optimization: Scope access is now a Kotlin interface, compiler uses direct slot access also for closures

AGENTS.md

@@ -12,3 +12,9 @@
 - `void` is a singleton of class `Void` (syntax sugar for return type).
 - Object members are always allowed even on unknown types; non-Object members require explicit casts. Remove `inspect` from Object and use `toInspectString()` instead.
 - Do not reintroduce bytecode fallback opcodes (e.g., `GET_NAME`, `EVAL_*`, `CALL_FALLBACK`) or runtime name-resolution fallbacks; all symbol resolution must stay compile-time only.
+
+## Bytecode frame-first migration plan
+- Treat frame slots as the only storage for locals/temps by default; avoid pre-creating scope slot mappings for compiled functions.
+- Create closure references only when a capture is detected; use a direct frame+slot reference (foreign slot ref) instead of scope slots.
+- Keep Scope as a lazy reflection facade: resolve name -> slot only on demand for Kotlin interop (no eager name mapping on every call).
+- Avoid PUSH_SCOPE/POP_SCOPE in bytecode for loops/functions unless dynamic name access or Kotlin reflection is requested.

docs/samples/happy_numbers.lyng.bad

@@ -4,15 +4,21 @@
     test the Lyng way. It is not meant to be effective.
 */
 
-fun naiveCountHappyNumbers() {
+fun naiveCountHappyNumbers(): Int {
     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++
+                        }
+                    }
+                }
+            }
+        }
+    }
     count
 }
 
@@ -28,4 +34,3 @@ for( r in 1..900 ) {
     assert( found == 55252 )
     delay(0.05)
 }
-

lyng/src/jvmTest/kotlin/net/sergeych/lyng_cli/FsIntegrationJvmTest.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.
@@ -56,7 +56,7 @@ class FsIntegrationJvmTest {
                 """
                     import lyng.io.fs
                     // list current folder files
-                    println( Path(".").list().toList() )
+                    println( Path(".").list() )
                     """.trimIndent()
             )
         }

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

@@ -1131,6 +1131,7 @@ class Compiler(
                             "<script>",
                             allowLocalSlots = true,
                             allowedScopeNames = modulePlan.keys,
+                            moduleScopeId = moduleSlotPlan()?.id,
                             slotTypeByScopeId = slotTypeByScopeId,
                             knownNameObjClass = knownClassMapForBytecode()
                         )
@@ -1357,7 +1358,7 @@ class Compiler(
             if (scope == null) return
             for ((name, rec) in scope.objects) {
                 val cls = rec.value as? ObjClass ?: continue
-                result.putIfAbsent(name, cls)
+                if (!result.containsKey(name)) result[name] = cls
             }
         }
         addScope(seedScope)
@@ -1367,7 +1368,7 @@ class Compiler(
         }
         for (name in compileClassInfos.keys) {
             val cls = resolveClassByName(name) ?: continue
-            result.putIfAbsent(name, cls)
+            if (!result.containsKey(name)) result[name] = cls
         }
         return result
     }
@@ -1411,6 +1412,7 @@ class Compiler(
             returnLabels = returnLabels,
             rangeLocalNames = currentRangeParamNames,
             allowedScopeNames = allowedScopeNames,
+            moduleScopeId = moduleSlotPlan()?.id,
             slotTypeByScopeId = slotTypeByScopeId,
             knownNameObjClass = knownClassMapForBytecode()
         )
@@ -1441,6 +1443,7 @@ class Compiler(
             returnLabels = returnLabels,
             rangeLocalNames = currentRangeParamNames,
             allowedScopeNames = allowedScopeNames,
+            moduleScopeId = moduleSlotPlan()?.id,
             slotTypeByScopeId = slotTypeByScopeId,
             knownNameObjClass = knownNames
         )

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

@@ -0,0 +1,57 @@
+/*
+ * 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.SlotType
+import net.sergeych.lyng.obj.*
+
+interface FrameAccess {
+    fun getSlotTypeCode(slot: Int): Byte
+    fun getObj(slot: Int): Obj
+    fun getInt(slot: Int): Long
+    fun getReal(slot: Int): Double
+    fun getBool(slot: Int): Boolean
+    fun setObj(slot: Int, value: Obj)
+    fun setInt(slot: Int, value: Long)
+    fun setReal(slot: Int, value: Double)
+    fun setBool(slot: Int, value: Boolean)
+}
+
+class FrameSlotRef(
+    private val frame: FrameAccess,
+    private val slot: Int,
+) : net.sergeych.lyng.obj.Obj() {
+    fun read(): Obj {
+        return when (frame.getSlotTypeCode(slot)) {
+            SlotType.INT.code -> ObjInt.of(frame.getInt(slot))
+            SlotType.REAL.code -> ObjReal.of(frame.getReal(slot))
+            SlotType.BOOL.code -> if (frame.getBool(slot)) ObjTrue else ObjFalse
+            SlotType.OBJ.code -> frame.getObj(slot)
+            else -> ObjNull
+        }
+    }
+
+    fun write(value: Obj) {
+        when (value) {
+            is ObjInt -> frame.setInt(slot, value.value)
+            is ObjReal -> frame.setReal(slot, value.value)
+            is ObjBool -> frame.setBool(slot, value.value)
+            else -> frame.setObj(slot, value)
+        }
+    }
+}

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

@@ -17,9 +17,9 @@
 
 package net.sergeych.lyng
 
-import net.sergeych.lyng.obj.*
-import net.sergeych.lyng.bytecode.CmdDisassembler
 import net.sergeych.lyng.bytecode.BytecodeStatement
+import net.sergeych.lyng.bytecode.CmdDisassembler
+import net.sergeych.lyng.obj.*
 import net.sergeych.lyng.pacman.ImportManager
 import net.sergeych.lyng.pacman.ImportProvider
 
@@ -414,7 +414,13 @@ open class Scope(
     // Slot fast-path API
     fun getSlotRecord(index: Int): ObjRecord = slots[index]
     fun setSlotValue(index: Int, newValue: Obj) {
-        slots[index].value = newValue
+        val record = slots[index]
+        val value = record.value
+        if (value is FrameSlotRef) {
+            value.write(newValue)
+            return
+        }
+        record.value = newValue
     }
     val slotCount: Int
         get() = slots.size
@@ -839,11 +845,21 @@ open class Scope(
     }
 
     suspend fun resolve(rec: ObjRecord, name: String): Obj {
+        val value = rec.value
+        if (value is FrameSlotRef) {
+            return value.read()
+        }
         val receiver = rec.receiver ?: thisObj
         return receiver.resolveRecord(this, rec, name, rec.declaringClass).value
     }
 
     suspend fun assign(rec: ObjRecord, name: String, newValue: Obj) {
+        val value = rec.value
+        if (value is FrameSlotRef) {
+            if (!rec.isMutable && value.read() !== ObjUnset) raiseIllegalAssignment("can't reassign val $name")
+            value.write(newValue)
+            return
+        }
         if (rec.type == ObjRecord.Type.Delegated) {
             val receiver = rec.receiver ?: thisObj
             val del = rec.delegate ?: run {

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

@@ -25,6 +25,7 @@ class BytecodeCompiler(
     private val returnLabels: Set<String> = emptySet(),
     private val rangeLocalNames: Set<String> = emptySet(),
     private val allowedScopeNames: Set<String>? = null,
+    private val moduleScopeId: Int? = null,
     private val slotTypeByScopeId: Map<Int, Map<Int, ObjClass>> = emptyMap(),
     private val knownNameObjClass: Map<String, ObjClass> = emptyMap(),
 ) {
@@ -58,6 +59,7 @@ class BytecodeCompiler(
     private val intLoopVarNames = LinkedHashSet<String>()
     private val loopStack = ArrayDeque<LoopContext>()
     private var forceScopeSlots = false
+    private var currentPos: Pos? = null
 
     private data class LoopContext(
         val label: String?,
@@ -70,6 +72,7 @@ class BytecodeCompiler(
 
     fun compileStatement(name: String, stmt: net.sergeych.lyng.Statement): CmdFunction? {
         prepareCompilation(stmt)
+        setPos(stmt.pos)
         return when (stmt) {
             is ExpressionStatement -> compileExpression(name, stmt)
             is net.sergeych.lyng.IfStatement -> compileIf(name, stmt)
@@ -321,6 +324,7 @@ class BytecodeCompiler(
     }
 
