Stabilize bytecode interpreter and fallbacks

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

@@ -0,0 +1,35 @@
+/*
+ * 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
+
+class BlockStatement(
+    val block: Script,
+    val slotPlan: Map<String, Int>,
+    private val startPos: Pos,
+) : Statement() {
+    override val pos: Pos = startPos
+
+    override suspend fun execute(scope: Scope): Obj {
+        val target = if (scope.skipScopeCreation) scope else scope.createChildScope(startPos)
+        if (slotPlan.isNotEmpty()) target.applySlotPlan(slotPlan)
+        return block.execute(target)
+    }
+
+    fun statements(): List<Statement> = block.debugStatements()
+}

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

@@ -0,0 +1,23 @@
+/*
+ * 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.bytecode.BytecodeStatement
+
+interface BytecodeBodyProvider {
+    fun bytecodeBody(): BytecodeStatement?
+}

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

@@ -239,11 +239,12 @@ class Compiler(
         val statements = mutableListOf<Statement>()
         val start = cc.currentPos()
         // Track locals at script level for fast local refs
-        return withLocalNames(emptySet()) {
+        return try {
-            // package level declarations
+            withLocalNames(emptySet()) {
-            // Notify sink about script start
+                // package level declarations
-            miniSink?.onScriptStart(start)
+                // Notify sink about script start
-            do {
+                miniSink?.onScriptStart(start)
+                do {
                 val t = cc.current()
                 if (t.type == Token.Type.NEWLINE || t.type == Token.Type.SINGLE_LINE_COMMENT || t.type == Token.Type.MULTILINE_COMMENT) {
                     when (t.type) {
@@ -337,14 +338,16 @@ class Compiler(
                     break
                 }
 
-            } while (true)
+                } while (true)
-            Script(start, statements)
+                Script(start, statements)
-        }.also {
+            }.also {
-            // Best-effort script end notification (use current position)
+                // Best-effort script end notification (use current position)
-            miniSink?.onScriptEnd(
+                miniSink?.onScriptEnd(
-                cc.currentPos(),
+                    cc.currentPos(),
-                MiniScript(MiniRange(start, cc.currentPos()))
+                    MiniScript(MiniRange(start, cc.currentPos()))
-            )
+                )
+            }
+        } finally {
         }
     }
 
@@ -373,6 +376,40 @@ class Compiler(
         return BytecodeStatement.wrap(stmt, "stmt@${stmt.pos}", allowLocalSlots = true)
     }
 
+    private fun wrapFunctionBytecode(stmt: Statement, name: String): Statement {
+        if (!useBytecodeStatements) return stmt
+        return BytecodeStatement.wrap(stmt, "fn@$name", allowLocalSlots = true)
+    }
+
+    private fun unwrapBytecodeDeep(stmt: Statement): Statement {
+        return when (stmt) {
+            is BytecodeStatement -> unwrapBytecodeDeep(stmt.original)
+            is BlockStatement -> {
+                val unwrapped = stmt.statements().map { unwrapBytecodeDeep(it) }
+                val script = Script(stmt.block.pos, unwrapped)
+                BlockStatement(script, stmt.slotPlan, stmt.pos)
+            }
+            is VarDeclStatement -> {
+                val init = stmt.initializer?.let { unwrapBytecodeDeep(it) }
+                VarDeclStatement(
+                    stmt.name,
+                    stmt.isMutable,
+                    stmt.visibility,
+                    init,
+                    stmt.isTransient,
+                    stmt.pos
+                )
+            }
+            is IfStatement -> {
+                val cond = unwrapBytecodeDeep(stmt.condition)
+                val ifBody = unwrapBytecodeDeep(stmt.ifBody)
+                val elseBody = stmt.elseBody?.let { unwrapBytecodeDeep(it) }
+                IfStatement(cond, ifBody, elseBody, stmt.pos)
+            }
+            else -> stmt
+        }
+    }
+
     private suspend fun parseStatement(braceMeansLambda: Boolean = false): Statement? {
         lastAnnotation = null
         lastLabel = null
@@ -2376,7 +2413,7 @@ class Compiler(
                     slotPlanStack.add(classSlotPlan)
                     val st = try {
                         withLocalNames(constructorArgsDeclaration?.params?.map { it.name }?.toSet() ?: emptySet()) {
-                            parseScript()
+                        parseScript()
                         }
                     } finally {
                         slotPlanStack.removeLast()
@@ -2574,11 +2611,23 @@ class Compiler(
     }
 
     private fun constIntRangeOrNull(ref: ObjRef): ConstIntRange? {
-        if (ref !is RangeRef) return null
+        when (ref) {
-        val start = constIntValueOrNull(ref.left) ?: return null
+            is ConstRef -> {
-        val end = constIntValueOrNull(ref.right) ?: return null
+                val range = ref.constValue as? ObjRange ?: return null
-        val endExclusive = if (ref.isEndInclusive) end + 1 else end
+                if (!range.isIntRange) return null
-        return ConstIntRange(start, endExclusive)
+                val start = range.start?.toLong() ?: return null
+                val end = range.end?.toLong() ?: return null
+                val endExclusive = if (range.isEndInclusive) end + 1 else end
+                return ConstIntRange(start, endExclusive)
+            }
+            is RangeRef -> {
+                val start = constIntValueOrNull(ref.left) ?: return null
+                val end = constIntValueOrNull(ref.right) ?: return null
+                val endExclusive = if (ref.isEndInclusive) end + 1 else end
+                return ConstIntRange(start, endExclusive)
+            }
+            else -> return null
+        }
     }
 
     private fun constIntValueOrNull(ref: ObjRef?): Long? {
@@ -2595,10 +2644,17 @@ class Compiler(
     @Suppress("UNUSED_VARIABLE")
     private suspend fun parseDoWhileStatement(): Statement {
         val label = getLabel()?.also { cc.labels += it }
-        val (canBreak, body) = cc.parseLoop {
+        val loopSlotPlan = SlotPlan(mutableMapOf(), 0)
-            parseStatement() ?: throw ScriptError(cc.currentPos(), "Bad do-while statement: expected body statement")
+        slotPlanStack.add(loopSlotPlan)
+        val (canBreak, parsedBody) = try {
+            cc.parseLoop {
+                parseStatement() ?: throw ScriptError(cc.currentPos(), "Bad do-while statement: expected body statement")
+            }
+        } finally {
+            slotPlanStack.removeLast()
         }
         label?.also { cc.labels -= it }
+        val body = unwrapBytecodeDeep(parsedBody)
 
         cc.skipWsTokens()
         val tWhile = cc.next()
@@ -2606,12 +2662,18 @@ class Compiler(
             throw ScriptError(tWhile.pos, "Expected 'while' after do body")
 
         ensureLparen()
-        val condition = parseExpression() ?: throw ScriptError(cc.currentPos(), "Expected condition after 'while'")
+        slotPlanStack.add(loopSlotPlan)
+        val condition = try {
+            parseExpression() ?: throw ScriptError(cc.currentPos(), "Expected condition after 'while'")
+        } finally {
+            slotPlanStack.removeLast()
+        }
         ensureRparen()
 
         cc.skipTokenOfType(Token.Type.NEWLINE, isOptional = true)
         val elseStatement = if (cc.next().let { it.type == Token.Type.ID && it.value == "else" }) {
-            parseStatement()
+            val parsedElse = parseStatement()
+            parsedElse?.let { unwrapBytecodeDeep(it) }
         } else {
             cc.previous()
             null
@@ -2655,15 +2717,23 @@ class Compiler(
             parseExpression() ?: throw ScriptError(start, "Bad while statement: expected expression")
         ensureRparen()
 
