diff --git a/internal/compiler/funchandler.go b/internal/compiler/funchandler.go
new file mode 100644
index 0000000..ee254e5
--- /dev/null
+++ b/internal/compiler/funchandler.go
@@ -0,0 +1,657 @@
+package compiler
+
+import (
+	"fmt"
+	"strings"
+
+	"c65gm/internal/preproc"
+)
+
+// ParamDirection represents parameter passing direction
+type ParamDirection uint8
+
+const (
+	DirIn ParamDirection = 1 << iota
+	DirOut
+)
+
+func (d ParamDirection) Has(flag ParamDirection) bool {
+	return d&flag != 0
+}
+
+// FuncParam represents a function parameter
+type FuncParam struct {
+	Symbol    *Symbol
+	Direction ParamDirection
+}
+
+// FuncDecl represents a function declaration
+type FuncDecl struct {
+	Name   string
+	Params []*FuncParam
+}
+
+// FunctionHandler manages function declarations and calls
+type FunctionHandler struct {
+	functions       []*FuncDecl
+	currentFuncs    []string // stack of current function names (for nested scope)
+	symTable        *SymbolTable
+	labelStack      *LabelStack
+	constStrHandler *ConstantStringHandler
+	pragma          *preproc.Pragma
+}
+
+// NewFunctionHandler creates a new function handler
+func NewFunctionHandler(st *SymbolTable, ls *LabelStack, csh *ConstantStringHandler, pragma *preproc.Pragma) *FunctionHandler {
+	return &FunctionHandler{
+		functions:       make([]*FuncDecl, 0),
+		currentFuncs:    make([]string, 0),
+		symTable:        st,
+		labelStack:      ls,
+		constStrHandler: csh,
+		pragma:          pragma,
+	}
+}
+
+// HandleFuncDecl parses and processes a FUNC declaration
+// Syntax: FUNC name ( param1 param2 ... )
+// Or: FUNC name (void function)
+func (fh *FunctionHandler) HandleFuncDecl(line preproc.Line) ([]string, error) {
+	// Normalize parentheses and commas
+	text := fixIntuitiveFuncs(line.Text)
+
+	params, err := parseParams(text)
+	if err != nil {
+		return nil, fmt.Errorf("%s:%d: %w", line.Filename, line.LineNo, err)
+	}
+
+	if len(params) < 2 {
+		return nil, fmt.Errorf("%s:%d: FUNC: expected at least function name", line.Filename, line.LineNo)
+	}
+
+	if strings.ToUpper(params[0]) != "FUNC" {
+		return nil, fmt.Errorf("%s:%d: not a FUNC declaration", line.Filename, line.LineNo)
+	}
+
+	funcName := params[1]
+
+	// Check for redeclaration
+	if fh.FuncExists(funcName) {
+		return nil, fmt.Errorf("%s:%d: function %q already declared", line.Filename, line.LineNo, funcName)
+	}
+
+	// Push function name to current function stack early
+	// (so param declarations get correct scope)
+	fh.currentFuncs = append(fh.currentFuncs, funcName)
+
+	// Parse parameters
+	var funcParams []*FuncParam
+
+	if len(params) == 2 {
+		// Void function: FUNC name
+		// No parameters
+	} else if len(params) >= 5 {
+		// FUNC name ( param1 param2 )
+		if params[2] != "(" || params[len(params)-1] != ")" {
+			fh.currentFuncs = fh.currentFuncs[:len(fh.currentFuncs)-1]
+			return nil, fmt.Errorf("%s:%d: FUNC: expected parentheses around parameters", line.Filename, line.LineNo)
+		}
+
+		// Extract params between ( and ) - need to handle {BYTE x} specially
+		rawParamTokens := params[3 : len(params)-1]
+		paramSpecs, err := buildComplexParams(rawParamTokens)
+		if err != nil {
+			fh.currentFuncs = fh.currentFuncs[:len(fh.currentFuncs)-1]
+			return nil, fmt.Errorf("%s:%d: FUNC %s: %w", line.Filename, line.LineNo, funcName, err)
+		}
+
+		for _, spec := range paramSpecs {
+			direction, varName, isImplicit, implicitDecl, err := parseParamSpec(spec)
+			if err != nil {
+				fh.currentFuncs = fh.currentFuncs[:len(fh.currentFuncs)-1]
+				return nil, fmt.Errorf("%s:%d: FUNC %s: %w", line.Filename, line.LineNo, funcName, err)
+			}
+
+			if isImplicit {
+				// Parse and add implicit variable declaration
+				// Format: {BYTE varname} or {WORD varname}
+				if err := fh.parseImplicitDecl(implicitDecl, funcName); err != nil {
+					fh.currentFuncs = fh.currentFuncs[:len(fh.currentFuncs)-1]
+					return nil, fmt.Errorf("%s:%d: FUNC %s: implicit declaration: %w", line.Filename, line.LineNo, funcName, err)
+				}
+			}
+
+			// Look up variable in symbol table
+			sym := fh.symTable.Lookup(varName, []string{funcName})
+			if sym == nil {
+				fh.currentFuncs = fh.currentFuncs[:len(fh.currentFuncs)-1]
+				return nil, fmt.Errorf("%s:%d: FUNC %s: parameter %q not declared", line.Filename, line.LineNo, funcName, varName)
+			}
+
+			if sym.IsConst() {
+				fh.currentFuncs = fh.currentFuncs[:len(fh.currentFuncs)-1]
+				return nil, fmt.Errorf("%s:%d: FUNC %s: parameter %q cannot be a constant", line.Filename, line.LineNo, funcName, varName)
+			}
+
+			funcParams = append(funcParams, &FuncParam{
+				Symbol:    sym,
+				Direction: direction,
+			})
+		}
+	} else {
