improved lazy delegate; added with(newThis) {} to stdlib

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Unreleased
 
+- Language: stdlib improvements
+  - Added `with(self, block)` function to `root.lyng` which executes a block with `this` set to the provided object.
 - Language: Abstract Classes and Interfaces
   - Support for `abstract` modifier on classes, methods, and variables.
   - Introduced `interface` as a synonym for `abstract class`, supporting full state (constructors, fields, `init` blocks) and implementation by parts via MI.

docs/tutorial.md

@@ -298,6 +298,16 @@ It works much like `also`, but is executed in the context of the source object:
     assertEquals(p, Point(2,3))
     >>> void
 
+## with
+
+Sets `this` to the first argument and executes the block. Returns the value returned by the block:
+
+    class Point(x,y)
+    val p = Point(1,2)
+    val sum = with(p) { x + y }
+    assertEquals(3, sum)
+    >>> void
+
 ## run
 
 Executes a block after it returning the value passed by the block. for example, can be used with elvis operator:
@@ -1519,7 +1529,7 @@ See [math functions](math.md). Other general purpose functions are:
 | flow {}                               | create flow sequence, see [parallelism]                    |
 | delay, launch, yield                  | see [parallelism]                                          |
 | cached(builder)                       | [Lazy evaluation with `cached`](#lazy-evaluation-with-cached) |
-| let, also, apply, run                 | see above, flow controls                                   |
+| let, also, apply, run, with       | see above, flow controls                                   |
 
 (1)
 : `fn` is optional lambda returning string message to add to exception string. 

lynglib/build.gradle.kts

@@ -17,6 +17,7 @@
 
 import com.codingfeline.buildkonfig.compiler.FieldSpec.Type.STRING
 import org.jetbrains.kotlin.gradle.ExperimentalKotlinGradlePluginApi
+import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 group = "net.sergeych"
@@ -65,11 +66,11 @@ kotlin {
         browser()
         nodejs()
     }
-//    @OptIn(ExperimentalWasmDsl::class)
-//    wasmJs() {
-//        browser()
-//        nodejs()
-//    }
+    @OptIn(ExperimentalWasmDsl::class)
+    wasmJs() {
+        browser()
+        nodejs()
+    }
 
     // Suppress Beta warning for expect/actual classes across all targets
     targets.configureEach {

lynglib/src/commonTest/kotlin/StdlibTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ * Copyright 2026 Sergey S. Chernov real.sergeych@gmail.com
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -113,4 +113,22 @@ class StdlibTest {
             assertEquals(5, (1..10).toList().count { it % 2 == 1 } )
         """)
     }
+
+    @Test
+    fun testWith() = runTest {
+        eval("""
+            class Person(val name, var age)
+            val p = Person("Alice", 30)
+            
+            val result = with(p) {
+                assertEquals("Alice", name)
+                assertEquals(30, age)
+                age = 31
+                "done"
+            }
+            
+            assertEquals("done", result)
+            assertEquals(31, p.age)
+        """.trimIndent())
+    }
 }

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

@@ -287,4 +287,40 @@ class DelegationTest {
         """.trimIndent())
     }
 
+    @Test
+    fun testThisInLazy() = runTest {
+        eval("""
+            class A {
+                val numbers = [1,2,3]
+                val tags by lazy { this.numbers }
+            }
+            class B {
+                val a by lazy { A() }
+                val test by lazy { a.tags + [4] }
+            }
+            assertEquals( [1,2,3], A().tags)
+            assertEquals( [1,2,3,4], B().test)
+        """)
+    }
+
+    @Test
+    fun testScopeInLazy() = runTest {
+        val s1 = Script.newScope()
+        s1.eval("""
+            class A {
+                val tags by lazy { GLOBAL_NUMBERS }
+            }
+            """.trimIndent())
+        // on the same scope, it will see my GLOBAL_NUMBERS:
+        s1.eval("""
+            val GLOBAL_NUMBERS = [1,2,3]
+            class B {
+                val a by lazy { A() }
+                val test by lazy { a.tags + [4] }
+            }
+            assertEquals( [1,2,3], A().tags)
+            assertEquals( [1,2,3,4], B().test)
+        """)
+    }
+
 }

lynglib/stdlib/lyng/root.lyng

@@ -310,6 +310,16 @@ interface Delegate {
     fun bind(name, access, thisRef) = this
 }
 
+/*
+    Executes the block with `this` set to self and
+    returns what the block returns.
+*/
+fun with(self, block) {
+    var result = Unset
+    self.apply { result = block() }
+    result
+}
+
 /*
 Standard implementation of a lazy-initialized property delegate.
 The provided creator lambda is called once on the first access to compute the value.
@@ -325,7 +335,7 @@ class lazy(creatorParam) : Delegate {
     }
 
     override fun getValue(thisRef, name) {
-        if (value == Unset) value = creator()
+        if (value == Unset) value = with(thisRef,creator)
         value
     }
 }