScope()
+        scope.eval(
+            """
+            import lyng.decimal
+
+            assertEquals("0.3333333333333333333333333333333333", (1.d / 3.d).toStringExpanded())
+            assertEquals("0.3333333333", withDecimalContext(10) { (1.d / 3.d).toStringExpanded() })
+            assertEquals("0.666667", withDecimalContext(6) { ("2".d / 3.d).toStringExpanded() })
+            assertEquals("0.666667", withDecimalContext(DecimalContext(6)) { ("2".d / 3.d).toStringExpanded() })
+            assertEquals("0.12", withDecimalContext(2) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("0.13", withDecimalContext(2, DecimalRounding.HalfAwayFromZero) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("0.13", withDecimalContext(DecimalContext(2, DecimalRounding.HalfAwayFromZero)) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("0.3333333333333333333333333333333333", (1.d / 3.d).toStringExpanded())
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun testDecimalDivisionRoundingMatrix() = runTest {
+        val scope = Script.newScope()
+        scope.eval(
+            """
+            import lyng.decimal
+
+            assertEquals("0.12", withDecimalContext(2, DecimalRounding.HalfEven) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("-0.12", withDecimalContext(2, DecimalRounding.HalfEven) { (-1.d / 8.d).toStringExpanded() })
+
+            assertEquals("0.13", withDecimalContext(2, DecimalRounding.HalfAwayFromZero) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("-0.13", withDecimalContext(2, DecimalRounding.HalfAwayFromZero) { (-1.d / 8.d).toStringExpanded() })
+
+            assertEquals("0.12", withDecimalContext(2, DecimalRounding.HalfTowardsZero) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("-0.12", withDecimalContext(2, DecimalRounding.HalfTowardsZero) { (-1.d / 8.d).toStringExpanded() })
+
+            assertEquals("0.13", withDecimalContext(2, DecimalRounding.Ceiling) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("-0.12", withDecimalContext(2, DecimalRounding.Ceiling) { (-1.d / 8.d).toStringExpanded() })
+
+            assertEquals("0.12", withDecimalContext(2, DecimalRounding.Floor) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("-0.13", withDecimalContext(2, DecimalRounding.Floor) { (-1.d / 8.d).toStringExpanded() })
+
+            assertEquals("0.13", withDecimalContext(2, DecimalRounding.AwayFromZero) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("-0.13", withDecimalContext(2, DecimalRounding.AwayFromZero) { (-1.d / 8.d).toStringExpanded() })
+
+            assertEquals("0.12", withDecimalContext(2, DecimalRounding.TowardsZero) { (1.d / 8.d).toStringExpanded() })
+            assertEquals("-0.12", withDecimalContext(2, DecimalRounding.TowardsZero) { (-1.d / 8.d).toStringExpanded() })
+            """.trimIndent()
+        )
+    }
+}

lynglib/src/commonTest/kotlin/net/sergeych/lyng/DelegationTest.kt

@@ -212,6 +212,96 @@ class DelegationTest {
         assertTrue(badThrown)
     }
 
