v2.2

compiler/res/prog8lib/prog8lib.asm

@@ -2078,3 +2078,127 @@ ror2_array_uw	.proc
 		sta  (c64.SCRATCH_ZPWORD1),y
 +		rts
 		.pend
+
+		
+strcpy		.proc
+		; copy a string (0-terminated) from A/Y to (ZPWORD1)
+		; it is assumed the target string is large enough.
+		sta  c64.SCRATCH_ZPWORD2
+		sty  c64.SCRATCH_ZPWORD2+1
+		ldy  #$ff
+-		iny
+		lda  (c64.SCRATCH_ZPWORD2),y
+		sta  (c64.SCRATCH_ZPWORD1),y
+		bne  -
+		rts
+		.pend
+		
+		
+func_leftstr	.proc
+		; leftstr(source, target, length) with params on stack
+		inx
+		lda  c64.ESTACK_LO,x
+		tay			; length
+		inx
+		lda  c64.ESTACK_LO,x
+		sta  c64.SCRATCH_ZPWORD2
+		lda  c64.ESTACK_HI,x
+		sta  c64.SCRATCH_ZPWORD2+1
+		inx
+		lda  c64.ESTACK_LO,x
+		sta  c64.SCRATCH_ZPWORD1
+		lda  c64.ESTACK_HI,x
+		sta  c64.SCRATCH_ZPWORD1+1
+		lda  #0
+		sta  (c64.SCRATCH_ZPWORD2),y
+-		dey
+		cpy  #$ff
+		bne  +
+		rts
++		lda  (c64.SCRATCH_ZPWORD1),y
+		sta  (c64.SCRATCH_ZPWORD2),y
+		jmp  -
+		.pend
+
+func_rightstr	.proc
+		; rightstr(source, target, length) with params on stack
+		; make place for the 4 parameters for substr()
+		dex
+		dex
+		dex
+		dex
+		; X-> .
+		; x+1 -> length of segment
+		; x+2 -> start index
+		; X+3 -> target LO+HI
+		; X+4 -> source LO+HI
+		; original parameters:
+		;  x+5 -> original length LO
+		;  x+6 -> original targetLO + HI
+		;  x+7 -> original sourceLO + HI
+		; replicate paramters:
+		lda  c64.ESTACK_LO+5,x
+		sta  c64.ESTACK_LO+1,x
+		lda  c64.ESTACK_LO+6,x
+		sta  c64.ESTACK_LO+3,x
+		lda  c64.ESTACK_HI+6,x
+		sta  c64.ESTACK_HI+3,x
+		lda  c64.ESTACK_LO+7,x
+		sta  c64.ESTACK_LO+4,x
+		sta  c64.SCRATCH_ZPWORD1
+		lda  c64.ESTACK_HI+7,x
+		sta  c64.ESTACK_HI+4,x
+		sta  c64.SCRATCH_ZPWORD1+1
+		; determine string length
+		ldy  #0
+-		lda  (c64.SCRATCH_ZPWORD1),y
+		beq  +
+		iny
+		bne  -
++		tya
+		sec
+		sbc  c64.ESTACK_LO+1,x  ; start index = strlen - segment length
+		sta  c64.ESTACK_LO+2,x
+		jsr  func_substr
+		; unwind original params
+		inx
+		inx
+		inx
+		rts
+		.pend
+
+func_substr	.proc
+		; substr(source, target, start, length) with params on stack
+		inx
+		ldy  c64.ESTACK_LO,x	; length
+		inx
+		lda  c64.ESTACK_LO,x	; start
+		sta  c64.SCRATCH_ZPB1
+		inx
+		lda  c64.ESTACK_LO,x	
+		sta  c64.SCRATCH_ZPWORD2
+		lda  c64.ESTACK_HI,x
+		sta  c64.SCRATCH_ZPWORD2+1
+		inx
+		lda  c64.ESTACK_LO,x	
+		sta  c64.SCRATCH_ZPWORD1
+		lda  c64.ESTACK_HI,x
+		sta  c64.SCRATCH_ZPWORD1+1
+		; adjust src location
+		clc
+		lda  c64.SCRATCH_ZPWORD1
+		adc  c64.SCRATCH_ZPB1
+		sta  c64.SCRATCH_ZPWORD1
+		bcc  +
+		inc  c64.SCRATCH_ZPWORD1+1
++		lda  #0
+		sta  (c64.SCRATCH_ZPWORD2),y
+		jmp  _startloop
+-		lda  (c64.SCRATCH_ZPWORD1),y
+		sta  (c64.SCRATCH_ZPWORD2),y
+_startloop	dey
+		cpy  #$ff
+		bne  -
+		rts
+
+		.pend

compiler/res/version.txt

@@ -1 +1 @@
-2.1
+2.2

compiler/src/prog8/ast/AstToSourceCode.kt

@@ -102,6 +102,12 @@ class AstToSourceCode(val output: (text: String) -> Unit, val program: Program):
     }
 
     override fun visit(decl: VarDecl) {
+
+        // if the vardecl is a parameter of a subroutine, don't output it again
+        val paramNames = (decl.definingScope() as? Subroutine)?.parameters?.map { it.name }
+        if(paramNames!=null && decl.name in paramNames)
+            return
+
         when(decl.type) {
             VarDeclType.VAR -> {}
             VarDeclType.CONST -> output("const ")

compiler/src/prog8/ast/AstToplevel.kt

@@ -4,7 +4,6 @@ import prog8.ast.base.*
 import prog8.ast.expressions.Expression
 import prog8.ast.expressions.IdentifierReference
 import prog8.ast.processing.AstWalker
-import prog8.ast.processing.IAstModifyingVisitor
 import prog8.ast.processing.IAstVisitor
 import prog8.ast.statements.*
 import prog8.functions.BuiltinFunctions
@@ -264,7 +263,6 @@ class Module(override val name: String,
 
     override fun toString() = "Module(name=$name, pos=$position, lib=$isLibraryModule)"
 
-    fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     fun accept(visitor: IAstVisitor) = visitor.visit(this)
     fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }

compiler/src/prog8/ast/base/Errors.kt

@@ -2,7 +2,7 @@ package prog8.ast.base
 
 import prog8.ast.expressions.IdentifierReference
 
-class FatalAstException (override var message: String) : Exception(message)
+open class FatalAstException (override var message: String) : Exception(message)
 
 open class AstException (override var message: String) : Exception(message)
 

compiler/src/prog8/ast/base/Extensions.kt

@@ -56,20 +56,21 @@ internal fun Program.checkRecursion(errors: ErrorReporter) {
 }
 
 internal fun Program.checkIdentifiers(errors: ErrorReporter) {
-    val checker = AstIdentifiersChecker(this, errors)
-    checker.visit(this)
+
+    val checker2 = AstIdentifiersChecker(this, errors)
+    checker2.visit(this)
+
+    if(errors.isEmpty()) {
+        val transforms = AstVariousTransforms(this)
+        transforms.visit(this)
+        transforms.applyModifications()
+    }
 
     if (modules.map { it.name }.toSet().size != modules.size) {
         throw FatalAstException("modules should all be unique")
     }
 }
 
-internal fun Program.makeForeverLoops() {
-    val checker = ForeverLoopsMaker()
-    checker.visit(this)
-    checker.applyModifications()
-}
-
 internal fun Program.removeNopsFlattenAnonScopes() {
     val flattener = FlattenAnonymousScopesAndNopRemover()
     flattener.visit(this)

compiler/src/prog8/ast/expressions/AstExpressions.kt

@@ -4,11 +4,11 @@ import prog8.ast.*
 import prog8.ast.antlr.escape
 import prog8.ast.base.*
 import prog8.ast.processing.AstWalker
-import prog8.ast.processing.IAstModifyingVisitor
 import prog8.ast.processing.IAstVisitor
 import prog8.ast.statements.*
 import prog8.compiler.target.CompilationTarget
 import prog8.functions.BuiltinFunctions
+import prog8.functions.CannotEvaluateException
 import prog8.functions.NotConstArgumentException
 import prog8.functions.builtinFunctionReturnType
 import java.util.*
@@ -20,7 +20,6 @@ val associativeOperators = setOf("+", "*", "&", "|", "^", "or", "and", "xor", "=
 
 sealed class Expression: Node {
     abstract fun constValue(program: Program): NumericLiteralValue?
-    abstract fun accept(visitor: IAstModifyingVisitor): Expression
     abstract fun accept(visitor: IAstVisitor)
     abstract fun accept(visitor: AstWalker, parent: Node)
     abstract fun referencesIdentifiers(vararg name: String): Boolean     // todo: remove this and add identifier usage tracking into CallGraph instead
@@ -65,7 +64,6 @@ class PrefixExpression(val operator: String, var expression: Expression, overrid
     }
 
     override fun constValue(program: Program): NumericLiteralValue? = null
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -123,7 +121,6 @@ class BinaryExpression(var left: Expression, var operator: String, var right: Ex
     // binary expression should actually have been optimized away into a single value, before const value was requested...
     override fun constValue(program: Program): NumericLiteralValue? = null
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -237,7 +234,6 @@ class ArrayIndexedExpression(var identifier: IdentifierReference,
     }
 
     override fun constValue(program: Program): NumericLiteralValue? = null
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -274,7 +270,6 @@ class TypecastExpression(var expression: Expression, var type: DataType, val imp
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -309,7 +304,6 @@ data class AddressOf(var identifier: IdentifierReference, override val position:
     override fun constValue(program: Program): NumericLiteralValue? = null
     override fun referencesIdentifiers(vararg name: String) = false
     override fun inferType(program: Program): InferredTypes.InferredType = InferredTypes.knownFor(DataType.UWORD)
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 }
@@ -328,7 +322,6 @@ class DirectMemoryRead(var addressExpression: Expression, override val position:
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -388,7 +381,6 @@ class NumericLiteralValue(val type: DataType,    // only numerical types allowed
     override fun referencesIdentifiers(vararg name: String) = false
     override fun constValue(program: Program) = this
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -479,7 +471,6 @@ class StructLiteralValue(var values: List<Expression>,
     }
 
     override fun constValue(program: Program): NumericLiteralValue?  = null
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -510,7 +501,6 @@ class StringLiteralValue(val value: String,
 
     override fun referencesIdentifiers(vararg name: String) = false
     override fun constValue(program: Program): NumericLiteralValue? = null
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -546,12 +536,11 @@ class ArrayLiteralValue(val type: InferredTypes.InferredType,     // inferred be
 
     override fun referencesIdentifiers(vararg name: String) = value.any { it.referencesIdentifiers(*name) }
     override fun constValue(program: Program): NumericLiteralValue? = null
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
     override fun toString(): String = "$value"
-    override fun inferType(program: Program): InferredTypes.InferredType = if(type.isUnknown) type else guessDatatype(program)
+    override fun inferType(program: Program): InferredTypes.InferredType = if(type.isKnown) type else guessDatatype(program)
 
     operator fun compareTo(other: ArrayLiteralValue): Int = throw ExpressionError("cannot order compare arrays", position)
     override fun hashCode(): Int = Objects.hash(value, type)
@@ -640,7 +629,6 @@ class RangeExpr(var from: Expression,
     }
 
     override fun constValue(program: Program): NumericLiteralValue? = null
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -720,7 +708,6 @@ class RegisterExpr(val register: Register, override val position: Position) : Ex
     }
 
     override fun constValue(program: Program): NumericLiteralValue? = null
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -768,7 +755,6 @@ data class IdentifierReference(val nameInSource: List<String>, override val posi
         return "IdentifierRef($nameInSource)"
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 
@@ -848,13 +834,16 @@ class FunctionCall(override var target: IdentifierReference,
             // const-evaluating the builtin function call failed.
             return null
         }
+        catch(x: CannotEvaluateException) {
+            // const-evaluating the builtin function call failed.
+            return null
+        }
     }
 
     override fun toString(): String {
         return "FunctionCall(target=$target, pos=$position)"
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node)= visitor.visit(this, parent)
 

compiler/src/prog8/ast/processing/AstIdentifiersChecker.kt

@@ -1,8 +1,6 @@
 package prog8.ast.processing
 
-import prog8.ast.INameScope
 import prog8.ast.Module
-import prog8.ast.Node
 import prog8.ast.Program
 import prog8.ast.base.*
 import prog8.ast.expressions.*
@@ -10,98 +8,69 @@ import prog8.ast.statements.*
 import prog8.compiler.target.CompilationTarget
 import prog8.functions.BuiltinFunctions
 
-// TODO implement using AstWalker instead of IAstModifyingVisitor
-internal class AstIdentifiersChecker(private val program: Program,
-                                     private val errors: ErrorReporter) : IAstModifyingVisitor {
+internal class AstIdentifiersChecker(private val program: Program, private val errors: ErrorReporter) : IAstVisitor {
     private var blocks = mutableMapOf<String, Block>()
-    private val vardeclsToAdd = mutableMapOf<INameScope, MutableList<VarDecl>>()
 
     private fun nameError(name: String, position: Position, existing: Statement) {
         errors.err("name conflict '$name', also defined in ${existing.position.file} line ${existing.position.line}", position)
     }
 
     override fun visit(module: Module) {
-        vardeclsToAdd.clear()
         blocks.clear()  // blocks may be redefined within a different module
+
         super.visit(module)
-        // add any new vardecls to the various scopes
-        for((where, decls) in vardeclsToAdd) {
-            where.statements.addAll(0, decls)
-            decls.forEach { it.linkParents(where as Node) }
-        }
     }
 
-    override fun visit(block: Block): Statement {
+    override fun visit(block: Block) {
         val existing = blocks[block.name]
         if(existing!=null)
             nameError(block.name, block.position, existing)
         else
             blocks[block.name] = block
 
-        return super.visit(block)
+        super.visit(block)
     }
 
-    override fun visit(functionCall: FunctionCall): Expression {
-        if(functionCall.target.nameInSource.size==1 && functionCall.target.nameInSource[0]=="lsb") {
-            // lsb(...) is just an alias for type cast to ubyte, so replace with "... as ubyte"
-            val typecast = TypecastExpression(functionCall.args.single(), DataType.UBYTE, false, functionCall.position)
-            typecast.linkParents(functionCall.parent)
-            return super.visit(typecast)
-        }
-        return super.visit(functionCall)
-    }
-
-    override fun visit(decl: VarDecl): Statement {
-        // first, check if there are datatype errors on the vardecl
+    override fun visit(decl: VarDecl) {
         decl.datatypeErrors.forEach { errors.err(it.message, it.position) }
 
-        // now check the identifier
         if(decl.name in BuiltinFunctions)
-            // the builtin functions can't be redefined
             errors.err("builtin function cannot be redefined", decl.position)
 
         if(decl.name in CompilationTarget.machine.opcodeNames)
             errors.err("can't use a cpu opcode name as a symbol: '${decl.name}'", decl.position)
 
-        // is it a struct variable? then define all its struct members as mangled names,
-        //    and include the original decl as well.
         if(decl.datatype==DataType.STRUCT) {
-            if(decl.structHasBeenFlattened)
+            if (decl.structHasBeenFlattened)
                 return super.visit(decl)    // don't do this multiple times
 
-            if(decl.struct==null) {
+            if (decl.struct == null) {
                 errors.err("undefined struct type", decl.position)
                 return super.visit(decl)
             }
 
-            if(decl.struct!!.statements.any { (it as VarDecl).datatype !in NumericDatatypes})
+            if (decl.struct!!.statements.any { (it as VarDecl).datatype !in NumericDatatypes })
                 return super.visit(decl)     // a non-numeric member, not supported. proper error is given by AstChecker later
 
-            if(decl.value is NumericLiteralValue) {
+            if (decl.value is NumericLiteralValue) {
                 errors.err("you cannot initialize a struct using a single value", decl.position)
                 return super.visit(decl)
             }
 
-            if(decl.value != null && decl.value !is StructLiteralValue) {
+            if (decl.value != null && decl.value !is StructLiteralValue) {
                 errors.err("initializing requires struct literal value", decl.value?.position ?: decl.position)
                 return super.visit(decl)
             }
-
-            val decls = decl.flattenStructMembers()
-            decls.add(decl)
-            val result = AnonymousScope(decls, decl.position)
-            result.linkParents(decl.parent)
-            return result
         }
 
         val existing = program.namespace.lookup(listOf(decl.name), decl)
         if (existing != null && existing !== decl)
             nameError(decl.name, decl.position, existing)
 
-        return super.visit(decl)
+        super.visit(decl)
     }
 
-    override fun visit(subroutine: Subroutine): Statement {
+    override fun visit(subroutine: Subroutine) {
         if(subroutine.name in CompilationTarget.machine.opcodeNames) {
             errors.err("can't use a cpu opcode name as a symbol: '${subroutine.name}'", subroutine.position)
         } else if(subroutine.name in BuiltinFunctions) {
@@ -138,30 +107,15 @@ internal class AstIdentifiersChecker(private val program: Program,
                     nameError(name, sub.position, subroutine)
             }
 
-            // inject subroutine params as local variables (if they're not there yet) (for non-kernel subroutines and non-asm parameters)
-            // NOTE:
-            // - numeric types BYTE and WORD and FLOAT are passed by value;
-            // - strings, arrays, matrices are passed by reference (their 16-bit address is passed as an uword parameter)
-            if(subroutine.asmAddress==null) {
-                if(subroutine.asmParameterRegisters.isEmpty()) {
-                    subroutine.parameters
-                            .filter { it.name !in namesInSub }
-                            .forEach {
-                                val vardecl = ParameterVarDecl(it.name, it.type, subroutine.position)
-                                vardecl.linkParents(subroutine)
-                                subroutine.statements.add(0, vardecl)
-                            }
-                }
-            }
-
             if(subroutine.isAsmSubroutine && subroutine.statements.any{it !is InlineAssembly}) {
                 errors.err("asmsub can only contain inline assembly (%asm)", subroutine.position)
             }
         }
-        return super.visit(subroutine)
+
+        super.visit(subroutine)
     }
 
-    override fun visit(label: Label): Statement {
+    override fun visit(label: Label) {
         if(label.name in CompilationTarget.machine.opcodeNames)
             errors.err("can't use a cpu opcode name as a symbol: '${label.name}'", label.position)
 
