diff --git a/dub.sdl b/dub.sdl
index 1325a01..c56910c 100644
--- a/dub.sdl
+++ b/dub.sdl
@@ -3,27 +3,30 @@ description "A minimal D application."
 authors "tanya"
 copyright "Copyright © 2025, tanya"
 license "MPL-2.0"
-dependency "commandr" version="~>1.1.0"
-dependency "colored" version="~>0.0.33"
 targetType "executable"
 sourcePaths
 
 configuration "clox" {
 	buildOptions "betterC"
-	/* debugVersions "memTrace" */
-	/* debugVersions "traceExec" */
+	sourcePaths "src/clox"
+	buildRequirements "requireContracts"
+}
+
+configuration "clox-dbg" {
+	buildRequirements "requireBoundsCheck" "requireContracts"
+	debugVersions "memTrace"
 	debugVersions "printCode"
+	debugVersions "traceExec"
+	dependency "colored" version="~>0.0.33"
 	dflags "-checkaction=C"
 	libs "libbacktrace"
-	targetType "executable"
 	sourcePaths "src/clox"
-	buildRequirements "requireBoundsCheck" "requireContracts"
 }
 
 configuration "jlox" {
-	targetType "executable"
+	dependency "colored" version="~>0.0.33"
+	dependency "commandr" version="~>1.1.0"
 	sourcePaths "src/jlox" "src/common"
 	versions "LoxConcatNonStrings" "LoxExtraNativeFuncs" "LoxPrintMultiple"
-	buildRequirements "requireBoundsCheck" "requireContracts"
 }
 
diff --git a/src/clox/chunk.d b/src/clox/chunk.d
index 39a4f47..333feee 100644
--- a/src/clox/chunk.d
+++ b/src/clox/chunk.d
@@ -13,6 +13,7 @@ struct OpColour{
 enum OpConst;
 enum OpStack;
 enum OpJump;
+enum OpCall;
 
 enum OpCode : ubyte{
 	@OpConst @(OpColour("200", "200", "100")) Constant,
@@ -48,7 +49,9 @@ enum OpCode : ubyte{
 	@(OpColour("200", "100", "100")) Not,
 	@(OpColour("100", "100", "200")) Negate,
 	@(OpColour("000", "200", "100")) Print,
-	@(OpColour("000", "200", "100")) Return,
+
+	@OpCall @(OpColour("250", "200", "250")) Call,
+	@(OpColour("250", "190", "200")) Return,
 }
 
 struct Chunk{
@@ -68,12 +71,12 @@ struct Chunk{
 		code ~= b;
 		lines ~= line;
 	}
-	size_t addConstant(Value value){
-		long index = constants[].countUntil(value);
+	int addConstant(Value value){
+		int index = cast(int)constants[].countUntil(value);
 		if(index >= 0)
 			return index;
 		constants ~= value;
-		return constants.count - 1;
+		return cast(int)constants.count - 1;
 	}
 	void free(){
 		code.free();
diff --git a/src/clox/compiler.d b/src/clox/compiler.d
index 6a5b138..a9e4153 100644
--- a/src/clox/compiler.d
+++ b/src/clox/compiler.d
@@ -5,14 +5,21 @@ import core.stdc.stdio;
 import clox.scanner;
 import clox.parser;
 import clox.chunk;
-import clox.emitter;
 import clox.dbg;
+import clox.vm;
+import clox.object;
+import clox.value;
 import clox.container.dynarray;
+import clox.container.varint;
+
+Parser parser;
+Compiler* currentCompiler;
 
 struct Compiler{
-	Scanner scanner;
-	Parser parser;
-	Emitter emitter;
+	Compiler* enclosing;
+	Obj.Function* func;
+	enum FunctionType{ None, Function, Script }
+	FunctionType ftype = FunctionType.Script;
 	struct Local{
 		enum Uninitialised = -1;
 		Token name;
@@ -21,28 +28,58 @@ struct Compiler{
 	DynArray!Local locals;
 	int scopeDepth;
 	private Chunk* compilingChunk;
-	Chunk* currentChunk() => compilingChunk;
-	bool compile(const(char)* source, Chunk* chunk){
-		scanner.initialise(source);
-		parser.initialise(&this);
-		emitter.initialise(&this);
+	Chunk* currentChunk() => &func.chunk;
+	void initialise(FunctionType ftype){
+		this.ftype = ftype;
+		enclosing = currentCompiler;
+		currentCompiler = &this;
 		locals.initialise();
-		compilingChunk = chunk;
 