-        val (canBreak, body) = cc.parseLoop {
+        val loopSlotPlan = SlotPlan(mutableMapOf(), 0)
-            if (cc.current().type == Token.Type.LBRACE) parseBlock()
+        slotPlanStack.add(loopSlotPlan)
-            else parseStatement() ?: throw ScriptError(start, "Bad while statement: expected statement")
+        val (canBreak, parsedBody) = try {
+            cc.parseLoop {
+                if (cc.current().type == Token.Type.LBRACE) parseBlock()
+                else parseStatement() ?: throw ScriptError(start, "Bad while statement: expected statement")
+            }
+        } finally {
+            slotPlanStack.removeLast()
         }
         label?.also { cc.labels -= it }
+        val body = unwrapBytecodeDeep(parsedBody)
 
         cc.skipTokenOfType(Token.Type.NEWLINE, isOptional = true)
         val elseStatement = if (cc.next().let { it.type == Token.Type.ID && it.value == "else" }) {
-            parseStatement()
+            val parsedElse = parseStatement()
+            parsedElse?.let { unwrapBytecodeDeep(it) }
         } else {
             cc.previous()
             null
@@ -2986,8 +3056,9 @@ class Compiler(
             var closure: Scope? = null
 
             val paramSlotPlanSnapshot = slotPlanIndices(paramSlotPlan)
-            val fnBody = object : Statement() {
+            val fnBody = object : Statement(), BytecodeBodyProvider {
                 override val pos: Pos = t.pos
+                override fun bytecodeBody(): BytecodeStatement? = fnStatements as? BytecodeStatement
                 override suspend fun execute(callerContext: Scope): Obj {
                     callerContext.pos = start
 
@@ -3082,6 +3153,7 @@ class Compiler(
 
                     val annotatedFnBody = annotation?.invoke(context, ObjString(name), fnBody)
                         ?: fnBody
+                    val compiledFnBody = annotatedFnBody
 
                     extTypeName?.let { typeName ->
                         // class extension method
@@ -3092,10 +3164,10 @@ class Compiler(
                             override suspend fun execute(scope: Scope): Obj {
                                 // ObjInstance has a fixed instance scope, so we need to build a closure
                                 val result = (scope.thisObj as? ObjInstance)?.let { i ->
-                                    annotatedFnBody.execute(ClosureScope(scope, i.instanceScope))
+                                    compiledFnBody.execute(ClosureScope(scope, i.instanceScope))
                                 }
                                 // other classes can create one-time scope for this rare case:
-                                    ?: annotatedFnBody.execute(scope.thisObj.autoInstanceScope(scope))
+                                    ?: compiledFnBody.execute(scope.thisObj.autoInstanceScope(scope))
                                 return result
                             }
                         }
@@ -3127,18 +3199,18 @@ class Compiler(
                                                 newThisObj = i
                                             )
                                             execScope.currentClassCtx = cls
-                                            annotatedFnBody.execute(execScope)
+                                            compiledFnBody.execute(execScope)
-                                        } ?: annotatedFnBody.execute(thisObj.autoInstanceScope(this))
+                                        } ?: compiledFnBody.execute(thisObj.autoInstanceScope(this))
                                     } finally {
                                         this.currentClassCtx = savedCtx
                                     }
                                 }
                                 // also expose the symbol in the class scope for possible references
-                                context.addItem(name, false, annotatedFnBody, visibility)
+                                context.addItem(name, false, compiledFnBody, visibility)
-                                annotatedFnBody
+                                compiledFnBody
                             } else {
                                 // top-level or nested function
-                                context.addItem(name, false, annotatedFnBody, visibility)
+                                context.addItem(name, false, compiledFnBody, visibility)
                             }
                         }
                     // as the function can be called from anywhere, we have
@@ -3194,15 +3266,7 @@ class Compiler(
             slotPlanStack.removeLast()
         }
         val planSnapshot = slotPlanIndices(blockSlotPlan)
-        val stmt = object : Statement() {
+        val stmt = BlockStatement(block, planSnapshot, startPos)
-            override val pos: Pos = startPos
-            override suspend fun execute(scope: Scope): Obj {
-                // block run on inner context:
-                val target = if (scope.skipScopeCreation) scope else scope.createChildScope(startPos)
-                if (planSnapshot.isNotEmpty()) target.applySlotPlan(planSnapshot)
-                return block.execute(target)
-            }
-        }
         val wrapped = wrapBytecode(stmt)
         return wrapped.also {
             val t1 = cc.next()
@@ -3456,6 +3520,17 @@ class Compiler(
             pendingDeclDoc = null
         }
 
+        if (declaringClassNameCaptured == null &&
+            extTypeName == null &&
+            !isStatic &&
+            !isProperty &&
+            !isDelegate &&
+            !actualExtern &&
+            !isAbstract
+        ) {
+            return VarDeclStatement(name, isMutable, visibility, initialExpression, isTransient, start)
+        }
+
         if (isStatic) {
             // find objclass instance: this is tricky: this code executes in object initializer,
             // when creating instance, but we need to execute it in the class initializer which

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

@@ -18,6 +18,8 @@
 package net.sergeych.lyng
 
 import net.sergeych.lyng.obj.*
+import net.sergeych.lyng.bytecode.BytecodeDisassembler
+import net.sergeych.lyng.bytecode.BytecodeStatement
 import net.sergeych.lyng.pacman.ImportManager
 import net.sergeych.lyng.pacman.ImportProvider
 
@@ -410,6 +412,34 @@ open class Scope(
         }
     }
 
+    fun applySlotPlanWithSnapshot(plan: Map<String, Int>): Map<String, Int?> {
+        if (plan.isEmpty()) return emptyMap()
+        val maxIndex = plan.values.maxOrNull() ?: return emptyMap()
+        if (slots.size <= maxIndex) {
+            val targetSize = maxIndex + 1
+            while (slots.size < targetSize) {
+                slots.add(ObjRecord(ObjUnset, isMutable = true))
+            }
+        }
+        val snapshot = LinkedHashMap<String, Int?>(plan.size)
+        for ((name, idx) in plan) {
+            snapshot[name] = nameToSlot[name]
+            nameToSlot[name] = idx
+        }
+        return snapshot
+    }
+
+    fun restoreSlotPlan(snapshot: Map<String, Int?>) {
+        if (snapshot.isEmpty()) return
+        for ((name, idx) in snapshot) {
+            if (idx == null) {
+                nameToSlot.remove(name)
+            } else {
+                nameToSlot[name] = idx
+            }
+        }
+    }
+
     /**
      * Clear all references and maps to prevent memory leaks when pooled.
      */
@@ -615,6 +645,15 @@ open class Scope(
         }
     }
 