@@ -179,163 +133,39 @@ internal class AstIdentifiersChecker(private val program: Program,
                 }
             }
         }
-        return super.visit(label)
+
+        super.visit(label)
     }
 
-    override fun visit(forLoop: ForLoop): Statement {
-        // If the for loop has a decltype, it means to declare the loopvar inside the loop body
-        // rather than reusing an already declared loopvar from an outer scope.
-        // For loops that loop over an interable variable (instead of a range of numbers) get an
-        // additional interation count variable in their scope.
-        if(forLoop.loopRegister!=null) {
-            if(forLoop.loopRegister == Register.X)
+    override fun visit(forLoop: ForLoop) {
+        if (forLoop.loopRegister != null) {
+            if (forLoop.loopRegister == Register.X)
                 errors.warn("writing to the X register is dangerous, because it's used as an internal pointer", forLoop.position)
-        } else {
-            val loopVar = forLoop.loopVar
-            if (loopVar != null) {
-                val validName = forLoop.body.name.replace("<", "").replace(">", "").replace("-", "")
-                val loopvarName = "prog8_loopvar_$validName"
-                if (forLoop.iterable !is RangeExpr) {
-                    val existing = if (forLoop.body.containsNoCodeNorVars()) null else forLoop.body.lookup(listOf(loopvarName), forLoop.body.statements.first())
-                    if (existing == null) {
-                        // create loop iteration counter variable (without value, to avoid an assignment)
-                        val vardecl = VarDecl(VarDeclType.VAR, DataType.UBYTE, ZeropageWish.PREFER_ZEROPAGE, null, loopvarName, null, null,
-                                isArray = false, autogeneratedDontRemove = true, position = loopVar.position)
-                        vardecl.linkParents(forLoop.body)
-                        forLoop.body.statements.add(0, vardecl)
-                        loopVar.parent = forLoop.body   // loopvar 'is defined in the body'
-                    }
-                }
-            }
         }
-        return super.visit(forLoop)
+
+        super.visit(forLoop)
     }
 
-    override fun visit(assignTarget: AssignTarget): AssignTarget {
+    override fun visit(assignTarget: AssignTarget) {
         if(assignTarget.register== Register.X)
             errors.warn("writing to the X register is dangerous, because it's used as an internal pointer", assignTarget.position)
-        return super.visit(assignTarget)
+        super.visit(assignTarget)
     }
 
-    override fun visit(arrayLiteral: ArrayLiteralValue): Expression {
-        val array = super.visit(arrayLiteral)
-        if(array is ArrayLiteralValue) {
-            val vardecl = array.parent as? VarDecl
-            // adjust the datatype of the array (to an educated guess)
-            if(vardecl!=null) {
-                val arrayDt = array.type
-                if(!arrayDt.istype(vardecl.datatype)) {
-                    val cast = array.cast(vardecl.datatype)
-                    if (cast != null) {
-                        vardecl.value = cast
-                        cast.linkParents(vardecl)
-                        return cast
-                    }
-                }
-                return array
-            }
-            else {
-                val arrayDt = array.guessDatatype(program)
-                if(arrayDt.isKnown) {
-                    // this array literal is part of an expression, turn it into an identifier reference
-                    val litval2 = array.cast(arrayDt.typeOrElse(DataType.STRUCT))
-                    return if (litval2 != null) {
-                        litval2.parent = array.parent
-                        makeIdentifierFromRefLv(litval2)
-                    } else array
-                }
-            }
-        }
-        return array
+    override fun visit(string: StringLiteralValue) {
+        if (string.value.length !in 1..255)
+            errors.err("string literal length must be between 1 and 255", string.position)
+
+        super.visit(string)
     }
 
-    override fun visit(stringLiteral: StringLiteralValue): Expression {
-        val string = super.visit(stringLiteral)
-        if(string is StringLiteralValue) {
-            val vardecl = string.parent as? VarDecl
-            // intern the string; move it into the heap
-            if (string.value.length !in 1..255)
-                errors.err("string literal length must be between 1 and 255", string.position)
-            return if (vardecl != null)
-                string
-            else
-                makeIdentifierFromRefLv(string)  // replace the literal string by a identifier reference.
-        }
-        return string
-    }
-
-    private fun makeIdentifierFromRefLv(array: ArrayLiteralValue): IdentifierReference {
-        // a referencetype literal value that's not declared as a variable
-        // we need to introduce an auto-generated variable for this to be able to refer to the value
-        // note: if the var references the same literal value, it is not yet de-duplicated here.
-        val scope = array.definingScope()
-        val variable = VarDecl.createAuto(array)
-        return replaceWithIdentifier(variable, scope, array.parent)
-    }
-
-    private fun makeIdentifierFromRefLv(string: StringLiteralValue): IdentifierReference {
-        // a referencetype literal value that's not declared as a variable
-        // we need to introduce an auto-generated variable for this to be able to refer to the value
-        // note: if the var references the same literal value, it is not yet de-duplicated here.
-        val scope = string.definingScope()
-        val variable = VarDecl.createAuto(string)
-        return replaceWithIdentifier(variable, scope, string.parent)
-    }
-
-    private fun replaceWithIdentifier(variable: VarDecl, scope: INameScope, parent: Node): IdentifierReference {
-        val variable1 = addVarDecl(scope, variable)
-        // replace the reference literal by a identifier reference
-        val identifier = IdentifierReference(listOf(variable1.name), variable1.position)
-        identifier.parent = parent
-        return identifier
-    }
-
-    override fun visit(structDecl: StructDecl): Statement {
+    override fun visit(structDecl: StructDecl) {
         for(member in structDecl.statements){
             val decl = member as? VarDecl
             if(decl!=null && decl.datatype !in NumericDatatypes)
                 errors.err("structs can only contain numerical types", decl.position)
         }
 
-        return super.visit(structDecl)
+        super.visit(structDecl)
     }
-
-    override fun visit(expr: BinaryExpression): Expression {
-        return when {
-            expr.left is StringLiteralValue ->
-                processBinaryExprWithString(expr.left as StringLiteralValue, expr.right, expr)
-            expr.right is StringLiteralValue ->
-                processBinaryExprWithString(expr.right as StringLiteralValue, expr.left, expr)
-            else -> super.visit(expr)
-        }
-    }
-
-    private fun processBinaryExprWithString(string: StringLiteralValue, operand: Expression, expr: BinaryExpression): Expression {
-        val constvalue = operand.constValue(program)
-        if(constvalue!=null) {
-            if (expr.operator == "*") {
-                // repeat a string a number of times
-                return StringLiteralValue(string.value.repeat(constvalue.number.toInt()), string.altEncoding, expr.position)
-            }
-        }
-        if(expr.operator == "+" && operand is StringLiteralValue) {
-            // concatenate two strings
-            return StringLiteralValue("${string.value}${operand.value}", string.altEncoding, expr.position)
-        }
-        return expr
-    }
-
-    private fun addVarDecl(scope: INameScope, variable: VarDecl): VarDecl {
-        if(scope !in vardeclsToAdd)
-            vardeclsToAdd[scope] = mutableListOf()
-        val declList = vardeclsToAdd.getValue(scope)
-        val existing = declList.singleOrNull { it.name==variable.name }
-        return if(existing!=null) {
-            existing
-        } else {
-            declList.add(variable)
-            variable
-        }
-    }
-
 }

compiler/src/prog8/ast/processing/AstVariousTransforms.kt

@@ -0,0 +1,133 @@
+package prog8.ast.processing
+
+import prog8.ast.Node
+import prog8.ast.Program
+import prog8.ast.base.*
+import prog8.ast.expressions.*
+import prog8.ast.statements.*
+
+
+internal class AstVariousTransforms(private val program: Program) : AstWalker() {
+    private val noModifications = emptyList<IAstModification>()
+
+    override fun before(functionCall: FunctionCall, parent: Node): Iterable<IAstModification> {
+        if(functionCall.target.nameInSource.size==1 && functionCall.target.nameInSource[0]=="lsb") {
+            // lsb(...) is just an alias for type cast to ubyte, so replace with "... as ubyte"
+            val typecast = TypecastExpression(functionCall.args.single(), DataType.UBYTE, false, functionCall.position)
+            return listOf(IAstModification.ReplaceNode(
+                    functionCall, typecast, parent
+            ))
+        }
+
+        return noModifications
+    }
+
+    override fun before(decl: VarDecl, parent: Node): Iterable<IAstModification> {
+        // is it a struct variable? then define all its struct members as mangled names,
+        //    and include the original decl as well.
+        if(decl.datatype==DataType.STRUCT && !decl.structHasBeenFlattened) {
+            val decls = decl.flattenStructMembers()
+            decls.add(decl)
+            val result = AnonymousScope(decls, decl.position)
+            return listOf(IAstModification.ReplaceNode(
+                    decl, result, parent
+            ))
+        }
+
+        return noModifications
+    }
+
+    override fun after(subroutine: Subroutine, parent: Node): Iterable<IAstModification> {
+        // For non-kernel subroutines and non-asm parameters:
+        // inject subroutine params as local variables (if they're not there yet).
+        val symbolsInSub = subroutine.allDefinedSymbols()
+        val namesInSub = symbolsInSub.map{ it.first }.toSet()
+        if(subroutine.asmAddress==null) {
+            if(subroutine.asmParameterRegisters.isEmpty()) {
+                return subroutine.parameters
+                        .filter { it.name !in namesInSub }
+                        .map {
+                            val vardecl = ParameterVarDecl(it.name, it.type, subroutine.position)
+                            IAstModification.InsertFirst(vardecl, subroutine)
+                        }
+            }
+        }
+
+        return noModifications
+    }
+
+    override fun before(expr: BinaryExpression, parent: Node): Iterable<IAstModification> {
+        when {
+            expr.left is StringLiteralValue ->
+                return listOf(IAstModification.ReplaceNode(
+                        expr,
+                        processBinaryExprWithString(expr.left as StringLiteralValue, expr.right, expr),
+                        parent
+                ))
+            expr.right is StringLiteralValue ->
+                return listOf(IAstModification.ReplaceNode(
+                        expr,
+                        processBinaryExprWithString(expr.right as StringLiteralValue, expr.left, expr),
+                        parent
+                ))
+        }
+
+        return noModifications
+    }
+
+    override fun after(string: StringLiteralValue, parent: Node): Iterable<IAstModification> {
+        if(string.parent !is VarDecl) {
+            // replace the literal string by a identifier reference to a new local vardecl
+            val vardecl = VarDecl.createAuto(string)
+            val identifier = IdentifierReference(listOf(vardecl.name), vardecl.position)
+            return listOf(
+                    IAstModification.ReplaceNode(string, identifier, parent),
+                    IAstModification.InsertFirst(vardecl, string.definingScope() as Node)
+            )
+        }
+        return noModifications
+    }
+
+    override fun after(array: ArrayLiteralValue, parent: Node): Iterable<IAstModification> {
+        val vardecl = array.parent as? VarDecl
+        if(vardecl!=null) {
+            // adjust the datatype of the array (to an educated guess)
+            val arrayDt = array.type
+            if(!arrayDt.istype(vardecl.datatype)) {
+                val cast = array.cast(vardecl.datatype)
+                if (cast != null && cast!=array)
+                    return listOf(IAstModification.ReplaceNode(vardecl.value!!, cast, vardecl))
+            }
+        } else {
+            val arrayDt = array.guessDatatype(program)
+            if(arrayDt.isKnown) {
+                // this array literal is part of an expression, turn it into an identifier reference
+                val litval2 = array.cast(arrayDt.typeOrElse(DataType.STRUCT))
+                if(litval2!=null && litval2!=array) {
+                    val vardecl = VarDecl.createAuto(litval2)
+                    val identifier = IdentifierReference(listOf(vardecl.name), vardecl.position)
+                    return listOf(
+                            IAstModification.ReplaceNode(array, identifier, parent),
+                            IAstModification.InsertFirst(vardecl, array.definingScope() as Node)
+                    )
+                }
+            }
+        }
+        return noModifications
+    }
+
+    private fun processBinaryExprWithString(string: StringLiteralValue, operand: Expression, expr: BinaryExpression): Expression {
+        val constvalue = operand.constValue(program)
+        if(constvalue!=null) {
+            if (expr.operator == "*") {
+                // repeat a string a number of times
+                return StringLiteralValue(string.value.repeat(constvalue.number.toInt()), string.altEncoding, expr.position)
+            }
+        }
+        if(expr.operator == "+" && operand is StringLiteralValue) {
+            // concatenate two strings
+            return StringLiteralValue("${string.value}${operand.value}", string.altEncoding, expr.position)
+        }
+        return expr
+    }
+}

compiler/src/prog8/ast/processing/AstWalker.kt

@@ -1,9 +1,6 @@
 package prog8.ast.processing
 
-import prog8.ast.INameScope
-import prog8.ast.Module
-import prog8.ast.Node
-import prog8.ast.Program
+import prog8.ast.*
 import prog8.ast.base.FatalAstException
 import prog8.ast.expressions.*
 import prog8.ast.statements.*
@@ -15,7 +12,7 @@ interface IAstModification {
     class Remove(val node: Node, val parent: Node) : IAstModification {
         override fun perform() {
             if(parent is INameScope) {
-                if (!parent.statements.remove(node))
+                if (!parent.statements.remove(node) && parent !is GlobalNamespace)
                     throw FatalAstException("attempt to remove non-existing node $node")
             } else {
                 throw FatalAstException("parent of a remove modification is not an INameScope")

compiler/src/prog8/ast/processing/ForeverLoopsMaker.kt

@@ -1,28 +0,0 @@
-package prog8.ast.processing
-
-import prog8.ast.Node
-import prog8.ast.expressions.NumericLiteralValue
-import prog8.ast.statements.ForeverLoop
-import prog8.ast.statements.RepeatLoop
-import prog8.ast.statements.WhileLoop
-
-
-internal class ForeverLoopsMaker: AstWalker() {
-    override fun before(repeatLoop: RepeatLoop, parent: Node): Iterable<IAstModification> {
-        val numeric = repeatLoop.untilCondition as? NumericLiteralValue
-        if(numeric!=null && numeric.number.toInt() == 0) {
-            val forever = ForeverLoop(repeatLoop.body, repeatLoop.position)
-            return listOf(IAstModification.ReplaceNode(repeatLoop, forever, parent))
-        }
-        return emptyList()
-    }
-
-    override fun before(whileLoop: WhileLoop, parent: Node): Iterable<IAstModification> {
-        val numeric = whileLoop.condition as? NumericLiteralValue
-        if(numeric!=null && numeric.number.toInt() != 0) {
-            val forever = ForeverLoop(whileLoop.body, whileLoop.position)
-            return listOf(IAstModification.ReplaceNode(whileLoop, forever, parent))
-        }
-        return emptyList()
-    }
-}