+    @Test
+    fun testPureLyngLazyPreservesReceiverAndClosure() = runTest {
+        val scope = Script.newScope()
+        scope.eval(
+            """
+            val GLOBAL_NUMBERS = [1,2,3]
+
+            class PureLazy<T,ThisRefType=Object>(creatorParam: ThisRefType.()->T) : Delegate<T,ThisRefType> {
+                private val creator: ThisRefType.()->T = creatorParam
+                private var value = Unset
+
+                override fun bind(name: String, access, thisRef: ThisRefType): Object = this
+
+                override fun getValue(thisRef: ThisRefType, name: String): T {
+                    if (value == Unset)
+                        value = creator(thisRef)
+                    value as T
+                }
+            }
+
+            fun pureLazy<T,ThisRefType=Object>(creator: ThisRefType.()->T): Delegate<T,ThisRefType> = PureLazy(creator)
+
+            class A {
+                val numbers = [1,2,3]
+                val fromThis: List by pureLazy { this.numbers }
+                val fromScope: List by pureLazy { GLOBAL_NUMBERS }
+            }
+
+            class B {
+                val a: A by pureLazy { A() }
+                val test: List by pureLazy { (a as A).fromThis + [4] }
+            }
+
+            assertEquals([1,2,3], A().fromThis)
+            assertEquals([1,2,3], A().fromScope)
+            assertEquals([1,2,3,4], B().test)
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun testImportedPureLyngLazyPreservesReceiverAndClosure() = runTest {
+        val scope = Script.newScope()
+        scope.importManager.addTextPackages(
+            """
+            package repro.lazy
+
+            import lyng.stdlib
+
+            class PureLazy<T,ThisRefType=Object>(creatorParam: ThisRefType.()->T) : Delegate<T,ThisRefType> {
+                private val creator: ThisRefType.()->T = creatorParam
+                private var value = Unset
+
+                override fun bind(name: String, access: DelegateAccess, thisRef: ThisRefType): Object {
+                    if (access != DelegateAccess.Val) throw "lazy delegate can only be used with 'val'"
+                    this
+                }
+
+                override fun getValue(thisRef: ThisRefType, name: String): T {
+                    if (value == Unset)
+                        value = with(thisRef, creator)
+                    value as T
+                }
+            }
+            """.trimIndent()
+        )
+        scope.eval(
+            """
+            import repro.lazy
+
+            val GLOBAL_NUMBERS = [1,2,3]
+
+            class A {
+                val numbers = [1,2,3]
+                val fromThis: List by PureLazy { this.numbers }
+                val fromScope: List by PureLazy { GLOBAL_NUMBERS }
+            }
+
+            class B {
+                val a: A by PureLazy { A() }
+                val test: List by PureLazy { (a as A).fromThis + [4] }
+            }
+
+            assertEquals([1,2,3], A().fromThis)
+            assertEquals([1,2,3], A().fromScope)
+            assertEquals([1,2,3,4], B().test)
+            """.trimIndent()
+        )
+    }
+
     @Test
     fun testLazyIsDelegate() = runTest {
         eval("""

lynglib/src/commonTest/kotlin/net/sergeych/lyng/OperatorInteropTest.kt

@@ -0,0 +1,111 @@
+/*
+ * 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
+
+import kotlinx.coroutines.test.runTest
+import kotlin.test.Test
+
+class OperatorInteropTest {
+    @Test
+    fun testPureLyngOperatorInteropRegistration() = runTest {
+        val im = Script.defaultImportManager.copy()
+        im.addPackage("test.decimalbox") { scope ->
+            scope.eval(
+                """
+                package test.decimalbox
+                import lyng.operators
+
+                class DecimalBox(val value: Int) {
+                    fun plus(other: DecimalBox) = DecimalBox(value + other.value)
+                    fun minus(other: DecimalBox) = DecimalBox(value - other.value)
+                    fun mul(other: DecimalBox) = DecimalBox(value * other.value)
+                    fun div(other: DecimalBox) = DecimalBox(value / other.value)
+                    fun mod(other: DecimalBox) = DecimalBox(value % other.value)
+                    fun compareTo(other: DecimalBox) = value <=> other.value
+                }
+
+                OperatorInterop.register(
+                    Int,
+                    DecimalBox,
+                    DecimalBox,
+                    [BinaryOperator.Plus, BinaryOperator.Minus, BinaryOperator.Mul, BinaryOperator.Div, BinaryOperator.Mod, BinaryOperator.Compare, BinaryOperator.Equals],
+                    { x: Int -> DecimalBox(x) },
+                    { x: DecimalBox -> x }
+                )
+                """.trimIndent()
+            )
+        }
+
+        val scope = im.newStdScope()
+        scope.eval(
+            """
+            import test.decimalbox
+
+            assertEquals(DecimalBox(3), 1 + DecimalBox(2))
+            assertEquals(DecimalBox(1), 3 - DecimalBox(2))
+            assertEquals(DecimalBox(8), 4 * DecimalBox(2))
+            assertEquals(DecimalBox(4), 8 / DecimalBox(2))
+            assertEquals(DecimalBox(1), 7 % DecimalBox(2))
+            assert(1 < DecimalBox(2))
+            assert(2 <= DecimalBox(2))
+            assert(3 > DecimalBox(2))
+            assert(2 >= DecimalBox(2))
+            assert(2 == DecimalBox(2))
+            assert(2 != DecimalBox(3))
+            """.trimIndent()
+        )
+    }
+
+    @Test
+    fun testRealInteropRegistrationUsesTopLevelModuleCode() = runTest {
+        val im = Script.defaultImportManager.copy()
+        im.addPackage("test.realbox") { scope ->
+            scope.eval(
+                """
+                package test.realbox
+                import lyng.operators
+
+                class RealBox(val value: Real) {
+                    fun plus(other: RealBox) = RealBox(value + other.value)
+                    fun compareTo(other: RealBox) = value <=> other.value
+                }
+
+                OperatorInterop.register(
+                    Real,
+                    RealBox,
+                    RealBox,
+                    [BinaryOperator.Plus, BinaryOperator.Compare, BinaryOperator.Equals],
+                    { x: Real -> RealBox(x) },
+                    { x: RealBox -> x }
+                )
+                """.trimIndent()
+            )
+        }
+
+        val scope = im.newStdScope()
+        scope.eval(
+            """
+            import test.realbox
+
+            assertEquals(RealBox(1.75), 0.5 + RealBox(1.25))
+            assert(1.5 < RealBox(2.0))
+            assert(2.0 == RealBox(2.0))
+            """.trimIndent()
+        )
+    }
+}