+    fun disassembleSymbol(name: String): String {
+        val record = get(name) ?: return "$name is not found"
+        val stmt = record.value as? Statement ?: return "$name is not a compiled body"
+        val bytecode = (stmt as? BytecodeStatement)?.bytecodeFunction()
+            ?: (stmt as? BytecodeBodyProvider)?.bytecodeBody()?.bytecodeFunction()
+            ?: return "$name is not a compiled body"
+        return BytecodeDisassembler.disassemble(bytecode)
+    }
+
     fun addFn(vararg names: String, fn: suspend Scope.() -> Obj) {
         val newFn = object : Statement() {
             override val pos: Pos = Pos.builtIn

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

@@ -43,6 +43,8 @@ class Script(
         return lastResult
     }
 
+    internal fun debugStatements(): List<Statement> = statements
+
     suspend fun execute() = execute(
         defaultImportManager.newStdScope()
     )
@@ -462,4 +464,4 @@ class Script(
         }
 
     }
-}
+}

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

@@ -0,0 +1,45 @@
+/*
+ * 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.ObjNull
+import net.sergeych.lyng.obj.ObjRecord
+
+class VarDeclStatement(
+    val name: String,
+    val isMutable: Boolean,
+    val visibility: Visibility,
+    val initializer: Statement?,
+    val isTransient: Boolean,
+    private val startPos: Pos,
+) : Statement() {
+    override val pos: Pos = startPos
+
+    override suspend fun execute(context: Scope): Obj {
+        val initValue = initializer?.execute(context)?.byValueCopy() ?: ObjNull
+        context.addItem(
+            name,
+            isMutable,
+            initValue,
+            visibility,
+            recordType = ObjRecord.Type.Other,
+            isTransient = isTransient
+        )
+        return initValue
+    }
+}

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

@@ -129,7 +129,7 @@ class BytecodeBuilder {
 
     private fun operandKinds(op: Opcode): List<OperandKind> {
         return when (op) {
-            Opcode.NOP, Opcode.RET_VOID, Opcode.POP_SCOPE -> emptyList()
+            Opcode.NOP, Opcode.RET_VOID, Opcode.POP_SCOPE, Opcode.POP_SLOT_PLAN -> emptyList()
             Opcode.MOVE_OBJ, Opcode.MOVE_INT, Opcode.MOVE_REAL, Opcode.MOVE_BOOL, Opcode.BOX_OBJ,
             Opcode.INT_TO_REAL, Opcode.REAL_TO_INT, Opcode.BOOL_TO_INT, Opcode.INT_TO_BOOL,
             Opcode.NEG_INT, Opcode.NEG_REAL, Opcode.NOT_BOOL, Opcode.INV_INT ->
@@ -138,8 +138,10 @@ class BytecodeBuilder {
                 listOf(OperandKind.SLOT)
             Opcode.CONST_OBJ, Opcode.CONST_INT, Opcode.CONST_REAL, Opcode.CONST_BOOL ->
                 listOf(OperandKind.CONST, OperandKind.SLOT)
-            Opcode.PUSH_SCOPE ->
+            Opcode.PUSH_SCOPE, Opcode.PUSH_SLOT_PLAN ->
                 listOf(OperandKind.CONST)
+            Opcode.DECL_LOCAL ->
+                listOf(OperandKind.CONST, OperandKind.SLOT)
             Opcode.ADD_INT, Opcode.SUB_INT, Opcode.MUL_INT, Opcode.DIV_INT, Opcode.MOD_INT,
             Opcode.ADD_REAL, Opcode.SUB_REAL, Opcode.MUL_REAL, Opcode.DIV_REAL,
             Opcode.AND_INT, Opcode.OR_INT, Opcode.XOR_INT, Opcode.SHL_INT, Opcode.SHR_INT, Opcode.USHR_INT,

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

@@ -16,12 +16,14 @@
 
 package net.sergeych.lyng.bytecode
 
+import net.sergeych.lyng.BlockStatement
 import net.sergeych.lyng.ExpressionStatement
 import net.sergeych.lyng.IfStatement
 import net.sergeych.lyng.ParsedArgument
 import net.sergeych.lyng.Pos
 import net.sergeych.lyng.Statement
 import net.sergeych.lyng.ToBoolStatement
+import net.sergeych.lyng.VarDeclStatement
 import net.sergeych.lyng.obj.*
 
 class BytecodeCompiler(
@@ -36,6 +38,10 @@ class BytecodeCompiler(
     private val scopeSlotMap = LinkedHashMap<ScopeSlotKey, Int>()
     private val scopeSlotNameMap = LinkedHashMap<ScopeSlotKey, String>()
     private val slotTypes = mutableMapOf<Int, SlotType>()
+    private val intLoopVarNames = LinkedHashSet<String>()
+    private val loopVarNames = LinkedHashSet<String>()
+    private val loopVarSlotIndexByName = LinkedHashMap<String, Int>()
+    private val loopVarSlotIdByName = LinkedHashMap<String, Int>()
 