     private fun compileImplicitThisMethodCall(ref: ImplicitThisMethodCallRef): CompiledValue? {
+        val callPos = ref.pos()
         val receiver = ref.preferredThisTypeName()?.let { typeName ->
             compileThisVariantRef(typeName) ?: return null
         } ?: compileThisRef()
@@ -330,6 +334,7 @@ class BytecodeCompiler(
             if (!ref.optionalInvoke()) {
                 val args = compileCallArgs(ref.arguments(), ref.hasTailBlock()) ?: return null
                 val encodedCount = encodeCallArgCount(args) ?: return null
+                setPos(callPos)
                 builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
                 return CompiledValue(dst, SlotType.OBJ)
             }
@@ -345,6 +350,7 @@ class BytecodeCompiler(
             )
             val args = compileCallArgs(ref.arguments(), ref.hasTailBlock()) ?: return null
             val encodedCount = encodeCallArgCount(args) ?: return null
+            setPos(callPos)
             builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
             builder.emit(Opcode.JMP, listOf(CmdBuilder.Operand.LabelRef(endLabel)))
             builder.mark(nullLabel)
@@ -365,6 +371,7 @@ class BytecodeCompiler(
         if (!ref.optionalInvoke()) {
             val args = compileCallArgsWithReceiver(receiver, ref.arguments(), ref.hasTailBlock()) ?: return null
             val encodedCount = encodeCallArgCount(args) ?: return null
+            setPos(callPos)
             builder.emit(Opcode.CALL_SLOT, calleeObj.slot, args.base, encodedCount, dst)
             return CompiledValue(dst, SlotType.OBJ)
         }
@@ -380,6 +387,7 @@ class BytecodeCompiler(
         )
         val args = compileCallArgsWithReceiver(receiver, ref.arguments(), ref.hasTailBlock()) ?: return null
         val encodedCount = encodeCallArgCount(args) ?: return null
+        setPos(callPos)
         builder.emit(Opcode.CALL_SLOT, calleeObj.slot, args.base, encodedCount, dst)
         builder.emit(Opcode.JMP, listOf(CmdBuilder.Operand.LabelRef(endLabel)))
         builder.mark(nullLabel)
@@ -2707,6 +2715,7 @@ class BytecodeCompiler(
     }
 
     private fun compileCall(ref: CallRef): CompiledValue? {
+        val callPos = callSitePos()
         val localTarget = ref.target as? LocalVarRef
         if (localTarget != null) {
             val direct = resolveDirectNameSlot(localTarget.name)
@@ -2732,11 +2741,12 @@ class BytecodeCompiler(
             "Map" -> ObjMap.type
             else -> null
         }
-        val callee = compileRefWithFallback(ref.target, null, Pos.builtIn) ?: return null
+        val callee = compileRefWithFallback(ref.target, null, refPosOrCurrent(ref.target)) ?: return null
         val dst = allocSlot()
         if (!ref.isOptionalInvoke) {
             val args = compileCallArgs(ref.args, ref.tailBlock) ?: return null
             val encodedCount = encodeCallArgCount(args) ?: return null
+            setPos(callPos)
             builder.emit(Opcode.CALL_SLOT, callee.slot, args.base, encodedCount, dst)
             if (initClass != null) {
                 slotObjClass[dst] = initClass
@@ -2755,6 +2765,7 @@ class BytecodeCompiler(
         )
         val args = compileCallArgs(ref.args, ref.tailBlock) ?: return null
         val encodedCount = encodeCallArgCount(args) ?: return null
+        setPos(callPos)
         builder.emit(Opcode.CALL_SLOT, callee.slot, args.base, encodedCount, dst)
         if (initClass != null) {
             slotObjClass[dst] = initClass
@@ -2805,6 +2816,7 @@ class BytecodeCompiler(
     }
 
     private fun compileMethodCall(ref: MethodCallRef): CompiledValue? {
+        val callPos = callSitePos()
         val receiverClass = resolveReceiverClass(ref.receiver)
             ?: if (isAllowedObjectMember(ref.name)) {
                 Obj.rootObjectType
@@ -2814,13 +2826,14 @@ class BytecodeCompiler(
                     Pos.builtIn
                 )
             }
-        val receiver = compileRefWithFallback(ref.receiver, null, Pos.builtIn) ?: return null
+        val receiver = compileRefWithFallback(ref.receiver, null, refPosOrCurrent(ref.receiver)) ?: return null
         val dst = allocSlot()
         val methodId = receiverClass.instanceMethodIdMap(includeAbstract = true)[ref.name]
         if (methodId != null) {
             if (!ref.isOptional) {
                 val args = compileCallArgs(ref.args, ref.tailBlock) ?: return null
                 val encodedCount = encodeCallArgCount(args) ?: return null
+                setPos(callPos)
                 builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
                 return CompiledValue(dst, SlotType.OBJ)
             }
@@ -2836,6 +2849,7 @@ class BytecodeCompiler(
             )
             val args = compileCallArgs(ref.args, ref.tailBlock) ?: return null
             val encodedCount = encodeCallArgCount(args) ?: return null
+            setPos(callPos)
             builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
             builder.emit(Opcode.JMP, listOf(CmdBuilder.Operand.LabelRef(endLabel)))
             builder.mark(nullLabel)
@@ -2852,6 +2866,7 @@ class BytecodeCompiler(
         if (!ref.isOptional) {
             val args = compileCallArgsWithReceiver(receiver, ref.args, ref.tailBlock) ?: return null
             val encodedCount = encodeCallArgCount(args) ?: return null
+            setPos(callPos)
             builder.emit(Opcode.CALL_SLOT, callee.slot, args.base, encodedCount, dst)
             return CompiledValue(dst, SlotType.OBJ)
         }
@@ -2867,6 +2882,7 @@ class BytecodeCompiler(
         )
         val args = compileCallArgsWithReceiver(receiver, ref.args, ref.tailBlock) ?: return null
         val encodedCount = encodeCallArgCount(args) ?: return null
+        setPos(callPos)
         builder.emit(Opcode.CALL_SLOT, callee.slot, args.base, encodedCount, dst)
         builder.emit(Opcode.JMP, listOf(CmdBuilder.Operand.LabelRef(endLabel)))
         builder.mark(nullLabel)
@@ -2876,6 +2892,7 @@ class BytecodeCompiler(
     }
 
     private fun compileThisMethodSlotCall(ref: ThisMethodSlotCallRef): CompiledValue? {
+        val callPos = callSitePos()
         val receiver = compileThisRef()
         val methodId = ref.methodId() ?: throw BytecodeCompileException(
             "Missing member id for ${ref.methodName()}",
@@ -2885,6 +2902,7 @@ class BytecodeCompiler(
         if (!ref.optionalInvoke()) {
             val args = compileCallArgs(ref.arguments(), ref.hasTailBlock()) ?: return null
             val encodedCount = encodeCallArgCount(args) ?: return null
+            setPos(callPos)
             builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
             return CompiledValue(dst, SlotType.OBJ)
         }
@@ -2900,6 +2918,7 @@ class BytecodeCompiler(
         )
         val args = compileCallArgs(ref.arguments(), ref.hasTailBlock()) ?: return null
         val encodedCount = encodeCallArgCount(args) ?: return null
+        setPos(callPos)
         builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
         builder.emit(Opcode.JMP, listOf(CmdBuilder.Operand.LabelRef(endLabel)))
         builder.mark(nullLabel)
@@ -2932,6 +2951,7 @@ class BytecodeCompiler(
     }
 
     private fun compileQualifiedThisMethodSlotCall(ref: QualifiedThisMethodSlotCallRef): CompiledValue? {
+        val callPos = callSitePos()
         val receiver = compileThisVariantRef(ref.receiverTypeName()) ?: return null
         val methodId = ref.methodId() ?: throw BytecodeCompileException(
             "Missing member id for ${ref.methodName()}",
@@ -2941,6 +2961,7 @@ class BytecodeCompiler(
         if (!ref.optionalInvoke()) {
             val args = compileCallArgs(ref.arguments(), ref.hasTailBlock()) ?: return null
             val encodedCount = encodeCallArgCount(args) ?: return null
+            setPos(callPos)
             builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
             return CompiledValue(dst, SlotType.OBJ)
         }
@@ -2956,6 +2977,7 @@ class BytecodeCompiler(
         )
         val args = compileCallArgs(ref.arguments(), ref.hasTailBlock()) ?: return null
         val encodedCount = encodeCallArgCount(args) ?: return null
+        setPos(callPos)
         builder.emit(Opcode.CALL_MEMBER_SLOT, receiver.slot, methodId, args.base, encodedCount, dst)
         builder.emit(Opcode.JMP, listOf(CmdBuilder.Operand.LabelRef(endLabel)))
         builder.mark(nullLabel)
@@ -3163,7 +3185,11 @@ class BytecodeCompiler(
     }
 
     private fun compileBlock(name: String, stmt: BlockStatement): CmdFunction? {
-        val result = emitBlock(stmt, true) ?: return null
+        val result = if (shouldInlineBlock(stmt)) {
+            emitInlineStatements(stmt.statements(), true)
+        } else {
+            emitBlock(stmt, true)
+        } ?: return null
         builder.emit(Opcode.RET, result.slot)
         val localCount = maxOf(nextSlot, result.slot + 1) - scopeSlotCount
         return builder.build(
@@ -3217,6 +3243,7 @@ class BytecodeCompiler(
 
     private fun compileStatementValueOrFallback(stmt: Statement, needResult: Boolean = true): CompiledValue? {
         val target = if (stmt is BytecodeStatement) stmt.original else stmt
+        setPos(target.pos)
         return if (needResult) {
             when (target) {
                 is ExpressionStatement -> compileRefWithFallback(target.ref, null, target.pos)
@@ -3307,6 +3334,9 @@ class BytecodeCompiler(
     }
 
     private fun emitBlock(stmt: BlockStatement, needResult: Boolean): CompiledValue? {
+        if (shouldInlineBlock(stmt)) {
+            return emitInlineStatements(stmt.statements(), needResult)
+        }
         val captureNames = if (stmt.captureSlots.isEmpty()) emptyList() else stmt.captureSlots.map { it.name }
         val planId = builder.addConst(BytecodeConst.SlotPlan(stmt.slotPlan, captureNames))
         builder.emit(Opcode.PUSH_SCOPE, planId)
@@ -3386,6 +3416,10 @@ class BytecodeCompiler(
     private fun emitInlineBlock(stmt: BlockStatement, needResult: Boolean): CompiledValue? =
         emitInlineStatements(stmt.statements(), needResult)
 