+		fh.currentFuncs = fh.currentFuncs[:len(fh.currentFuncs)-1]
+		return nil, fmt.Errorf("%s:%d: FUNC: invalid syntax", line.Filename, line.LineNo)
+	}
+
+	// Store function declaration
+	fh.functions = append(fh.functions, &FuncDecl{
+		Name:   funcName,
+		Params: funcParams,
+	})
+
+	// Generate assembler label
+	return []string{funcName}, nil
+}
+
+// buildComplexParams handles parameter lists that may contain {BYTE x} style declarations
+// Tokens like {BYTE x} are spread across multiple tokens and need to be reassembled
+func buildComplexParams(tokens []string) ([]string, error) {
+	var result []string
+	var current string
+	inBraces := false
+
+	for _, token := range tokens {
+		hasStart := strings.Contains(token, "{")
+		hasEnd := strings.Contains(token, "}")
+
+		if !inBraces {
+			// Not currently in braces
+			if hasEnd && !hasStart {
+				return nil, fmt.Errorf("unexpected } without matching {")
+			}
+			if hasStart {
+				// Starting a brace block
+				inBraces = true
+				current = token
+				// Check if it also ends on same token
+				if hasEnd {
+					result = append(result, current)
+					current = ""
+					inBraces = false
+				}
+			} else {
+				// Regular param
+				result = append(result, token)
+			}
+		} else {
+			// Currently accumulating in braces
+			if hasStart {
+				return nil, fmt.Errorf("unexpected { while already in braces")
+			}
+			current += " " + token
+			if hasEnd {
+				result = append(result, current)
+				current = ""
+				inBraces = false
+			}
+		}
+	}
+
+	if inBraces {
+		return nil, fmt.Errorf("unclosed { in parameter list")
+	}
+
+	return result, nil
+}
+
+// HandleFuncCall generates code for a function call
+// Syntax: CALL funcname ( arg1 arg2 ... )
+// Or: funcname ( arg1 arg2 ... )
+func (fh *FunctionHandler) HandleFuncCall(line preproc.Line) ([]string, error) {
+	// Normalize parentheses and commas
+	text := fixIntuitiveFuncs(line.Text)
+
+	params, err := parseParams(text)
+	if err != nil {
+		return nil, fmt.Errorf("%s:%d: %w", line.Filename, line.LineNo, err)
+	}
+
+	if len(params) < 1 {
+		return nil, fmt.Errorf("%s:%d: CALL: empty line", line.Filename, line.LineNo)
+	}
+
+	// Check if starts with CALL keyword
+	startsWithCall := strings.ToUpper(params[0]) == "CALL"
+
+	funcNameIdx := 0
+	if startsWithCall {
+		if len(params) < 2 {
+			return nil, fmt.Errorf("%s:%d: CALL: expected function name", line.Filename, line.LineNo)
+		}
+		funcNameIdx = 1
+	}
+
+	funcName := params[funcNameIdx]
+
+	// Check if function exists
+	funcDecl := fh.findFunc(funcName)
+	if funcDecl == nil {
+		return nil, fmt.Errorf("%s:%d: function %q not declared", line.Filename, line.LineNo, funcName)
+	}
+
+	// Parse call arguments
+	var callArgs []string
+
+	if len(params) == funcNameIdx+1 {
+		// No arguments: funcname or CALL funcname
+		callArgs = []string{}
+	} else if len(params) >= funcNameIdx+4 {
+		// funcname ( arg1 arg2 ) or CALL funcname ( arg1 arg2 )
+		if params[funcNameIdx+1] != "(" || params[len(params)-1] != ")" {
+			return nil, fmt.Errorf("%s:%d: CALL %s: expected parentheses around arguments", line.Filename, line.LineNo, funcName)
+		}
+		callArgs = params[funcNameIdx+2 : len(params)-1]
+	} else {
+		return nil, fmt.Errorf("%s:%d: CALL %s: invalid syntax", line.Filename, line.LineNo, funcName)
+	}
+
+	// Check argument count matches
+	if len(callArgs) != len(funcDecl.Params) {
+		return nil, fmt.Errorf("%s:%d: CALL %s: expected %d arguments, got %d",
+			line.Filename, line.LineNo, funcName, len(funcDecl.Params), len(callArgs))
+	}
+
+	// Get pragma set for this line
+	pragmaSet := fh.pragma.GetPragmaSetByIndex(line.PragmaSetIndex)
+
+	var asmLines []string
+	var inAssigns []string
+	var outAssigns []string
+
+	// Process each argument
+	for i, arg := range callArgs {
+		param := funcDecl.Params[i]
+
+		// Handle different argument types
+		if strings.HasPrefix(arg, "@") {
+			// Label reference: @labelname
+			if err := fh.processLabelArg(arg, param, funcName, line, &inAssigns); err != nil {
+				return nil, err
+			}
+		} else if strings.HasPrefix(arg, "\"") && strings.HasSuffix(arg, "\"") {
+			// String constant
+			if err := fh.processStringArg(arg, param, funcName, line, pragmaSet, &inAssigns); err != nil {
+				return nil, err
+			}
+		} else if sym := fh.symTable.Lookup(arg, fh.currentFuncs); sym != nil {
+			// Variable reference
+			if err := fh.processVarArg(sym, param, funcName, line, &inAssigns, &outAssigns); err != nil {
+				return nil, err
+			}
+		} else {
+			// Numeric constant
+			if err := fh.processConstArg(arg, param, funcName, line, &inAssigns); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	// Generate final assembly
+	asmLines = append(asmLines, inAssigns...)