lynglib/stdlib/lyng/root.lyng

@@ -421,7 +421,6 @@ fun with<T,R>(self: T, block: T.()->R): R {
     Can only be used with 'val' properties.
 */
 class lazy<T,ThisRefType=Object>(creatorParam: ThisRefType.()->T) : Delegate<T,ThisRefType> {
-    private val creator: ThisRefType.()->T = creatorParam
     private var value = Unset
 
     override fun bind(name: String, access: DelegateAccess, thisRef: ThisRefType): Object {
@@ -431,7 +430,7 @@ class lazy<T,ThisRefType=Object>(creatorParam: ThisRefType.()->T) : Delegate<T,T
 
     override fun getValue(thisRef: ThisRefType, name: String): T {
         if (value == Unset)
-            value = with(thisRef,creator)
+            value = with(thisRef, creatorParam)
         value as T
     }
 }

notes/lynglib_compiler_vm_review_2026-03-26.md

@@ -0,0 +1,69 @@
+# :lynglib Compiler and VM Review (2026-03-26)
+
+## Scope
+- Reviewed `:lynglib` compiler and bytecode VM paths, focusing on compile/execution correctness.
+- Read core files around `Compiler`, `Script`, `BytecodeCompiler`, `CmdRuntime`, `Scope`, `ModuleScope`, and capture/slot plumbing.
+- Ran `./gradlew :lynglib:jvmTest` on 2026-03-26: PASS.
+
+## Findings
+
+### 1. High: local seeding uses the wrong slot index when checking for self-referential `FrameSlotRef`
+- Status: fixed in worktree on 2026-03-26; covered by `SeedLocalsRegressionTest`.
+- File: `lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/SeedLocals.kt:39`
+- The self-reference guard compares `FrameSlotRef` against `base + i`, but `FrameSlotRef` stores the underlying `BytecodeFrame` local slot index, not the VM absolute slot id.
+- The same slot is then written using `setObjUnchecked(base + i, value)` at `SeedLocals.kt:42`, which means a self-reference is not filtered out before being reinserted.
+- Impact: this can seed a local with a reference to itself, creating recursive `FrameSlotRef` chains. Reads then recurse through `BytecodeFrame.getObj()` / `FrameSlotRef.read()` instead of resolving to a value, which is a realistic path to stack overflow or non-terminating execution in bytecode-only helper execution (`executeBytecodeWithSeed`).
+- Why this looks real: the equivalent check in `CmdFrame.applyCaptureRecords()` uses the local index directly (`CmdRuntime.kt:3867`), and `Script.seedModuleLocals()` also compares with the local index, not `scopeSlotCount + i` (`Script.kt:109`).
+- Suggested fix: compare with `i`, not `base + i`, and add a regression test around `executeBytecodeWithSeed` seeding a scope that already contains a `FrameSlotRef` to the same local.
+
+### 2. Design note: script-specific import/module preparation should stay explicit, not hidden in `execute(scope)`
+- Status: resolved by API addition, without changing `Script.execute(scope)` semantics.
+- File: `lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt:51-57`
+- `shouldSeedModule` is only true when `execScope` is a `ModuleScope` or `thisObj === ObjVoid`.
+- If a compiled script is executed against a non-module scope with a real receiver object, `seedModuleSlots()` is skipped entirely, so script imports and explicit module bindings are never installed into `moduleTarget`.
+- Original concern: top-level bytecode that expects imported names or module globals can see different behavior depending on whether the host prepared the target scope explicitly.
+- Resolution taken: do **not** change `Script.execute(scope)`, because in this codebase it is expected to run on exactly the provided scope and many embedding flows already rely on explicit scope setup via `Script.newScope()`, `Scope.eval(...)`, `addFn(...)`, `addConst(...)`, and direct import-manager configuration.
+- New explicit APIs added instead:
+  - `Script.importInto(scope, seedScope = scope)`
+  - `Script.instantiateModule(seedScope = null, pos = script.pos)`
+- This keeps existing execution behavior stable while giving hosts an opt-in way to apply a script's import/module bindings when they actually want that preparation step.
+- Coverage added: `ScriptImportPreparationTest`.
+
+### 3. Medium: missing module captures are silently converted into fresh `Unset` slots