+    private fun shouldInlineBlock(stmt: BlockStatement): Boolean {
+        return allowLocalSlots && !forceScopeSlots
+    }
+
     private fun compileInlineBlock(name: String, stmt: net.sergeych.lyng.InlineBlockStatement): CmdFunction? {
         val result = emitInlineStatements(stmt.statements(), true) ?: return null
         builder.emit(Opcode.RET, result.slot)
@@ -3406,7 +3440,7 @@ class BytecodeCompiler(
     private fun compileLoopBody(stmt: Statement, needResult: Boolean): CompiledValue? {
         val target = if (stmt is BytecodeStatement) stmt.original else stmt
         if (target is BlockStatement) {
-            val useInline = target.slotPlan.isEmpty() && target.captureSlots.isEmpty()
+            val useInline = !forceScopeSlots && target.slotPlan.isEmpty() && target.captureSlots.isEmpty()
             return if (useInline) emitInlineBlock(target, needResult) else emitBlock(target, needResult)
         }
         return compileStatementValueOrFallback(target, needResult)
@@ -3415,17 +3449,18 @@ class BytecodeCompiler(
     private fun emitVarDecl(stmt: VarDeclStatement): CompiledValue? {
         updateNameObjClass(stmt.name, stmt.initializer, stmt.initializerObjClass)
         val scopeId = stmt.scopeId ?: 0
+        val isModuleSlot = isModuleSlot(scopeId, stmt.name)
         val scopeSlot = stmt.slotIndex?.let { slotIndex ->
             val key = ScopeSlotKey(scopeId, slotIndex)
             scopeSlotMap[key]
         } ?: run {
-            if (scopeId == 0) {
+            if (isModuleSlot) {
                 scopeSlotIndexByName[stmt.name]
             } else {
                 null
             }
         }
-        if (scopeId == 0 && scopeSlot != null) {
+        if (isModuleSlot && scopeSlot != null) {
             val value = stmt.initializer?.let { compileStatementValueOrFallback(it) } ?: run {
                 val unsetId = builder.addConst(BytecodeConst.ObjRef(ObjUnset))
                 builder.emit(Opcode.CONST_OBJ, unsetId, scopeSlot)
@@ -3469,15 +3504,18 @@ class BytecodeCompiler(
             updateSlotType(localSlot, value.type)
             updateSlotObjClass(localSlot, stmt.initializer, stmt.initializerObjClass)
             updateNameObjClassFromSlot(stmt.name, localSlot)
-            val declId = builder.addConst(
+            val shadowedScopeSlot = scopeSlotIndexByName.containsKey(stmt.name)
-                BytecodeConst.LocalDecl(
+            if (forceScopeSlots || !shadowedScopeSlot) {
-                    stmt.name,
+                val declId = builder.addConst(
-                    stmt.isMutable,
+                    BytecodeConst.LocalDecl(
-                    stmt.visibility,
+                        stmt.name,
-                    stmt.isTransient
+                        stmt.isMutable,
+                        stmt.visibility,
+                        stmt.isTransient
+                    )
                 )
-            )
+                builder.emit(Opcode.DECL_LOCAL, declId, localSlot)
-            builder.emit(Opcode.DECL_LOCAL, declId, localSlot)
+            }
             return CompiledValue(localSlot, value.type)
         }
         if (scopeSlot != null) {
@@ -3605,15 +3643,11 @@ class BytecodeCompiler(
             rangeRef = extractRangeFromLocal(stmt.source)
         }
         val typedRangeLocal = if (range == null && rangeRef == null) extractTypedRangeLocal(stmt.source) else null
-        val useLoopScope = stmt.loopSlotPlan.isNotEmpty()
+        val loopSlotPlan = stmt.loopSlotPlan
-        val planId = if (useLoopScope) {
+        var useLoopScope = loopSlotPlan.isNotEmpty()
-            builder.addConst(BytecodeConst.SlotPlan(stmt.loopSlotPlan, emptyList()))
-        } else {
-            -1
-        }
         val loopLocalIndex = localSlotIndexByName[stmt.loopVarName]
         var usedOverride = false
-        val loopSlotId = when {
+        var loopSlotId = when {
             loopLocalIndex != null -> scopeSlotCount + loopLocalIndex
             else -> {
                 val localKey = localSlotInfoMap.entries.firstOrNull { it.value.name == stmt.loopVarName }?.key
@@ -3629,7 +3663,36 @@ class BytecodeCompiler(
             usedOverride = true
             slot
         }
-        val loopDeclId = if (usedOverride) {
+        var emitDeclLocal = usedOverride
+        if (useLoopScope && !forceScopeSlots) {
+            val loopVarOnly = loopSlotPlan.size == 1 && loopSlotPlan.containsKey(stmt.loopVarName)
+            val loopVarIsLocal = loopSlotId >= scopeSlotCount
+            if (loopVarOnly && loopVarIsLocal) {
+                useLoopScope = false
+            }
+        }
+        if (useLoopScope && allowLocalSlots && !forceScopeSlots) {
+            val needsScope = allowedScopeNames?.let { names ->
+                loopSlotPlan.keys.any { names.contains(it) }
+            } == true
+            if (!needsScope) {
+                useLoopScope = false
+            }
+        }
+        emitDeclLocal = emitDeclLocal && useLoopScope
+        if (!forceScopeSlots && loopSlotId < scopeSlotCount) {
+            val localSlot = allocSlot()
+            loopSlotOverrides[stmt.loopVarName] = localSlot
+            usedOverride = true
+            emitDeclLocal = false
+            loopSlotId = localSlot
+        }
+        val planId = if (useLoopScope) {
+            builder.addConst(BytecodeConst.SlotPlan(loopSlotPlan, emptyList()))
+        } else {
+            -1
+        }
+        val loopDeclId = if (emitDeclLocal) {
             builder.addConst(
                 BytecodeConst.LocalDecl(
                     stmt.loopVarName,
@@ -3702,7 +3765,7 @@ class BytecodeCompiler(
             builder.emit(Opcode.MOVE_OBJ, nextObj.slot, loopSlotId)
             updateSlotType(loopSlotId, SlotType.OBJ)
             updateSlotTypeByName(stmt.loopVarName, SlotType.OBJ)
-            if (usedOverride) {
+            if (emitDeclLocal) {
                 builder.emit(Opcode.DECL_LOCAL, loopDeclId, loopSlotId)
             }
 
@@ -3809,7 +3872,7 @@ class BytecodeCompiler(
                 builder.emit(Opcode.MOVE_INT, iSlot, loopSlotId)
                 updateSlotType(loopSlotId, SlotType.INT)
                 updateSlotTypeByName(stmt.loopVarName, SlotType.INT)
-                if (usedOverride) {
+                if (emitDeclLocal) {
                     builder.emit(Opcode.DECL_LOCAL, loopDeclId, loopSlotId)
                 }
                 loopStack.addLast(
@@ -3886,7 +3949,7 @@ class BytecodeCompiler(
         builder.emit(Opcode.MOVE_INT, iSlot, loopSlotId)
         updateSlotType(loopSlotId, SlotType.INT)
         updateSlotTypeByName(stmt.loopVarName, SlotType.INT)
-        if (usedOverride) {
+        if (emitDeclLocal) {
             builder.emit(Opcode.DECL_LOCAL, loopDeclId, loopSlotId)
         }
         loopStack.addLast(
@@ -4414,7 +4477,27 @@ class BytecodeCompiler(
         }
     }
 