     fun compileStatement(name: String, stmt: net.sergeych.lyng.Statement): BytecodeFunction? {
         prepareCompilation(stmt)
@@ -43,6 +49,8 @@ class BytecodeCompiler(
             is ExpressionStatement -> compileExpression(name, stmt)
             is net.sergeych.lyng.IfStatement -> compileIf(name, stmt)
             is net.sergeych.lyng.ForInStatement -> compileForIn(name, stmt)
+            is BlockStatement -> compileBlock(name, stmt)
+            is VarDeclStatement -> compileVarDecl(name, stmt)
             else -> null
         }
     }
@@ -66,8 +74,14 @@ class BytecodeCompiler(
                 if (!allowLocalSlots) return null
                 if (ref.isDelegated) return null
                 if (ref.name.isEmpty()) return null
-                val mapped = scopeSlotMap[ScopeSlotKey(refDepth(ref), refSlot(ref))] ?: return null
+                val loopSlotId = loopVarSlotIdByName[ref.name]
-                CompiledValue(mapped, slotTypes[mapped] ?: SlotType.UNKNOWN)
+                val mapped = loopSlotId ?: scopeSlotMap[ScopeSlotKey(refDepth(ref), refSlot(ref))] ?: return null
+                val resolved = slotTypes[mapped] ?: SlotType.UNKNOWN
+                if (resolved == SlotType.UNKNOWN && intLoopVarNames.contains(ref.name)) {
+                    updateSlotType(mapped, SlotType.INT)
+                    return CompiledValue(mapped, SlotType.INT)
+                }
+                CompiledValue(mapped, resolved)
             }
             is BinaryOpRef -> compileBinary(ref)
             is UnaryOpRef -> compileUnary(ref)
@@ -150,8 +164,30 @@ class BytecodeCompiler(
         if (op == BinOp.AND || op == BinOp.OR) {
             return compileLogical(op, binaryLeft(ref), binaryRight(ref), refPos(ref))
         }
-        val a = compileRef(binaryLeft(ref)) ?: return null
+        val leftRef = binaryLeft(ref)
-        val b = compileRef(binaryRight(ref)) ?: return null
+        val rightRef = binaryRight(ref)
+        var a = compileRef(leftRef) ?: return null
+        var b = compileRef(rightRef) ?: return null
+        val intOps = setOf(
+            BinOp.PLUS, BinOp.MINUS, BinOp.STAR, BinOp.SLASH, BinOp.PERCENT,
+            BinOp.BAND, BinOp.BOR, BinOp.BXOR, BinOp.SHL, BinOp.SHR
+        )
+        val leftIsLoopVar = (leftRef as? LocalSlotRef)?.name?.let { intLoopVarNames.contains(it) } == true
+        val rightIsLoopVar = (rightRef as? LocalSlotRef)?.name?.let { intLoopVarNames.contains(it) } == true
+        if (a.type == SlotType.UNKNOWN && b.type == SlotType.INT && op in intOps && leftIsLoopVar) {
+            updateSlotType(a.slot, SlotType.INT)
+            a = CompiledValue(a.slot, SlotType.INT)
+        }
+        if (b.type == SlotType.UNKNOWN && a.type == SlotType.INT && op in intOps && rightIsLoopVar) {
+            updateSlotType(b.slot, SlotType.INT)
+            b = CompiledValue(b.slot, SlotType.INT)
+        }
+        if (a.type == SlotType.UNKNOWN && b.type == SlotType.UNKNOWN && op in intOps && leftIsLoopVar && rightIsLoopVar) {
+            updateSlotType(a.slot, SlotType.INT)
+            updateSlotType(b.slot, SlotType.INT)
+            a = CompiledValue(a.slot, SlotType.INT)
+            b = CompiledValue(b.slot, SlotType.INT)
+        }
         val typesMismatch = a.type != b.type && a.type != SlotType.UNKNOWN && b.type != SlotType.UNKNOWN
         if (typesMismatch && op !in setOf(BinOp.EQ, BinOp.NEQ, BinOp.LT, BinOp.LTE, BinOp.GT, BinOp.GTE)) {
             return null
@@ -701,9 +737,8 @@ class BytecodeCompiler(
         val target = ref.target as? LocalSlotRef ?: return null
         if (!allowLocalSlots) return null
         if (!target.isMutable || target.isDelegated) return null
-        if (refDepth(target) > 0) return null
         val slot = scopeSlotMap[ScopeSlotKey(refDepth(target), refSlot(target))] ?: return null
-        val slotType = slotTypes[slot] ?: return null
+        val slotType = slotTypes[slot] ?: SlotType.UNKNOWN
         return when (slotType) {
             SlotType.INT -> {
                 if (ref.isPost) {
@@ -732,6 +767,41 @@ class BytecodeCompiler(
                     CompiledValue(slot, SlotType.REAL)
                 }
             }
+            SlotType.OBJ -> {
+                val oneSlot = allocSlot()
+                val oneId = builder.addConst(BytecodeConst.ObjRef(ObjInt.One))
+                builder.emit(Opcode.CONST_OBJ, oneId, oneSlot)
+                val current = allocSlot()
+                builder.emit(Opcode.BOX_OBJ, slot, current)
+                if (ref.isPost) {
+                    val result = allocSlot()
+                    val op = if (ref.isIncrement) Opcode.ADD_OBJ else Opcode.SUB_OBJ
+                    builder.emit(op, current, oneSlot, result)
+                    builder.emit(Opcode.MOVE_OBJ, result, slot)
+                    updateSlotType(slot, SlotType.OBJ)
+                    CompiledValue(current, SlotType.OBJ)
+                } else {
+                    val result = allocSlot()
+                    val op = if (ref.isIncrement) Opcode.ADD_OBJ else Opcode.SUB_OBJ
+                    builder.emit(op, current, oneSlot, result)
+                    builder.emit(Opcode.MOVE_OBJ, result, slot)
+                    updateSlotType(slot, SlotType.OBJ)
+                    CompiledValue(result, SlotType.OBJ)
+                }
+            }
+            SlotType.UNKNOWN -> {
+                if (ref.isPost) {
+                    val old = allocSlot()
+                    builder.emit(Opcode.MOVE_INT, slot, old)
+                    builder.emit(if (ref.isIncrement) Opcode.INC_INT else Opcode.DEC_INT, slot)
+                    updateSlotType(slot, SlotType.INT)
+                    CompiledValue(old, SlotType.INT)
+                } else {
+                    builder.emit(if (ref.isIncrement) Opcode.INC_INT else Opcode.DEC_INT, slot)
+                    updateSlotType(slot, SlotType.INT)
+                    CompiledValue(slot, SlotType.INT)
+                }
+            }
             else -> null
         }
     }
@@ -794,6 +864,20 @@ class BytecodeCompiler(
 
     private fun compileCall(ref: CallRef): CompiledValue? {
         if (ref.isOptionalInvoke) return null
+        if (ref.target is LocalVarRef || ref.target is FastLocalVarRef || ref.target is BoundLocalVarRef) {
+            return null
+        }
+        val fieldTarget = ref.target as? FieldRef
+        if (fieldTarget != null && !fieldTarget.isOptional) {
+            val receiver = compileRefWithFallback(fieldTarget.target, null, Pos.builtIn) ?: return null
+            val args = compileCallArgs(ref.args, ref.tailBlock) ?: return null
+            val encodedCount = encodeCallArgCount(args) ?: return null
+            val methodId = builder.addConst(BytecodeConst.StringVal(fieldTarget.name))
+            if (methodId > 0xFFFF) return null
+            val dst = allocSlot()
+            builder.emit(Opcode.CALL_VIRTUAL, receiver.slot, methodId, args.base, encodedCount, dst)
+            return CompiledValue(dst, SlotType.UNKNOWN)
+        }
         val callee = compileRefWithFallback(ref.target, null, Pos.builtIn) ?: return null
         val args = compileCallArgs(ref.args, ref.tailBlock) ?: return null
         val encodedCount = encodeCallArgCount(args) ?: return null
@@ -890,12 +974,112 @@ class BytecodeCompiler(
     }
 