compiler/src/prog8/ast/processing/IAstModifyingVisitor.kt

@@ -1,267 +0,0 @@
-package prog8.ast.processing
-
-import prog8.ast.Module
-import prog8.ast.Program
-import prog8.ast.base.FatalAstException
-import prog8.ast.expressions.*
-import prog8.ast.statements.*
-
-// TODO replace all occurrences of this with AstWalker
-interface IAstModifyingVisitor {
-    fun visit(program: Program) {
-        program.modules.forEach { it.accept(this) }
-    }
-
-    fun visit(module: Module) {
-        module.statements = module.statements.map { it.accept(this) }.toMutableList()
-    }
-
-    fun visit(expr: PrefixExpression): Expression {
-        expr.expression = expr.expression.accept(this)
-        return expr
-    }
-
-    fun visit(expr: BinaryExpression): Expression {
-        expr.left = expr.left.accept(this)
-        expr.right = expr.right.accept(this)
-        return expr
-    }
-
-    fun visit(directive: Directive): Statement {
-        return directive
-    }
-
-    fun visit(block: Block): Statement {
-        block.statements = block.statements.map { it.accept(this) }.toMutableList()
-        return block
-    }
-
-    fun visit(decl: VarDecl): Statement {
-        decl.value = decl.value?.accept(this)
-        decl.arraysize?.accept(this)
-        return decl
-    }
-
-    fun visit(subroutine: Subroutine): Statement {
-        subroutine.statements = subroutine.statements.map { it.accept(this) }.toMutableList()
-        return subroutine
-    }
-
-    fun visit(functionCall: FunctionCall): Expression {
-        val newtarget = functionCall.target.accept(this)
-        if(newtarget is IdentifierReference)
-            functionCall.target = newtarget
-        else
-            throw FatalAstException("cannot change class of function call target")
-        functionCall.args = functionCall.args.map { it.accept(this) }.toMutableList()
-        return functionCall
-    }
-
-    fun visit(functionCallStatement: FunctionCallStatement): Statement {
-        val newtarget = functionCallStatement.target.accept(this)
-        if(newtarget is IdentifierReference)
-            functionCallStatement.target = newtarget
-        else
-            throw FatalAstException("cannot change class of function call target")
-        functionCallStatement.args = functionCallStatement.args.map { it.accept(this) }.toMutableList()
-        return functionCallStatement
-    }
-
-    fun visit(identifier: IdentifierReference): Expression {
-        // note: this is an identifier that is used in an expression.
-        // other identifiers are simply part of the other statements (such as jumps, subroutine defs etc)
-        return identifier
-    }
-
-    fun visit(jump: Jump): Statement {
-        if(jump.identifier!=null) {
-            val ident = jump.identifier.accept(this)
-            if(ident is IdentifierReference && ident!==jump.identifier) {
-                return Jump(null, ident, null, jump.position)
-            }
-        }
-        return jump
-    }
-
-    fun visit(ifStatement: IfStatement): Statement {
-        ifStatement.condition = ifStatement.condition.accept(this)
-        ifStatement.truepart = ifStatement.truepart.accept(this) as AnonymousScope
-        ifStatement.elsepart = ifStatement.elsepart.accept(this) as AnonymousScope
-        return ifStatement
-    }
-
-    fun visit(branchStatement: BranchStatement): Statement {
-        branchStatement.truepart = branchStatement.truepart.accept(this) as AnonymousScope
-        branchStatement.elsepart = branchStatement.elsepart.accept(this) as AnonymousScope
-        return branchStatement
-    }
-
-    fun visit(range: RangeExpr): Expression {
-        range.from = range.from.accept(this)
-        range.to = range.to.accept(this)
-        range.step = range.step.accept(this)
-        return range
-    }
-
-    fun visit(label: Label): Statement {
-        return label
-    }
-
-    fun visit(literalValue: NumericLiteralValue): NumericLiteralValue {
-        return literalValue
-    }
-
-    fun visit(stringLiteral: StringLiteralValue): Expression {
-        return stringLiteral
-    }
-
-    fun visit(arrayLiteral: ArrayLiteralValue): Expression {
-        for(av in arrayLiteral.value.withIndex()) {
-            val newvalue = av.value.accept(this)
-            arrayLiteral.value[av.index] = newvalue
-        }
-        return arrayLiteral
-    }
-
-    fun visit(assignment: Assignment): Statement {
-        assignment.target = assignment.target.accept(this)
-        assignment.value = assignment.value.accept(this)
-        return assignment
-    }
-
-    fun visit(postIncrDecr: PostIncrDecr): Statement {
-        postIncrDecr.target = postIncrDecr.target.accept(this)
-        return postIncrDecr
-    }
-
-    fun visit(contStmt: Continue): Statement {
-        return contStmt
-    }
-
-    fun visit(breakStmt: Break): Statement {
-        return breakStmt
-    }
-
-    fun visit(forLoop: ForLoop): Statement {
-        when(val newloopvar = forLoop.loopVar?.accept(this)) {
-            is IdentifierReference -> forLoop.loopVar = newloopvar
-            null -> forLoop.loopVar = null
-            else -> throw FatalAstException("can't change class of loopvar")
-        }
-        forLoop.iterable = forLoop.iterable.accept(this)
-        forLoop.body = forLoop.body.accept(this) as AnonymousScope
-        return forLoop
-    }
-
-    fun visit(whileLoop: WhileLoop): Statement {
-        whileLoop.condition = whileLoop.condition.accept(this)
-        whileLoop.body = whileLoop.body.accept(this) as AnonymousScope
-        return whileLoop
-    }
-
-    fun visit(foreverLoop: ForeverLoop): Statement {
-        foreverLoop.body = foreverLoop.body.accept(this) as AnonymousScope
-        return foreverLoop
-    }
-
-    fun visit(repeatLoop: RepeatLoop): Statement {
-        repeatLoop.untilCondition = repeatLoop.untilCondition.accept(this)
-        repeatLoop.body = repeatLoop.body.accept(this) as AnonymousScope
-        return repeatLoop
-    }
-
-    fun visit(returnStmt: Return): Statement {
-        returnStmt.value = returnStmt.value?.accept(this)
-        return returnStmt
-    }
-
-    fun visit(arrayIndexedExpression: ArrayIndexedExpression): ArrayIndexedExpression {
-        val ident = arrayIndexedExpression.identifier.accept(this)
-        if(ident is IdentifierReference)
-            arrayIndexedExpression.identifier = ident
-        arrayIndexedExpression.arrayspec.accept(this)
-        return arrayIndexedExpression
-    }
-
-    fun visit(assignTarget: AssignTarget): AssignTarget {
-        when (val ident = assignTarget.identifier?.accept(this)) {
-            is IdentifierReference -> assignTarget.identifier = ident
-            null -> assignTarget.identifier = null
-            else -> throw FatalAstException("can't change class of assign target identifier")
-        }
-        assignTarget.arrayindexed = assignTarget.arrayindexed?.accept(this)
-        assignTarget.memoryAddress?.let { visit(it) }
-        return assignTarget
-    }
-
-    fun visit(scope: AnonymousScope): Statement {
-        scope.statements = scope.statements.map { it.accept(this) }.toMutableList()
-        return scope
-    }
-
-    fun visit(typecast: TypecastExpression): Expression {
-        typecast.expression = typecast.expression.accept(this)
-        return typecast
-    }
-
-    fun visit(memread: DirectMemoryRead): Expression {
-        memread.addressExpression = memread.addressExpression.accept(this)
-        return memread
-    }
-
-    fun visit(memwrite: DirectMemoryWrite) {
-        memwrite.addressExpression = memwrite.addressExpression.accept(this)
-    }
-
-    fun visit(addressOf: AddressOf): Expression {
-        val ident = addressOf.identifier.accept(this)
-        if(ident is IdentifierReference)
-            addressOf.identifier = ident
-        else
-            throw FatalAstException("can't change class of addressof identifier")
-        return addressOf
-    }
-
-    fun visit(inlineAssembly: InlineAssembly): Statement {
-        return inlineAssembly
-    }
-
-    fun visit(registerExpr: RegisterExpr): Expression {
-        return registerExpr
-    }
-
-    fun visit(builtinFunctionStatementPlaceholder: BuiltinFunctionStatementPlaceholder): Statement {
-        return builtinFunctionStatementPlaceholder
-    }
-
-    fun visit(nopStatement: NopStatement): Statement {
-        return nopStatement
-    }
-
-    fun visit(whenStatement: WhenStatement): Statement {
-        whenStatement.condition = whenStatement.condition.accept(this)
-        whenStatement.choices.forEach { it.accept(this) }
-        return whenStatement
-    }
-
-    fun visit(whenChoice: WhenChoice) {
-        whenChoice.values = whenChoice.values?.map { it.accept(this) }
-        val stmt = whenChoice.statements.accept(this)
-        if(stmt is AnonymousScope)
-            whenChoice.statements = stmt
-        else {
-            whenChoice.statements = AnonymousScope(mutableListOf(stmt), stmt.position)
-            whenChoice.statements.linkParents(whenChoice)
-        }
-    }
-
-    fun visit(structDecl: StructDecl): Statement {
-        structDecl.statements = structDecl.statements.map{ it.accept(this) }.toMutableList()
-        return structDecl
-    }
-
-    fun visit(structLv: StructLiteralValue): Expression {
-        structLv.values = structLv.values.map { it.accept(this) }
-        return structLv
-    }
-}

compiler/src/prog8/ast/processing/ImportedModuleDirectiveRemover.kt

@@ -10,11 +10,12 @@ internal class ImportedModuleDirectiveRemover: AstWalker() {
      */
 
     private val moduleLevelDirectives = listOf("%output", "%launcher", "%zeropage", "%zpreserved", "%address")
+    private val noModifications = emptyList<IAstModification>()
 
     override fun before(directive: Directive, parent: Node): Iterable<IAstModification> {
         if(directive.directive in moduleLevelDirectives) {
             return listOf(IAstModification.Remove(directive, parent))
         }
-        return emptyList()
+        return noModifications
     }
 }

compiler/src/prog8/ast/processing/StatementReorderer.kt

@@ -19,7 +19,7 @@ internal class StatementReorderer(val program: Program) : AstWalker() {
     // - sorts the choices in when statement.
     // - insert AddressOf (&) expression where required (string params to a UWORD function param etc).
 
-
+    private val noModifications = emptyList<IAstModification>()
     private val directivesToMove = setOf("%output", "%launcher", "%zeropage", "%zpreserved", "%address", "%option")
 
     override fun after(module: Module, parent: Node): Iterable<IAstModification> {
@@ -33,7 +33,7 @@ internal class StatementReorderer(val program: Program) : AstWalker() {
         }
 
         reorderVardeclsAndDirectives(module.statements)
-        return emptyList()
+        return noModifications
     }
 
     private fun reorderVardeclsAndDirectives(statements: MutableList<Statement>) {
@@ -56,7 +56,7 @@ internal class StatementReorderer(val program: Program) : AstWalker() {
         }
 
         reorderVardeclsAndDirectives(block.statements)
-        return emptyList()
+        return noModifications
     }
 
     override fun before(subroutine: Subroutine, parent: Node): Iterable<IAstModification> {
@@ -68,7 +68,7 @@ internal class StatementReorderer(val program: Program) : AstWalker() {
                 )
             }
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(decl: VarDecl, parent: Node): Iterable<IAstModification> {
@@ -86,7 +86,7 @@ internal class StatementReorderer(val program: Program) : AstWalker() {
                 )
             }
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(whenStatement: WhenStatement, parent: Node): Iterable<IAstModification> {
@@ -95,7 +95,7 @@ internal class StatementReorderer(val program: Program) : AstWalker() {
         }
         whenStatement.choices.clear()
         choices.mapTo(whenStatement.choices) { it.second }
-        return emptyList()
+        return noModifications
     }
 
     override fun before(assignment: Assignment, parent: Node): Iterable<IAstModification> {
@@ -119,7 +119,7 @@ internal class StatementReorderer(val program: Program) : AstWalker() {
             }
         }
 
-        return emptyList()
+        return noModifications
     }
 
     private fun flattenStructAssignmentFromStructLiteral(structAssignment: Assignment, program: Program): List<Assignment> {

compiler/src/prog8/ast/processing/TypecastsAdder.kt

@@ -16,6 +16,8 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
      * (this includes function call arguments)
      */
 
+    private val noModifications = emptyList<IAstModification>()
+
     override fun after(expr: BinaryExpression, parent: Node): Iterable<IAstModification> {
         val leftDt = expr.left.inferType(program)
         val rightDt = expr.right.inferType(program)
@@ -32,7 +34,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
                 }
             }
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(assignment: Assignment, parent: Node): Iterable<IAstModification> {
@@ -72,7 +74,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
                 }
             }
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(functionCallStatement: FunctionCallStatement, parent: Node): Iterable<IAstModification> {
@@ -143,7 +145,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
         if(typecast.implicit && typecast.type in setOf(DataType.FLOAT, DataType.ARRAY_F)) {
             errors.warn("byte or word value implicitly converted to float. Suggestion: use explicit cast as float, a float number, or revert to integer arithmetic", typecast.position)
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(memread: DirectMemoryRead, parent: Node): Iterable<IAstModification> {
@@ -154,7 +156,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
                     ?: TypecastExpression(memread.addressExpression, DataType.UWORD, true, memread.addressExpression.position)
             return listOf(IAstModification.ReplaceNode(memread.addressExpression, typecast, memread))
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(memwrite: DirectMemoryWrite, parent: Node): Iterable<IAstModification> {
@@ -165,7 +167,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
                     ?: TypecastExpression(memwrite.addressExpression, DataType.UWORD, true, memwrite.addressExpression.position)
             return listOf(IAstModification.ReplaceNode(memwrite.addressExpression, typecast, memwrite))
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(structLv: StructLiteralValue, parent: Node): Iterable<IAstModification> {
@@ -210,7 +212,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
                 }
             }
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(returnStmt: Return, parent: Node): Iterable<IAstModification> {
@@ -221,7 +223,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
             if(subroutine.returntypes.size==1) {
                 val subReturnType = subroutine.returntypes.first()
                 if (returnValue.inferType(program).istype(subReturnType))
-                    return emptyList()
+                    return noModifications
                 if (returnValue is NumericLiteralValue) {
                     returnStmt.value = returnValue.cast(subroutine.returntypes.single())
                 } else {
@@ -232,6 +234,6 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
                 }
             }
         }
-        return emptyList()
+        return noModifications
     }
 }

compiler/src/prog8/ast/statements/AstStatements.kt

@@ -4,12 +4,10 @@ import prog8.ast.*
 import prog8.ast.base.*
 import prog8.ast.expressions.*
 import prog8.ast.processing.AstWalker
-import prog8.ast.processing.IAstModifyingVisitor
 import prog8.ast.processing.IAstVisitor
 
 
 sealed class Statement : Node {
-    abstract fun accept(visitor: IAstModifyingVisitor) : Statement
     abstract fun accept(visitor: IAstVisitor)
     abstract fun accept(visitor: AstWalker, parent: Node)
 
@@ -44,7 +42,6 @@ sealed class Statement : Node {
 class BuiltinFunctionStatementPlaceholder(val name: String, override val position: Position) : Statement() {
     override var parent: Node = ParentSentinel
     override fun linkParents(parent: Node) {}
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
     override fun definingScope(): INameScope = BuiltinFunctionScopePlaceholder
@@ -77,7 +74,6 @@ class Block(override val name: String,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -98,7 +94,6 @@ data class Directive(val directive: String, val args: List<DirectiveArg>, overri
     }
 
     override fun replaceChildNode(node: Node, replacement: Node) = throw FatalAstException("can't replace here")
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -121,7 +116,6 @@ data class Label(val name: String, override val position: Position) : Statement(
     }
 
     override fun replaceChildNode(node: Node, replacement: Node) = throw FatalAstException("can't replace here")
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -145,7 +139,6 @@ open class Return(var value: Expression?, override val position: Position) : Sta
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -155,7 +148,6 @@ open class Return(var value: Expression?, override val position: Position) : Sta
 }
 
 class ReturnFromIrq(override val position: Position) : Return(null, position) {
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
 
     override fun toString(): String {
@@ -173,7 +165,6 @@ class Continue(override val position: Position) : Statement() {
     }
 
     override fun replaceChildNode(node: Node, replacement: Node) = throw FatalAstException("can't replace here")
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -187,7 +178,6 @@ class Break(override val position: Position) : Statement() {
     }
 
     override fun replaceChildNode(node: Node, replacement: Node) = throw FatalAstException("can't replace here")
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -281,7 +271,6 @@ open class VarDecl(val type: VarDeclType,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -338,11 +327,8 @@ class ArrayIndex(var index: Expression, override val position: Position) : Node
         }
     }
 
-    fun accept(visitor: IAstModifyingVisitor) {
-        index = index.accept(visitor)
-    }
     fun accept(visitor: IAstVisitor) = index.accept(visitor)
-    fun accept(visitor: AstWalker, parent: Node) = index.accept(visitor, parent)
+    fun accept(visitor: AstWalker, parent: Node) = index.accept(visitor, this)
 
     override fun toString(): String {
         return("ArrayIndex($index, pos=$position)")
@@ -371,7 +357,6 @@ open class Assignment(var target: AssignTarget, var aug_op : String?, var value:
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -427,7 +412,6 @@ data class AssignTarget(val register: Register?,
         replacement.parent = this
     }
 
-    fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     fun accept(visitor: IAstVisitor) = visitor.visit(this)
     fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -538,7 +522,6 @@ class PostIncrDecr(var target: AssignTarget, val operator: String, override val
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -560,7 +543,6 @@ class Jump(val address: Int?,
     }
 
     override fun replaceChildNode(node: Node, replacement: Node) = throw FatalAstException("can't replace here")
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -593,7 +575,6 @@ class FunctionCallStatement(override var target: IdentifierReference,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -611,7 +592,6 @@ class InlineAssembly(val assembly: String, override val position: Position) : St
     }
 
     override fun replaceChildNode(node: Node, replacement: Node) = throw FatalAstException("can't replace here")
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -644,7 +624,6 @@ class AnonymousScope(override var statements: MutableList<Statement>,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -658,7 +637,6 @@ class NopStatement(override val position: Position): Statement() {
     }
 
     override fun replaceChildNode(node: Node, replacement: Node) = throw FatalAstException("can't replace here")
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -708,7 +686,6 @@ class Subroutine(override val name: String,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -765,7 +742,6 @@ class IfStatement(var condition: Expression,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -794,7 +770,6 @@ class BranchStatement(var condition: BranchCondition,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -825,7 +800,6 @@ class ForLoop(val loopRegister: Register?,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
@@ -861,7 +835,6 @@ class WhileLoop(var condition: Expression,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -881,7 +854,6 @@ class ForeverLoop(var body: AnonymousScope, override val position: Position) : S
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -907,7 +879,6 @@ class RepeatLoop(var body: AnonymousScope,
         replacement.parent = this
     }
 
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
@@ -952,7 +923,6 @@ class WhenStatement(var condition: Expression,
     }
 
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
 
@@ -978,7 +948,6 @@ class WhenChoice(var values: List<Expression>?,           // if null,  this is t
     }
 
     fun accept(visitor: IAstVisitor) = visitor.visit(this)
-    fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }
 
@@ -1006,7 +975,6 @@ class StructDecl(override val name: String,
         get() = this.statements.size
 
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
-    override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
     fun nameOfFirstMember() = (statements.first() as VarDecl).name
@@ -1031,6 +999,5 @@ class DirectMemoryWrite(var addressExpression: Expression, override val position
     }
 
     fun accept(visitor: IAstVisitor) = visitor.visit(this)
-    fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 }

compiler/src/prog8/compiler/BeforeAsmGenerationAstChanger.kt

@@ -11,12 +11,14 @@ import prog8.ast.statements.*
 
 internal class BeforeAsmGenerationAstChanger(val program: Program, val errors: ErrorReporter) : AstWalker() {
 
+    private val noModifications = emptyList<IAstModification>()
+
     override fun after(decl: VarDecl, parent: Node): Iterable<IAstModification> {
         if (decl.value == null && decl.type == VarDeclType.VAR && decl.datatype in NumericDatatypes) {
             // a numeric vardecl without an initial value is initialized with zero.
             decl.value = decl.zeroElementValue()
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(scope: AnonymousScope, parent: Node): Iterable<IAstModification> {
@@ -45,7 +47,7 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, val errors: E
                      decls.map { IAstModification.InsertFirst(it, sub) }    // move it up to the subroutine
             }
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(subroutine: Subroutine, parent: Node): Iterable<IAstModification> {
@@ -99,6 +101,6 @@ internal class BeforeAsmGenerationAstChanger(val program: Program, val errors: E
             }
         }
 
-        return emptyList()
+        return noModifications
     }
 }

compiler/src/prog8/compiler/Main.kt

@@ -144,7 +144,6 @@ private fun processAst(programAst: Program, errors: ErrorReporter, compilerOptio
     println("Processing...")
     programAst.checkIdentifiers(errors)
     errors.handle()
-    programAst.makeForeverLoops()
     programAst.constantFold(errors)
     errors.handle()
     programAst.removeNopsFlattenAnonScopes()
@@ -194,7 +193,7 @@ private fun writeAssembly(programAst: Program, errors: ErrorReporter, outputDir:
     programAst.processAstBeforeAsmGeneration(errors)
     errors.handle()
 