+    private fun setPos(pos: Pos?) {
+        currentPos = pos
+        builder.setPos(pos)
+    }
+
+    private fun callSitePos(): Pos = currentPos ?: Pos.builtIn
+
+    private fun refPosOrCurrent(ref: ObjRef): Pos {
+        val refPos = when (ref) {
+            is LocalVarRef -> ref.pos()
+            is LocalSlotRef -> ref.pos()
+            is QualifiedThisRef -> ref.pos()
+            is ImplicitThisMethodCallRef -> ref.pos()
+            is StatementRef -> ref.statement.pos
+            else -> null
+        }
+        return refPos ?: callSitePos()
+    }
+
     private fun compileRefWithFallback(ref: ObjRef, forceType: SlotType?, pos: Pos): CompiledValue? {
+        setPos(pos)
         var compiled = compileRef(ref)
         if (compiled != null) {
             if (forceType == null) return compiled
@@ -4706,8 +4789,9 @@ class BytecodeCompiler(
     private fun refPos(ref: BinaryOpRef): Pos = Pos.builtIn
 
     private fun resolveSlot(ref: LocalSlotRef): Int? {
+        loopSlotOverrides[ref.name]?.let { return it }
         val scopeId = refScopeId(ref)
-        if (scopeId == 0) {
+        if (isModuleSlot(scopeId, ref.name)) {
             val key = ScopeSlotKey(scopeId, refSlot(ref))
             scopeSlotMap[key]?.let { return it }
             scopeSlotIndexByName[ref.name]?.let { return it }
@@ -4718,6 +4802,10 @@ class BytecodeCompiler(
             if (ownerLocal != null) {
                 return scopeSlotCount + ownerLocal
             }
+            val nameLocal = localSlotIndexByName[ref.name]
+            if (nameLocal != null) {
+                return scopeSlotCount + nameLocal
+            }
             val scopeKey = ScopeSlotKey(refScopeId(ref), refSlot(ref))
             return scopeSlotMap[scopeKey]
         }
@@ -4725,7 +4813,6 @@ class BytecodeCompiler(
             val scopeKey = ScopeSlotKey(refScopeId(ref), refSlot(ref))
             return scopeSlotMap[scopeKey]
         }
-        loopSlotOverrides[ref.name]?.let { return it }
         val localKey = ScopeSlotKey(refScopeId(ref), refSlot(ref))
         val localIndex = localSlotIndexByKey[localKey]
         if (localIndex != null) return scopeSlotCount + localIndex
@@ -4805,7 +4892,7 @@ class BytecodeCompiler(
             val name = scopeSlotNameMap[key]
             scopeSlotIndices[index] = key.slot
             scopeSlotNames[index] = name
-            scopeSlotIsModule[index] = key.scopeId == 0
+            scopeSlotIsModule[index] = key.scopeId == (moduleScopeId ?: 0)
             scopeSlotMutableMap[key]?.let { scopeSlotMutables[index] = it }
         }
         if (allowLocalSlots && localSlotInfoMap.isNotEmpty()) {
@@ -4878,7 +4965,8 @@ class BytecodeCompiler(
                         slotInitClassByKey[ScopeSlotKey(scopeId, slotIndex)] = cls
                     }
                 }
-                if (allowLocalSlots && !forceScopeSlots && slotIndex != null && scopeId != 0) {
+                val isModuleSlot = isModuleSlot(scopeId, stmt.name)
+                if (allowLocalSlots && !forceScopeSlots && slotIndex != null && !isModuleSlot) {
                     val key = ScopeSlotKey(scopeId, slotIndex)
                     declaredLocalKeys.add(key)
                     if (!localSlotInfoMap.containsKey(key)) {
@@ -5052,6 +5140,13 @@ class BytecodeCompiler(
         }
     }
 
+    private fun isModuleSlot(scopeId: Int, name: String?): Boolean {
+        val moduleId = moduleScopeId ?: 0
+        if (scopeId != moduleId) return false
+        if (allowedScopeNames == null || name == null) return true
+        return allowedScopeNames.contains(name)
+    }
+
     private fun collectLoopVarNames(stmt: Statement) {
         if (stmt is BytecodeStatement) {
             collectLoopVarNames(stmt.original)
@@ -5154,7 +5249,7 @@ class BytecodeCompiler(
                     return
                 }
                 val shouldLocalize = !forceScopeSlots || intLoopVarNames.contains(ref.name)
-                val isModuleSlot = scopeId == 0
+                val isModuleSlot = isModuleSlot(scopeId, ref.name)
                 if (allowLocalSlots && !ref.isDelegated && shouldLocalize && !isModuleSlot) {
                     if (!localSlotInfoMap.containsKey(key)) {
                         localSlotInfoMap[key] = LocalSlotInfo(ref.name, ref.isMutable)
@@ -5203,7 +5298,7 @@ class BytecodeCompiler(
                         }
                     } else {
                         val shouldLocalize = !forceScopeSlots || intLoopVarNames.contains(target.name)
-                        val isModuleSlot = scopeId == 0
+                        val isModuleSlot = isModuleSlot(scopeId, target.name)
                         if (allowLocalSlots && !target.isDelegated && shouldLocalize && !isModuleSlot) {
                             if (!localSlotInfoMap.containsKey(key)) {
                                 localSlotInfoMap[key] = LocalSlotInfo(target.name, target.isMutable)

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2026 Sergey S. Chernov
+ * 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.
@@ -12,17 +12,19 @@
  * 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.bytecode
 
+import net.sergeych.lyng.FrameAccess
 import net.sergeych.lyng.obj.Obj
 import net.sergeych.lyng.obj.ObjNull
 
 class BytecodeFrame(
     val localCount: Int,
     val argCount: Int,
-) {
+) : FrameAccess {
     val slotCount: Int = localCount + argCount
     val argBase: Int = localCount
 
@@ -33,31 +35,31 @@ class BytecodeFrame(
     private val boolSlots: BooleanArray = BooleanArray(slotCount)
 
     fun getSlotType(slot: Int): SlotType = SlotType.values().first { it.code == slotTypes[slot] }
-    fun getSlotTypeCode(slot: Int): Byte = slotTypes[slot]
+    override fun getSlotTypeCode(slot: Int): Byte = slotTypes[slot]
     fun setSlotType(slot: Int, type: SlotType) {
         slotTypes[slot] = type.code
     }
 
-    fun getObj(slot: Int): Obj = objSlots[slot] ?: ObjNull
+    override fun getObj(slot: Int): Obj = objSlots[slot] ?: ObjNull
-    fun setObj(slot: Int, value: Obj) {
+    override fun setObj(slot: Int, value: Obj) {
         objSlots[slot] = value
         slotTypes[slot] = SlotType.OBJ.code
     }
 
-    fun getInt(slot: Int): Long = intSlots[slot]
+    override fun getInt(slot: Int): Long = intSlots[slot]
-    fun setInt(slot: Int, value: Long) {
+    override fun setInt(slot: Int, value: Long) {
         intSlots[slot] = value
         slotTypes[slot] = SlotType.INT.code
     }
 
-    fun getReal(slot: Int): Double = realSlots[slot]
+    override fun getReal(slot: Int): Double = realSlots[slot]
-    fun setReal(slot: Int, value: Double) {
+    override fun setReal(slot: Int, value: Double) {
         realSlots[slot] = value
         slotTypes[slot] = SlotType.REAL.code
     }
 
-    fun getBool(slot: Int): Boolean = boolSlots[slot]
+    override fun getBool(slot: Int): Boolean = boolSlots[slot]
-    fun setBool(slot: Int, value: Boolean) {
+    override fun setBool(slot: Int, value: Boolean) {
         boolSlots[slot] = value
         slotTypes[slot] = SlotType.BOOL.code
     }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2026 Sergey S. Chernov
+ * 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.
@@ -12,23 +12,14 @@
  * 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.bytecode
 
-import net.sergeych.lyng.Pos
+import net.sergeych.lyng.*
-import net.sergeych.lyng.Scope
-import net.sergeych.lyng.Statement
-import net.sergeych.lyng.DestructuringVarDeclStatement
-import net.sergeych.lyng.WhenCase
-import net.sergeych.lyng.WhenCondition
-import net.sergeych.lyng.WhenEqualsCondition
-import net.sergeych.lyng.WhenInCondition
-import net.sergeych.lyng.WhenIsCondition
-import net.sergeych.lyng.WhenStatement
 import net.sergeych.lyng.obj.Obj
 import net.sergeych.lyng.obj.ObjClass
-import net.sergeych.lyng.obj.RangeRef
 
 class BytecodeStatement private constructor(
     val original: Statement,
@@ -51,13 +42,14 @@ class BytecodeStatement private constructor(
             returnLabels: Set<String> = emptySet(),
             rangeLocalNames: Set<String> = emptySet(),
             allowedScopeNames: Set<String>? = null,
+            moduleScopeId: Int? = null,
             slotTypeByScopeId: Map<Int, Map<Int, ObjClass>> = emptyMap(),
             knownNameObjClass: Map<String, ObjClass> = emptyMap(),
         ): Statement {
             if (statement is BytecodeStatement) return statement
             val hasUnsupported = containsUnsupportedStatement(statement)
             if (hasUnsupported) {
-                val statementName = statement::class.qualifiedName ?: statement::class.simpleName ?: "UnknownStatement"
+                val statementName = statement.toString()
                 throw BytecodeCompileException(
                     "Bytecode compile error: unsupported statement $statementName in '$nameHint'",
                     statement.pos
@@ -69,6 +61,7 @@ class BytecodeStatement private constructor(
                 returnLabels = returnLabels,
                 rangeLocalNames = rangeLocalNames,
                 allowedScopeNames = allowedScopeNames,
+                moduleScopeId = moduleScopeId,
                 slotTypeByScopeId = slotTypeByScopeId,
                 knownNameObjClass = knownNameObjClass
             )