+	asmLines = append(asmLines, fmt.Sprintf("  jsr %s", funcName))
+	asmLines = append(asmLines, outAssigns...)
+
+	return asmLines, nil
+}
+
+// processLabelArg handles @label arguments
+func (fh *FunctionHandler) processLabelArg(arg string, param *FuncParam, funcName string, line preproc.Line, inAssigns *[]string) error {
+	labelName := arg[1:] // strip @
+
+	if param.Symbol.IsByte() {
+		return fmt.Errorf("%s:%d: CALL %s: cannot pass label to byte parameter", line.Filename, line.LineNo, funcName)
+	}
+
+	if param.Direction.Has(DirOut) {
+		return fmt.Errorf("%s:%d: CALL %s: cannot pass label to out/io parameter", line.Filename, line.LineNo, funcName)
+	}
+
+	*inAssigns = append(*inAssigns,
+		fmt.Sprintf("  lda #<%s", labelName),
+		fmt.Sprintf("  sta %s", param.Symbol.FullName()),
+		fmt.Sprintf("  lda #>%s", labelName),
+		fmt.Sprintf("  sta %s+1", param.Symbol.FullName()),
+	)
+
+	return nil
+}
+
+// processStringArg handles "string" arguments
+func (fh *FunctionHandler) processStringArg(arg string, param *FuncParam, funcName string, line preproc.Line, pragmaSet preproc.PragmaSet, inAssigns *[]string) error {
+	if param.Symbol.IsByte() {
+		return fmt.Errorf("%s:%d: CALL %s: cannot pass string to byte parameter", line.Filename, line.LineNo, funcName)
+	}
+
+	if param.Direction.Has(DirOut) {
+		return fmt.Errorf("%s:%d: CALL %s: cannot pass string to out/io parameter", line.Filename, line.LineNo, funcName)
+	}
+
+	// Generate label for string constant
+	labelName := fh.labelStack.Push()
+	fh.constStrHandler.AddConstStr(labelName, arg, true, pragmaSet)
+
+	*inAssigns = append(*inAssigns,
+		fmt.Sprintf("  lda #<%s", labelName),
+		fmt.Sprintf("  sta %s", param.Symbol.FullName()),
+		fmt.Sprintf("  lda #>%s", labelName),
+		fmt.Sprintf("  sta %s+1", param.Symbol.FullName()),
+	)
+
+	return nil
+}
+
+// processVarArg handles variable arguments
+func (fh *FunctionHandler) processVarArg(sym *Symbol, param *FuncParam, funcName string, line preproc.Line, inAssigns, outAssigns *[]string) error {
+	// Check type compatibility
+	if (sym.IsByte() && param.Symbol.IsWord()) || (sym.IsWord() && param.Symbol.IsByte()) {
+		return fmt.Errorf("%s:%d: CALL %s: type mismatch for parameter %s", line.Filename, line.LineNo, funcName, param.Symbol.Name)
+	}
+
+	if sym.IsConst() {
+		return fmt.Errorf("%s:%d: CALL %s: cannot pass constant to function", line.Filename, line.LineNo, funcName)
+	}
+
+	// Generate IN assignments
+	if param.Direction.Has(DirIn) {
+		*inAssigns = append(*inAssigns,
+			fmt.Sprintf("  lda %s", sym.FullName()),
+			fmt.Sprintf("  sta %s", param.Symbol.FullName()),
+		)
+		if sym.IsWord() {
+			*inAssigns = append(*inAssigns,
+				fmt.Sprintf("  lda %s+1", sym.FullName()),
+				fmt.Sprintf("  sta %s+1", param.Symbol.FullName()),
+			)
+		}
+	}
+
+	// Generate OUT assignments
+	if param.Direction.Has(DirOut) {
+		*outAssigns = append(*outAssigns,
+			fmt.Sprintf("  lda %s", param.Symbol.FullName()),
+			fmt.Sprintf("  sta %s", sym.FullName()),
+		)
+		if sym.IsWord() {
+			*outAssigns = append(*outAssigns,
+				fmt.Sprintf("  lda %s+1", param.Symbol.FullName()),
+				fmt.Sprintf("  sta %s+1", sym.FullName()),
+			)
+		}
+	}
+
+	return nil
+}
+
+// processConstArg handles numeric constant arguments
+func (fh *FunctionHandler) processConstArg(arg string, param *FuncParam, funcName string, line preproc.Line, inAssigns *[]string) error {
+	if param.Direction.Has(DirOut) {
+		return fmt.Errorf("%s:%d: CALL %s: cannot pass constant to out/io parameter", line.Filename, line.LineNo, funcName)
+	}
+
+	// Parse numeric value (supports decimal and hex with $ prefix)
+	var value int64
+	var err error
+
+	if strings.HasPrefix(arg, "$") {
+		_, err = fmt.Sscanf(arg[1:], "%x", &value)
+	} else {
+		_, err = fmt.Sscanf(arg, "%d", &value)
+	}
+
+	if err != nil {
+		return fmt.Errorf("%s:%d: CALL %s: invalid numeric constant %q", line.Filename, line.LineNo, funcName, arg)
+	}
+
+	if param.Symbol.IsByte() && (value < 0 || value > 255) {
+		return fmt.Errorf("%s:%d: CALL %s: constant %d out of byte range", line.Filename, line.LineNo, funcName, value)
+	}
+
+	if value < 0 || value > 65535 {
+		return fmt.Errorf("%s:%d: CALL %s: constant %d out of word range", line.Filename, line.LineNo, funcName, value)
+	}
+
+	lowByte := uint8(value & 0xFF)
+	highByte := uint8((value >> 8) & 0xFF)
+
+	*inAssigns = append(*inAssigns,
+		fmt.Sprintf("  lda #%d", lowByte),
+		fmt.Sprintf("  sta %s", param.Symbol.FullName()),
+	)
+