-    // printAst(programAst)        // TODO
+    // printAst(programAst)
 
     val assembly = CompilationTarget.asmGenerator(
             programAst,

compiler/src/prog8/compiler/target/c64/codegen/AssignmentAsmGen.kt

@@ -293,15 +293,15 @@ internal class AssignmentAsmGen(private val program: Program, private val errors
                 val sourceName = asmgen.asmIdentifierName(assign.value as IdentifierReference)
                 TODO("$assign")
             }
-            is AddressOf -> {
-                TODO("$assign")
-            }
             is DirectMemoryRead -> {
-                TODO("$assign")
+                val memory = (assign.value as DirectMemoryRead).addressExpression.constValue(program)!!.number.toHex()
+                asmgen.out(" lda  $memory |  sta  $hexAddr")
+                return true
             }
             is ArrayIndexedExpression -> {
                 TODO("$assign")
             }
+            is AddressOf -> throw AssemblyError("can't assign address to byte")
             else -> {
                 fallbackAssignment(assign)
                 return true
@@ -773,6 +773,21 @@ internal class AssignmentAsmGen(private val program: Program, private val errors
                     }
                 }
             }
+            DataType.STR -> {
+                val identifier = assign.value as? IdentifierReference
+                        ?: throw AssemblyError("string value assignment expects identifier value")
+                val sourceName = asmgen.asmIdentifierName(identifier)
+                asmgen.out("""
+                    lda  #<$targetName
+                    sta  ${C64Zeropage.SCRATCH_W1}
+                    lda  #>$targetName
+                    sta  ${C64Zeropage.SCRATCH_W1+1}
+                    lda  #<$sourceName
+                    ldy  #>$sourceName
+                    jsr  prog8_lib.strcpy
+                """)
+                return true
+            }
             else -> throw AssemblyError("assignment to identifier: invalid target datatype: $targetType")
         }
         return false

compiler/src/prog8/compiler/target/c64/codegen/ExpressionsAsmGen.kt

@@ -28,7 +28,7 @@ internal class ExpressionsAsmGen(private val program: Program, private val asmge
             is RegisterExpr -> translateExpression(expression)
             is IdentifierReference -> translateExpression(expression)
             is FunctionCall -> translateExpression(expression)
-            is ArrayLiteralValue, is StringLiteralValue -> throw AssemblyError("no asm gen for string/array assignment")
+            is ArrayLiteralValue, is StringLiteralValue -> throw AssemblyError("no asm gen for string/array literal value assignment - should have been replaced by a variable")
             is StructLiteralValue -> throw AssemblyError("struct literal value assignment should have been flattened")
             is RangeExpr -> throw AssemblyError("range expression should have been changed into array values")
         }

compiler/src/prog8/compiler/target/c64/codegen/ForLoopsAsmGen.kt

@@ -37,7 +37,7 @@ internal class ForLoopsAsmGen(private val program: Program, private val asmgen:
             is IdentifierReference -> {
                 translateForOverIterableVar(stmt, iterableDt.typeOrElse(DataType.STRUCT), stmt.iterable as IdentifierReference)
             }
-            else -> throw AssemblyError("can't iterate over ${stmt.iterable}")
+            else -> throw AssemblyError("can't iterate over ${stmt.iterable.javaClass} - should have been replaced by a variable")
         }
     }
 

compiler/src/prog8/functions/BuiltinFunctions.kt

@@ -87,7 +87,20 @@ val BuiltinFunctions = mapOf(
                             FParam("address", IterableDatatypes + DataType.UWORD),
                             FParam("numwords", setOf(DataType.UWORD)),
                             FParam("wordvalue", setOf(DataType.UWORD, DataType.WORD))), null),
-    "strlen"      to FSignature(true, listOf(FParam("string", setOf(DataType.STR))), DataType.UBYTE, ::builtinStrlen)
+    "strlen"      to FSignature(true, listOf(FParam("string", setOf(DataType.STR))), DataType.UBYTE, ::builtinStrlen),
+    "substr"      to FSignature(false, listOf(
+            FParam("source", IterableDatatypes + DataType.UWORD),
+            FParam("target", IterableDatatypes + DataType.UWORD),
+            FParam("start", setOf(DataType.UBYTE)),
+            FParam("length", setOf(DataType.UBYTE))), null),
+    "leftstr"      to FSignature(false, listOf(
+            FParam("source", IterableDatatypes + DataType.UWORD),
+            FParam("target", IterableDatatypes + DataType.UWORD),
+            FParam("length", setOf(DataType.UBYTE))), null),
+    "rightstr"      to FSignature(false, listOf(
+            FParam("source", IterableDatatypes + DataType.UWORD),
+            FParam("target", IterableDatatypes + DataType.UWORD),
+            FParam("length", setOf(DataType.UBYTE))), null)
 )
 
 fun builtinMax(array: List<Number>): Number = array.maxBy { it.toDouble() }!!
@@ -172,6 +185,7 @@ fun builtinFunctionReturnType(function: String, args: List<Expression>, program:
 
 
 class NotConstArgumentException: AstException("not a const argument to a built-in function")
+class CannotEvaluateException(func:String, msg: String): FatalAstException("cannot evaluate built-in function $func: $msg")
 
 
 private fun oneDoubleArg(args: List<Expression>, position: Position, program: Program, function: (arg: Double)->Number): NumericLiteralValue {
@@ -252,17 +266,22 @@ private fun builtinLen(args: List<Expression>, position: Position, program: Prog
         return NumericLiteralValue.optimalInteger((args[0] as ArrayLiteralValue).value.size, position)
     if(args[0] !is IdentifierReference)
         throw SyntaxError("len argument should be an identifier, but is ${args[0]}", position)
-    val target = (args[0] as IdentifierReference).targetVarDecl(program.namespace)!!
+    val target = (args[0] as IdentifierReference).targetVarDecl(program.namespace)
+            ?: throw CannotEvaluateException("len", "no target vardecl")
 
     return when(target.datatype) {
         DataType.ARRAY_UB, DataType.ARRAY_B, DataType.ARRAY_UW, DataType.ARRAY_W -> {
-            arraySize = target.arraysize!!.size()!!
+            arraySize = target.arraysize?.size()
+            if(arraySize==null)
+                throw CannotEvaluateException("len", "arraysize unknown")
             if(arraySize>256)
                 throw CompilerException("array length exceeds byte limit ${target.position}")
             NumericLiteralValue.optimalInteger(arraySize, args[0].position)
         }
         DataType.ARRAY_F -> {
-            arraySize = target.arraysize!!.size()!!
+            arraySize = target.arraysize?.size()
+            if(arraySize==null)
+                throw CannotEvaluateException("len", "arraysize unknown")
             if(arraySize>256)
                 throw CompilerException("array length exceeds byte limit ${target.position}")
             NumericLiteralValue.optimalInteger(arraySize, args[0].position)

compiler/src/prog8/optimizer/AssignmentTransformer.kt

@@ -14,6 +14,7 @@ import prog8.ast.statements.PostIncrDecr
 internal class AssignmentTransformer(val program: Program, val errors: ErrorReporter) : AstWalker() {
 
     var optimizationsDone: Int = 0
+    private val noModifications = emptyList<IAstModification>()
 
     override fun before(assignment: Assignment, parent: Node): Iterable<IAstModification> {
         // modify A = A + 5 back into augmented form A += 5 for easier code generation for optimized in-place assignments
@@ -27,7 +28,7 @@ internal class AssignmentTransformer(val program: Program, val errors: ErrorRepo
                     assignment.aug_op = binExpr.operator + "="
                     assignment.value.parent = assignment
                     optimizationsDone++
-                    return emptyList()
+                    return noModifications
                 }
             }
             assignment.aug_op = "setvalue"
@@ -151,6 +152,6 @@ internal class AssignmentTransformer(val program: Program, val errors: ErrorRepo
                 }
             }
         }
-        return emptyList()
+        return noModifications
     }
 }

compiler/src/prog8/optimizer/ConstantFoldingOptimizer.kt

@@ -1,25 +1,46 @@
 package prog8.optimizer
 
-import prog8.ast.IFunctionCall
+import prog8.ast.Node
 import prog8.ast.Program
 import prog8.ast.base.*
 import prog8.ast.expressions.*
-import prog8.ast.processing.IAstModifyingVisitor
+import prog8.ast.processing.AstWalker
+import prog8.ast.processing.IAstModification
 import prog8.ast.statements.*
 import prog8.compiler.target.CompilationTarget
-import prog8.functions.BuiltinFunctions
 
 
-// TODO implement using AstWalker instead of IAstModifyingVisitor
-internal class ConstantFoldingOptimizer(private val program: Program, private val errors: ErrorReporter) : IAstModifyingVisitor {
-    var optimizationsDone: Int = 0
+// First thing to do is replace all constant identifiers with their actual value,
+// and the array var initializer values and sizes.
+// This is needed because further constant optimizations depend on those.
+internal class ConstantIdentifierReplacer(private val program: Program, private val errors: ErrorReporter) : AstWalker() {
+    private val noModifications = emptyList<IAstModification>()
 
-    override fun visit(decl: VarDecl): Statement {
+    override fun after(identifier: IdentifierReference, parent: Node): Iterable<IAstModification> {
+        // replace identifiers that refer to const value, with the value itself
+        // if it's a simple type and if it's not a left hand side variable
+        if(identifier.parent is AssignTarget)
+            return noModifications
+        var forloop = identifier.parent as? ForLoop
+        if(forloop==null)
+            forloop = identifier.parent.parent as? ForLoop
+        if(forloop!=null && identifier===forloop.loopVar)
+            return noModifications
+
+        val cval = identifier.constValue(program) ?: return noModifications
+        return when (cval.type) {
+            in NumericDatatypes -> listOf(IAstModification.ReplaceNode(identifier, NumericLiteralValue(cval.type, cval.number, identifier.position), identifier.parent))
+            in PassByReferenceDatatypes -> throw FatalAstException("pass-by-reference type should not be considered a constant")
+            else -> noModifications
+        }
+    }
+
+    override fun before(decl: VarDecl, parent: Node): Iterable<IAstModification> {
         // the initializer value can't refer to the variable itself (recursive definition)
         // TODO: use call graph for this?
         if(decl.value?.referencesIdentifiers(decl.name) == true || decl.arraysize?.index?.referencesIdentifiers(decl.name) == true) {
             errors.err("recursive var declaration", decl.position)
-            return decl
+            return noModifications
         }
 
         if(decl.type==VarDeclType.CONST || decl.type==VarDeclType.VAR) {
@@ -28,15 +49,20 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
                     // for arrays that have no size specifier (or a non-constant one) attempt to deduce the size
                     val arrayval = decl.value as? ArrayLiteralValue
                     if(arrayval!=null) {
-                        decl.arraysize = ArrayIndex(NumericLiteralValue.optimalInteger(arrayval.value.size, decl.position), decl.position)
-                        optimizationsDone++
+                        return listOf(IAstModification.SetExpression(
+                                { decl.arraysize = ArrayIndex(it, decl.position) },
+                                NumericLiteralValue.optimalInteger(arrayval.value.size, decl.position),
+                                decl
+                        ))
                     }
                 }
                 else if(decl.arraysize?.size()==null) {
-                    val size = decl.arraysize!!.index.accept(this)
-                    if(size is NumericLiteralValue) {
-                        decl.arraysize = ArrayIndex(size, decl.position)
-                        optimizationsDone++
+                    val size = decl.arraysize!!.index.constValue(program)
+                    if(size!=null) {
+                        return listOf(IAstModification.SetExpression(
+                                { decl.arraysize = ArrayIndex(it, decl.position) },
+                                size, decl
+                        ))
                     }
                 }
             }
@@ -47,9 +73,7 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
                     val litval = decl.value as? NumericLiteralValue
                     if (litval!=null && litval.type in IntegerDatatypes) {
                         val newValue = NumericLiteralValue(DataType.FLOAT, litval.number.toDouble(), litval.position)
-                        decl.value = newValue
-                        optimizationsDone++
-                        return super.visit(decl)
+                        return listOf(IAstModification.ReplaceNode(decl.value!!, newValue, decl))
                     }
                 }
                 DataType.ARRAY_UB, DataType.ARRAY_B, DataType.ARRAY_UW, DataType.ARRAY_W -> {
@@ -63,23 +87,21 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
                         val constRange = rangeExpr.toConstantIntegerRange()
                         if(constRange!=null) {
                             val eltType = rangeExpr.inferType(program).typeOrElse(DataType.UBYTE)
-                            if(eltType in ByteDatatypes) {
-                                decl.value = ArrayLiteralValue(InferredTypes.InferredType.known(decl.datatype),
+                            val newValue = if(eltType in ByteDatatypes) {
+                                ArrayLiteralValue(InferredTypes.InferredType.known(decl.datatype),
                                         constRange.map { NumericLiteralValue(eltType, it.toShort(), decl.value!!.position) }.toTypedArray(),
                                         position = decl.value!!.position)
                             } else {
-                                decl.value = ArrayLiteralValue(InferredTypes.InferredType.known(decl.datatype),
+                                ArrayLiteralValue(InferredTypes.InferredType.known(decl.datatype),
                                         constRange.map { NumericLiteralValue(eltType, it, decl.value!!.position) }.toTypedArray(),
                                         position = decl.value!!.position)
                             }
-                            decl.value!!.linkParents(decl)
-                            optimizationsDone++
-                            return super.visit(decl)
+                            return listOf(IAstModification.ReplaceNode(decl.value!!, newValue, decl))
                         }
                     }
-                    if(numericLv!=null && numericLv.type== DataType.FLOAT)
+                    if(numericLv!=null && numericLv.type==DataType.FLOAT)
                         errors.err("arraysize requires only integers here", numericLv.position)
-                    val size = decl.arraysize?.size() ?: return decl
+                    val size = decl.arraysize?.size() ?: return noModifications
                     if (rangeExpr==null && numericLv!=null) {
                         // arraysize initializer is empty or a single int, and we know the size; create the arraysize.
                         val fillvalue = numericLv.number.toInt()
@@ -105,19 +127,27 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
                         // create the array itself, filled with the fillvalue.
                         val array = Array(size) {fillvalue}.map { NumericLiteralValue(ArrayElementTypes.getValue(decl.datatype), it, numericLv.position) as Expression}.toTypedArray()
                         val refValue = ArrayLiteralValue(InferredTypes.InferredType.known(decl.datatype), array, position = numericLv.position)
-                        decl.value = refValue
-                        refValue.parent=decl
-                        optimizationsDone++
-                        return super.visit(decl)
+                        return listOf(IAstModification.ReplaceNode(decl.value!!, refValue, decl))
                     }
                 }
                 DataType.ARRAY_F  -> {
-                    val size = decl.arraysize?.size() ?: return decl
+                    val size = decl.arraysize?.size() ?: return noModifications
                     val litval = decl.value as? NumericLiteralValue
-                    if(litval==null) {
-                        // there's no initialization value, but the size is known, so we're ok.
-                        return super.visit(decl)
-                    } else {
+                    val rangeExpr = decl.value as? RangeExpr
+                    if(rangeExpr!=null) {
+                        // convert the initializer range expression to an actual array of floats
+                        val declArraySize = decl.arraysize?.size()
+                        if(declArraySize!=null && declArraySize!=rangeExpr.size())
+                            errors.err("range expression size doesn't match declared array size", decl.value?.position!!)
+                        val constRange = rangeExpr.toConstantIntegerRange()
+                        if(constRange!=null) {
+                            val newValue = ArrayLiteralValue(InferredTypes.InferredType.known(DataType.ARRAY_F),
+                                        constRange.map { NumericLiteralValue(DataType.FLOAT, it.toDouble(), decl.value!!.position) }.toTypedArray(),
+                                        position = decl.value!!.position)
+                            return listOf(IAstModification.ReplaceNode(decl.value!!, newValue, decl))
+                        }
+                    }
+                    if(rangeExpr==null && litval!=null) {
                         // arraysize initializer is a single int, and we know the size.
                         val fillvalue = litval.number.toDouble()
                         if (fillvalue < CompilationTarget.machine.FLOAT_MAX_NEGATIVE || fillvalue > CompilationTarget.machine.FLOAT_MAX_POSITIVE)
@@ -126,10 +156,7 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
                             // create the array itself, filled with the fillvalue.
                             val array = Array(size) {fillvalue}.map { NumericLiteralValue(DataType.FLOAT, it, litval.position) as Expression}.toTypedArray()
                             val refValue = ArrayLiteralValue(InferredTypes.InferredType.known(DataType.ARRAY_F), array, position = litval.position)
-                            decl.value = refValue
-                            refValue.parent=decl
-                            optimizationsDone++
-                            return super.visit(decl)
+                            return listOf(IAstModification.ReplaceNode(decl.value!!, refValue, decl))
                         }
                     }
                 }
@@ -144,135 +171,69 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
         if(declValue!=null && decl.type==VarDeclType.VAR
                 && declValue is NumericLiteralValue && !declValue.inferType(program).istype(decl.datatype)) {
             // cast the numeric literal to the appropriate datatype of the variable
-            decl.value = declValue.cast(decl.datatype)
+            return listOf(IAstModification.ReplaceNode(decl.value!!, declValue.cast(decl.datatype), decl))
         }
 
-        return super.visit(decl)
+        return noModifications
     }
+}
 
-    /**
-     * replace identifiers that refer to const value, with the value itself (if it's a simple type)
-     */
-    override fun visit(identifier: IdentifierReference): Expression {
-        // don't replace when it's an assignment target or loop variable
-        if(identifier.parent is AssignTarget)
-            return identifier
-        var forloop = identifier.parent as? ForLoop
-        if(forloop==null)
-            forloop = identifier.parent.parent as? ForLoop
-        if(forloop!=null && identifier===forloop.loopVar)
-            return identifier
 
-        val cval = identifier.constValue(program) ?: return identifier
-        return when (cval.type) {
-            in NumericDatatypes -> {
-                val copy = NumericLiteralValue(cval.type, cval.number, identifier.position)
-                copy.parent = identifier.parent
-                copy
-            }
-            in PassByReferenceDatatypes -> throw FatalAstException("pass-by-reference type should not be considered a constant")
-            else -> identifier
-        }
-    }
+internal class ConstantFoldingOptimizer(private val program: Program, private val errors: ErrorReporter) : AstWalker() {
+    private val noModifications = emptyList<IAstModification>()
 