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2026 Sergey S. Chernov
+ * 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.
@@ -12,6 +12,7 @@
  * 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.bytecode
@@ -27,9 +28,11 @@ class CmdBuilder {
     data class Instr(val op: Opcode, val operands: List<Operand>)
 
     private val instructions = mutableListOf<Instr>()
+    private val posByInstr = mutableListOf<net.sergeych.lyng.Pos?>()
     private val constPool = mutableListOf<BytecodeConst>()
     private val labelPositions = mutableMapOf<Label, Int>()
     private var nextLabelId = 0
+    private var currentPos: net.sergeych.lyng.Pos? = null
 
     fun addConst(c: BytecodeConst): Int {
         constPool += c
@@ -38,10 +41,16 @@ class CmdBuilder {
 
     fun emit(op: Opcode, vararg operands: Int) {
         instructions += Instr(op, operands.map { Operand.IntVal(it) })
+        posByInstr += currentPos
     }
 
     fun emit(op: Opcode, operands: List<Operand>) {
         instructions += Instr(op, operands)
+        posByInstr += currentPos
+    }
+
+    fun setPos(pos: net.sergeych.lyng.Pos?) {
+        currentPos = pos
     }
 
     fun label(): Label = Label(nextLabelId++)
@@ -103,7 +112,8 @@ class CmdBuilder {
             localSlotNames = localSlotNames,
             localSlotMutables = localSlotMutables,
             constants = constPool.toList(),
-            cmds = cmds.toTypedArray()
+            cmds = cmds.toTypedArray(),
+            posByIp = posByInstr.toTypedArray()
         )
     }
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2026 Sergey S. Chernov
+ * 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.
@@ -12,6 +12,7 @@
  * 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.bytecode
@@ -29,6 +30,7 @@ data class CmdFunction(
     val localSlotMutables: BooleanArray,
     val constants: List<BytecodeConst>,
     val cmds: Array<Cmd>,
+    val posByIp: Array<net.sergeych.lyng.Pos?>,
 ) {
     init {
         require(scopeSlotIndices.size == scopeSlotCount) { "scopeSlotIndices size mismatch" }
@@ -37,5 +39,8 @@ data class CmdFunction(
         require(localSlotNames.size == localSlotMutables.size) { "localSlot metadata size mismatch" }
         require(localSlotNames.size <= localCount) { "localSlotNames exceed localCount" }
         require(addrCount >= 0) { "addrCount must be non-negative" }
+        if (posByIp.isNotEmpty()) {
+            require(posByIp.size == cmds.size) { "posByIp size mismatch" }
+        }
     }
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2026 Sergey S. Chernov
+ * 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.
@@ -12,17 +12,12 @@
  * 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.bytecode
 
-import net.sergeych.lyng.Arguments
+import net.sergeych.lyng.*
-import net.sergeych.lyng.ModuleScope
-import net.sergeych.lyng.PerfFlags
-import net.sergeych.lyng.Pos
-import net.sergeych.lyng.ReturnException
-import net.sergeych.lyng.Scope
-import net.sergeych.lyng.Statement
 import net.sergeych.lyng.obj.*
 
 class CmdVm {
@@ -152,7 +147,7 @@ class CmdConstBool(internal val constId: Int, internal val dst: Int) : Cmd() {
 
 class CmdLoadThis(internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        frame.setObj(dst, frame.scope.thisObj)
+        frame.setObj(dst, frame.ensureScope().thisObj)
         return
     }
 }
@@ -165,8 +160,8 @@ class CmdLoadThisVariant(
         val typeConst = frame.fn.constants.getOrNull(typeId) as? BytecodeConst.StringVal
             ?: error("LOAD_THIS_VARIANT expects StringVal at $typeId")
         val typeName = typeConst.value
-        val receiver = frame.scope.thisVariants.firstOrNull { it.isInstanceOf(typeName) }
+        val receiver = frame.ensureScope().thisVariants.firstOrNull { it.isInstanceOf(typeName) }
-            ?: frame.scope.raiseClassCastError("Cannot cast ${frame.scope.thisObj.objClass.className} to $typeName")
+            ?: frame.ensureScope().raiseClassCastError("Cannot cast ${frame.ensureScope().thisObj.objClass.className} to $typeName")
         frame.setObj(dst, receiver)
         return
     }
@@ -222,11 +217,11 @@ class CmdAssertIs(internal val objSlot: Int, internal val typeSlot: Int) : Cmd()
     override suspend fun perform(frame: CmdFrame) {
         val obj = frame.slotToObj(objSlot)
         val typeObj = frame.slotToObj(typeSlot)
-        val clazz = typeObj as? ObjClass ?: frame.scope.raiseClassCastError(
+        val clazz = typeObj as? ObjClass ?: frame.ensureScope().raiseClassCastError(
-            "${typeObj.inspect(frame.scope)} is not the class instance"
+            "${typeObj.inspect(frame.ensureScope())} is not the class instance"
         )
         if (!obj.isInstanceOf(clazz)) {
-            frame.scope.raiseClassCastError("expected ${clazz.className}, got ${obj.objClass.className}")
+            frame.ensureScope().raiseClassCastError("expected ${clazz.className}, got ${obj.objClass.className}")
         }
         return
     }
@@ -240,8 +235,8 @@ class CmdMakeQualifiedView(
     override suspend fun perform(frame: CmdFrame) {
         val obj0 = frame.slotToObj(objSlot)
         val typeObj = frame.slotToObj(typeSlot)
-        val clazz = typeObj as? ObjClass ?: frame.scope.raiseClassCastError(
+        val clazz = typeObj as? ObjClass ?: frame.ensureScope().raiseClassCastError(
-            "${typeObj.inspect(frame.scope)} is not the class instance"
+            "${typeObj.inspect(frame.ensureScope())} is not the class instance"
         )
         val base = when (obj0) {
             is ObjQualifiedView -> obj0.instance
@@ -787,7 +782,7 @@ class CmdCmpEqObj(internal val a: Int, internal val b: Int, internal val dst: In
     override suspend fun perform(frame: CmdFrame) {
         val left = frame.slotToObj(a)
         val right = frame.slotToObj(b)
-        frame.setBool(dst, left.equals(frame.scope, right))
+        frame.setBool(dst, left.equals(frame.ensureScope(), right))
         return
     }
 }
@@ -796,7 +791,7 @@ class CmdCmpNeqObj(internal val a: Int, internal val b: Int, internal val dst: I
     override suspend fun perform(frame: CmdFrame) {
         val left = frame.slotToObj(a)
         val right = frame.slotToObj(b)
-        frame.setBool(dst, !left.equals(frame.scope, right))
+        frame.setBool(dst, !left.equals(frame.ensureScope(), right))
         return
     }
 }
@@ -838,28 +833,28 @@ class CmdOrBool(internal val a: Int, internal val b: Int, internal val dst: Int)
 
 class CmdCmpLtObj(internal val a: Int, internal val b: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.scope, frame.slotToObj(b)) < 0)
+        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.ensureScope(), frame.slotToObj(b)) < 0)
         return
     }
 }
 
 class CmdCmpLteObj(internal val a: Int, internal val b: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.scope, frame.slotToObj(b)) <= 0)
+        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.ensureScope(), frame.slotToObj(b)) <= 0)
         return
     }
 }
 
 class CmdCmpGtObj(internal val a: Int, internal val b: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.scope, frame.slotToObj(b)) > 0)
+        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.ensureScope(), frame.slotToObj(b)) > 0)
         return
     }
 }
 
 class CmdCmpGteObj(internal val a: Int, internal val b: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.scope, frame.slotToObj(b)) >= 0)
+        frame.setBool(dst, frame.slotToObj(a).compareTo(frame.ensureScope(), frame.slotToObj(b)) >= 0)
         return
     }
 }
@@ -883,7 +878,7 @@ class CmdAddObj(internal val a: Int, internal val b: Int, internal val dst: Int)
                 return
             }
         }
-        frame.setObj(dst, frame.slotToObj(a).plus(frame.scope, frame.slotToObj(b)))
+        frame.setObj(dst, frame.slotToObj(a).plus(frame.ensureScope(), frame.slotToObj(b)))
         return
     }
 }
@@ -907,7 +902,7 @@ class CmdSubObj(internal val a: Int, internal val b: Int, internal val dst: Int)
                 return
             }
         }
-        frame.setObj(dst, frame.slotToObj(a).minus(frame.scope, frame.slotToObj(b)))
+        frame.setObj(dst, frame.slotToObj(a).minus(frame.ensureScope(), frame.slotToObj(b)))
         return
     }
 }
@@ -931,7 +926,7 @@ class CmdMulObj(internal val a: Int, internal val b: Int, internal val dst: Int)
                 return
             }
         }
-        frame.setObj(dst, frame.slotToObj(a).mul(frame.scope, frame.slotToObj(b)))
+        frame.setObj(dst, frame.slotToObj(a).mul(frame.ensureScope(), frame.slotToObj(b)))
         return
     }
 }
@@ -955,7 +950,7 @@ class CmdDivObj(internal val a: Int, internal val b: Int, internal val dst: Int)
                 return
             }
         }
-        frame.setObj(dst, frame.slotToObj(a).div(frame.scope, frame.slotToObj(b)))
+        frame.setObj(dst, frame.slotToObj(a).div(frame.ensureScope(), frame.slotToObj(b)))
         return
     }
 }
@@ -979,14 +974,14 @@ class CmdModObj(internal val a: Int, internal val b: Int, internal val dst: Int)
                 return
             }
         }
-        frame.setObj(dst, frame.slotToObj(a).mod(frame.scope, frame.slotToObj(b)))
+        frame.setObj(dst, frame.slotToObj(a).mod(frame.ensureScope(), frame.slotToObj(b)))
         return
     }
 }
 