+- Status: fixed in worktree on 2026-03-27; covered by `CompilerVmReviewRegressionTest`.
+- File: `lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/CmdRuntime.kt:3950-3970`
+- In `CmdFrame.buildCaptureRecords()`, the module-capture path first tries several lookups. If the requested `slotId` is missing but the capture has a `name`, it calls `target.applySlotPlan(mapOf(name to slotId))` and immediately returns `target.getSlotRecord(slotId)`.
+- That record is a newly created placeholder from `Scope.applySlotPlan()` (`Scope.kt:460-471`) and defaults to `ObjUnset`.
+- Impact: a compiler/runtime disagreement in capture resolution is masked as a normal capture of `Unset`, so the failure moves far away from closure creation and becomes data corruption or an unrelated later exception. This will be difficult to debug when it happens.
+- Resolution taken: the VM now refuses to treat synthetic placeholder slots as real module/captured bindings. Reads and capture construction fail with a source-positioned `ScriptError` when the execution scope was not prepared with the script's required module/import bindings.
+
+### 4. Medium: subject-less `when { ... }` still crashes through a raw Kotlin `TODO`
+- Status: fixed in worktree on 2026-03-27; covered by `CompilerVmReviewRegressionTest`.
+- File: `lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt:6447-6449`
+- The unsupported branch uses `TODO("when without object is not yet implemented")`.
+- Current docs explicitly say subject-less `when` is not implemented, so the language limitation itself is documented. The problem is the failure mode: the compiler throws a raw Kotlin `NotImplementedError` instead of a normal `ScriptError` or a feature diagnostic.
+- Impact: IDE/embedding callers get an implementation exception rather than a source-positioned language error, which is especially bad across non-JVM targets and for editor tooling.
+- Resolution taken: the parser now throws a normal `ScriptError` at the `when` position with an explicit "when without subject is not implemented" message.
+
+## Risks Worth Checking Next
+
+### 5. Medium risk: module frame growth only retargets records stored in `objects`/`localBindings`
+- File: `lynglib/src/commonMain/kotlin/net/sergeych/lyng/ModuleScope.kt:39-67`
+- When `ensureModuleFrame()` replaces the old `BytecodeFrame` with a larger one, it retargets `FrameSlotRef`s only in `objects` and `localBindings`.
+- Existing closures/capture records that already hold `FrameSlotRef(oldFrame, slot)` are not retargeted here.
+- Impact: if a module scope survives across recompilation/re-execution with a larger local frame, previously exported closures can keep reading stale values from the old frame instance.
+- Confidence is lower because this depends on module reuse across differing compiled shapes, but the reference-retargeting logic is clearly incomplete for that scenario.
+- Suggested check: add a regression covering module re-execution with increased local count and an exported closure captured before the resize.
+
+## Test Status
+- `./gradlew :lynglib:jvmTest` passed during this review.
+- `./gradlew :lynglib:jvmTest --tests ScriptImportPreparationTest --tests SeedLocalsRegressionTest` passed after the fixes/API additions.
+- `./gradlew :lynglib:jvmTest --tests CompilerVmReviewRegressionTest --tests ScriptImportPreparationTest --tests SeedLocalsRegressionTest` passed after fixing findings 3 and 4.
+- Finding 1 is covered directly; finding 2 is covered by explicit preparation API tests.
+
+## Suggested Fix Order
+1. Fix finding 1 first: it is a concrete slot-index bug with likely recursive failure modes. Done.
+2. Keep `Script.execute(scope)` semantics stable and use explicit preparation APIs where script-owned import/module setup is needed. Done.
+3. Tighten finding 3 next: fail fast on capture mismatches. Done.
+4. Replace the raw `TODO` in finding 4 so unsupported syntax produces normal diagnostics. Done.
+5. Decide whether finding 5 matters for current module-reload workflows; add a regression before changing behavior.