     private fun compileForIn(name: String, stmt: net.sergeych.lyng.ForInStatement): BytecodeFunction? {
+        val resultSlot = emitForIn(stmt) ?: return null
+        builder.emit(Opcode.RET, resultSlot)
+        val localCount = maxOf(nextSlot, resultSlot + 1) - scopeSlotCount
+        return builder.build(name, localCount, scopeSlotDepths, scopeSlotIndices, scopeSlotNames)
+    }
+
+    private fun compileBlock(name: String, stmt: BlockStatement): BytecodeFunction? {
+        val result = emitBlock(stmt) ?: return null
+        builder.emit(Opcode.RET, result.slot)
+        val localCount = maxOf(nextSlot, result.slot + 1) - scopeSlotCount
+        return builder.build(name, localCount, scopeSlotDepths, scopeSlotIndices, scopeSlotNames)
+    }
+
+    private fun compileVarDecl(name: String, stmt: VarDeclStatement): BytecodeFunction? {
+        val result = emitVarDecl(stmt) ?: return null
+        builder.emit(Opcode.RET, result.slot)
+        val localCount = maxOf(nextSlot, result.slot + 1) - scopeSlotCount
+        return builder.build(name, localCount, scopeSlotDepths, scopeSlotIndices, scopeSlotNames)
+    }
+
+    private fun compileStatementValue(stmt: Statement): CompiledValue? {
+        return when (stmt) {
+            is ExpressionStatement -> compileRefWithFallback(stmt.ref, null, stmt.pos)
+            else -> null
+        }
+    }
+
+    private fun compileStatementValueOrFallback(stmt: Statement): CompiledValue? {
+        val target = if (stmt is BytecodeStatement) stmt.original else stmt
+        return when (target) {
+            is ExpressionStatement -> compileRefWithFallback(target.ref, null, target.pos)
+            is IfStatement -> compileIfExpression(target)
+            is net.sergeych.lyng.ForInStatement -> {
+                val resultSlot = emitForIn(target) ?: return null
+                updateSlotType(resultSlot, SlotType.OBJ)
+                CompiledValue(resultSlot, SlotType.OBJ)
+            }
+            is BlockStatement -> emitBlock(target)
+            is VarDeclStatement -> emitVarDecl(target)
+            else -> {
+                val slot = allocSlot()
+                val id = builder.addFallback(target)
+                builder.emit(Opcode.EVAL_FALLBACK, id, slot)
+                builder.emit(Opcode.BOX_OBJ, slot, slot)
+                updateSlotType(slot, SlotType.OBJ)
+                CompiledValue(slot, SlotType.OBJ)
+            }
+        }
+    }
+
+    private fun emitBlock(stmt: BlockStatement): CompiledValue? {
+        val planId = builder.addConst(BytecodeConst.SlotPlan(stmt.slotPlan))
+        builder.emit(Opcode.PUSH_SCOPE, planId)
+        val statements = stmt.statements()
+        var lastValue: CompiledValue? = null
+        for (statement in statements) {
+            lastValue = compileStatementValueOrFallback(statement) ?: return null
+        }
+        var result = lastValue ?: run {
+            val slot = allocSlot()
+            val voidId = builder.addConst(BytecodeConst.ObjRef(ObjVoid))
+            builder.emit(Opcode.CONST_OBJ, voidId, slot)
+            CompiledValue(slot, SlotType.OBJ)
+        }
+        if (result.slot < scopeSlotCount) {
+            val captured = allocSlot()
+            emitMove(result, captured)
+            result = CompiledValue(captured, result.type)
+        }
+        builder.emit(Opcode.POP_SCOPE)
+        return result
+    }
+
+    private fun emitVarDecl(stmt: VarDeclStatement): CompiledValue? {
+        val value = stmt.initializer?.let { compileStatementValueOrFallback(it) } ?: run {
+            val slot = allocSlot()
+            builder.emit(Opcode.CONST_NULL, slot)
+            updateSlotType(slot, SlotType.OBJ)
+            CompiledValue(slot, SlotType.OBJ)
+        }
+        val declId = builder.addConst(
+            BytecodeConst.LocalDecl(
+                stmt.name,
+                stmt.isMutable,
+                stmt.visibility,
+                stmt.isTransient
+            )
+        )
+        builder.emit(Opcode.DECL_LOCAL, declId, value.slot)
+        if (value.type != SlotType.UNKNOWN) {
+            updateSlotTypeByName(stmt.name, value.type)
+        }
+        return value
+    }
+    private fun emitForIn(stmt: net.sergeych.lyng.ForInStatement): Int? {
         if (stmt.canBreak) return null
         val range = stmt.constRange ?: return null
-        val loopSlotIndex = stmt.loopSlotPlan[stmt.loopVarName] ?: return null
+        val loopSlotId = loopVarSlotIdByName[stmt.loopVarName] ?: return null
-        val loopSlot = scopeSlotMap[ScopeSlotKey(0, loopSlotIndex)] ?: return null
+        val slotIndex = loopVarSlotIndexByName[stmt.loopVarName] ?: return null
-        val planId = builder.addConst(BytecodeConst.SlotPlan(stmt.loopSlotPlan))
+        val planId = builder.addConst(BytecodeConst.SlotPlan(mapOf(stmt.loopVarName to slotIndex)))
-        builder.emit(Opcode.PUSH_SCOPE, planId)
+        val useLoopScope = scopeSlotMap.isEmpty()
+        if (useLoopScope) {
+            builder.emit(Opcode.PUSH_SCOPE, planId)
+        } else {
+            builder.emit(Opcode.PUSH_SLOT_PLAN, planId)
+        }
 
         val iSlot = allocSlot()
         val endSlot = allocSlot()
@@ -917,7 +1101,9 @@ class BytecodeCompiler(
             Opcode.JMP_IF_TRUE,
             listOf(BytecodeBuilder.Operand.IntVal(cmpSlot), BytecodeBuilder.Operand.LabelRef(endLabel))
         )
-        builder.emit(Opcode.MOVE_INT, iSlot, loopSlot)
+        builder.emit(Opcode.MOVE_INT, iSlot, loopSlotId)
+        updateSlotType(loopSlotId, SlotType.INT)
+        updateSlotTypeByName(stmt.loopVarName, SlotType.INT)
         val bodyValue = compileStatementValueOrFallback(stmt.body) ?: return null
         val bodyObj = ensureObjSlot(bodyValue)
         builder.emit(Opcode.MOVE_OBJ, bodyObj.slot, resultSlot)
@@ -930,30 +1116,23 @@ class BytecodeCompiler(
             val elseObj = ensureObjSlot(elseValue)
             builder.emit(Opcode.MOVE_OBJ, elseObj.slot, resultSlot)
         }
-        builder.emit(Opcode.POP_SCOPE)
+        if (useLoopScope) {
-        builder.emit(Opcode.RET, resultSlot)
+            builder.emit(Opcode.POP_SCOPE)
-
+        } else {
-        val localCount = maxOf(nextSlot, resultSlot + 1) - scopeSlotCount
+            builder.emit(Opcode.POP_SLOT_PLAN)
-        return builder.build(name, localCount, scopeSlotDepths, scopeSlotIndices, scopeSlotNames)
-    }
-
-    private fun compileStatementValue(stmt: Statement): CompiledValue? {
-        return when (stmt) {
-            is ExpressionStatement -> compileRefWithFallback(stmt.ref, null, stmt.pos)
-            else -> null
         }
+        return resultSlot
     }
 