-    override fun visit(functionCall: FunctionCall): Expression {
-        super.visit(functionCall)
-        typeCastConstArguments(functionCall)
-        return functionCall.constValue(program) ?: functionCall
-    }
-
-    override fun visit(functionCallStatement: FunctionCallStatement): Statement {
-        super.visit(functionCallStatement)
-        typeCastConstArguments(functionCallStatement)
-        return functionCallStatement
-    }
-
-    private fun typeCastConstArguments(functionCall: IFunctionCall) {
-        if(functionCall.target.nameInSource.size==1) {
-            val builtinFunction = BuiltinFunctions[functionCall.target.nameInSource.single()]
-            if(builtinFunction!=null) {
-                // match the arguments of a builtin function signature.
-                for(arg in functionCall.args.withIndex().zip(builtinFunction.parameters)) {
-                    val possibleDts = arg.second.possibleDatatypes
-                    val argConst = arg.first.value.constValue(program)
-                    if(argConst!=null && argConst.type !in possibleDts) {
-                        val convertedValue = argConst.cast(possibleDts.first())
-                        functionCall.args[arg.first.index] = convertedValue
-                        optimizationsDone++
-                    }
-                }
-                return
-            }
-        }
-        // match the arguments of a subroutine.
-        val subroutine = functionCall.target.targetSubroutine(program.namespace)
-        if(subroutine!=null) {
-            // if types differ, try to typecast constant arguments to the function call to the desired data type of the parameter
-            for(arg in functionCall.args.withIndex().zip(subroutine.parameters)) {
-                val expectedDt = arg.second.type
-                val argConst = arg.first.value.constValue(program)
-                if(argConst!=null && argConst.type!=expectedDt) {
-                    val convertedValue = argConst.cast(expectedDt)
-                    functionCall.args[arg.first.index] = convertedValue
-                    optimizationsDone++
-                }
-            }
-        }
-    }
-
-    override fun visit(memread: DirectMemoryRead): Expression {
+    override fun before(memread: DirectMemoryRead, parent: Node): Iterable<IAstModification> {
         // @( &thing )  -->  thing
         val addrOf = memread.addressExpression as? AddressOf
-        if(addrOf!=null)
-            return super.visit(addrOf.identifier)
-        return super.visit(memread)
+        return if(addrOf!=null)
+            listOf(IAstModification.ReplaceNode(memread, addrOf.identifier, parent))
+        else
+            noModifications
     }
 
-    /**
-     * Try to accept a unary prefix expression.
-     * Compile-time constant sub expressions will be evaluated on the spot.
-     * For instance, the expression for "- 4.5" will be optimized into the float literal -4.5
-     */
-    override fun visit(expr: PrefixExpression): Expression {
-        val prefixExpr=super.visit(expr)
-        if(prefixExpr !is PrefixExpression)
-            return prefixExpr
-
-        val subexpr = prefixExpr.expression
+    override fun after(expr: PrefixExpression, parent: Node): Iterable<IAstModification> {
+        // Try to turn a unary prefix expression into a single constant value.
+        // Compile-time constant sub expressions will be evaluated on the spot.
+        // For instance, the expression for "- 4.5" will be optimized into the float literal -4.5
+        val subexpr = expr.expression
         if (subexpr is NumericLiteralValue) {
             // accept prefixed literal values (such as -3, not true)
-            return when (prefixExpr.operator) {
-                "+" -> subexpr
+            return when (expr.operator) {
+                "+" -> listOf(IAstModification.ReplaceNode(expr, subexpr, parent))
                 "-" -> when (subexpr.type) {
                     in IntegerDatatypes -> {
-                        optimizationsDone++
-                        NumericLiteralValue.optimalNumeric(-subexpr.number.toInt(), subexpr.position)
+                        listOf(IAstModification.ReplaceNode(expr,
+                                NumericLiteralValue.optimalNumeric(-subexpr.number.toInt(), subexpr.position),
+                                parent))
                     }
                     DataType.FLOAT -> {
-                        optimizationsDone++
-                        NumericLiteralValue(DataType.FLOAT, -subexpr.number.toDouble(), subexpr.position)
+                        listOf(IAstModification.ReplaceNode(expr,
+                                NumericLiteralValue(DataType.FLOAT, -subexpr.number.toDouble(), subexpr.position),
+                                parent))
                     }
                     else -> throw ExpressionError("can only take negative of int or float", subexpr.position)
                 }
                 "~" -> when (subexpr.type) {
                     in IntegerDatatypes -> {
-                        optimizationsDone++
-                        NumericLiteralValue.optimalNumeric(subexpr.number.toInt().inv(), subexpr.position)
+                        listOf(IAstModification.ReplaceNode(expr,
+                                NumericLiteralValue.optimalNumeric(subexpr.number.toInt().inv(), subexpr.position),
+                                parent))
                     }
                     else -> throw ExpressionError("can only take bitwise inversion of int", subexpr.position)
                 }
                 "not" -> {
-                    optimizationsDone++
-                    NumericLiteralValue.fromBoolean(subexpr.number.toDouble() == 0.0, subexpr.position)
+                    listOf(IAstModification.ReplaceNode(expr,
+                            NumericLiteralValue.fromBoolean(subexpr.number.toDouble() == 0.0, subexpr.position),
+                            parent))
                 }
-                else -> throw ExpressionError(prefixExpr.operator, subexpr.position)
+                else -> throw ExpressionError(expr.operator, subexpr.position)
             }
         }
-        return prefixExpr
+        return noModifications
     }
 
     /**
-     * Try to accept a binary expression.
+     * Try to constfold a binary expression.
      * Compile-time constant sub expressions will be evaluated on the spot.
      * For instance, "9 * (4 + 2)" will be optimized into the integer literal 54.
      *
@@ -288,13 +249,7 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
      *        (X / c1) * c2  ->  X / (c2/c1)
      *        (X + c1) - c2  ->  X + (c1-c2)
      */
-    override fun visit(expr: BinaryExpression): Expression {
-        super.visit(expr)
-
-        if(expr.left is StringLiteralValue || expr.left is ArrayLiteralValue
-                || expr.right is StringLiteralValue || expr.right is ArrayLiteralValue)
-            throw FatalAstException("binexpr with reference litval instead of numeric")
-
+    override fun after(expr: BinaryExpression, parent: Node): Iterable<IAstModification> {
         val leftconst = expr.left.constValue(program)
         val rightconst = expr.right.constValue(program)
 
@@ -308,218 +263,62 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
             val subrightconst = subExpr.right.constValue(program)
             if ((subleftconst != null && subrightconst == null) || (subleftconst==null && subrightconst!=null)) {
                 // try reordering.
-                return groupTwoConstsTogether(expr, subExpr,
+                val change = groupTwoConstsTogether(expr, subExpr,
                         leftconst != null, rightconst != null,
                         subleftconst != null, subrightconst != null)
+                return change?.let { listOf(it) } ?: noModifications
             }
         }
 
         // const fold when both operands are a const
-        return when {
-            leftconst != null && rightconst != null -> {
-                optimizationsDone++
-                val evaluator = ConstExprEvaluator()
-                evaluator.evaluate(leftconst, expr.operator, rightconst)
-            }
-
-            else -> expr
+        if(leftconst != null && rightconst != null) {
+            val evaluator = ConstExprEvaluator()
+            return listOf(IAstModification.ReplaceNode(
+                    expr,
+                    evaluator.evaluate(leftconst, expr.operator, rightconst),
+                    parent
+            ))
         }
+
+        return noModifications
     }
 
-    private fun groupTwoConstsTogether(expr: BinaryExpression,
-                                       subExpr: BinaryExpression,
-                                       leftIsConst: Boolean,
-                                       rightIsConst: Boolean,
-                                       subleftIsConst: Boolean,
-                                       subrightIsConst: Boolean): Expression
-    {
-        // todo: this implements only a small set of possible reorderings at this time
-        if(expr.operator==subExpr.operator) {
-            // both operators are the isSameAs.
-            // If + or *,  we can simply swap the const of expr and Var in subexpr.
-            if(expr.operator=="+" || expr.operator=="*") {
-                if(leftIsConst) {
-                    if(subleftIsConst)
-                        expr.left = subExpr.right.also { subExpr.right = expr.left }
-                    else
-                        expr.left = subExpr.left.also { subExpr.left = expr.left }
-                } else {
-                    if(subleftIsConst)
-                        expr.right = subExpr.right.also {subExpr.right = expr.right }
-                    else
-                        expr.right = subExpr.left.also { subExpr.left = expr.right }
-                }
-                optimizationsDone++
-                return expr
-            }
+    override fun after(array: ArrayLiteralValue, parent: Node): Iterable<IAstModification> {
+        // because constant folding can result in arrays that are now suddenly capable
+        // of telling the type of all their elements (for instance, when they contained -2 which
+        // was a prefix expression earlier), we recalculate the array's datatype.
+        if(array.type.isKnown)
+            return noModifications
 
-            // If - or /,  we simetimes must reorder more, and flip operators (- -> +, / -> *)
-            if(expr.operator=="-" || expr.operator=="/") {
-                optimizationsDone++
-                if(leftIsConst) {
-                    return if(subleftIsConst) {
-                        val tmp = subExpr.right
-                        subExpr.right = subExpr.left
-                        subExpr.left = expr.left
-                        expr.left = tmp
-                        expr.operator = if(expr.operator=="-") "+" else "*"
-                        expr
-                    } else
-                        BinaryExpression(
-                                BinaryExpression(expr.left, if (expr.operator == "-") "+" else "*", subExpr.right, subExpr.position),
-                                expr.operator, subExpr.left, expr.position)
-                } else {
-                    return if(subleftIsConst) {
-                        expr.right = subExpr.right.also { subExpr.right = expr.right }
-                        expr
-                    } else
-                        BinaryExpression(
-                                subExpr.left, expr.operator,
-                                BinaryExpression(expr.right, if (expr.operator == "-") "+" else "*", subExpr.right, subExpr.position),
-                                expr.position)
-                }
+        // if the array literalvalue is inside an array vardecl, take the type from that
+        // otherwise infer it from the elements of the array
+        val vardeclType = (array.parent as? VarDecl)?.datatype
+        if(vardeclType!=null) {
+            val newArray = array.cast(vardeclType)
+            if (newArray != null && newArray != array)
+                return listOf(IAstModification.ReplaceNode(array, newArray, parent))
+        } else {
+            val arrayDt = array.guessDatatype(program)
+            if (arrayDt.isKnown) {
+                val newArray = array.cast(arrayDt.typeOrElse(DataType.STRUCT))
+                if (newArray != null && newArray != array)
+                    return listOf(IAstModification.ReplaceNode(array, newArray, parent))
             }
-            return expr
-
         }
+
+        return noModifications
+    }
+
+    override fun after(functionCall: FunctionCall, parent: Node): Iterable<IAstModification> {
+        // the args of a fuction are constfolded via recursion already.
+        val constvalue = functionCall.constValue(program)
+        return if(constvalue!=null)
+            listOf(IAstModification.ReplaceNode(functionCall, constvalue, parent))
         else
-        {
-
-            if(expr.operator=="/" && subExpr.operator=="*") {
-                optimizationsDone++
-                if(leftIsConst) {
-                    return if(subleftIsConst) {
-                        // C1/(C2*V) -> (C1/C2)/V
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "/", subExpr.left, subExpr.position),
-                                "/",
-                                subExpr.right, expr.position)
-                    } else {
-                        // C1/(V*C2) -> (C1/C2)/V
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "/", subExpr.right, subExpr.position),
-                                "/",
-                                subExpr.left, expr.position)
-                    }
-                } else {
-                    return if(subleftIsConst) {
-                        // (C1*V)/C2 -> (C1/C2)*V
-                        BinaryExpression(
-                                BinaryExpression(subExpr.left, "/", expr.right, subExpr.position),
-                                "*",
-                                subExpr.right, expr.position)
-                    } else {
-                        // (V*C1)/C2 -> (C1/C2)*V
-                        BinaryExpression(
-                                BinaryExpression(subExpr.right, "/", expr.right, subExpr.position),
-                                "*",
-                                subExpr.left, expr.position)
-                    }
-                }
-            }
-            else if(expr.operator=="*" && subExpr.operator=="/") {
-                optimizationsDone++
-                if(leftIsConst) {
-                    return if(subleftIsConst) {
-                        // C1*(C2/V) -> (C1*C2)/V
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "*", subExpr.left, subExpr.position),
-                                "/",
-                                subExpr.right, expr.position)
-                    } else {
-                        // C1*(V/C2) -> (C1/C2)*V
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "/", subExpr.right, subExpr.position),
-                                "*",
-                                subExpr.left, expr.position)
-                    }
-                } else {
-                    return if(subleftIsConst) {
-                        // (C1/V)*C2 -> (C1*C2)/V
-                        BinaryExpression(
-                                BinaryExpression(subExpr.left, "*", expr.right, subExpr.position),
-                                "/",
-                                subExpr.right, expr.position)
-                    } else {
-                        // (V/C1)*C2 -> (C1/C2)*V
-                        BinaryExpression(
-                                BinaryExpression(expr.right, "/", subExpr.right, subExpr.position),
-                                "*",
-                                subExpr.left, expr.position)
-                    }
-                }
-            }
-            else if(expr.operator=="+" && subExpr.operator=="-") {
-                optimizationsDone++
-                if(leftIsConst){
-                    return if(subleftIsConst){
-                        // c1+(c2-v)  ->  (c1+c2)-v
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "+", subExpr.left, subExpr.position),
-                                "-",
-                                subExpr.right, expr.position)
-                    } else {
-                        // c1+(v-c2)  ->  v+(c1-c2)
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "-", subExpr.right, subExpr.position),
-                                "+",
-                                subExpr.left, expr.position)
-                    }
-                } else {
-                    return if(subleftIsConst) {
-                        // (c1-v)+c2  ->  (c1+c2)-v
-                        BinaryExpression(
-                                BinaryExpression(subExpr.left, "+", expr.right, subExpr.position),
-                                "-",
-                                subExpr.right, expr.position)
-                    } else {
-                        // (v-c1)+c2  ->  v+(c2-c1)
-                        BinaryExpression(
-                                BinaryExpression(expr.right, "-", subExpr.right, subExpr.position),
-                                "+",
-                                subExpr.left, expr.position)
-                    }
-                }
-            }
-            else if(expr.operator=="-" && subExpr.operator=="+") {
-                optimizationsDone++
-                if(leftIsConst) {
-                    return if(subleftIsConst) {
-                        // c1-(c2+v)  ->  (c1-c2)-v
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "-", subExpr.left, subExpr.position),
-                                "-",
-                                subExpr.right, expr.position)
-                    } else {
-                        // c1-(v+c2)  ->  (c1-c2)-v
-                        BinaryExpression(
-                                BinaryExpression(expr.left, "-", subExpr.right, subExpr.position),
-                                "-",
-                                subExpr.left, expr.position)
-                    }
-                } else {
-                    return if(subleftIsConst) {
-                        // (c1+v)-c2  ->  v+(c1-c2)
-                        BinaryExpression(
-                                BinaryExpression(subExpr.left, "-", expr.right, subExpr.position),
-                                "+",
-                                subExpr.right, expr.position)
-                    } else {
-                        // (v+c1)-c2  ->  v+(c1-c2)
-                        BinaryExpression(
-                                BinaryExpression(subExpr.right, "-", expr.right, subExpr.position),
-                                "+",
-                                subExpr.left, expr.position)
-                    }
-                }
-            }
-
-            return expr
-        }
+            noModifications
     }
 
-    override fun visit(forLoop: ForLoop): Statement {
-
+    override fun after(forLoop: ForLoop, parent: Node): Iterable<IAstModification> {
         fun adjustRangeDt(rangeFrom: NumericLiteralValue, targetDt: DataType, rangeTo: NumericLiteralValue, stepLiteral: NumericLiteralValue?, range: RangeExpr): RangeExpr {
             val newFrom: NumericLiteralValue
             val newTo: NumericLiteralValue
@@ -537,87 +336,259 @@ internal class ConstantFoldingOptimizer(private val program: Program, private va
             return RangeExpr(newFrom, newTo, newStep, range.position)
         }
 
-        val forLoop2 = super.visit(forLoop) as ForLoop
-
-        // check if we need to adjust an array literal to the loop variable's datatype
-        val array = forLoop2.iterable as? ArrayLiteralValue
-        if(array!=null) {
-            val loopvarDt: DataType = when {
-                forLoop.loopVar!=null -> forLoop.loopVar!!.inferType(program).typeOrElse(DataType.UBYTE)
-                forLoop.loopRegister!=null -> DataType.UBYTE
-                else -> throw FatalAstException("weird for loop")
-            }
-
-            val arrayType = when(loopvarDt) {
-                DataType.UBYTE -> DataType.ARRAY_UB
-                DataType.BYTE -> DataType.ARRAY_B
-                DataType.UWORD -> DataType.ARRAY_UW
-                DataType.WORD -> DataType.ARRAY_W
-                DataType.FLOAT -> DataType.ARRAY_F
-                else -> throw FatalAstException("invalid array elt type")
-            }
-            val array2 = array.cast(arrayType)
-            if(array2!=null && array2!==array) {
-                forLoop2.iterable = array2
-                array2.linkParents(forLoop2)
-            }
-        }
-
         // adjust the datatype of a range expression in for loops to the loop variable.
-        val iterableRange = forLoop2.iterable as? RangeExpr ?: return forLoop2
+        val iterableRange = forLoop.iterable as? RangeExpr ?: return noModifications
         val rangeFrom = iterableRange.from as? NumericLiteralValue
         val rangeTo = iterableRange.to as? NumericLiteralValue
-        if(rangeFrom==null || rangeTo==null) return forLoop2
+        if(rangeFrom==null || rangeTo==null) return noModifications
 