proposals/wasm_vs_lyng_memory.md

@@ -0,0 +1,46 @@
+WASM использует стековую модель памяти. Lyng стеки не использует. В чем разница?
+
+Стек это очень древняя структура, была придумана в 1955 (магазинная память Бауэра и Самельсона), и приняла современную форму в 1960, благодаря Барбаре Лисокв, вполседствии лауреата премии Тьюринга, которого, в свою очередь, за выдающийся вклад в развитие IT кастрировали, формально, за гомосексуализм, но в британии, где на трех джентльменов приходилось тогда, и приходится и теперь, четыре гомосексуала, все понимают, что это был просто предлог.
+
+Стек был прекрасен в 60е годы, когда IBM планировала продавать по компьютеру в год в лучшем случае, а за идеи о микропроцессорах или ядрах можно было устроиться только пациентом психушки. Стек это заранее жестко выделенная область памяти, которая обычно вообще не используется, и по ней в одну сторону растет используемая область, которая хранит локальные переменные, адреса возврата и иногда состояние процессора.
+
+Она крайне плохо подходит для многозадачности. Представь себе что у тебя есть wasm процесс, со своим стеком, и ему надо переключиться, остановив текущий поток исполнения (например, он ждет ответа от сети). Тогда тебе придется создать _новый стек_ — пока еще пустой, переключиться на него и исполнять там другую задачу. Сколько потоков - столько и стеков. И все они по большей части не используются — там просто запас памяти "на вырост", если исполнение потребует. А оценить заранее адекватно почти невозможно, дают с запасом.
+
+Далее, васм использует фиксированную память выделенную на процесс. Ее тоже приходится брать "с запасом", так как если по ходу не хватит, процесс вылетит. И она тоже в изрядной части пустая. Ну и назасладочку, васм был задуман однозадачным, и все попытки туда хотя бы треды засунуть, получаются очень кривыми.
+
+Линг использует фреймы и сопрограммы. Линг вообще треды не использует. Основная команда исполнения программы на линге - сопрограмма (coroutine), ей не нужен стейк, она им не пользуется. Вместо этого каждый вызов в линге, грубо говоря, это вызов сопрограммы. Для него формируется фрейм (не на стеке, а в динамической памяти!), которого гарантировано достаточно для исполнения собственно кода. Он заменяет собой "стековый фрейм", но его размер известен заранее, и его можно распределять и освобождать проще, как обычную динамическую память.
+
+Далее, линг использует ту же динамическую память, что и его родительская платформа. Если он работает на Java, то использует память со сборкой мусора JVM, на Javascript - память машины JS, в нативных машинах - специальнй менеджер памяти со сборкой мусора, от Kotlin Native (довольно хороший и очень быстро развивающийся). В результате, запустить одновременно десять, или сто тысяч программ на лигне, которые будут исполняться конкурентно, вполне реально. Просто попытка запустить 10к васм-машин на v8 или другом движке скорее всего убьет систему, да и 10 тысяч тредов редко какой сервер приложению даст. Огромный перерасход ресурсов и тормоза.
+
+Далее. Васм СТЕКОВАЯ машина со стековыми командами, он без стека вообще не может. Посмотрим как он считает примитивное выражение:
+
+```wasm
+(module
+  ;; Экспортируем функцию, чтобы её можно было вызвать из JS
+  (func (export "calc") (param $a i32) (param $b i32) (param $c i32) (param $d i32) (result i32)
+    ;; --- вычисление (a + b) / c * d ---
+    local.get $a      ;; помещаем a на стек
+    local.get $b      ;; помещаем b на стек
+    i32.add           ;; складываем: стек содержит (a+b)
+
+    local.get $c      ;; помещаем c
+    i32.div_s         ;; знаковое деление: стек содержит ((a+b) / c)
+
+    local.get $d      ;; помещаем d
+    i32.mul           ;; умножение: стек содержит (((a+b)/c) * d)
+
+    ;; результат остаётся на стеке — это возвращаемое значение функции
+  )
+)
+```
+
+На ВМ Линга нет стека, он трехадресный универсальный ассемблер, если можно так сказать:
+
+```
+    add_int s1, s2 -> s5 // a + b -> s5
+    div_int s5, s3 -> s5 // s5 -> s5 / c
+    mul_int s5, s4 -> s5 // s5 -> s5 * d
+    return s5
+```
+
+Этот код крайне эффективно реализуется на любом реальном процессоре, и хорошо оптимизируется. Исполняется он без всякого стека.