 class CmdContainsObj(internal val target: Int, internal val value: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        frame.setBool(dst, frame.slotToObj(target).contains(frame.scope, frame.slotToObj(value)))
+        frame.setBool(dst, frame.slotToObj(target).contains(frame.ensureScope(), frame.slotToObj(value)))
         return
     }
 }
@@ -1002,17 +997,17 @@ class CmdAssignOpObj(
         val target = frame.slotToObj(targetSlot)
         val value = frame.slotToObj(valueSlot)
         val result = when (BinOp.values().getOrNull(opId)) {
-            BinOp.PLUS -> target.plusAssign(frame.scope, value)
+            BinOp.PLUS -> target.plusAssign(frame.ensureScope(), value)
-            BinOp.MINUS -> target.minusAssign(frame.scope, value)
+            BinOp.MINUS -> target.minusAssign(frame.ensureScope(), value)
-            BinOp.STAR -> target.mulAssign(frame.scope, value)
+            BinOp.STAR -> target.mulAssign(frame.ensureScope(), value)
-            BinOp.SLASH -> target.divAssign(frame.scope, value)
+            BinOp.SLASH -> target.divAssign(frame.ensureScope(), value)
-            BinOp.PERCENT -> target.modAssign(frame.scope, value)
+            BinOp.PERCENT -> target.modAssign(frame.ensureScope(), value)
             else -> null
         }
         if (result == null) {
             val name = (frame.fn.constants.getOrNull(nameId) as? BytecodeConst.StringVal)?.value
-            if (name != null) frame.scope.raiseIllegalAssignment("symbol is readonly: $name")
+            if (name != null) frame.ensureScope().raiseIllegalAssignment("symbol is readonly: $name")
-            frame.scope.raiseIllegalAssignment("symbol is readonly")
+            frame.ensureScope().raiseIllegalAssignment("symbol is readonly")
         }
         frame.storeObjResult(dst, result)
         return
@@ -1118,7 +1113,7 @@ class CmdDeclLocal(internal val constId: Int, internal val slot: Int) : Cmd() {
         val decl = frame.fn.constants[constId] as? BytecodeConst.LocalDecl
             ?: error("DECL_LOCAL expects LocalDecl at $constId")
         val value = frame.slotToObj(slot).byValueCopy()
-        frame.scope.addItem(
+        frame.ensureScope().addItem(
             decl.name,
             decl.isMutable,
             value,
@@ -1134,12 +1129,12 @@ class CmdDeclExtProperty(internal val constId: Int, internal val slot: Int) : Cm
     override suspend fun perform(frame: CmdFrame) {
         val decl = frame.fn.constants[constId] as? BytecodeConst.ExtensionPropertyDecl
             ?: error("DECL_EXT_PROPERTY expects ExtensionPropertyDecl at $constId")
-        val type = frame.scope[decl.extTypeName]?.value
+        val type = frame.ensureScope()[decl.extTypeName]?.value
-            ?: frame.scope.raiseSymbolNotFound("class ${decl.extTypeName} not found")
+            ?: frame.ensureScope().raiseSymbolNotFound("class ${decl.extTypeName} not found")
         if (type !is ObjClass) {
-            frame.scope.raiseClassCastError("${decl.extTypeName} is not the class instance")
+            frame.ensureScope().raiseClassCastError("${decl.extTypeName} is not the class instance")
         }
-        frame.scope.addExtension(
+        frame.ensureScope().addExtension(
             type,
             decl.property.name,
             ObjRecord(
@@ -1164,16 +1159,16 @@ class CmdCallDirect(
 ) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
         if (frame.fn.localSlotNames.isNotEmpty()) {
-            frame.syncFrameToScope()
+            frame.syncFrameToScope(useRefs = true)
         }
         val ref = frame.fn.constants.getOrNull(id) as? BytecodeConst.ObjRef
             ?: error("CALL_DIRECT expects ObjRef at $id")
         val callee = ref.value
         val args = frame.buildArguments(argBase, argCount)
         val result = if (PerfFlags.SCOPE_POOL) {
-            frame.scope.withChildFrame(args) { child -> callee.callOn(child) }
+            frame.ensureScope().withChildFrame(args) { child -> callee.callOn(child) }
         } else {
-            callee.callOn(frame.scope.createChildScope(frame.scope.pos, args = args))
+            callee.callOn(frame.ensureScope().createChildScope(frame.ensureScope().pos, args = args))
         }
         if (frame.fn.localSlotNames.isNotEmpty()) {
             frame.syncScopeToFrame()
@@ -1191,7 +1186,7 @@ class CmdCallSlot(
 ) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
         if (frame.fn.localSlotNames.isNotEmpty()) {
-            frame.syncFrameToScope()
+            frame.syncFrameToScope(useRefs = true)
         }
         val callee = frame.slotToObj(calleeSlot)
         if (callee === ObjUnset) {
@@ -1203,15 +1198,15 @@ class CmdCallSlot(
             }
             val message = name?.let { "property '$it' is unset (not initialized)" }
                 ?: "property is unset (not initialized) in ${frame.fn.name} at slot $calleeSlot"
-            frame.scope.raiseUnset(message)
+            frame.ensureScope().raiseUnset(message)
         }
         val args = frame.buildArguments(argBase, argCount)
         val canPool = PerfFlags.SCOPE_POOL && callee !is Statement
         val result = if (canPool) {
-            frame.scope.withChildFrame(args) { child -> callee.callOn(child) }
+            frame.ensureScope().withChildFrame(args) { child -> callee.callOn(child) }
         } else {
             // Pooling for Statement-based callables (lambdas) can still alter closure semantics; keep safe path for now.
-            callee.callOn(frame.scope.createChildScope(frame.scope.pos, args = args))
+            callee.callOn(frame.ensureScope().createChildScope(frame.ensureScope().pos, args = args))
         }
         if (frame.fn.localSlotNames.isNotEmpty()) {
             frame.syncScopeToFrame()
@@ -1239,7 +1234,7 @@ class CmdListLiteral(
                         list.ensureCapacity(list.size + value.list.size)
                         list.addAll(value.list)
                     }
-                    else -> frame.scope.raiseError("Spread element must be list")
+                    else -> frame.ensureScope().raiseError("Spread element must be list")
                 }
             } else {
                 list.add(value)
@@ -1266,14 +1261,14 @@ class CmdGetMemberSlot(
             if (methodId >= 0) {
                 inst?.methodRecordForId(methodId) ?: receiver.objClass.methodRecordForId(methodId)
             } else null
-        } ?: frame.scope.raiseSymbolNotFound("member")
+        } ?: frame.ensureScope().raiseSymbolNotFound("member")
         val name = rec.memberName ?: "<member>"
         if (receiver is ObjQualifiedView) {
-            val resolved = receiver.readField(frame.scope, name)
+            val resolved = receiver.readField(frame.ensureScope(), name)
             frame.storeObjResult(dst, resolved.value)
             return
         }
-        val resolved = receiver.resolveRecord(frame.scope, rec, name, rec.declaringClass)
+        val resolved = receiver.resolveRecord(frame.ensureScope(), rec, name, rec.declaringClass)
         frame.storeObjResult(dst, resolved.value)
         return
     }
@@ -1295,13 +1290,13 @@ class CmdSetMemberSlot(
             if (methodId >= 0) {
                 inst?.methodRecordForId(methodId) ?: receiver.objClass.methodRecordForId(methodId)
             } else null
-        } ?: frame.scope.raiseSymbolNotFound("member")
+        } ?: frame.ensureScope().raiseSymbolNotFound("member")
         val name = rec.memberName ?: "<member>"
         if (receiver is ObjQualifiedView) {
-            receiver.writeField(frame.scope, name, frame.slotToObj(valueSlot))
+            receiver.writeField(frame.ensureScope(), name, frame.slotToObj(valueSlot))
             return
         }
-        frame.scope.assign(rec, name, frame.slotToObj(valueSlot))
+        frame.ensureScope().assign(rec, name, frame.slotToObj(valueSlot))
         return
     }
 }
@@ -1315,17 +1310,17 @@ class CmdCallMemberSlot(
 ) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
         if (frame.fn.localSlotNames.isNotEmpty()) {
-            frame.syncFrameToScope()
+            frame.syncFrameToScope(useRefs = true)
         }
         val receiver = frame.slotToObj(recvSlot)
         val inst = receiver as? ObjInstance
         val rec = inst?.methodRecordForId(methodId)
             ?: receiver.objClass.methodRecordForId(methodId)
-            ?: frame.scope.raiseError("member id $methodId not found on ${receiver.objClass.className}")
+            ?: frame.ensureScope().raiseError("member id $methodId not found on ${receiver.objClass.className}")
         val callArgs = frame.buildArguments(argBase, argCount)
         val name = rec.memberName ?: "<member>"
         if (receiver is ObjQualifiedView) {
-            val result = receiver.invokeInstanceMethod(frame.scope, name, callArgs)
+            val result = receiver.invokeInstanceMethod(frame.ensureScope(), name, callArgs)
             if (frame.fn.localSlotNames.isNotEmpty()) {
                 frame.syncScopeToFrame()
             }
@@ -1335,14 +1330,14 @@ class CmdCallMemberSlot(
         val decl = rec.declaringClass ?: receiver.objClass
         val result = when (rec.type) {
             ObjRecord.Type.Property -> {
-                if (callArgs.isEmpty()) (rec.value as ObjProperty).callGetter(frame.scope, receiver, decl)
+                if (callArgs.isEmpty()) (rec.value as ObjProperty).callGetter(frame.ensureScope(), receiver, decl)
-                else frame.scope.raiseError("property $name cannot be called with arguments")
+                else frame.ensureScope().raiseError("property $name cannot be called with arguments")
             }
             ObjRecord.Type.Fun, ObjRecord.Type.Delegated -> {
-                val callScope = inst?.instanceScope ?: frame.scope
+                val callScope = inst?.instanceScope ?: frame.ensureScope()
                 rec.value.invoke(callScope, receiver, callArgs, decl)
             }
-            else -> frame.scope.raiseError("member $name is not callable")
+            else -> frame.ensureScope().raiseError("member $name is not callable")
         }
         if (frame.fn.localSlotNames.isNotEmpty()) {
             frame.syncScopeToFrame()
@@ -1358,7 +1353,7 @@ class CmdGetIndex(
     internal val dst: Int,
 ) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        val result = frame.slotToObj(targetSlot).getAt(frame.scope, frame.slotToObj(indexSlot))
+        val result = frame.slotToObj(targetSlot).getAt(frame.ensureScope(), frame.slotToObj(indexSlot))
         frame.storeObjResult(dst, result)
         return
     }
@@ -1370,7 +1365,7 @@ class CmdSetIndex(
     internal val valueSlot: Int,
 ) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
-        frame.slotToObj(targetSlot).putAt(frame.scope, frame.slotToObj(indexSlot), frame.slotToObj(valueSlot))
+        frame.slotToObj(targetSlot).putAt(frame.ensureScope(), frame.slotToObj(indexSlot), frame.slotToObj(valueSlot))
         return
     }
 }
@@ -1378,11 +1373,11 @@ class CmdSetIndex(
 class CmdEvalRef(internal val id: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
         if (frame.fn.localSlotNames.isNotEmpty()) {
-            frame.syncFrameToScope()
+            frame.syncFrameToScope(useRefs = true)
         }
         val ref = frame.fn.constants[id] as? BytecodeConst.Ref
             ?: error("EVAL_REF expects Ref at $id")
-        val result = ref.value.evalValue(frame.scope)
+        val result = ref.value.evalValue(frame.ensureScope())
         if (frame.fn.localSlotNames.isNotEmpty()) {
             frame.syncScopeToFrame()
         }
@@ -1394,11 +1389,11 @@ class CmdEvalRef(internal val id: Int, internal val dst: Int) : Cmd() {
 class CmdEvalStmt(internal val id: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
         if (frame.fn.localSlotNames.isNotEmpty()) {
-            frame.syncFrameToScope()
+            frame.syncFrameToScope(useRefs = true)
         }
         val stmt = frame.fn.constants.getOrNull(id) as? BytecodeConst.StatementVal
             ?: error("EVAL_STMT expects StatementVal at $id")
-        val result = stmt.statement.execute(frame.scope)
+        val result = stmt.statement.execute(frame.ensureScope())
         if (frame.fn.localSlotNames.isNotEmpty()) {
             frame.syncScopeToFrame()
         }
@@ -1410,11 +1405,11 @@ class CmdEvalStmt(internal val id: Int, internal val dst: Int) : Cmd() {
 class CmdMakeValueFn(internal val id: Int, internal val dst: Int) : Cmd() {
     override suspend fun perform(frame: CmdFrame) {
         if (frame.fn.localSlotNames.isNotEmpty()) {
-            frame.syncFrameToScope()
+            frame.syncFrameToScope(useRefs = true)
         }
         val valueFn = frame.fn.constants.getOrNull(id) as? BytecodeConst.ValueFn
             ?: error("MAKE_VALUE_FN expects ValueFn at $id")
-        val result = valueFn.fn(frame.scope).value
+        val result = valueFn.fn(frame.ensureScope()).value
         if (frame.fn.localSlotNames.isNotEmpty()) {
             frame.syncScopeToFrame()
         }
@@ -1458,6 +1453,8 @@ class CmdFrame(
     var ip: Int = 0
     var scope: Scope = scope0
     private val moduleScope: Scope = resolveModuleScope(scope0)
+    private val scopeSlotNames: Set<String> = fn.scopeSlotNames.filterNotNull().toSet()
+    private var lastScopePosIp = -1
 