-    private fun compileStatementValueOrFallback(stmt: Statement): CompiledValue? {
+    private fun updateSlotTypeByName(name: String, type: SlotType) {
-        return when (stmt) {
+        val loopSlotId = loopVarSlotIdByName[name]
-            is ExpressionStatement -> compileRefWithFallback(stmt.ref, null, stmt.pos)
+        if (loopSlotId != null) {
-            is IfStatement -> compileIfExpression(stmt)
+            updateSlotType(loopSlotId, type)
-            else -> {
+            return
-                val slot = allocSlot()
+        }
-                val id = builder.addFallback(stmt)
+        for ((key, index) in scopeSlotMap) {
-                builder.emit(Opcode.EVAL_FALLBACK, id, slot)
+            if (scopeSlotNameMap[key] == name) {
-                updateSlotType(slot, SlotType.OBJ)
+                updateSlotType(index, type)
-                CompiledValue(slot, SlotType.OBJ)
             }
         }
     }
@@ -1025,8 +1204,13 @@ class BytecodeCompiler(
         }
         val id = builder.addFallback(stmt)
         builder.emit(Opcode.EVAL_FALLBACK, id, slot)
-        updateSlotType(slot, forceType ?: SlotType.OBJ)
+        if (forceType == null) {
-        return CompiledValue(slot, forceType ?: SlotType.OBJ)
+            builder.emit(Opcode.BOX_OBJ, slot, slot)
+            updateSlotType(slot, SlotType.OBJ)
+            return CompiledValue(slot, SlotType.OBJ)
+        }
+        updateSlotType(slot, forceType)
+        return CompiledValue(slot, forceType)
     }
 
     private fun refSlot(ref: LocalSlotRef): Int = ref.slot
@@ -1053,7 +1237,12 @@ class BytecodeCompiler(
         nextSlot = 0
         slotTypes.clear()
         scopeSlotMap.clear()
+        intLoopVarNames.clear()
+        loopVarNames.clear()
+        loopVarSlotIndexByName.clear()
+        loopVarSlotIdByName.clear()
         if (allowLocalSlots) {
+            collectLoopVarNames(stmt)
             collectScopeSlots(stmt)
         }
         scopeSlotCount = scopeSlotMap.size
@@ -1062,31 +1251,55 @@ class BytecodeCompiler(
         scopeSlotNames = arrayOfNulls(scopeSlotCount)
         for ((key, index) in scopeSlotMap) {
             scopeSlotDepths[index] = key.depth
+            val name = scopeSlotNameMap[key]
             scopeSlotIndices[index] = key.slot
-            scopeSlotNames[index] = scopeSlotNameMap[key]
+            scopeSlotNames[index] = name
+        }
+        if (loopVarNames.isNotEmpty()) {
+            var maxSlotIndex = scopeSlotMap.keys.maxOfOrNull { it.slot } ?: -1
+            for (name in loopVarNames) {
+                maxSlotIndex += 1
+                loopVarSlotIndexByName[name] = maxSlotIndex
+            }
+            val start = scopeSlotCount
+            val total = scopeSlotCount + loopVarSlotIndexByName.size
+            scopeSlotDepths = scopeSlotDepths.copyOf(total)
+            scopeSlotIndices = scopeSlotIndices.copyOf(total)
+            scopeSlotNames = scopeSlotNames.copyOf(total)
+            var cursor = start
+            for ((name, slotIndex) in loopVarSlotIndexByName) {
+                loopVarSlotIdByName[name] = cursor
+                scopeSlotDepths[cursor] = 0
+                scopeSlotIndices[cursor] = slotIndex
+                scopeSlotNames[cursor] = name
+                cursor += 1
+            }
+            scopeSlotCount = total
         }
         nextSlot = scopeSlotCount
     }
 
     private fun collectScopeSlots(stmt: Statement) {
+        if (stmt is BytecodeStatement) {
+            collectScopeSlots(stmt.original)
+            return
+        }
         when (stmt) {
             is ExpressionStatement -> collectScopeSlotsRef(stmt.ref)
+            is BlockStatement -> {
+                for (child in stmt.statements()) {
+                    collectScopeSlots(child)
+                }
+            }
+            is VarDeclStatement -> {
+                stmt.initializer?.let { collectScopeSlots(it) }
+            }
             is IfStatement -> {
                 collectScopeSlots(stmt.condition)
                 collectScopeSlots(stmt.ifBody)
                 stmt.elseBody?.let { collectScopeSlots(it) }
             }
             is net.sergeych.lyng.ForInStatement -> {
-                val loopSlotIndex = stmt.loopSlotPlan[stmt.loopVarName]
-                if (loopSlotIndex != null) {
-                    val key = ScopeSlotKey(0, loopSlotIndex)
-                    if (!scopeSlotMap.containsKey(key)) {
-                        scopeSlotMap[key] = scopeSlotMap.size
-                    }
-                    if (!scopeSlotNameMap.containsKey(key)) {
-                        scopeSlotNameMap[key] = stmt.loopVarName
-                    }
-                }
                 collectScopeSlots(stmt.source)
                 collectScopeSlots(stmt.body)
                 stmt.elseStatement?.let { collectScopeSlots(it) }
@@ -1095,9 +1308,69 @@ class BytecodeCompiler(
         }
     }
 
+    private fun collectLoopVarNames(stmt: Statement) {
+        if (stmt is BytecodeStatement) {
+            collectLoopVarNames(stmt.original)
+            return
+        }
+        when (stmt) {
+            is net.sergeych.lyng.ForInStatement -> {
+                if (stmt.constRange != null) {
+                    intLoopVarNames.add(stmt.loopVarName)
+                    loopVarNames.add(stmt.loopVarName)
+                }
+                collectLoopVarNames(stmt.source)
+                collectLoopVarNames(stmt.body)
+                stmt.elseStatement?.let { collectLoopVarNames(it) }
+            }
+            is BlockStatement -> {
+                for (child in stmt.statements()) {
+                    collectLoopVarNames(child)
+                }
+            }
+            is VarDeclStatement -> {
+                stmt.initializer?.let { collectLoopVarNames(it) }
+            }
+            is IfStatement -> {
+                collectLoopVarNames(stmt.condition)
+                collectLoopVarNames(stmt.ifBody)
+                stmt.elseBody?.let { collectLoopVarNames(it) }
+            }
+            is ExpressionStatement -> collectLoopVarNamesRef(stmt.ref)
+            else -> {}
+        }
+    }
+
+    private fun collectLoopVarNamesRef(ref: ObjRef) {
+        when (ref) {
+            is BinaryOpRef -> {
+                collectLoopVarNamesRef(binaryLeft(ref))
+                collectLoopVarNamesRef(binaryRight(ref))
+            }
+            is UnaryOpRef -> collectLoopVarNamesRef(unaryOperand(ref))
+            is AssignRef -> collectLoopVarNamesRef(assignValue(ref))
+            is AssignOpRef -> {
+                collectLoopVarNamesRef(ref.target)
+                collectLoopVarNamesRef(ref.value)
+            }
+            is IncDecRef -> collectLoopVarNamesRef(ref.target)
+            is ConditionalRef -> {
+                collectLoopVarNamesRef(ref.condition)
+                collectLoopVarNamesRef(ref.ifTrue)
+                collectLoopVarNamesRef(ref.ifFalse)
+            }
+            is ElvisRef -> {
+                collectLoopVarNamesRef(ref.left)
+                collectLoopVarNamesRef(ref.right)
+            }
+            else -> {}
+        }
+    }
+
     private fun collectScopeSlotsRef(ref: ObjRef) {
         when (ref) {
             is LocalSlotRef -> {
+                if (loopVarNames.contains(ref.name)) return
                 val key = ScopeSlotKey(refDepth(ref), refSlot(ref))
                 if (!scopeSlotMap.containsKey(key)) {
                     scopeSlotMap[key] = scopeSlotMap.size