proposals/why_not_wasm.md

@@ -0,0 +1,21 @@
+Почему не WASM?
+
+- wasm очень громоздкий и неудобный для разработки, он проектировался очень давно и с другими целями, так что сейчас его безуспешно пытаются "перезаточить" в современные области, но он поддается с трудом. Компилировать в wasm была бы задача по сложности превосходящая весь проект, а результат был бы уныл: мы и так имеем все достоинсва wasm, полезные для Lyng, но не имеем многих его недостатков.
+
+Виртуалка lyng легкая, и доступна на всех платформах уже сейчас, а вот прикрутить скажем wasm машину к котлину на сервере, чтобы она работала как сопрограммы первого класса вместе с котлинскими, задача сейчас неразрешимая.
+
+То есть, преимущества wasm что он доступен на многих платформах, для нас неважно - мы и так на тех же платформах имеем полную поддержку.
+
+- Lyng VM изначально заточена на исполнение именно сопрограмм со сборкой мусора. Эти два ключевых механизма линга практически отсутствуют в wasm, их мучительно прикручивают как расширения, и они довольно слабо поддерживаются.
+
+- LyngVM заточен на исполнение программ с гибридной ООП-ФП моделью, она хорошо поддерживает множественное наследование, делегацию, работу со сложными списками аргументов (ФП фичи, подстановки, деструктурирование), на васме это очень непросто написать, будет медленно и громоздко.
+
+- одна из целей Lyng была получить быстрое безопасное и очень мощное скриптовое решение для вклучения в проекты на Java/Kotlin multiplatform. На wasm это в принципе невозможно - его включение это кошмар, он громоздкий. К тому же требует компиляции, а Lyng работает с JIT (исполняет прямо исходник, компилируя его на лету, как JS), и может использоваться как скрипт (wasm не может)
+
+- типы данных которые мы используем в Lyng в WASM отсутстсвтуют, их бы пришлось добавлять
+
+В результате если бы мы компилировали Lyng->WASM мы бы получили огромный и медленный код. Для которого потребовалась бы огромная wasm VM. Практического смысла в этом нет.
+
+Если же ты рассматриваешь идею в единой платформе использовать разные языки, а wasm как промежуточный язых совместимости, то это собственно противоречит идее использовать общую кодовую базу и интерфейсы. Разные языки имеют несовпадающие, несовместимые интерфейсы вызовов, так что приходится писать руками биндинги, которые не добавляют скорости и добавляют ошибки, к тому же, разные языки предоставляют часто вообще несовместимые модели программирования (например прототипы в JS, множественное наследование С++ или Линга и кошмар на улице вязов от руста, в владением ссылками).
+
+Платформ на васме полно, и там и ловить нечего, и неинтересно. Я же предлагаю вылезти в другой класс. Навеяно реальным опоытом переносов контрактов из старого золота в мольтпей, которое получается на удивление хорошо