-        val loopvar = forLoop2.loopVar?.targetVarDecl(program.namespace)
+        val loopvar = forLoop.loopVar?.targetVarDecl(program.namespace)
         if(loopvar!=null) {
             val stepLiteral = iterableRange.step as? NumericLiteralValue
             when(loopvar.datatype) {
                 DataType.UBYTE -> {
                     if(rangeFrom.type!= DataType.UBYTE) {
                         // attempt to translate the iterable into ubyte values
-                        forLoop2.iterable = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        val newIter = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        return listOf(IAstModification.ReplaceNode(forLoop.iterable, newIter, forLoop))
                     }
                 }
                 DataType.BYTE -> {
                     if(rangeFrom.type!= DataType.BYTE) {
                         // attempt to translate the iterable into byte values
-                        forLoop2.iterable = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        val newIter = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        return listOf(IAstModification.ReplaceNode(forLoop.iterable, newIter, forLoop))
                     }
                 }
                 DataType.UWORD -> {
                     if(rangeFrom.type!= DataType.UWORD) {
                         // attempt to translate the iterable into uword values
-                        forLoop2.iterable = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        val newIter = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        return listOf(IAstModification.ReplaceNode(forLoop.iterable, newIter, forLoop))
                     }
                 }
                 DataType.WORD -> {
                     if(rangeFrom.type!= DataType.WORD) {
                         // attempt to translate the iterable into word values
-                        forLoop2.iterable = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        val newIter = adjustRangeDt(rangeFrom, loopvar.datatype, rangeTo, stepLiteral, iterableRange)
+                        return listOf(IAstModification.ReplaceNode(forLoop.iterable, newIter, forLoop))
                     }
                 }
                 else -> throw FatalAstException("invalid loopvar datatype $loopvar")
             }
         }
-        return forLoop2
+
+        return noModifications
     }
 
-    override fun visit(arrayLiteral: ArrayLiteralValue): Expression {
-        // because constant folding can result in arrays that are now suddenly capable
-        // of telling the type of all their elements (for instance, when they contained -2 which
-        // was a prefix expression earlier), we recalculate the array's datatype.
-        val array = super.visit(arrayLiteral)
-        if(array is ArrayLiteralValue) {
-            if(array.type.isKnown)
-                return array
-            val arrayDt = array.guessDatatype(program)
-            if(arrayDt.isKnown) {
-                val newArray = arrayLiteral.cast(arrayDt.typeOrElse(DataType.STRUCT))
-                if(newArray!=null)
-                    return newArray
-            }
+    private class ShuffleOperands(val expr: BinaryExpression,
+                                  val exprOperator: String?,
+                                  val subExpr: BinaryExpression,
+                                  val newExprLeft: Expression?,
+                                  val newExprRight: Expression?,
+                                  val newSubexprLeft: Expression?,
+                                  val newSubexprRight: Expression?
+                                  ): IAstModification {
+        override fun perform() {
+            if(exprOperator!=null) expr.operator = exprOperator
+            if(newExprLeft!=null) expr.left = newExprLeft
+            if(newExprRight!=null) expr.right = newExprRight
+            if(newSubexprLeft!=null) subExpr.left = newSubexprLeft
+            if(newSubexprRight!=null) subExpr.right = newSubexprRight
         }
-        return array
     }
+
+    private fun groupTwoConstsTogether(expr: BinaryExpression,
+                                       subExpr: BinaryExpression,
+                                       leftIsConst: Boolean,
+                                       rightIsConst: Boolean,
+                                       subleftIsConst: Boolean,
+                                       subrightIsConst: Boolean): IAstModification?
+    {
+        // todo: this implements only a small set of possible reorderings at this time
+        if(expr.operator==subExpr.operator) {
+            // both operators are the same.
+            // If + or *,  we can simply shuffle the const operands around to optimize.
+            if(expr.operator=="+" || expr.operator=="*") {
+                return if(leftIsConst) {
+                    if(subleftIsConst)
+                        ShuffleOperands(expr, null, subExpr, subExpr.right, null, null, expr.left)
+                    else
+                        ShuffleOperands(expr, null, subExpr, subExpr.left, null, expr.left, null)
+                } else {
+                    if(subleftIsConst)
+                        ShuffleOperands(expr, null, subExpr, null, subExpr.right, null, expr.right)
+                    else
+                        ShuffleOperands(expr, null, subExpr, null, subExpr.left, expr.right, null)
+                }
+            }
+
+            // If - or /,  we simetimes must reorder more, and flip operators (- -> +, / -> *)
+            if(expr.operator=="-" || expr.operator=="/") {
+                if(leftIsConst) {
+                    return if (subleftIsConst) {
+                        ShuffleOperands(expr, if (expr.operator == "-") "+" else "*", subExpr, subExpr.right, null, expr.left, subExpr.left)
+                    } else {
+                        IAstModification.ReplaceNode(expr,
+                                BinaryExpression(
+                                        BinaryExpression(expr.left, if (expr.operator == "-") "+" else "*", subExpr.right, subExpr.position),
+                                        expr.operator, subExpr.left, expr.position),
+                                expr.parent)
+                    }
+                } else {
+                    return if(subleftIsConst) {
+                        return ShuffleOperands(expr, null, subExpr, null, subExpr.right, null, expr.right)
+                    } else {
+                        IAstModification.ReplaceNode(expr,
+                                BinaryExpression(
+                                        subExpr.left, expr.operator,
+                                        BinaryExpression(expr.right, if (expr.operator == "-") "+" else "*", subExpr.right, subExpr.position),
+                                        expr.position),
+                                expr.parent)
+                    }
+                }
+            }
+            return null
+
+        }
+        else
+        {
+
+            if(expr.operator=="/" && subExpr.operator=="*") {
+                if(leftIsConst) {
+                    val change = if(subleftIsConst) {
+                        // C1/(C2*V) -> (C1/C2)/V
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "/", subExpr.left, subExpr.position),
+                                "/",
+                                subExpr.right, expr.position)
+                    } else {
+                        // C1/(V*C2) -> (C1/C2)/V
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "/", subExpr.right, subExpr.position),
+                                "/",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                } else {
+                    val change = if(subleftIsConst) {
+                        // (C1*V)/C2 -> (C1/C2)*V
+                        BinaryExpression(
+                                BinaryExpression(subExpr.left, "/", expr.right, subExpr.position),
+                                "*",
+                                subExpr.right, expr.position)
+                    } else {
+                        // (V*C1)/C2 -> (C1/C2)*V
+                        BinaryExpression(
+                                BinaryExpression(subExpr.right, "/", expr.right, subExpr.position),
+                                "*",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                }
+            }
+            else if(expr.operator=="*" && subExpr.operator=="/") {
+                if(leftIsConst) {
+                    val change = if(subleftIsConst) {
+                        // C1*(C2/V) -> (C1*C2)/V
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "*", subExpr.left, subExpr.position),
+                                "/",
+                                subExpr.right, expr.position)
+                    } else {
+                        // C1*(V/C2) -> (C1/C2)*V
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "/", subExpr.right, subExpr.position),
+                                "*",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                } else {
+                    val change = if(subleftIsConst) {
+                        // (C1/V)*C2 -> (C1*C2)/V
+                        BinaryExpression(
+                                BinaryExpression(subExpr.left, "*", expr.right, subExpr.position),
+                                "/",
+                                subExpr.right, expr.position)
+                    } else {
+                        // (V/C1)*C2 -> (C1/C2)*V
+                        BinaryExpression(
+                                BinaryExpression(expr.right, "/", subExpr.right, subExpr.position),
+                                "*",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                }
+            }
+            else if(expr.operator=="+" && subExpr.operator=="-") {
+                if(leftIsConst){
+                    val change = if(subleftIsConst){
+                        // c1+(c2-v)  ->  (c1+c2)-v
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "+", subExpr.left, subExpr.position),
+                                "-",
+                                subExpr.right, expr.position)
+                    } else {
+                        // c1+(v-c2)  ->  v+(c1-c2)
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "-", subExpr.right, subExpr.position),
+                                "+",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                } else {
+                    val change = if(subleftIsConst) {
+                        // (c1-v)+c2  ->  (c1+c2)-v
+                        BinaryExpression(
+                                BinaryExpression(subExpr.left, "+", expr.right, subExpr.position),
+                                "-",
+                                subExpr.right, expr.position)
+                    } else {
+                        // (v-c1)+c2  ->  v+(c2-c1)
+                        BinaryExpression(
+                                BinaryExpression(expr.right, "-", subExpr.right, subExpr.position),
+                                "+",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                }
+            }
+            else if(expr.operator=="-" && subExpr.operator=="+") {
+                if(leftIsConst) {
+                    val change = if(subleftIsConst) {
+                        // c1-(c2+v)  ->  (c1-c2)-v
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "-", subExpr.left, subExpr.position),
+                                "-",
+                                subExpr.right, expr.position)
+                    } else {
+                        // c1-(v+c2)  ->  (c1-c2)-v
+                        BinaryExpression(
+                                BinaryExpression(expr.left, "-", subExpr.right, subExpr.position),
+                                "-",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                } else {
+                    val change = if(subleftIsConst) {
+                        // (c1+v)-c2  ->  v+(c1-c2)
+                        BinaryExpression(
+                                BinaryExpression(subExpr.left, "-", expr.right, subExpr.position),
+                                "+",
+                                subExpr.right, expr.position)
+                    } else {
+                        // (v+c1)-c2  ->  v+(c1-c2)
+                        BinaryExpression(
+                                BinaryExpression(subExpr.right, "-", expr.right, subExpr.position),
+                                "+",
+                                subExpr.left, expr.position)
+                    }
+                    return IAstModification.ReplaceNode(expr, change, expr.parent)
+                }
+            }
+
+            return null
+        }
+    }
+
 }

compiler/src/prog8/optimizer/ExpressionSimplifier.kt

@@ -22,11 +22,12 @@ import kotlin.math.pow
 internal class ExpressionSimplifier(private val program: Program) : AstWalker() {
     private val powersOfTwo = (1..16).map { (2.0).pow(it) }.toSet()
     private val negativePowersOfTwo = powersOfTwo.map { -it }.toSet()
+    private val noModifications = emptyList<IAstModification>()
 
     override fun after(assignment: Assignment, parent: Node): Iterable<IAstModification> {
         if (assignment.aug_op != null)
             throw FatalAstException("augmented assignments should have been converted to normal assignments before this optimizer: $assignment")
-        return emptyList()
+        return noModifications
     }
 
     override fun after(typecast: TypecastExpression, parent: Node): Iterable<IAstModification> {
@@ -82,10 +83,10 @@ internal class ExpressionSimplifier(private val program: Program) : AstWalker()
                     if (newExpr != null)
                         return listOf(IAstModification.ReplaceNode(expr, newExpr, parent))
                 }
-                else -> return emptyList()
+                else -> return noModifications
             }
         }
-        return emptyList()
+        return noModifications
     }
 
     override fun after(expr: BinaryExpression, parent: Node): Iterable<IAstModification> {
@@ -297,7 +298,7 @@ internal class ExpressionSimplifier(private val program: Program) : AstWalker()
         if(newExpr != null)
             return listOf(IAstModification.ReplaceNode(expr, newExpr, parent))
 
-        return emptyList()
+        return noModifications
     }
 
     private fun determineY(x: Expression, subBinExpr: BinaryExpression): Expression? {

compiler/src/prog8/optimizer/Extensions.kt

@@ -5,12 +5,21 @@ import prog8.ast.base.ErrorReporter
 
 
 internal fun Program.constantFold(errors: ErrorReporter) {
-    val optimizer = ConstantFoldingOptimizer(this, errors)
-    optimizer.visit(this)
+    val replacer = ConstantIdentifierReplacer(this, errors)
+    replacer.visit(this)
+    if(errors.isEmpty()) {
+        replacer.applyModifications()
 
-    while(errors.isEmpty() && optimizer.optimizationsDone>0) {
-        optimizer.optimizationsDone = 0
+        val optimizer = ConstantFoldingOptimizer(this, errors)
         optimizer.visit(this)
+        while (errors.isEmpty() && optimizer.applyModifications() > 0) {
+            optimizer.visit(this)
+        }
+
+        if(errors.isEmpty()) {
+            replacer.visit(this)
+            replacer.applyModifications()
+        }
     }
 
     if(errors.isEmpty())
@@ -21,9 +30,11 @@ internal fun Program.constantFold(errors: ErrorReporter) {
 internal fun Program.optimizeStatements(errors: ErrorReporter): Int {
     val optimizer = StatementOptimizer(this, errors)
     optimizer.visit(this)
+    val optimizationCount = optimizer.applyModifications()
+
     modules.forEach { it.linkParents(this.namespace) }   // re-link in final configuration
 
-    return optimizer.optimizationsDone
+    return optimizationCount
 }
 
 internal fun Program.simplifyExpressions() : Int {

compiler/src/prog8/optimizer/StatementOptimizer.kt

@@ -1,10 +1,12 @@
 package prog8.optimizer
 
 import prog8.ast.INameScope
+import prog8.ast.Node
 import prog8.ast.Program
 import prog8.ast.base.*
 import prog8.ast.expressions.*
-import prog8.ast.processing.IAstModifyingVisitor
+import prog8.ast.processing.AstWalker
+import prog8.ast.processing.IAstModification
 import prog8.ast.processing.IAstVisitor
 import prog8.ast.statements.*
 import prog8.compiler.target.CompilationTarget
@@ -18,50 +20,34 @@ import kotlin.math.floor
 */
 
 
-// TODO implement using AstWalker instead of IAstModifyingVisitor
 internal class StatementOptimizer(private val program: Program,
-                                  private val errors: ErrorReporter) : IAstModifyingVisitor {
-    var optimizationsDone: Int = 0
-        private set
+                                  private val errors: ErrorReporter) : AstWalker() {
 
-    private val pureBuiltinFunctions = BuiltinFunctions.filter { it.value.pure }
+    private val noModifications = emptyList<IAstModification>()
     private val callgraph = CallGraph(program)
-    private val vardeclsToRemove = mutableListOf<VarDecl>()
+    private val pureBuiltinFunctions = BuiltinFunctions.filter { it.value.pure }
 
-    override fun visit(program: Program) {
-        super.visit(program)
-
-        for(decl in vardeclsToRemove) {
-            decl.definingScope().remove(decl)
-        }
-    }
-
-    override fun visit(block: Block): Statement {
+    override fun after(block: Block, parent: Node): Iterable<IAstModification> {
         if("force_output" !in block.options()) {
             if (block.containsNoCodeNorVars()) {
-                optimizationsDone++
                 errors.warn("removing empty block '${block.name}'", block.position)
-                return NopStatement.insteadOf(block)
+                return listOf(IAstModification.Remove(block, parent))
             }
 
             if (block !in callgraph.usedSymbols) {
-                optimizationsDone++
                 errors.warn("removing unused block '${block.name}'", block.position)
-                return NopStatement.insteadOf(block)  // remove unused block
+                return listOf(IAstModification.Remove(block, parent))
             }
         }
-
-        return super.visit(block)
+        return noModifications
     }
 
-    override fun visit(subroutine: Subroutine): Statement {
-        super.visit(subroutine)
+    override fun after(subroutine: Subroutine, parent: Node): Iterable<IAstModification> {
         val forceOutput = "force_output" in subroutine.definingBlock().options()
         if(subroutine.asmAddress==null && !forceOutput) {
             if(subroutine.containsNoCodeNorVars()) {
                 errors.warn("removing empty subroutine '${subroutine.name}'", subroutine.position)
-                optimizationsDone++
-                return NopStatement.insteadOf(subroutine)
+                return listOf(IAstModification.Remove(subroutine, parent))
             }
         }
 
@@ -72,23 +58,341 @@ internal class StatementOptimizer(private val program: Program,
 
         if(subroutine !in callgraph.usedSymbols && !forceOutput) {
             errors.warn("removing unused subroutine '${subroutine.name}'", subroutine.position)
-            optimizationsDone++
-            return NopStatement.insteadOf(subroutine)
+            return listOf(IAstModification.Remove(subroutine, parent))
         }
 
-        return subroutine
+        return noModifications
     }
 
-    override fun visit(decl: VarDecl): Statement {
+    override fun after(scope: AnonymousScope, parent: Node): Iterable<IAstModification> {
+        val linesToRemove = deduplicateAssignments(scope.statements)
+        return linesToRemove.reversed().map { IAstModification.Remove(scope.statements[it], scope) }
+    }
+
+    override fun after(decl: VarDecl, parent: Node): Iterable<IAstModification> {
         val forceOutput = "force_output" in decl.definingBlock().options()
         if(decl !in callgraph.usedSymbols && !forceOutput) {
             if(decl.type == VarDeclType.VAR)
-                errors.warn("removing unused variable ${decl.type} '${decl.name}'", decl.position)
-            optimizationsDone++
-            return NopStatement.insteadOf(decl)
+                errors.warn("removing unused variable '${decl.name}'", decl.position)
+
+            return listOf(IAstModification.Remove(decl, parent))
         }
 