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

@@ -16,6 +16,7 @@
 
 package net.sergeych.lyng.bytecode
 
+import net.sergeych.lyng.Visibility
 import net.sergeych.lyng.obj.Obj
 
 sealed class BytecodeConst {
@@ -26,6 +27,12 @@ sealed class BytecodeConst {
     data class StringVal(val value: String) : BytecodeConst()
     data class ObjRef(val value: Obj) : BytecodeConst()
     data class SlotPlan(val plan: Map<String, Int>) : BytecodeConst()
+    data class LocalDecl(
+        val name: String,
+        val isMutable: Boolean,
+        val visibility: Visibility,
+        val isTransient: Boolean,
+    ) : BytecodeConst()
     data class CallArgsPlan(val tailBlock: Boolean, val specs: List<CallArgSpec>) : BytecodeConst()
     data class CallArgSpec(val name: String?, val isSplat: Boolean)
 }

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

@@ -82,7 +82,7 @@ object BytecodeDisassembler {
 
     private fun operandKinds(op: Opcode): List<OperandKind> {
         return when (op) {
-            Opcode.NOP, Opcode.RET_VOID, Opcode.POP_SCOPE -> emptyList()
+            Opcode.NOP, Opcode.RET_VOID, Opcode.POP_SCOPE, Opcode.POP_SLOT_PLAN -> emptyList()
             Opcode.MOVE_OBJ, Opcode.MOVE_INT, Opcode.MOVE_REAL, Opcode.MOVE_BOOL, Opcode.BOX_OBJ,
             Opcode.INT_TO_REAL, Opcode.REAL_TO_INT, Opcode.BOOL_TO_INT, Opcode.INT_TO_BOOL,
             Opcode.NEG_INT, Opcode.NEG_REAL, Opcode.NOT_BOOL, Opcode.INV_INT ->
@@ -91,8 +91,10 @@ object BytecodeDisassembler {
                 listOf(OperandKind.SLOT)
             Opcode.CONST_OBJ, Opcode.CONST_INT, Opcode.CONST_REAL, Opcode.CONST_BOOL ->
                 listOf(OperandKind.CONST, OperandKind.SLOT)
-            Opcode.PUSH_SCOPE ->
+            Opcode.PUSH_SCOPE, Opcode.PUSH_SLOT_PLAN ->
                 listOf(OperandKind.CONST)
+            Opcode.DECL_LOCAL ->
+                listOf(OperandKind.CONST, OperandKind.SLOT)
             Opcode.ADD_INT, Opcode.SUB_INT, Opcode.MUL_INT, Opcode.DIV_INT, Opcode.MOD_INT,
             Opcode.ADD_REAL, Opcode.SUB_REAL, Opcode.MUL_REAL, Opcode.DIV_REAL,
             Opcode.AND_INT, Opcode.OR_INT, Opcode.XOR_INT, Opcode.SHL_INT, Opcode.SHR_INT, Opcode.USHR_INT,

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

@@ -31,6 +31,8 @@ class BytecodeStatement private constructor(
         return BytecodeVm().execute(function, scope, emptyList())
     }
 
+    internal fun bytecodeFunction(): BytecodeFunction = function
+
     companion object {
         fun wrap(statement: Statement, nameHint: String, allowLocalSlots: Boolean): Statement {
             if (statement is BytecodeStatement) return statement

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

@@ -19,6 +19,7 @@ package net.sergeych.lyng.bytecode
 import net.sergeych.lyng.Arguments
 import net.sergeych.lyng.PerfFlags
 import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjRecord
 import net.sergeych.lyng.obj.*
 
 class BytecodeVm {
@@ -27,11 +28,16 @@ class BytecodeVm {
         private const val ARG_PLAN_MASK = 0x7FFF
     }
 
+    private var virtualDepth = 0
+
     suspend fun execute(fn: BytecodeFunction, scope0: Scope, args: List<Obj>): Obj {
         val scopeStack = ArrayDeque<Scope>()
+        val scopeVirtualStack = ArrayDeque<Boolean>()
+        val slotPlanStack = ArrayDeque<Map<String, Int?>>()
         var scope = scope0
         val methodCallSites = BytecodeCallSiteCache.methodCallSites(fn)
         val frame = BytecodeFrame(fn.localCount, args.size)
+        virtualDepth = 0
         for (i in args.indices) {
             frame.setObj(frame.argBase + i, args[i])
         }
@@ -734,16 +740,65 @@ class BytecodeVm {
                     ip += fn.constIdWidth
                     val planConst = fn.constants[constId] as? BytecodeConst.SlotPlan
                         ?: error("PUSH_SCOPE expects SlotPlan at $constId")
-                    scopeStack.addLast(scope)
+                    if (scope.skipScopeCreation) {
-                    scope = scope.createChildScope()
+                        val snapshot = scope.applySlotPlanWithSnapshot(planConst.plan)
-                    if (planConst.plan.isNotEmpty()) {
+                        slotPlanStack.addLast(snapshot)
-                        scope.applySlotPlan(planConst.plan)
+                        virtualDepth += 1
+                        scopeStack.addLast(scope)
+                        scopeVirtualStack.addLast(true)
+                    } else {
+                        scopeStack.addLast(scope)
+                        scopeVirtualStack.addLast(false)
+                        scope = scope.createChildScope()
+                        if (planConst.plan.isNotEmpty()) {
+                            scope.applySlotPlan(planConst.plan)
+                        }
                     }
                 }
                 Opcode.POP_SCOPE -> {
+                    val isVirtual = scopeVirtualStack.removeLastOrNull()
+                        ?: error("Scope stack underflow in POP_SCOPE")
+                    if (isVirtual) {
+                        val snapshot = slotPlanStack.removeLastOrNull()
+                            ?: error("Slot plan stack underflow in POP_SCOPE")
+                        scope.restoreSlotPlan(snapshot)
+                        virtualDepth -= 1
+                    }
                     scope = scopeStack.removeLastOrNull()
                         ?: error("Scope stack underflow in POP_SCOPE")
                 }
+                Opcode.PUSH_SLOT_PLAN -> {
+                    val constId = decoder.readConstId(code, ip, fn.constIdWidth)
+                    ip += fn.constIdWidth
+                    val planConst = fn.constants[constId] as? BytecodeConst.SlotPlan
+                        ?: error("PUSH_SLOT_PLAN expects SlotPlan at $constId")
+                    val snapshot = scope.applySlotPlanWithSnapshot(planConst.plan)
+                    slotPlanStack.addLast(snapshot)
+                    virtualDepth += 1
+                }
+                Opcode.POP_SLOT_PLAN -> {
+                    val snapshot = slotPlanStack.removeLastOrNull()
+                        ?: error("Slot plan stack underflow in POP_SLOT_PLAN")
+                    scope.restoreSlotPlan(snapshot)
+                    virtualDepth -= 1
+                }
+                Opcode.DECL_LOCAL -> {
+                    val constId = decoder.readConstId(code, ip, fn.constIdWidth)
+                    ip += fn.constIdWidth
+                    val slot = decoder.readSlot(code, ip)
+                    ip += fn.slotWidth
+                    val decl = fn.constants[constId] as? BytecodeConst.LocalDecl
+                        ?: error("DECL_LOCAL expects LocalDecl at $constId")
+                    val value = slotToObj(fn, frame, scope, slot).byValueCopy()
+                    scope.addItem(
+                        decl.name,
+                        decl.isMutable,
+                        value,
+                        decl.visibility,
+                        recordType = ObjRecord.Type.Other,
+                        isTransient = decl.isTransient
+                    )
+                }
                 Opcode.CALL_SLOT -> {
                     val calleeSlot = decoder.readSlot(code, ip)
                     ip += fn.slotWidth
@@ -979,11 +1034,16 @@ class BytecodeVm {
 