+	if param.Symbol.IsWord() {
+		// Optimize: only reload A if high byte differs
+		if highByte != lowByte {
+			*inAssigns = append(*inAssigns, fmt.Sprintf("  lda #%d", highByte))
+		}
+		*inAssigns = append(*inAssigns, fmt.Sprintf("  sta %s+1", param.Symbol.FullName()))
+	}
+
+	return nil
+}
+
+// parseImplicitDecl parses {BYTE varname} or {WORD varname} and adds to symbol table
+func (fh *FunctionHandler) parseImplicitDecl(decl string, funcName string) error {
+	parts := strings.Fields(decl)
+	if len(parts) != 2 {
+		return fmt.Errorf("implicit declaration must be 'BYTE name' or 'WORD name', got: %q", decl)
+	}
+
+	typeStr := strings.ToUpper(parts[0])
+	varName := parts[1]
+
+	var kind VarKind
+	switch typeStr {
+	case "BYTE":
+		kind = KindByte
+	case "WORD":
+		kind = KindWord
+	default:
+		return fmt.Errorf("implicit declaration type must be BYTE or WORD, got: %s", typeStr)
+	}
+
+	// Add variable to symbol table with function scope
+	return fh.symTable.AddVar(varName, funcName, kind, 0)
+}
+
+// EndFunction pops all functions from the stack (called by FEND)
+func (fh *FunctionHandler) EndFunction() {
+	fh.currentFuncs = fh.currentFuncs[:0]
+}
+
+// FuncExists checks if a function is declared
+func (fh *FunctionHandler) FuncExists(name string) bool {
+	return fh.findFunc(name) != nil
+}
+
+// CurrentFunction returns the current function name (or empty if global scope)
+func (fh *FunctionHandler) CurrentFunction() string {
+	if len(fh.currentFuncs) == 0 {
+		return ""
+	}
+	return fh.currentFuncs[len(fh.currentFuncs)-1]
+}
+
+// findFunc finds a function declaration by name
+func (fh *FunctionHandler) findFunc(name string) *FuncDecl {
+	for _, f := range fh.functions {
+		if f.Name == name {
+			return f
+		}
+	}
+	return nil
+}
+
+// fixIntuitiveFuncs normalizes function syntax
+// Separates '(' and ')' into own tokens, removes commas
+// Example: "func(a,b)" -> "func ( a b )"
+func fixIntuitiveFuncs(s string) string {
+	var result strings.Builder
+	inString := false
+
+	for i := 0; i < len(s); i++ {
+		ch := s[i]
+
+		if ch == '"' {
+			inString = !inString
+			result.WriteByte(ch)
+			continue
+		}
+
+		if !inString {
+			if ch == '(' || ch == ')' {
+				result.WriteByte(' ')
+				result.WriteByte(ch)
+				result.WriteByte(' ')
+			} else if ch == ',' {
+				result.WriteByte(' ')
+			} else {
+				result.WriteByte(ch)
+			}
+		} else {
+			result.WriteByte(ch)
+		}
+	}
+
+	return normalizeSpaces(result.String())
+}
+
+// normalizeSpaces reduces multiple spaces to single space
+func normalizeSpaces(s string) string {
+	s = strings.TrimSpace(s)
+	var result strings.Builder
+	inString := false
+	lastWasSpace := false
+
+	for i := 0; i < len(s); i++ {
+		ch := s[i]
+
+		if ch == '"' {
+			inString = !inString
+			result.WriteByte(ch)
+			lastWasSpace = false
+			continue
+		}
+
+		if !inString {
+			if ch == ' ' || ch == '\t' {
+				if !lastWasSpace {
+					result.WriteByte(' ')
+					lastWasSpace = true
+				}
+			} else {
+				result.WriteByte(ch)
+				lastWasSpace = false
+			}
+		} else {
+			result.WriteByte(ch)
+			lastWasSpace = false
+		}
+	}
+
+	return result.String()
+}
+
+// parseParams splits line into space-separated parameters, respecting quoted strings
+func parseParams(s string) ([]string, error) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return []string{}, nil
+	}
+
+	var params []string
+	var current strings.Builder
+	inString := false
+
+	for i := 0; i < len(s); i++ {
+		ch := s[i]
+
+		if ch == '"' {
+			inString = !inString
+			current.WriteByte(ch)
+			continue
+		}
+
+		if !inString && (ch == ' ' || ch == '\t') {
+			if current.Len() > 0 {
+				params = append(params, current.String())
+				current.Reset()
+			}
+		} else {
+			current.WriteByte(ch)
+		}
+	}
+
+	if current.Len() > 0 {
+		params = append(params, current.String())
+	}
+
+	if inString {
+		return nil, fmt.Errorf("unterminated string in line")
+	}
+
+	return params, nil
+}
+
+// parseParamSpec parses a parameter specification
+// Returns: direction, varName, isImplicit, implicitDecl, error
+// Examples:
+//
+//	"varname" -> DirIn, "varname", false, "", nil
+//	"in:varname" -> DirIn, "varname", false, "", nil
+//	"out:varname" -> DirOut, "varname", false, "", nil
+//	"io:varname" -> DirIn|DirOut, "varname", false, "", nil
+//	"{BYTE temp}" -> DirIn, "temp", true, "BYTE temp", nil
+//	"out:{WORD result}" -> DirOut, "result", true, "WORD result", nil
+func parseParamSpec(spec string) (ParamDirection, string, bool, string, error) {