-        return super.visit(decl)
+        return noModifications
+    }
+
+    override fun after(functionCallStatement: FunctionCallStatement, parent: Node): Iterable<IAstModification> {
+        if(functionCallStatement.target.nameInSource.size==1 && functionCallStatement.target.nameInSource[0] in BuiltinFunctions) {
+            val functionName = functionCallStatement.target.nameInSource[0]
+            if (functionName in pureBuiltinFunctions) {
+                errors.warn("statement has no effect (function return value is discarded)", functionCallStatement.position)
+                return listOf(IAstModification.Remove(functionCallStatement, parent))
+            }
+        }
+
+        // printing a literal string of just 2 or 1 characters is replaced by directly outputting those characters
+        // this is a C-64 specific optimization
+        if(functionCallStatement.target.nameInSource==listOf("c64scr", "print")) {
+            val arg = functionCallStatement.args.single()
+            val stringVar: IdentifierReference?
+            stringVar = if(arg is AddressOf) {
+                arg.identifier
+            } else {
+                arg as? IdentifierReference
+            }
+            if(stringVar!=null) {
+                val vardecl = stringVar.targetVarDecl(program.namespace)!!
+                val string = vardecl.value!! as StringLiteralValue
+                val pos = functionCallStatement.position
+                if(string.value.length==1) {
+                    val firstCharEncoded = CompilationTarget.encodeString(string.value, string.altEncoding)[0]
+                    val chrout = FunctionCallStatement(
+                            IdentifierReference(listOf("c64", "CHROUT"), pos),
+                            mutableListOf(NumericLiteralValue(DataType.UBYTE, firstCharEncoded.toInt(), pos)),
+                            functionCallStatement.void, pos
+                    )
+                    return listOf(IAstModification.ReplaceNode(functionCallStatement, chrout, parent))
+                } else if(string.value.length==2) {
+                    val firstTwoCharsEncoded = CompilationTarget.encodeString(string.value.take(2), string.altEncoding)
+                    val chrout1 = FunctionCallStatement(
+                            IdentifierReference(listOf("c64", "CHROUT"), pos),
+                            mutableListOf(NumericLiteralValue(DataType.UBYTE, firstTwoCharsEncoded[0].toInt(), pos)),
+                            functionCallStatement.void, pos
+                    )
+                    val chrout2 = FunctionCallStatement(
+                            IdentifierReference(listOf("c64", "CHROUT"), pos),
+                            mutableListOf(NumericLiteralValue(DataType.UBYTE, firstTwoCharsEncoded[1].toInt(), pos)),
+                            functionCallStatement.void, pos
+                    )
+                    val anonscope = AnonymousScope(mutableListOf(), pos)
+                    anonscope.statements.add(chrout1)
+                    anonscope.statements.add(chrout2)
+                    return listOf(IAstModification.ReplaceNode(functionCallStatement, anonscope, parent))
+                }
+            }
+        }
+
+        // if the first instruction in the called subroutine is a return statement, remove the jump altogeter
+        val subroutine = functionCallStatement.target.targetSubroutine(program.namespace)
+        if(subroutine!=null) {
+            val first = subroutine.statements.asSequence().filterNot { it is VarDecl || it is Directive }.firstOrNull()
+            if(first is ReturnFromIrq || first is Return)
+                return listOf(IAstModification.Remove(functionCallStatement, parent))
+        }
+
+        return noModifications
+    }
+
+    override fun before(functionCall: FunctionCall, parent: Node): Iterable<IAstModification> {
+        // if the first instruction in the called subroutine is a return statement with constant value, replace with the constant value
+        val subroutine = functionCall.target.targetSubroutine(program.namespace)
+        if(subroutine!=null) {
+            val first = subroutine.statements.asSequence().filterNot { it is VarDecl || it is Directive }.firstOrNull()
+            if(first is Return && first.value!=null) {
+                val constval = first.value?.constValue(program)
+                if(constval!=null)
+                    return listOf(IAstModification.ReplaceNode(functionCall, constval, parent))
+            }
+        }
+        return noModifications
+    }
+
+    override fun after(ifStatement: IfStatement, parent: Node): Iterable<IAstModification> {
+        // remove empty if statements
+        if(ifStatement.truepart.containsNoCodeNorVars() && ifStatement.elsepart.containsNoCodeNorVars())
+            return listOf(IAstModification.Remove(ifStatement, parent))
+
+        // empty true part? switch with the else part
+        if(ifStatement.truepart.containsNoCodeNorVars() && ifStatement.elsepart.containsCodeOrVars()) {
+            val invertedCondition = PrefixExpression("not", ifStatement.condition, ifStatement.condition.position)
+            val emptyscope = AnonymousScope(mutableListOf(), ifStatement.elsepart.position)
+            val truepart = AnonymousScope(ifStatement.elsepart.statements, ifStatement.truepart.position)
+            return listOf(
+                    IAstModification.ReplaceNode(ifStatement.condition, invertedCondition, ifStatement),
+                    IAstModification.ReplaceNode(ifStatement.truepart, truepart, ifStatement),
+                    IAstModification.ReplaceNode(ifStatement.elsepart, emptyscope, ifStatement)
+            )
+        }
+
+        val constvalue = ifStatement.condition.constValue(program)
+        if(constvalue!=null) {
+            return if(constvalue.asBooleanValue){
+                // always true -> keep only if-part
+                errors.warn("condition is always true", ifStatement.position)
+                listOf(IAstModification.ReplaceNode(ifStatement, ifStatement.truepart, parent))
+            } else {
+                // always false -> keep only else-part
+                errors.warn("condition is always false", ifStatement.position)
+                listOf(IAstModification.ReplaceNode(ifStatement, ifStatement.elsepart, parent))
+            }
+        }
+
+        return noModifications
+    }
+
+    override fun after(forLoop: ForLoop, parent: Node): Iterable<IAstModification> {
+        if(forLoop.body.containsNoCodeNorVars()) {
+            // remove empty for loop
+            return listOf(IAstModification.Remove(forLoop, parent))
+        } else if(forLoop.body.statements.size==1) {
+            val loopvar = forLoop.body.statements[0] as? VarDecl
+            if(loopvar!=null && loopvar.name==forLoop.loopVar?.nameInSource?.singleOrNull()) {
+                // remove empty for loop (only loopvar decl in it)
+                return listOf(IAstModification.Remove(forLoop, parent))
+            }
+        }
+
+        val range = forLoop.iterable as? RangeExpr
+        if(range!=null) {
+            if(range.size()==1) {
+                // for loop over a (constant) range of just a single value-- optimize the loop away
+                // loopvar/reg = range value , follow by block
+                val scope = AnonymousScope(mutableListOf(), forLoop.position)
+                scope.statements.add(Assignment(AssignTarget(forLoop.loopRegister, forLoop.loopVar, null, null, forLoop.position), null, range.from, forLoop.position))
+                scope.statements.addAll(forLoop.body.statements)
+                return listOf(IAstModification.ReplaceNode(forLoop, scope, parent))
+            }
+        }
+        val iterable = (forLoop.iterable as? IdentifierReference)?.targetVarDecl(program.namespace)
+        if(iterable!=null) {
+            if(iterable.datatype==DataType.STR) {
+                val sv = iterable.value as StringLiteralValue
+                val size = sv.value.length
+                if(size==1) {
+                    // loop over string of length 1 -> just assign the single character
+                    val character = CompilationTarget.encodeString(sv.value, sv.altEncoding)[0]
+                    val byte = NumericLiteralValue(DataType.UBYTE, character, iterable.position)
+                    val scope = AnonymousScope(mutableListOf(), forLoop.position)
+                    scope.statements.add(Assignment(AssignTarget(forLoop.loopRegister, forLoop.loopVar, null, null, forLoop.position), null, byte, forLoop.position))
+                    scope.statements.addAll(forLoop.body.statements)
+                    return listOf(IAstModification.ReplaceNode(forLoop, scope, parent))
+                }
+            }
+            else if(iterable.datatype in ArrayDatatypes) {
+                val size = iterable.arraysize!!.size()
+                if(size==1) {
+                    // loop over array of length 1 -> just assign the single value
+                    val av = (iterable.value as ArrayLiteralValue).value[0].constValue(program)?.number
+                    if(av!=null) {
+                        val scope = AnonymousScope(mutableListOf(), forLoop.position)
+                        scope.statements.add(Assignment(
+                                AssignTarget(forLoop.loopRegister, forLoop.loopVar, null, null, forLoop.position), null, NumericLiteralValue.optimalInteger(av.toInt(), iterable.position),
+                                forLoop.position))
+                        scope.statements.addAll(forLoop.body.statements)
+                        return listOf(IAstModification.ReplaceNode(forLoop, scope, parent))
+                    }
+                }
+            }
+        }
+
+        return noModifications
+    }
+
+    override fun before(repeatLoop: RepeatLoop, parent: Node): Iterable<IAstModification> {
+        val constvalue = repeatLoop.untilCondition.constValue(program)
+        if(constvalue!=null) {
+            if(constvalue.asBooleanValue) {
+                // always true -> keep only the statement block (if there are no continue and break statements)
+                errors.warn("condition is always true", repeatLoop.untilCondition.position)
+                if(!hasContinueOrBreak(repeatLoop.body))
+                    return listOf(IAstModification.ReplaceNode(repeatLoop, repeatLoop.body, parent))
+            } else {
+                // always false
+                val forever = ForeverLoop(repeatLoop.body, repeatLoop.position)
+                return listOf(IAstModification.ReplaceNode(repeatLoop, forever, parent))
+            }
+        }
+        return noModifications
+    }
+
+    override fun before(whileLoop: WhileLoop, parent: Node): Iterable<IAstModification> {
+        val constvalue = whileLoop.condition.constValue(program)
+        if(constvalue!=null) {
+            return if(constvalue.asBooleanValue) {
+                // always true
+                val forever = ForeverLoop(whileLoop.body, whileLoop.position)
+                listOf(IAstModification.ReplaceNode(whileLoop, forever, parent))
+            } else {
+                // always false -> remove the while statement altogether
+                errors.warn("condition is always false", whileLoop.condition.position)
+                listOf(IAstModification.Remove(whileLoop, parent))
+            }
+        }
+        return noModifications
+    }
+
+    override fun after(whenStatement: WhenStatement, parent: Node): Iterable<IAstModification> {
+        // remove empty choices
+        class ChoiceRemover(val choice: WhenChoice) : IAstModification {
+            override fun perform() {
+                whenStatement.choices.remove(choice)
+            }
+        }
+        return whenStatement.choices
+                .filter { !it.statements.containsCodeOrVars() }
+                .map { ChoiceRemover(it) }
+    }
+
+    override fun after(jump: Jump, parent: Node): Iterable<IAstModification> {
+        // if the jump is to the next statement, remove the jump
+        val scope = jump.definingScope()
+        val label = jump.identifier?.targetStatement(scope)
+        if(label!=null && scope.statements.indexOf(label) == scope.statements.indexOf(jump)+1)
+            return listOf(IAstModification.Remove(jump, parent))
+
+        return noModifications
+    }
+
+    override fun after(assignment: Assignment, parent: Node): Iterable<IAstModification> {
+        if(assignment.aug_op!=null)
+            throw FatalAstException("augmented assignments should have been converted to normal assignments before this optimizer: $assignment")
+
+        // remove assignments to self
+        if(assignment.target isSameAs assignment.value) {
+            if(assignment.target.isNotMemory(program.namespace))
+                return listOf(IAstModification.Remove(assignment, parent))
+        }
+
+        val targetIDt = assignment.target.inferType(program, assignment)
+        if(!targetIDt.isKnown)
+            throw FatalAstException("can't infer type of assignment target")
+
+
+        // optimize binary expressions a bit
+        val targetDt = targetIDt.typeOrElse(DataType.STRUCT)
+        val bexpr=assignment.value as? BinaryExpression
+        if(bexpr!=null) {
+            val cv = bexpr.right.constValue(program)?.number?.toDouble()
+            if (cv != null && assignment.target isSameAs bexpr.left) {
+                // assignments of the form:  X = X <operator> <expr>
+                // remove assignments that have no effect (such as X=X+0)
+                // optimize/rewrite some other expressions
+                val vardeclDt = (assignment.target.identifier?.targetVarDecl(program.namespace))?.type
+                when (bexpr.operator) {
+                    "+" -> {
+                        if (cv == 0.0) {
+                            return listOf(IAstModification.Remove(assignment, parent))
+                        } else if (targetDt in IntegerDatatypes && floor(cv) == cv) {
+                            if ((vardeclDt == VarDeclType.MEMORY && cv in 1.0..3.0) || (vardeclDt != VarDeclType.MEMORY && cv in 1.0..8.0)) {
+                                // replace by several INCs (a bit less when dealing with memory targets)
+                                val incs = AnonymousScope(mutableListOf(), assignment.position)
+                                repeat(cv.toInt()) {
+                                    incs.statements.add(PostIncrDecr(assignment.target, "++", assignment.position))
+                                }
+                                return listOf(IAstModification.ReplaceNode(assignment, incs, parent))
+                            }
+                        }
+                    }
+                    "-" -> {
+                        if (cv == 0.0) {
+                            return listOf(IAstModification.Remove(assignment, parent))
+                        } else if (targetDt in IntegerDatatypes && floor(cv) == cv) {
+                            if ((vardeclDt == VarDeclType.MEMORY && cv in 1.0..3.0) || (vardeclDt != VarDeclType.MEMORY && cv in 1.0..8.0)) {
+                                // replace by several DECs (a bit less when dealing with memory targets)
+                                val decs = AnonymousScope(mutableListOf(), assignment.position)
+                                repeat(cv.toInt()) {
+                                    decs.statements.add(PostIncrDecr(assignment.target, "--", assignment.position))
+                                }
+                                return listOf(IAstModification.ReplaceNode(assignment, decs, parent))
+                            }
+                        }
+                    }
+                    "*" -> if (cv == 1.0) return listOf(IAstModification.Remove(assignment, parent))
+                    "/" -> if (cv == 1.0) return listOf(IAstModification.Remove(assignment, parent))
+                    "**" -> if (cv == 1.0) return listOf(IAstModification.Remove(assignment, parent))
+                    "|" -> if (cv == 0.0) return listOf(IAstModification.Remove(assignment, parent))
+                    "^" -> if (cv == 0.0) return listOf(IAstModification.Remove(assignment, parent))
+                    "<<" -> {
+                        if (cv == 0.0)
+                            return listOf(IAstModification.Remove(assignment, parent))
+                        // replace by in-place lsl(...) call
+                        val scope = AnonymousScope(mutableListOf(), assignment.position)
+                        var numshifts = cv.toInt()
+                        while (numshifts > 0) {
+                            scope.statements.add(FunctionCallStatement(IdentifierReference(listOf("lsl"), assignment.position),
+                                    mutableListOf(bexpr.left), true, assignment.position))
+                            numshifts--
+                        }
+                        return listOf(IAstModification.ReplaceNode(assignment, scope, parent))
+                    }
+                    ">>" -> {
+                        if (cv == 0.0)
+                            return listOf(IAstModification.Remove(assignment, parent))
+                        // replace by in-place lsr(...) call
+                        val scope = AnonymousScope(mutableListOf(), assignment.position)
+                        var numshifts = cv.toInt()
+                        while (numshifts > 0) {
+                            scope.statements.add(FunctionCallStatement(IdentifierReference(listOf("lsr"), assignment.position),
+                                    mutableListOf(bexpr.left), true, assignment.position))
+                            numshifts--
+                        }
+                        return listOf(IAstModification.ReplaceNode(assignment, scope, parent))
+                    }
+                }
+
+            }
+        }
+        return noModifications
     }
 
     private fun deduplicateAssignments(statements: List<Statement>): MutableList<Int> {
@@ -116,207 +420,6 @@ internal class StatementOptimizer(private val program: Program,
         return linesToRemove
     }
 