     private fun resolveScope(scope: Scope, depth: Int): Scope {
         if (depth == 0) return scope
+        var effectiveDepth = depth
+        if (virtualDepth > 0) {
+            if (effectiveDepth <= virtualDepth) return scope
+            effectiveDepth -= virtualDepth
+        }
         val next = when (scope) {
             is net.sergeych.lyng.ClosureScope -> scope.closureScope
             else -> scope.parent
         }
-        return next?.let { resolveScope(it, depth - 1) }
+        return next?.let { resolveScope(it, effectiveDepth - 1) }
             ?: error("Scope depth $depth is out of range")
     }
 }

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

@@ -109,6 +109,9 @@ enum class Opcode(val code: Int) {
     RET_VOID(0x84),
     PUSH_SCOPE(0x85),
     POP_SCOPE(0x86),
+    PUSH_SLOT_PLAN(0x87),
+    POP_SLOT_PLAN(0x88),
+    DECL_LOCAL(0x89),
 
     CALL_DIRECT(0x90),
     CALL_VIRTUAL(0x91),

lynglib/src/commonTest/kotlin/NestedRangeBenchmarkTest.kt

@@ -17,7 +17,12 @@
 
 import kotlinx.coroutines.test.runTest
 import net.sergeych.lyng.Benchmarks
-import net.sergeych.lyng.eval
+import net.sergeych.lyng.Compiler
+import net.sergeych.lyng.ForInStatement
+import net.sergeych.lyng.Script
+import net.sergeych.lyng.Statement
+import net.sergeych.lyng.bytecode.BytecodeDisassembler
+import net.sergeych.lyng.bytecode.BytecodeStatement
 import net.sergeych.lyng.obj.ObjInt
 import kotlin.time.TimeSource
 import kotlin.test.Test
@@ -27,25 +32,65 @@ class NestedRangeBenchmarkTest {
     @Test
     fun benchmarkHappyNumbersNestedRanges() = runTest {
         if (!Benchmarks.enabled) return@runTest
-        val script = """
+        val bodyScript = """
-            fun naiveCountHappyNumbers() {
+            var count = 0
-                var count = 0
+            for( n1 in 0..9 )
-                for( n1 in 0..9 )
+                for( n2 in 0..9 )
-                    for( n2 in 0..9 )
+                    for( n3 in 0..9 )
-                        for( n3 in 0..9 )
+                        for( n4 in 0..9 )
-                            for( n4 in 0..9 )
+                            for( n5 in 0..9 )
-                                for( n5 in 0..9 )
+                                for( n6 in 0..9 )
-                                    for( n6 in 0..9 )
+                                    if( n1 + n2 + n3 == n4 + n5 + n6 ) count++
-                                        if( n1 + n2 + n3 == n4 + n5 + n6 ) count++
+            count
-                count
-            }
-            naiveCountHappyNumbers()
         """.trimIndent()
 
+        val compiled = Compiler.compile(bodyScript)
+        dumpNestedLoopBytecode(compiled.debugStatements())
+
+        val script = """
+            fun naiveCountHappyNumbers() {
+                $bodyScript
+            }
+        """.trimIndent()
+
+        val scope = Script.newScope()
+        scope.eval(script)
+        val fnDisasm = scope.disassembleSymbol("naiveCountHappyNumbers")
+        println("[DEBUG_LOG] [BENCH] nested-happy function naiveCountHappyNumbers bytecode:\n$fnDisasm")
+
         val start = TimeSource.Monotonic.markNow()
-        val result = eval(script) as ObjInt
+        val result = scope.eval("naiveCountHappyNumbers()") as ObjInt
         val elapsedMs = start.elapsedNow().inWholeMilliseconds
         println("[DEBUG_LOG] [BENCH] nested-happy elapsed=${elapsedMs} ms")
         assertEquals(55252L, result.value)
     }
+
+    private fun dumpNestedLoopBytecode(statements: List<Statement>) {
+        var current: Statement? = statements.firstOrNull { stmt ->
+            stmt is BytecodeStatement && stmt.original is ForInStatement
+        }
+        var depth = 1
+        while (current is BytecodeStatement && current.original is ForInStatement) {
+            val original = current.original as ForInStatement
+            println(
+                "[DEBUG_LOG] [BENCH] nested-happy loop depth=$depth " +
+                    "constRange=${original.constRange} canBreak=${original.canBreak} " +
+                    "loopSlotPlan=${original.loopSlotPlan}"
+            )
+            val fn = current.bytecodeFunction()
+            val slots = fn.scopeSlotNames.mapIndexed { idx, name ->
+                val slotName = name ?: "s$idx"
+                "$slotName@${fn.scopeSlotDepths[idx]}:${fn.scopeSlotIndices[idx]}"
+            }
+            println("[DEBUG_LOG] [BENCH] nested-happy slots depth=$depth: ${slots.joinToString(", ")}")
+            val disasm = BytecodeDisassembler.disassemble(fn)
+            println("[DEBUG_LOG] [BENCH] nested-happy bytecode depth=$depth:\n$disasm")
+            current = original.body
+            depth += 1
+        }
+        if (depth == 1) {
+            println("[DEBUG_LOG] [BENCH] nested-happy bytecode: <not found>")
+        }
+    }
+
 }

lynglib/src/commonTest/kotlin/ScriptTest.kt

@@ -3989,6 +3989,7 @@ class ScriptTest {
         )
     }
 
+
     @Test
     fun testParserOverflow() = runTest {
         try {
@@ -5044,4 +5045,3 @@ class ScriptTest {
         """.trimIndent())
     }
 }
-