     internal val scopeStack = ArrayDeque<Scope>()
     internal val scopeVirtualStack = ArrayDeque<Boolean>()
@@ -1504,10 +1501,24 @@ class CmdFrame(
         return last
     }
 
+    fun ensureScope(): Scope {
+        val pos = posForIp(ip - 1)
+        if (pos != null && lastScopePosIp != ip) {
+            scope.pos = pos
+            lastScopePosIp = ip
+        }
+        return scope
+    }
+
+    private fun posForIp(ip: Int): Pos? {
+        if (ip < 0) return null
+        return fn.posByIp.getOrNull(ip)
+    }
+
     fun pushScope(plan: Map<String, Int>, captures: List<String>) {
         val parentScope = scope
         if (captures.isNotEmpty()) {
-            syncFrameToScope()
+            syncFrameToScope(useRefs = true)
         }
         val captureRecords = if (captures.isNotEmpty()) {
             captures.map { name ->
@@ -1555,7 +1566,7 @@ class CmdFrame(
         val captures = captureStack.removeLastOrNull() ?: emptyList()
         scopeDepth -= 1
         if (captures.isNotEmpty()) {
-            syncFrameToScope()
+            syncFrameToScope(useRefs = true)
         }
     }
 
@@ -1569,13 +1580,13 @@ class CmdFrame(
 
     suspend fun cancelTopIterator() {
         val iter = iterStack.removeLastOrNull() ?: return
-        iter.invokeInstanceMethod(scope, "cancelIteration") { ObjVoid }
+        iter.invokeInstanceMethod(ensureScope(), "cancelIteration") { ObjVoid }
     }
 
     suspend fun cancelIterators() {
         while (iterStack.isNotEmpty()) {
             val iter = iterStack.removeLast()
-            iter.invokeInstanceMethod(scope, "cancelIteration") { ObjVoid }
+            iter.invokeInstanceMethod(ensureScope(), "cancelIteration") { ObjVoid }
         }
     }
 
@@ -1781,7 +1792,7 @@ class CmdFrame(
 
     suspend fun throwObj(pos: Pos, value: Obj) {
         var errorObject = value
-        val throwScope = scope.createChildScope(pos = pos)
+        val throwScope = ensureScope().createChildScope(pos = pos)
         if (errorObject is ObjString) {
             errorObject = ObjException(throwScope, errorObject.value).apply { getStackTrace() }
         }
@@ -1803,18 +1814,21 @@ class CmdFrame(
         }
     }
 