+		func = Obj.Function.create();
+		if(ftype == FunctionType.Function){
+			currentCompiler.func.name = Obj.String.copy(parser.previous.lexeme);
+		}
+
+		Local local = Local();
+		local.depth = 0;
+		local.name.lexeme = "";
+		locals ~= local;
+	}
+	Obj.Function* compile(){
 		parser.advance();
 		while(!parser.match(Token.Type.EOF)){
 			parser.declaration();
 		}
-		end();
-		return !parser.hadError;
+
+		Obj.Function* f = end();
+		return parser.hadError ? null : f;
 	}
-	void end(){
-		emitter.emitReturn();
-		debug(printCode){
+	Obj.Function* end(){
+		emitReturn();
+		Obj.Function* f = func;
+		debug(printCode) if(vm.printCode){
 			if(!parser.hadError)
-				currentChunk.disassembleChunk();
+				currentChunk.disassembleChunk(func.name !is null ? func.name.chars.ptr : "<script>");
 		}
 		locals.free();
+		currentCompiler = enclosing;
+		return f;
+	}
+
+	void emit(Args...)(Args a){
+		static foreach(b; a)
+			currentCompiler.currentChunk.write(b, parser.previous.line);
+	}
+	void emitReturn(){
+		emit(OpCode.Nil, OpCode.Return);
+	}
+	void emitConstant(Value value){
+		int c = makeConstant(value);
+		emit(OpCode.Constant, VarUint(c).bytes);
+	}
+	int makeConstant(Value value){
+		int constant = currentCompiler.currentChunk.addConstant(value);
+		return constant;
 	}
 }
 
diff --git a/src/clox/container/dynarray.d b/src/clox/container/dynarray.d
index 5c67421..a536c1f 100644
--- a/src/clox/container/dynarray.d
+++ b/src/clox/container/dynarray.d
@@ -3,28 +3,31 @@ module clox.container.dynarray;
 import clox.memory;
 
 struct DynArray(T){
-	size_t count;
-	size_t capacity;
+	private size_t _count;
+	private size_t _capacity;
+	ref size_t count() => _count;
+	size_t capacity() => _capacity;
+	// TODO capacity setter
 	T* ptr;
 	void initialise(){
-		count = 0;
-		capacity = 0;
+		_count = 0;
+		_capacity = 0;
 		ptr = null;
 	}
 	void opOpAssign(string op: "~")(in T value){
 		if(capacity < count + 1){
 			size_t oldCapacity = capacity;
-			capacity = GROW_CAPACITY(oldCapacity);
+			_capacity = GROW_CAPACITY(oldCapacity);
 			ptr = GROW_ARRAY!T(ptr, oldCapacity, capacity);
 		}
 		ptr[count] = value;
-		count++;
+		_count++;
 	}
-	auto opSlice(){
+	ref auto opSlice(){
 		assert(ptr || !count);
 		return ptr[0 .. count];
 	}
-	auto opSlice(size_t i, size_t o){
+	ref auto opSlice(size_t i, size_t o){
 		assert(ptr || !count);
 		return ptr[i .. o];
 	}
@@ -35,15 +38,19 @@ struct DynArray(T){
 	size_t opDollar(size_t pos: 0)(){
 		return count;
 	}
+	auto pop(){
+		assert(count);
+		return this[--_count];
+	}
+	void reset(){
+		_count = 0;
+		debug foreach(ref item; this[])
+			item = T.init;
+	}
 	void free(){
 		if(ptr)
 			FREE_ARRAY!T(ptr, capacity);
 		initialise();
 	}
-	auto pop(){
-		assert(count);
-		count--;
-		return this[count-1];
-	}
 }
 
diff --git a/src/clox/container/stack.d b/src/clox/container/stack.d
deleted file mode 100644
index 6ac7551..0000000
--- a/src/clox/container/stack.d
+++ /dev/null
@@ -1,30 +0,0 @@
-module clox.container.stack;
-
-import clox.container.dynarray;
-
-struct Stack(T){
-	T* top;
-	private DynArray!T data;
-	void initialise(){
-		data.initialise();
-		top = data.ptr;
-	}
-	void opOpAssign(string op: "~")(T value){
-		data ~= value;
-		top = data.ptr + data.count;
-	}
-	T pop(){
-		assert(top > data.ptr);
-		T t = *(--top);
-		assert(data.count-- >= 0);
-		return t;
-	}
-	ref T opIndex(size_t i) => data[i];
-	const(T)[] live(){
-		return data[];
-	}
-	void free(){
-		data.free();
-	}
-}
-
diff --git a/src/clox/dbg.d b/src/clox/dbg.d
index c08b841..5e3575a 100644
--- a/src/clox/dbg.d
+++ b/src/clox/dbg.d
@@ -28,8 +28,10 @@ private long constantInstruction(alias OpCode op)(const char* name, Chunk* chunk
 private long jumpInstruction(alias OpCode op)(const char* name, int sign, Chunk* chunk, long offset){
 	ushort jump = cast(ushort)(chunk.code[offset + 1] << 8) | chunk.code[offset + 2];
 	enum c = getUDAs!(op, OpColour)[0];
-	printf(ctEval!(colour!("%-14s", c.r, c.g, c.b) ~ colour!(" %4ld ", Colour.Green)).ptr, name, (jump * sign) + offset + 3);
-	printf("%i ", sign * jump);
+	long pl = printf(ctEval!(colour!("%-14s", c.r, c.g, c.b) ~ colour!(" %4ld ", Colour.Green)).ptr, name, (jump * sign) + offset + 3);
+	pl += printf("%i ", sign * jump);
+	foreach(i; 0 .. 70-pl)
+		printf(" ");
 	return offset + 3;
 }
 private long stackIndexInstruction(alias OpCode op)(const char* name, Chunk* chunk, long offset){
@@ -39,6 +41,13 @@ private long stackIndexInstruction(alias OpCode op)(const char* name, Chunk* chu
 	printf("                ");
 	return offset + 1 + index.len;
 }
+private long callInstruction(alias OpCode op)(const char* name, Chunk* chunk, long offset){
+	VarUint index = VarUint.read(&chunk.code[offset + 1]);
+	enum c = getUDAs!(op, OpColour)[0];
+	printf(ctEval!(colour!("%-14s", c.r, c.g, c.b) ~ colour!(" %4d ", Colour.Pink)).ptr, name, index.i);
+	printf("                ");
+	return offset + 1 + index.len;
+}
 