+	direction := DirIn // default
+	varName := spec
+	isImplicit := false
+	implicitDecl := ""
+
+	// Check for direction prefix
+	if strings.Contains(spec, ":") {
+		parts := strings.SplitN(spec, ":", 2)
+		if len(parts) != 2 {
+			return 0, "", false, "", fmt.Errorf("invalid parameter spec: %q", spec)
+		}
+
+		dirStr := strings.ToLower(parts[0])
+		varName = parts[1]
+
+		switch dirStr {
+		case "in":
+			direction = DirIn
+		case "out":
+			direction = DirOut
+		case "io":
+			direction = DirIn | DirOut
+		default:
+			return 0, "", false, "", fmt.Errorf("invalid parameter direction: %q", dirStr)
+		}
+	}
+
+	// Check for implicit declaration {TYPE name}
+	if strings.HasPrefix(varName, "{") && strings.HasSuffix(varName, "}") {
+		isImplicit = true
+		implicitDecl = varName[1 : len(varName)-1] // strip { }
+
+		// Extract variable name from implicit declaration
+		parts := strings.Fields(implicitDecl)
+		if len(parts) < 2 {
+			return 0, "", false, "", fmt.Errorf("invalid implicit declaration: %q", varName)
+		}
+		varName = parts[1]
+	}
+
+	return direction, varName, isImplicit, implicitDecl, nil
+}
diff --git a/internal/compiler/funchandler_test.go b/internal/compiler/funchandler_test.go
new file mode 100644
index 0000000..74f4a0a
--- /dev/null
+++ b/internal/compiler/funchandler_test.go
@@ -0,0 +1,688 @@
+package compiler
+
+import (
+	"strings"
+	"testing"
+
+	"c65gm/internal/preproc"
+)
+
+// Helper to create a test Line
+func makeLine(text string) preproc.Line {
+	return preproc.Line{
+		RawText:        text,
+		Text:           text,
+		Filename:       "test.c65",
+		LineNo:         1,
+		Kind:           preproc.Source,
+		PragmaSetIndex: 0,
+	}
+}
+
+func TestFixIntuitiveFuncs(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"func(a,b)", "func ( a b )"},
+		{"func( a, b )", "func ( a b )"},
+		{"func(a,b,c)", "func ( a b c )"},
+		{"CALL func()", "CALL func ( )"},
+		{"func()", "func ( )"},
+		{`func("hello",x)`, `func ( "hello" x )`},
+		{`func("a,b",c)`, `func ( "a,b" c )`},
+		{"func  (  a  ,  b  )", "func ( a b )"},
+	}
+
+	for _, tt := range tests {
+		result := fixIntuitiveFuncs(tt.input)
+		if result != tt.expected {
+			t.Errorf("fixIntuitiveFuncs(%q) = %q, want %q", tt.input, result, tt.expected)
+		}
+	}
+}
+
+func TestBuildComplexParams(t *testing.T) {
+	tests := []struct {
+		input    []string
+		expected []string
+		wantErr  bool
+	}{
+		{
+			input:    []string{"a", "b", "c"},
+			expected: []string{"a", "b", "c"},
+			wantErr:  false,
+		},
+		{
+			input:    []string{"{BYTE", "x}"},
+			expected: []string{"{BYTE x}"},
+			wantErr:  false,
+		},
+		{
+			input:    []string{"{WORD", "ptr}"},
+			expected: []string{"{WORD ptr}"},
+			wantErr:  false,
+		},
+		{
+			input:    []string{"{BYTE", "a}", "{WORD", "b}"},
+			expected: []string{"{BYTE a}", "{WORD b}"},
+			wantErr:  false,
+		},
+		{
+			input:    []string{"x", "{BYTE", "a}", "y"},
+			expected: []string{"x", "{BYTE a}", "y"},
+			wantErr:  false,
+		},
+		{
+			input:    []string{"{BYTE", "x"},
+			expected: nil,
+			wantErr:  true, // unclosed
+		},
+		{
+			input:    []string{"x}"},
+			expected: nil,
+			wantErr:  true, // unmatched close
+		},
+		{
+			input:    []string{"{BYTE", "{WORD", "x}"},
+			expected: nil,
+			wantErr:  true, // nested open
+		},
+	}
+
+	for _, tt := range tests {
+		result, err := buildComplexParams(tt.input)
+		if tt.wantErr {
+			if err == nil {
+				t.Errorf("buildComplexParams(%v) expected error, got nil", tt.input)
+			}
+			continue
+		}
+		if err != nil {
+			t.Errorf("buildComplexParams(%v) unexpected error: %v", tt.input, err)
+			continue
+		}
+		if len(result) != len(tt.expected) {
+			t.Errorf("buildComplexParams(%v) = %v, want %v", tt.input, result, tt.expected)
+			continue
+		}
+		for i := range result {
+			if result[i] != tt.expected[i] {
+				t.Errorf("buildComplexParams(%v)[%d] = %q, want %q", tt.input, i, result[i], tt.expected[i])
+			}
+		}
+	}
+}
+
+func TestParseParams(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected []string
+		wantErr  bool
+	}{
+		{"FUNC test", []string{"FUNC", "test"}, false},
+		{"FUNC test ( a b )", []string{"FUNC", "test", "(", "a", "b", ")"}, false},
+		{`CALL print ( "hello world" )`, []string{"CALL", "print", "(", `"hello world"`, ")"}, false},
+		{"  FUNC   test  ", []string{"FUNC", "test"}, false},
+		{`func("unterminated`, nil, true},
+	}
+
+	for _, tt := range tests {
+		result, err := parseParams(tt.input)
+		if tt.wantErr {