-    override fun visit(functionCallStatement: FunctionCallStatement): Statement {
-        if(functionCallStatement.target.nameInSource.size==1 && functionCallStatement.target.nameInSource[0] in BuiltinFunctions) {
-            val functionName = functionCallStatement.target.nameInSource[0]
-            if (functionName in pureBuiltinFunctions) {
-                errors.warn("statement has no effect (function return value is discarded)", functionCallStatement.position)
-                optimizationsDone++
-                return NopStatement.insteadOf(functionCallStatement)
-            }
-        }
-
-        if(functionCallStatement.target.nameInSource==listOf("c64scr", "print") ||
-                functionCallStatement.target.nameInSource==listOf("c64scr", "print_p")) {
-            // printing a literal string of just 2 or 1 characters is replaced by directly outputting those characters
-            val arg = functionCallStatement.args.single()
-            val stringVar: IdentifierReference?
-            stringVar = if(arg is AddressOf) {
-                arg.identifier
-            } else {
-                arg as? IdentifierReference
-            }
-            if(stringVar!=null) {
-                val vardecl = stringVar.targetVarDecl(program.namespace)!!
-                val string = vardecl.value!! as StringLiteralValue
-                if(string.value.length==1) {
-                    val firstCharEncoded = CompilationTarget.encodeString(string.value, string.altEncoding)[0]
-                    functionCallStatement.args.clear()
-                    functionCallStatement.args.add(NumericLiteralValue.optimalInteger(firstCharEncoded.toInt(), functionCallStatement.position))
-                    functionCallStatement.target = IdentifierReference(listOf("c64", "CHROUT"), functionCallStatement.target.position)
-                    vardeclsToRemove.add(vardecl)
-                    optimizationsDone++
-                    return functionCallStatement
-                } else if(string.value.length==2) {
-                    val firstTwoCharsEncoded = CompilationTarget.encodeString(string.value.take(2), string.altEncoding)
-                    val scope = AnonymousScope(mutableListOf(), functionCallStatement.position)
-                    scope.statements.add(FunctionCallStatement(IdentifierReference(listOf("c64", "CHROUT"), functionCallStatement.target.position),
-                            mutableListOf(NumericLiteralValue.optimalInteger(firstTwoCharsEncoded[0].toInt(), functionCallStatement.position)),
-                            functionCallStatement.void, functionCallStatement.position))
-                    scope.statements.add(FunctionCallStatement(IdentifierReference(listOf("c64", "CHROUT"), functionCallStatement.target.position),
-                            mutableListOf(NumericLiteralValue.optimalInteger(firstTwoCharsEncoded[1].toInt(), functionCallStatement.position)),
-                            functionCallStatement.void, functionCallStatement.position))
-                    vardeclsToRemove.add(vardecl)
-                    optimizationsDone++
-                    return scope
-                }
-            }
-        }
-
-        // if it calls a subroutine,
-        // and the first instruction in the subroutine is a jump, call that jump target instead
-        // if the first instruction in the subroutine is a return statement, replace with a nop instruction
-        val subroutine = functionCallStatement.target.targetSubroutine(program.namespace)
-        if(subroutine!=null) {
-            val first = subroutine.statements.asSequence().filterNot { it is VarDecl || it is Directive }.firstOrNull()
-            if(first is Jump && first.identifier!=null) {
-                optimizationsDone++
-                return FunctionCallStatement(first.identifier, functionCallStatement.args, functionCallStatement.void, functionCallStatement.position)
-            }
-            if(first is ReturnFromIrq || first is Return) {
-                optimizationsDone++
-                return NopStatement.insteadOf(functionCallStatement)
-            }
-        }
-
-        return super.visit(functionCallStatement)
-    }
-
-    override fun visit(functionCall: FunctionCall): Expression {
-        // if it calls a subroutine,
-        // and the first instruction in the subroutine is a jump, call that jump target instead
-        // if the first instruction in the subroutine is a return statement with constant value, replace with the constant value
-        val subroutine = functionCall.target.targetSubroutine(program.namespace)
-        if(subroutine!=null) {
-            val first = subroutine.statements.asSequence().filterNot { it is VarDecl || it is Directive }.firstOrNull()
-            if(first is Jump && first.identifier!=null) {
-                optimizationsDone++
-                return FunctionCall(first.identifier, functionCall.args, functionCall.position)
-            }
-            if(first is Return && first.value!=null) {
-                val constval = first.value?.constValue(program)
-                if(constval!=null)
-                    return constval
-            }
-        }
-        return super.visit(functionCall)
-    }
-
-    override fun visit(ifStatement: IfStatement): Statement {
-        super.visit(ifStatement)
-
-        if(ifStatement.truepart.containsNoCodeNorVars() && ifStatement.elsepart.containsNoCodeNorVars()) {
-            optimizationsDone++
-            return NopStatement.insteadOf(ifStatement)
-        }
-
-        if(ifStatement.truepart.containsNoCodeNorVars() && ifStatement.elsepart.containsCodeOrVars()) {
-            // invert the condition and move else part to true part
-            ifStatement.truepart = ifStatement.elsepart
-            ifStatement.elsepart = AnonymousScope(mutableListOf(), ifStatement.elsepart.position)
-            ifStatement.condition = PrefixExpression("not", ifStatement.condition, ifStatement.condition.position)
-            optimizationsDone++
-            return ifStatement
-        }
-
-        val constvalue = ifStatement.condition.constValue(program)
-        if(constvalue!=null) {
-            return if(constvalue.asBooleanValue){
-                // always true -> keep only if-part
-                errors.warn("condition is always true", ifStatement.position)
-                optimizationsDone++
-                ifStatement.truepart
-            } else {
-                // always false -> keep only else-part
-                errors.warn("condition is always false", ifStatement.position)
-                optimizationsDone++
-                ifStatement.elsepart
-            }
-        }
-        return ifStatement
-    }
-
-    override fun visit(forLoop: ForLoop): Statement {
-        super.visit(forLoop)
-        if(forLoop.body.containsNoCodeNorVars()) {
-            // remove empty for loop
-            optimizationsDone++
-            return NopStatement.insteadOf(forLoop)
-        } else if(forLoop.body.statements.size==1) {
-            val loopvar = forLoop.body.statements[0] as? VarDecl
-            if(loopvar!=null && loopvar.name==forLoop.loopVar?.nameInSource?.singleOrNull()) {
-                // remove empty for loop
-                optimizationsDone++
-                return NopStatement.insteadOf(forLoop)
-            }
-        }
-
-
-        val range = forLoop.iterable as? RangeExpr
-        if(range!=null) {
-            if(range.size()==1) {
-                // for loop over a (constant) range of just a single value-- optimize the loop away
-                // loopvar/reg = range value , follow by block
-                val assignment = Assignment(AssignTarget(forLoop.loopRegister, forLoop.loopVar, null, null, forLoop.position), null, range.from, forLoop.position)
-                forLoop.body.statements.add(0, assignment)
-                optimizationsDone++
-                return forLoop.body
-            }
-        }
-        return forLoop
-    }
-
-    override fun visit(whileLoop: WhileLoop): Statement {
-        super.visit(whileLoop)
-        val constvalue = whileLoop.condition.constValue(program)
-        if(constvalue!=null) {
-            return if(constvalue.asBooleanValue){
-                // always true -> print a warning, and optimize into a forever-loop
-                errors.warn("condition is always true", whileLoop.condition.position)
-                optimizationsDone++
-                ForeverLoop(whileLoop.body, whileLoop.position)
-            } else {
-                // always false -> remove the while statement altogether
-                errors.warn("condition is always false", whileLoop.condition.position)
-                optimizationsDone++
-                NopStatement.insteadOf(whileLoop)
-            }
-        }
-        return whileLoop
-    }
-
-    override fun visit(repeatLoop: RepeatLoop): Statement {
-        super.visit(repeatLoop)
-        val constvalue = repeatLoop.untilCondition.constValue(program)
-        if(constvalue!=null) {
-            return if(constvalue.asBooleanValue){
-                // always true -> keep only the statement block (if there are no continue and break statements)
-                errors.warn("condition is always true", repeatLoop.untilCondition.position)
-                if(hasContinueOrBreak(repeatLoop.body))
-                    repeatLoop
-                else {
-                    optimizationsDone++
-                    repeatLoop.body
-                }
-            } else {
-                // always false -> print a warning, and optimize into a forever loop
-                errors.warn("condition is always false", repeatLoop.untilCondition.position)
-                optimizationsDone++
-                ForeverLoop(repeatLoop.body, repeatLoop.position)
-            }
-        }
-        return repeatLoop
-    }
-
-    override fun visit(whenStatement: WhenStatement): Statement {
-        val choices = whenStatement.choices.toList()
-        for(choice in choices) {
-            if(choice.statements.containsNoCodeNorVars())
-                whenStatement.choices.remove(choice)
-        }
-        return super.visit(whenStatement)
-    }
-
     private fun hasContinueOrBreak(scope: INameScope): Boolean {
 
         class Searcher: IAstVisitor
@@ -341,185 +444,4 @@ internal class StatementOptimizer(private val program: Program,
         return s.count > 0
     }
 
-    override fun visit(jump: Jump): Statement {
-        val subroutine = jump.identifier?.targetSubroutine(program.namespace)
-        if(subroutine!=null) {
-            // if the first instruction in the subroutine is another jump, shortcut this one
-            val first = subroutine.statements.asSequence().filterNot { it is VarDecl || it is Directive }.firstOrNull()
-            if(first is Jump) {
-                optimizationsDone++
-                return first
-            }
-        }
-
-        // if the jump is to the next statement, remove the jump
-        val scope = jump.definingScope()
-        val label = jump.identifier?.targetStatement(scope)
-        if(label!=null) {
-            if(scope.statements.indexOf(label) == scope.statements.indexOf(jump)+1) {
-                optimizationsDone++
-                return NopStatement.insteadOf(jump)
-            }
-        }
-
-        return jump
-    }
-
-    override fun visit(assignment: Assignment): Statement {
-        if(assignment.aug_op!=null)
-            throw FatalAstException("augmented assignments should have been converted to normal assignments before this optimizer: $assignment")
-
-        if(assignment.target isSameAs assignment.value) {
-            if(assignment.target.isNotMemory(program.namespace)) {
-                optimizationsDone++
-                return NopStatement.insteadOf(assignment)
-            }
-        }
-        val targetIDt = assignment.target.inferType(program, assignment)
-        if(!targetIDt.isKnown)
-            throw FatalAstException("can't infer type of assignment target")
-        val targetDt = targetIDt.typeOrElse(DataType.STRUCT)
-        val bexpr=assignment.value as? BinaryExpression
-        if(bexpr!=null) {
-            val cv = bexpr.right.constValue(program)?.number?.toDouble()
-            if (cv == null) {
-                if (bexpr.operator == "+" && targetDt != DataType.FLOAT) {
-                    if (bexpr.left isSameAs bexpr.right && assignment.target isSameAs bexpr.left) {
-                        bexpr.operator = "*"
-                        bexpr.right = NumericLiteralValue.optimalInteger(2, assignment.value.position)
-                        optimizationsDone++
-                        return assignment
-                    }
-                }
-            } else {
-                if (assignment.target isSameAs bexpr.left) {
-                    // remove assignments that have no effect  X=X , X+=0, X-=0, X*=1, X/=1, X//=1, A |= 0, A ^= 0, A<<=0, etc etc
-                    // A = A <operator> B
-                    val vardeclDt = (assignment.target.identifier?.targetVarDecl(program.namespace))?.type
-
-                    when (bexpr.operator) {
-                        "+" -> {
-                            if (cv == 0.0) {
-                                optimizationsDone++
-                                return NopStatement.insteadOf(assignment)
-                            } else if (targetDt in IntegerDatatypes && floor(cv) == cv) {
-                                if ((vardeclDt == VarDeclType.MEMORY && cv in 1.0..3.0) || (vardeclDt != VarDeclType.MEMORY && cv in 1.0..8.0)) {
-                                    // replace by several INCs (a bit less when dealing with memory targets)
-                                    val decs = AnonymousScope(mutableListOf(), assignment.position)
-                                    repeat(cv.toInt()) {
-                                        decs.statements.add(PostIncrDecr(assignment.target, "++", assignment.position))
-                                    }
-                                    return decs
-                                }
-                            }
-                        }
-                        "-" -> {
-                            if (cv == 0.0) {
-                                optimizationsDone++
-                                return NopStatement.insteadOf(assignment)
-                            } else if (targetDt in IntegerDatatypes && floor(cv) == cv) {
-                                if ((vardeclDt == VarDeclType.MEMORY && cv in 1.0..3.0) || (vardeclDt != VarDeclType.MEMORY && cv in 1.0..8.0)) {
-                                    // replace by several DECs (a bit less when dealing with memory targets)
-                                    val decs = AnonymousScope(mutableListOf(), assignment.position)
-                                    repeat(cv.toInt()) {
-                                        decs.statements.add(PostIncrDecr(assignment.target, "--", assignment.position))
-                                    }
-                                    return decs
-                                }
-                            }
-                        }
-                        "*" -> if (cv == 1.0) {
-                            optimizationsDone++
-                            return NopStatement.insteadOf(assignment)
-                        }
-                        "/" -> if (cv == 1.0) {
-                            optimizationsDone++
-                            return NopStatement.insteadOf(assignment)
-                        }
-                        "**" -> if (cv == 1.0) {
-                            optimizationsDone++
-                            return NopStatement.insteadOf(assignment)
-                        }
-                        "|" -> if (cv == 0.0) {
-                            optimizationsDone++
-                            return NopStatement.insteadOf(assignment)
-                        }
-                        "^" -> if (cv == 0.0) {
-                            optimizationsDone++
-                            return NopStatement.insteadOf(assignment)
-                        }
-                        "<<" -> {
-                            if (cv == 0.0) {
-                                optimizationsDone++
-                                return NopStatement.insteadOf(assignment)
-                            }
-                            if (((targetDt == DataType.UWORD || targetDt == DataType.WORD) && cv > 15.0) ||
-                                    ((targetDt == DataType.UBYTE || targetDt == DataType.BYTE) && cv > 7.0)) {
-                                assignment.value = NumericLiteralValue.optimalInteger(0, assignment.value.position)
-                                assignment.value.linkParents(assignment)
-                                optimizationsDone++
-                            } else {
-                                // replace by in-place lsl(...) call
-                                val scope = AnonymousScope(mutableListOf(), assignment.position)
-                                var numshifts = cv.toInt()
-                                while (numshifts > 0) {
-                                    scope.statements.add(FunctionCallStatement(IdentifierReference(listOf("lsl"), assignment.position),
-                                            mutableListOf(bexpr.left), true, assignment.position))
-                                    numshifts--
-                                }
-                                optimizationsDone++
-                                return scope
-                            }
-                        }
-                        ">>" -> {
-                            if (cv == 0.0) {
-                                optimizationsDone++
-                                return NopStatement.insteadOf(assignment)
-                            }
-                            if ((targetDt == DataType.UWORD && cv > 15.0) || (targetDt == DataType.UBYTE && cv > 7.0)) {
-                                assignment.value = NumericLiteralValue.optimalInteger(0, assignment.value.position)
-                                assignment.value.linkParents(assignment)
-                                optimizationsDone++
-                            } else {
-                                // replace by in-place lsr(...) call
-                                val scope = AnonymousScope(mutableListOf(), assignment.position)
-                                var numshifts = cv.toInt()
-                                while (numshifts > 0) {
-                                    scope.statements.add(FunctionCallStatement(IdentifierReference(listOf("lsr"), assignment.position),
-                                            mutableListOf(bexpr.left), true, assignment.position))
-                                    numshifts--
-                                }
-                                optimizationsDone++
-                                return scope
-                            }
-                        }
-                    }
-                }
-            }
-        }
-
-
-        return super.visit(assignment)
-    }
-
-    override fun visit(scope: AnonymousScope): Statement {
-        val linesToRemove = deduplicateAssignments(scope.statements)
-        if(linesToRemove.isNotEmpty()) {
-            linesToRemove.reversed().forEach{scope.statements.removeAt(it)}
-        }
-        return super.visit(scope)
-    }
-
-    override fun visit(label: Label): Statement {
-        // remove duplicate labels
-        val stmts = label.definingScope().statements
-        val startIdx = stmts.indexOf(label)
-        if(startIdx< stmts.lastIndex && stmts[startIdx+1] == label)
-            return NopStatement.insteadOf(label)
-
-        return super.visit(label)
-    }
 }
-
-
-

compiler/src/prog8/optimizer/UnusedCodeRemover.kt

@@ -30,7 +30,7 @@ internal class UnusedCodeRemover: AstWalker() {
         // remove modules that are not imported, or are empty (unless it's a library modules)
         program.modules.forEach {
             if (!it.isLibraryModule && (it.importedBy.isEmpty() || it.containsNoCodeNorVars()))
-                removals.add(IAstModification.Remove(it, it.parent))        // TODO does removing modules work like this?
+                removals.add(IAstModification.Remove(it, it.parent))
         }
 
         return removals

docs/source/index.rst

@@ -156,7 +156,7 @@ Design principles and features
 - The compiler tries to optimize the program and generated code a bit, but hand-tuning of the
   performance or space-critical parts will likely still be required. This is supported by
   the ability to easily write embedded assembly code directly in the program source code.
-- There are many built-in functions, such as ``sin``, ``cos``, ``rnd``, ``abs``, ``min``, ``max``, ``sqrt``, ``msb``, ``rol``, ``ror``, ``swap``, ``memset``, ``memcopy``, ``sort`` and ``reverse``
+- There are many built-in functions, such as ``sin``, ``cos``, ``rnd``, ``abs``, ``min``, ``max``, ``sqrt``, ``msb``, ``rol``, ``ror``, ``swap``, ``memset``, ``memcopy``, ``substr``, ``sort`` and ``reverse`` (and others)
 - Assembling the generated code into a program wil be done by an external cross-assembler tool.
 
 

docs/source/programming.rst

@@ -279,16 +279,23 @@ This @-prefix can also be used for character byte values.
 
 
 You can concatenate two string literals using '+' (not very useful though) or repeat
-a string literal a given number of times using '*'::
+a string literal a given number of times using '*'. You can also assign a new string
+value to another string. No bounds check is done so be sure the destination string is
+large enough to contain the new value::
 
     str string1 = "first part" + "second part"
     str string2 = "hello!" * 10
 
+    string1 = string2
+    string1 = "new value"
+
 
 .. caution::
-    Avoid changing strings after they've been created.
+    It's probably best to avoid changing strings after they've been created. This
+    includes changing certain letters by index, or by assigning a new value, or by
+    modifying the string via other means for example ``substr`` function and its cousins.
     This is because if your program exits and is restarted (without loading it again),
-    it will then start working with the changed strings instead of the original ones.
+    it will then start working with the changed strings instead of the original ones!
     The same is true for arrays.
 
 
@@ -802,6 +809,22 @@ memsetw(address, numwords, wordvalue)
     Efficiently set a part of memory to the given (u)word value.
     But the most efficient will always be to write a specialized fill routine in assembly yourself!
 
+leftstr(source, target, length)
+    Copies the left side of the source string of the given length to target string.
+    It is assumed the target string buffer is large enough to contain the result.
+    Modifies in-place, doesn't return a value (so can't be used in an expression).
+
+rightstr(source, target, length)
+    Copies the right side of the source string of the given length to target string.
+    It is assumed the target string buffer is large enough to contain the result.
+    Modifies in-place, doesn't return a value (so can't be used in an expression).
+
+substr(source, target, start, length)
+    Copies a segment from the source string, starting at the given index,
+    and of the given length to target string.
+    It is assumed the target string buffer is large enough to contain the result.
+    Modifies in-place, doesn't return a value (so can't be used in an expression).
+
 swap(x, y)
     Swap the values of numerical variables (or memory locations) x and y in a fast way.
 

docs/source/todo.rst

@@ -3,10 +3,10 @@ TODO
 ====
 
 - finalize (most) of the still missing "new" assignment asm code generation
-
 - aliases for imported symbols for example perhaps '%alias print = c64scr.print'
 - option to load library files from a directory instead of the embedded ones (easier library development/debugging)
 - investigate support for 8bitguy's Commander X16 platform https://murray2.com/forums/commander-x16.9/  and https://github.com/commanderx16/x16-docs
+- see if we can group some errors together for instance the (now single) errors about unidentified symbols
 
 
 More optimizations

examples/strings.p8

@@ -1,36 +0,0 @@
-%import c64lib
-%zeropage basicsafe
-
-main {
-
-sub start() {
-
-    str s1 = "apple"
-    str s2 = "banana"
-    byte[] a1 = [66,77,88,0]
-    ubyte i1 = 101
-    uword w1 = 000
-
-    c64.STROUT(s1)
-    c64.CHROUT('\n')
-    c64.STROUT(a1)
-    c64.CHROUT('\n')
-
-    c64scr.print("bla\n")
-
-;    c64scr.print_uwhex(s1, true)
-;    w1 = &s1
-;    c64scr.print_uwhex(w1, true)
-;
-;    c64scr.print_uwhex(a1, true)
-;    w1 = &a1
-;    c64scr.print_uwhex(w1, true)
-;
-;    s1 = s1
-;    s1 = s2
-;    s2 = "zzz"
-
-}
-}
-
-

examples/test.p8

@@ -4,43 +4,13 @@
 %zeropage basicsafe
 
 
+
 main {
+
     sub start() {
-
-        A += 50
-
-        A += Y + 1
-        A -= Y + 1
-        A += Y - 1
-        A -= Y - 1
-
-        A += Y + 2
-        A -= Y + 2
-        A += Y - 2
-        A -= Y - 2
-
-;        ubyte ubb
-;        byte bb
-;        uword uww
-;        word ww
-;        word ww2
-;
-;        A = ubb*0
-;        Y = ubb*1
-;        A = ubb*2
-;        Y = ubb*4
-;        A = ubb*8
-;        Y = ubb*16
-;        A = ubb*32
-;        Y = ubb*64
-;        A = ubb*128
-;        Y = ubb+ubb+ubb
-;        A = ubb+ubb+ubb+ubb
-;        ww = ww2+ww2
-;        ww = ww2+ww2+ww2
-;        ww = ww2+ww2+ww2+ww2
-
+        A=42
     }
+
 }