-    fun syncFrameToScope() {
+    fun syncFrameToScope(useRefs: Boolean = false) {
         val names = fn.localSlotNames
         if (names.isEmpty()) return
         for (i in names.indices) {
             val name = names[i] ?: continue
+            if (scopeSlotNames.contains(name)) continue
             val target = resolveLocalScope(i) ?: continue
-            val value = localSlotToObj(i)
+            val value = if (useRefs) FrameSlotRef(frame, i) else localSlotToObj(i)
             val rec = target.getLocalRecordDirect(name)
             if (rec == null) {
                 val isMutable = fn.localSlotMutables.getOrElse(i) { true }
                 target.addItem(name, isMutable, value)
             } else {
+                val existing = rec.value
+                if (existing is FrameSlotRef && !useRefs) continue
                 rec.value = value
             }
         }
@@ -1828,6 +1842,16 @@ class CmdFrame(
             val target = resolveLocalScope(i) ?: continue
             val rec = target.getLocalRecordDirect(name) ?: continue
             val value = rec.value
+            if (value is FrameSlotRef) {
+                val resolved = value.read()
+                when (resolved) {
+                    is ObjInt -> frame.setInt(i, resolved.value)
+                    is ObjReal -> frame.setReal(i, resolved.value)
+                    is ObjBool -> frame.setBool(i, resolved.value)
+                    else -> frame.setObj(i, resolved)
+                }
+                continue
+            }
             when (value) {
                 is ObjInt -> frame.setInt(i, value.value)
                 is ObjReal -> frame.setReal(i, value.value)
@@ -1856,6 +1880,7 @@ class CmdFrame(
         argBase: Int,
         plan: BytecodeConst.CallArgsPlan,
     ): Arguments {
+        val scope = ensureScope()
         val positional = ArrayList<Obj>(plan.specs.size)
         var named: LinkedHashMap<String, Obj>? = null
         var namedSeen = false
@@ -1931,7 +1956,9 @@ class CmdFrame(
         val target = scopeTarget(slot)
         val index = ensureScopeSlot(target, slot)
         val record = target.getSlotRecord(index)
-        if (record.value !== ObjUnset) return record.value
+        val direct = record.value
+        if (direct is FrameSlotRef) return direct.read()
+        if (direct !== ObjUnset) return direct
         val name = fn.scopeSlotNames[slot] ?: return record.value
         val resolved = target.get(name) ?: return record.value
         if (resolved.value !== ObjUnset) {
@@ -1944,7 +1971,9 @@ class CmdFrame(
         val target = addrScopes[addrSlot] ?: error("Address slot $addrSlot is not resolved")
         val index = addrIndices[addrSlot]
         val record = target.getSlotRecord(index)
-        if (record.value !== ObjUnset) return record.value
+        val direct = record.value
+        if (direct is FrameSlotRef) return direct.read()
+        if (direct !== ObjUnset) return direct
         val slotId = addrScopeSlots[addrSlot]
         val name = fn.scopeSlotNames[slotId] ?: return record.value
         val resolved = target.get(name) ?: return record.value

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

@@ -463,6 +463,7 @@ class CastRef(
 
 /** Qualified `this@Type`: resolves to a view of current `this` starting dispatch from the ancestor Type. */
 class QualifiedThisRef(val typeName: String, private val atPos: Pos) : ObjRef {
+    internal fun pos(): Pos = atPos
     override suspend fun get(scope: Scope): ObjRecord {
         val t = scope[typeName]?.value as? ObjClass
             ?: scope.raiseError("unknown type $typeName")
@@ -2107,6 +2108,7 @@ class ImplicitThisMethodCallRef(
     private val atPos: Pos,
     private val preferredThisTypeName: String? = null
 ) : ObjRef {
+    internal fun pos(): Pos = atPos
     internal fun methodName(): String = name
     internal fun arguments(): List<ParsedArgument> = args
     internal fun hasTailBlock(): Boolean = tailBlock
@@ -2184,13 +2186,38 @@ class LocalSlotRef(
         return null
     }
 
+    private fun resolveOwnerAndSlot(scope: Scope): Pair<Scope, Int>? {
+        var s: Scope? = scope
+        var guard = 0
+        while (s != null && guard++ < 1024) {
+            val idx = s.getSlotIndexOf(name)
+            if (idx != null) {
+                if (idx == slot) return s to slot
+                if (!strict || captureOwnerSlot != null) return s to idx
+            }
+            s = s.parent
+        }
+        return null
+    }
+
     override suspend fun get(scope: Scope): ObjRecord {
         scope.pos = atPos
-        val owner = resolveOwner(scope) ?: scope.raiseError("slot owner not found for $name")
+        val resolved = resolveOwnerAndSlot(scope)
-        if (slot < 0 || slot >= owner.slotCount()) {
+        if (resolved == null) {
+            val rec = scope.get(name) ?: scope.raiseError("slot owner not found for $name")
+            if (rec.declaringClass != null &&
+                !canAccessMember(rec.visibility, rec.declaringClass, scope.currentClassCtx, name)
+            ) {
+                scope.raiseError(ObjIllegalAccessException(scope, "private field access"))
+            }
+            return rec
+        }
+        val owner = resolved.first
+        val slotIndex = resolved.second
+        if (slotIndex < 0 || slotIndex >= owner.slotCount()) {
             scope.raiseError("slot index out of range for $name")
         }
-        val rec = owner.getSlotRecord(slot)
+        val rec = owner.getSlotRecord(slotIndex)
         if (rec.declaringClass != null && !canAccessMember(rec.visibility, rec.declaringClass, scope.currentClassCtx, name)) {
             scope.raiseError(ObjIllegalAccessException(scope, "private field access"))
         }
@@ -2199,11 +2226,22 @@ class LocalSlotRef(
 
     override suspend fun evalValue(scope: Scope): Obj {
         scope.pos = atPos
-        val owner = resolveOwner(scope) ?: scope.raiseError("slot owner not found for $name")
+        val resolved = resolveOwnerAndSlot(scope)
-        if (slot < 0 || slot >= owner.slotCount()) {
+        if (resolved == null) {
+            val rec = scope.get(name) ?: scope.raiseError("slot owner not found for $name")
+            if (rec.declaringClass != null &&
+                !canAccessMember(rec.visibility, rec.declaringClass, scope.currentClassCtx, name)
+            ) {
+                scope.raiseError(ObjIllegalAccessException(scope, "private field access"))
+            }
+            return scope.resolve(rec, name)
+        }
+        val owner = resolved.first
+        val slotIndex = resolved.second
+        if (slotIndex < 0 || slotIndex >= owner.slotCount()) {
             scope.raiseError("slot index out of range for $name")
         }
-        val rec = owner.getSlotRecord(slot)
+        val rec = owner.getSlotRecord(slotIndex)
         if (rec.declaringClass != null && !canAccessMember(rec.visibility, rec.declaringClass, scope.currentClassCtx, name)) {
             scope.raiseError(ObjIllegalAccessException(scope, "private field access"))
         }
@@ -2212,11 +2250,23 @@ class LocalSlotRef(
 
     override suspend fun setAt(pos: Pos, scope: Scope, newValue: Obj) {
         scope.pos = atPos
-        val owner = resolveOwner(scope) ?: scope.raiseError("slot owner not found for $name")
+        val resolved = resolveOwnerAndSlot(scope)
-        if (slot < 0 || slot >= owner.slotCount()) {
+        if (resolved == null) {
+            val rec = scope.get(name) ?: scope.raiseError("slot owner not found for $name")
+            if (rec.declaringClass != null &&
+                !canAccessMember(rec.visibility, rec.declaringClass, scope.currentClassCtx, name)
+            ) {
+                scope.raiseError(ObjIllegalAccessException(scope, "private field access"))
+            }
+            scope.assign(rec, name, newValue)
+            return
+        }
+        val owner = resolved.first
+        val slotIndex = resolved.second
+        if (slotIndex < 0 || slotIndex >= owner.slotCount()) {
             scope.raiseError("slot index out of range for $name")
         }
-        val rec = owner.getSlotRecord(slot)
+        val rec = owner.getSlotRecord(slotIndex)
         if (rec.declaringClass != null && !canAccessMember(rec.visibility, rec.declaringClass, scope.currentClassCtx, name)) {
             scope.raiseError(ObjIllegalAccessException(scope, "private field access"))
         }

notes/ai_state.md

@@ -7,12 +7,16 @@ Current focus
 - Enforce compile-time name/member resolution only; no runtime scope lookup or fallback.
 - Bytecode uses memberId-based ops (CALL_MEMBER_SLOT/GET_MEMBER_SLOT/SET_MEMBER_SLOT).
 - Runtime lookup opcodes (CALL_VIRTUAL/GET_FIELD/SET_FIELD) and fallback callsites are removed.
+- Migrate bytecode to frame-first locals with lazy scope reflection; avoid eager scope slot plans in compiled functions.
+- Use FrameSlotRef for captures and only materialize Scope for Kotlin interop; use frame.ip -> pos mapping for diagnostics.
 
 Key recent changes
 - Removed method callsite PICs and fallback opcodes; bytecode now relies on compile-time member ids only.
 - Operator dispatch emits memberId calls when known; falls back to Obj opcodes for allowed built-ins without name lookup.
 - Object members are allowed on unknown types; other members still require a statically known receiver type.
-- Renamed BytecodeFallbackException to BytecodeCompileException.
+- Added frame.ip -> pos mapping; call-site ops restore pos after args to keep stack traces accurate.
+- Loop var overrides now take precedence in slot resolution to keep loop locals in frame slots.
+- LocalSlotRef now falls back to name lookup when slot plans are missing (closure safety).
 
 Known failing tests
 - None (jvmTest passing).
@@ -20,14 +24,12 @@ Known failing tests
 Files touched recently
 - notes/type_system_spec.md (spec updated)
 - AGENTS.md (type inference reminders)
-- lynglib/src/commonMain/kotlin/net/sergeych/lyng/VarDeclStatement.kt
 - lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt
 - lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt
-- lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjIterable.kt
+- lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjRef.kt
-- various bytecode runtime/disassembler files (memberId ops)
 
 Last test run
-- ./gradlew :lynglib:jvmTest --tests ScriptTest.testForInIterableUnknownTypeDisasm
+- ./gradlew :lynglib:jvmTest
 
 Spec decisions (notes/type_system_spec.md)
 - Nullability: Kotlin-style, T non-null, T? nullable, !! asserts non-null.