+			if err == nil {
+				t.Errorf("parseParams(%q) expected error, got nil", tt.input)
+			}
+			continue
+		}
+		if err != nil {
+			t.Errorf("parseParams(%q) unexpected error: %v", tt.input, err)
+			continue
+		}
+		if len(result) != len(tt.expected) {
+			t.Errorf("parseParams(%q) = %v, want %v", tt.input, result, tt.expected)
+			continue
+		}
+		for i := range result {
+			if result[i] != tt.expected[i] {
+				t.Errorf("parseParams(%q)[%d] = %q, want %q", tt.input, i, result[i], tt.expected[i])
+			}
+		}
+	}
+}
+
+func TestParseParamSpec(t *testing.T) {
+	tests := []struct {
+		input        string
+		wantDir      ParamDirection
+		wantName     string
+		wantImplicit bool
+		wantImplDecl string
+		wantErr      bool
+	}{
+		{"varname", DirIn, "varname", false, "", false},
+		{"in:varname", DirIn, "varname", false, "", false},
+		{"out:varname", DirOut, "varname", false, "", false},
+		{"io:varname", DirIn | DirOut, "varname", false, "", false},
+		{"{BYTE temp}", DirIn, "temp", true, "BYTE temp", false},
+		{"{WORD result}", DirIn, "result", true, "WORD result", false},
+		{"out:{BYTE x}", DirOut, "x", true, "BYTE x", false},
+		{"io:{WORD ptr}", DirIn | DirOut, "ptr", true, "WORD ptr", false},
+		{"invalid:dir:x", 0, "", false, "", true},
+	}
+
+	for _, tt := range tests {
+		dir, name, isImpl, implDecl, err := parseParamSpec(tt.input)
+		if tt.wantErr {
+			if err == nil {
+				t.Errorf("parseParamSpec(%q) expected error, got nil", tt.input)
+			}
+			continue
+		}
+		if err != nil {
+			t.Errorf("parseParamSpec(%q) unexpected error: %v", tt.input, err)
+			continue
+		}
+		if dir != tt.wantDir {
+			t.Errorf("parseParamSpec(%q) direction = %v, want %v", tt.input, dir, tt.wantDir)
+		}
+		if name != tt.wantName {
+			t.Errorf("parseParamSpec(%q) name = %q, want %q", tt.input, name, tt.wantName)
+		}
+		if isImpl != tt.wantImplicit {
+			t.Errorf("parseParamSpec(%q) implicit = %v, want %v", tt.input, isImpl, tt.wantImplicit)
+		}
+		if implDecl != tt.wantImplDecl {
+			t.Errorf("parseParamSpec(%q) implDecl = %q, want %q", tt.input, implDecl, tt.wantImplDecl)
+		}
+	}
+}
+
+func TestHandleFuncDecl_VoidFunction(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	asm, err := fh.HandleFuncDecl(makeLine("FUNC test_void"))
+	if err != nil {
+		t.Fatalf("HandleFuncDecl failed: %v", err)
+	}
+
+	if len(asm) != 1 {
+		t.Fatalf("expected 1 asm line, got %d", len(asm))
+	}
+	if asm[0] != "test_void" {
+		t.Errorf("expected label 'test_void', got %q", asm[0])
+	}
+
+	if !fh.FuncExists("test_void") {
+		t.Error("function should exist")
+	}
+}
+
+func TestHandleFuncDecl_WithExistingParams(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	// Pre-declare parameters
+	st.AddVar("x", "test_func", KindByte, 0)
+	st.AddVar("y", "test_func", KindWord, 0)
+
+	asm, err := fh.HandleFuncDecl(makeLine("FUNC test_func ( x y )"))
+	if err != nil {
+		t.Fatalf("HandleFuncDecl failed: %v", err)
+	}
+
+	if len(asm) != 1 {
+		t.Fatalf("expected 1 asm line, got %d", len(asm))
+	}
+
+	funcDecl := fh.findFunc("test_func")
+	if funcDecl == nil {
+		t.Fatal("function not found")
+	}
+	if len(funcDecl.Params) != 2 {
+		t.Fatalf("expected 2 params, got %d", len(funcDecl.Params))
+	}
+}
+
+func TestHandleFuncDecl_ImplicitDeclarations(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	asm, err := fh.HandleFuncDecl(makeLine("FUNC test_impl ( {BYTE a} {WORD b} )"))
+	if err != nil {
+		t.Fatalf("HandleFuncDecl failed: %v", err)
+	}
+
+	if len(asm) != 1 {
+		t.Fatalf("expected 1 asm line, got %d", len(asm))
+	}
+
+	// Check that variables were declared
+	symA := st.Lookup("a", []string{"test_impl"})
+	if symA == nil {
+		t.Fatal("parameter 'a' not declared")
+	}
+	if !symA.IsByte() {
+		t.Error("parameter 'a' should be byte")
+	}
+
+	symB := st.Lookup("b", []string{"test_impl"})
+	if symB == nil {
+		t.Fatal("parameter 'b' not declared")
+	}
+	if !symB.IsWord() {
+		t.Error("parameter 'b' should be word")
+	}
+}
+
+func TestHandleFuncDecl_WithDirections(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	_, err := fh.HandleFuncDecl(makeLine("FUNC test_dir ( in:{BYTE a} out:{BYTE b} io:{WORD c} )"))
+	if err != nil {
+		t.Fatalf("HandleFuncDecl failed: %v", err)
+	}
+
+	funcDecl := fh.findFunc("test_dir")
+	if funcDecl == nil {
+		t.Fatal("function not found")
+	}
+
+	if len(funcDecl.Params) != 3 {
+		t.Fatalf("expected 3 params, got %d", len(funcDecl.Params))
+	}
+
+	if funcDecl.Params[0].Direction != DirIn {
+		t.Error("param 0 should be DirIn")