site/src/jsMain/kotlin/HomePage.kt

@@ -27,74 +27,85 @@ import org.jetbrains.compose.web.dom.*
 fun HomePage() {
     val samples = remember {
         listOf(
+            """
+            // Decimal arithmetic with explicit local precision
+            import lyng.decimal
+
+            val exact = "0.3".d
+            val fromReal = (0.1 + 0.2).d
+
+            println(exact.toStringExpanded())
+            println(fromReal.toStringExpanded())
+            println(withDecimalContext(10) { (1.d / 3.d).toStringExpanded() })
+            """.trimIndent(),
+            """
+            // Mixed operators for your own type
+            import lyng.operators
+
+            class Coins(val amount: Int) {
+                fun plus(other: Coins) = Coins(amount + other.amount)
+                fun compareTo(other: Coins) = amount <=> other.amount
+            }
+
+            OperatorInterop.register(
+                Int,
+                Coins,
+                Coins,
+                [BinaryOperator.Plus, BinaryOperator.Compare, BinaryOperator.Equals],
+                { x: Int -> Coins(x) },
+                { x: Coins -> x }
+            )
+
+            println(1 + Coins(2))
+            println(3 > Coins(2))
+            """.trimIndent(),
+            """
+            // Non-local returns from closures
+            fun findFirst<T>(list: Iterable<T>, predicate: (T)->Bool): T? {
+                list.forEach {
+                    if (predicate(it)) return@findFirst it
+                }
+                null
+            }
+
+            val found: Int? = findFirst([1, 5, 8, 12]) { it > 10 }
+            println("Found: " + found)
+            """.trimIndent(),
+            """
+            // Implicit coroutines: parallelism without ceremony
+            import lyng.time
+
+            val d1 = launch {
+                delay(100.milliseconds)
+                "Task A finished"
+            }
+            val d2 = launch {
+                delay(50.milliseconds)
+                "Task B finished"
+            }
+
+            println(d1.await())
+            println(d2.await())
+            """.trimIndent(),
             """
             // Everything is an expression
             val x: Int = 10
             val status: String = if (x > 0) "Positive" else "Zero or Negative"
 
-            // Even loops return values!
             val result = for (i in 1..5) {
                 if (i == 3) break "Found 3!"
             } else "Not found"
 
-            println("Result: " + result)
+            println(status)
+            println(result)
             """.trimIndent(),
             """
-            // Functional power with generics and collections
+            // Functional collections with strict static types
             val squares: List<Int> = (1..10)
                 .filter { it % 2 == 0 }
                 .map { it * it }
 