+	}
+	if funcDecl.Params[1].Direction != DirOut {
+		t.Error("param 1 should be DirOut")
+	}
+	if funcDecl.Params[2].Direction != (DirIn | DirOut) {
+		t.Error("param 2 should be DirIn|DirOut")
+	}
+}
+
+func TestHandleFuncDecl_Errors(t *testing.T) {
+	tests := []struct {
+		name    string
+		line    string
+		preDecl func(*SymbolTable)
+		wantErr string
+	}{
+		{
+			name:    "redeclaration",
+			line:    "FUNC duplicate ( {BYTE x} )",
+			preDecl: func(st *SymbolTable) {},
+			wantErr: "already declared",
+		},
+		{
+			name:    "missing param",
+			line:    "FUNC test ( missing )",
+			wantErr: "not declared",
+		},
+		{
+			name: "const param",
+			line: "FUNC test ( constval )",
+			preDecl: func(st *SymbolTable) {
+				st.AddConst("constval", "test", KindByte, 42)
+			},
+			wantErr: "cannot be a constant",
+		},
+		{
+			name:    "invalid implicit",
+			line:    "FUNC test ( {INVALID x} )",
+			wantErr: "must be BYTE or WORD",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			st := NewSymbolTable()
+			ls := NewLabelStack("L")
+			csh := NewConstantStringHandler()
+			pragma := preproc.NewPragma()
+			fh := NewFunctionHandler(st, ls, csh, pragma)
+
+			if tt.preDecl != nil {
+				tt.preDecl(st)
+			}
+
+			// Special case for redeclaration test
+			if tt.name == "redeclaration" {
+				fh.HandleFuncDecl(makeLine("FUNC duplicate ( {BYTE x} )"))
+			}
+
+			_, err := fh.HandleFuncDecl(makeLine(tt.line))
+			if err == nil {
+				t.Fatal("expected error, got nil")
+			}
+			if !strings.Contains(err.Error(), tt.wantErr) {
+				t.Errorf("error %q does not contain %q", err.Error(), tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestHandleFuncCall_VarArgs(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	// Declare function with params
+	st.AddVar("param_a", "test_func", KindByte, 0)
+	st.AddVar("param_b", "test_func", KindWord, 0)
+	fh.HandleFuncDecl(makeLine("FUNC test_func ( param_a param_b )"))
+
+	// Declare caller variables
+	st.AddVar("var_a", "", KindByte, 0)
+	st.AddVar("var_b", "", KindWord, 0)
+
+	asm, err := fh.HandleFuncCall(makeLine("CALL test_func ( var_a var_b )"))
+	if err != nil {
+		t.Fatalf("HandleFuncCall failed: %v", err)
+	}
+
+	// Check generated assembly
+	expectedLines := []string{
+		"  lda var_a",
+		"  sta test_func_param_a",
+		"  lda var_b",
+		"  sta test_func_param_b",
+		"  lda var_b+1",
+		"  sta test_func_param_b+1",
+		"  jsr test_func",
+	}
+
+	if len(asm) != len(expectedLines) {
+		t.Fatalf("expected %d asm lines, got %d", len(expectedLines), len(asm))
+	}
+
+	for i, expected := range expectedLines {
+		if asm[i] != expected {
+			t.Errorf("asm[%d] = %q, want %q", i, asm[i], expected)
+		}
+	}
+}
+
+func TestHandleFuncCall_OutParams(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	// Declare function with out param
+	st.AddVar("result", "get_result", KindByte, 0)
+	fh.HandleFuncDecl(makeLine("FUNC get_result ( out:result )"))
+
+	// Declare caller variable
+	st.AddVar("output", "", KindByte, 0)
+
+	asm, err := fh.HandleFuncCall(makeLine("CALL get_result ( output )"))
+	if err != nil {
+		t.Fatalf("HandleFuncCall failed: %v", err)
+	}
+
+	// Should have JSR and OUT assignment
+	found_jsr := false
+	found_out := false
+	for _, line := range asm {
+		if strings.Contains(line, "jsr get_result") {
+			found_jsr = true
+		}
+		if strings.Contains(line, "lda get_result_result") {
+			found_out = true
+		}
+	}
+
+	if !found_jsr {
+		t.Error("missing jsr instruction")
+	}
+	if !found_out {
+		t.Error("missing out assignment")
+	}
+}
+
+func TestHandleFuncCall_ConstArgs(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	// Declare function
+	st.AddVar("x", "test_const", KindByte, 0)
+	st.AddVar("y", "test_const", KindWord, 0)
+	fh.HandleFuncDecl(makeLine("FUNC test_const ( x y )"))
+
+	asm, err := fh.HandleFuncCall(makeLine("CALL test_const ( 42 $1234 )"))
+	if err != nil {
+		t.Fatalf("HandleFuncCall failed: %v", err)
+	}
+
+	// Check for immediate loads
+	foundByte := false
+	foundWord := false
+	for _, line := range asm {
+		if strings.Contains(line, "lda #42") {
+			foundByte = true
+		}
+		if strings.Contains(line, "lda #18") { // 0x12
+			foundWord = true
+		}
+	}
+
+	if !foundByte {
+		t.Error("missing byte constant load")
+	}
+	if !foundWord {
+		t.Error("missing word constant load")
+	}
+}
+
+func TestHandleFuncCall_LabelArg(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	// Declare function
+	st.AddVar("ptr", "test_label", KindWord, 0)