             println("Even squares: " + squares)
-            // Output: [4, 16, 36, 64, 100]
-            """.trimIndent(),
-            """
-            // Generics and type aliases
-            type Num = Int | Real
-            
-            class Box<out T: Num>(val value: T) {
-                fun get(): T = value
-            }
-            
-            val intBox = Box(42)
-            val realBox = Box(3.14)
-            println("Boxes: " + intBox.get() + ", " + realBox.get())
-            """.trimIndent(),
-            """
-            // Strict compile-time types and symbol resolution
-            fun greet(name: String, count: Int) {
-                for (i in 1..count) {
-                    println("Hello, " + name + "!")
-                }
-            }
-            
-            greet("Lyng", 3)
-            // greet(10, "error") // This would be a compile-time error!
-            """.trimIndent(),
-            """
-            // Flexible map literals and shorthands
-            val id = 101
-            val name = "Lyng"
-            val base = { id:, name: } // Shorthand for id: id, name: name
-
-            val full = { ...base, version: "1.5.0-SNAPSHOT", status: "active" }
-            println(full)
-            """.trimIndent(),
-            """
-            // Modern null safety
-            var config: Map<String, Int>? = null
-            config ?= { timeout: 30 } // Assign only if null
-
-            val timeout = config?["timeout"] ?: 60
-            println("Timeout is: " + timeout)
-            """.trimIndent(),
-            """
-            // Destructuring with splat operator
-            val [first, middle..., last] = [1, 2, 3, 4, 5, 6]
-
-            println("First: " + first)
-            println("Middle: " + middle)
-            println("Last: " + last)
             """.trimIndent(),
             """
             // Diamond-safe Multiple Inheritance (C3 MRO)
@@ -123,18 +134,6 @@ fun HomePage() {
             println([10, 20, 30].second)
             """.trimIndent(),
             """
-            // Non-local returns from closures
-            fun findFirst<T>(list: Iterable<T>, predicate: (T)->Bool): T? {
-                list.forEach {
-                    if (predicate(it)) return@findFirst it
-                }
-                null
-            }
-
-            val found: Int? = findFirst([1, 5, 8, 12]) { it > 10 }
-            println("Found: " + found)
-            """.trimIndent(),
-            """
             // Easy operator overloading
             class Vector(val x: Real, val y: Real) {
                 fun plus(other: Vector): Vector = Vector(x + other.x, y + other.y)
@@ -156,20 +155,13 @@ fun HomePage() {
             println("User name: " + u.name)
             """.trimIndent(),
             """
-            // Implicit coroutines: parallelism without ceremony
-            import lyng.time
+            // Flexible map literals and shorthands
+            val id = 101
+            val name = "Lyng"
+            val base = { id:, name: }
+            val full = { ...base, status: "active", tags: ["typed", "portable"] }
 
-            val d1 = launch {
-                delay(100.milliseconds)
-                "Task A finished"
-            }
-            val d2 = launch {
-                delay(50.milliseconds)
-                "Task B finished"
-            }
-
-            println(d1.await())
-            println(d2.await())
+            println(full)
             """.trimIndent()
         )
     }
@@ -195,6 +187,8 @@ fun HomePage() {
             Div({ classes("d-flex", "justify-content-center", "gap-2", "flex-wrap", "mb-4") }) {
                 // Benefits pills
                 listOf(
+                    "Decimal arithmetic",
+                    "Operator interop",
                     "Strict static typing",
                     "Generics & Type Aliases",
                     "Implicit coroutines",
@@ -233,6 +227,26 @@ fun HomePage() {
         }
     }
 
+    Div({ classes("row", "g-3", "mb-4") }) {
+        listOf(
+            Triple("New: Decimal", "Exact decimal values, local precision control, and mixed operators with Int and Real.", "#/docs/Decimal.md"),
+            Triple("New: Operator Interop", "Teach Lyng how your custom types interact with built-ins on the left-hand side.", "#/docs/OperatorInterop.md"),
+            Triple("What Changed", "Recent language, stdlib, and tooling improvements in one place.", "#/docs/whats_new.md")
+        ).forEach { (title, text, href) ->
+            Div({ classes("col-12", "col-lg-4") }) {
+                A(attrs = {
+                    classes("text-decoration-none")
+                    attr("href", href)
+                }) {
+                    Div({ classes("h-100", "p-3", "border", "rounded-3", "bg-body-tertiary") }) {
+                        H3({ classes("h5", "mb-2", "text-body") }) { Text(title) }
+                        P({ classes("mb-0", "text-muted") }) { Text(text) }
+                    }
+                }
+            }
+        }
+    }
+
     // Code sample slideshow
     Div({
         classes("markdown-body", "mt-0", "slide-container", "position-relative")