+	fh.HandleFuncDecl(makeLine("FUNC test_label ( ptr )"))
+
+	asm, err := fh.HandleFuncCall(makeLine("CALL test_label ( @my_label )"))
+	if err != nil {
+		t.Fatalf("HandleFuncCall failed: %v", err)
+	}
+
+	// Check for label reference
+	foundLow := false
+	foundHigh := false
+	for _, line := range asm {
+		if strings.Contains(line, "#<my_label") {
+			foundLow = true
+		}
+		if strings.Contains(line, "#>my_label") {
+			foundHigh = true
+		}
+	}
+
+	if !foundLow || !foundHigh {
+		t.Error("missing label reference code")
+	}
+}
+
+func TestHandleFuncCall_StringArg(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	// Declare function
+	st.AddVar("str_ptr", "print", KindWord, 0)
+	fh.HandleFuncDecl(makeLine("FUNC print ( str_ptr )"))
+
+	asm, err := fh.HandleFuncCall(makeLine(`CALL print ( "hello" )`))
+	if err != nil {
+		t.Fatalf("HandleFuncCall failed: %v", err)
+	}
+
+	// Check that label was generated
+	if ls.Size() != 1 {
+		t.Errorf("expected 1 label generated, got %d", ls.Size())
+	}
+
+	// Check for label reference in asm
+	foundLabel := false
+	for _, line := range asm {
+		if strings.Contains(line, "#<L1") || strings.Contains(line, "#>L1") {
+			foundLabel = true
+			break
+		}
+	}
+
+	if !foundLabel {
+		t.Error("missing string label reference")
+	}
+}
+
+func TestHandleFuncCall_Errors(t *testing.T) {
+	tests := []struct {
+		name    string
+		setup   func(*FunctionHandler, *SymbolTable)
+		line    string
+		wantErr string
+	}{
+		{
+			name:    "function not declared",
+			setup:   func(fh *FunctionHandler, st *SymbolTable) {},
+			line:    "CALL undefined ( )",
+			wantErr: "not declared",
+		},
+		{
+			name: "wrong arg count",
+			setup: func(fh *FunctionHandler, st *SymbolTable) {
+				st.AddVar("x", "test", KindByte, 0)
+				fh.HandleFuncDecl(makeLine("FUNC test ( x )"))
+			},
+			line:    "CALL test ( 1 2 )",
+			wantErr: "expected 1 arguments, got 2",
+		},
+		{
+			name: "type mismatch",
+			setup: func(fh *FunctionHandler, st *SymbolTable) {
+				st.AddVar("param", "test", KindByte, 0)
+				fh.HandleFuncDecl(makeLine("FUNC test ( param )"))
+				st.AddVar("wvar", "", KindWord, 0)
+			},
+			line:    "CALL test ( wvar )",
+			wantErr: "type mismatch",
+		},
+		{
+			name: "const to out param",
+			setup: func(fh *FunctionHandler, st *SymbolTable) {
+				st.AddVar("result", "test", KindByte, 0)
+				fh.HandleFuncDecl(makeLine("FUNC test ( out:result )"))
+			},
+			line:    "CALL test ( 42 )",
+			wantErr: "out/io parameter",
+		},
+		{
+			name: "label to byte param",
+			setup: func(fh *FunctionHandler, st *SymbolTable) {
+				st.AddVar("x", "test", KindByte, 0)
+				fh.HandleFuncDecl(makeLine("FUNC test ( x )"))
+			},
+			line:    "CALL test ( @label )",
+			wantErr: "byte parameter",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			st := NewSymbolTable()
+			ls := NewLabelStack("L")
+			csh := NewConstantStringHandler()
+			pragma := preproc.NewPragma()
+			fh := NewFunctionHandler(st, ls, csh, pragma)
+
+			tt.setup(fh, st)
+
+			_, err := fh.HandleFuncCall(makeLine(tt.line))
+			if err == nil {
+				t.Fatal("expected error, got nil")
+			}
+			if !strings.Contains(err.Error(), tt.wantErr) {
+				t.Errorf("error %q does not contain %q", err.Error(), tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestEndFunction(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	// Declare function (pushes to stack)
+	fh.HandleFuncDecl(makeLine("FUNC test ( {BYTE x} )"))
+
+	if fh.CurrentFunction() != "test" {
+		t.Errorf("current function = %q, want 'test'", fh.CurrentFunction())
+	}
+
+	// End function
+	fh.EndFunction()
+
+	if fh.CurrentFunction() != "" {
+		t.Errorf("current function = %q, want ''", fh.CurrentFunction())
+	}
+}
+
+func TestCurrentFunction(t *testing.T) {
+	st := NewSymbolTable()
+	ls := NewLabelStack("L")
+	csh := NewConstantStringHandler()
+	pragma := preproc.NewPragma()
+	fh := NewFunctionHandler(st, ls, csh, pragma)
+
+	if fh.CurrentFunction() != "" {
+		t.Error("expected empty current function initially")
+	}
+
+	fh.HandleFuncDecl(makeLine("FUNC func1 ( {BYTE x} )"))
+	if fh.CurrentFunction() != "func1" {
+		t.Errorf("expected 'func1', got %q", fh.CurrentFunction())
+	}
+
+	fh.HandleFuncDecl(makeLine("FUNC func2 ( {BYTE y} )"))
+	if fh.CurrentFunction() != "func2" {
+		t.Errorf("expected 'func2', got %q", fh.CurrentFunction())
+	}
+
+	fh.EndFunction()
+	if fh.CurrentFunction() != "" {
+		t.Errorf("expected '', got %q", fh.CurrentFunction())
+	}
+}