 void printHeader(Chunk* chunk, const char* name = "execution"){
 	printf("  ==============  %s  ==============\n", name);
@@ -74,6 +83,8 @@ long disassembleInstruction(Chunk* chunk, long offset){
 				case e: return stackIndexInstruction!e(e.stringof, chunk, offset);
 			} else static if(hasUDA!(e, OpJump)){
 				case e: return jumpInstruction!e(e.stringof, e == OpCode.Loop ? -1 : 1, chunk, offset);
+			} else static if(hasUDA!(e, OpCall)){
+				case e: return callInstruction!e(e.stringof, chunk, offset);
 			} else {
 				case e: return simpleInstruction!e(e.stringof, offset);
 			}
diff --git a/src/clox/emitter.d b/src/clox/emitter.d
deleted file mode 100644
index 64cdb09..0000000
--- a/src/clox/emitter.d
+++ /dev/null
@@ -1,31 +0,0 @@
-module clox.emitter;
-
-import core.stdc.stdio;
-
-import clox.chunk;
-import clox.compiler;
-import clox.value;
-import clox.container.varint;
-
-struct Emitter{
-	Compiler* compiler;
-	void initialise(Compiler* compiler){
-		this.compiler = compiler;
-	}
-	void emit(Args...)(Args a){
-		static foreach(b; a)
-			compiler.currentChunk.write(b, compiler.parser.previous.line);
-	}
-	void emitReturn(){
-		emit(OpCode.Return);
-	}
-	void emitConstant(Value value){
-		size_t c = makeConstant(value);
-		emit(OpCode.Constant, VarUint(c).bytes);
-	}
-	size_t makeConstant(Value value){
-		size_t constant = compiler.currentChunk.addConstant(value);
-		return constant;
-	}
-}
-
diff --git a/src/clox/main.d b/src/clox/main.d
index cc91926..5539af8 100644
--- a/src/clox/main.d
+++ b/src/clox/main.d
@@ -1,5 +1,6 @@
 module clox.main;
 
+import std.algorithm;
 import core.sys.posix.unistd : STDIN_FILENO;
 import core.stdc.stdio;
 import core.stdc.stdlib;
@@ -35,28 +36,52 @@ int runStdin(){
 		source.free();
 	return vm.interpret(source).interpretResult;
 }
-int runFile(const char* path){
-	char* source = path.readFile();
+int runFile(const char[] path){
+	auto source = path.readFile();
 	if(!source)
 		return 74;
 	scope(exit)
-		source.free();
-	return vm.interpret(source).interpretResult;
+		source.ptr.free();
+	return vm.interpret(source.ptr).interpretResult;
 }
 
 int runMain(ulong argc, const char** argv){
+	auto usage(){
+		debug(printCode) debug(traceExec) return stderr.fprintf("Usage: lox [path] [-pt]\n");
+		debug(printCode) return stderr.fprintf("Usage: lox [path] [-p]\n");
+		debug(traceExec) return stderr.fprintf("Usage: lox [path] [-t]\n");
+		stderr.fprintf("Usage: lox [path]\n");
+	}
+	const(char)[] file;
+
+	foreach(arg; argv[1 .. argc].map!parse){
+		if(arg[0] == '-'){
+			foreach(c; arg[1 .. $]){
+				switch(c){
+					debug(printCode) case 'p': vm.printCode = true; break;
+					debug(traceExec) case 't': vm.traceExec = true; break;
+					default:
+						usage();
+						return 64;
+				}
+			}
+		} else {
+			file = arg;
+		}
+	}
+
 	vm.initialise();
 	scope(exit)
 		vm.free();
 
-	if(argc == 1 && isatty(STDIN_FILENO)){
+	if(!file && isatty(STDIN_FILENO)){
 		return runPrompt();
-	} else if(argc == 1){
+	} else if(!file){
 		return runStdin();
-	} else if(argc == 2){
-		return runFile(argv[1]);
+	} else if(file){
+		return runFile(file);
 	} else {
-		stderr.fprintf("Usage: lox [path]\n");
+		usage();
 		return 64;
 	}
 }
diff --git a/src/clox/memory.d b/src/clox/memory.d
index bfdc5a1..ba615de 100644
--- a/src/clox/memory.d
+++ b/src/clox/memory.d
@@ -2,6 +2,8 @@ module clox.memory;
 
 import core.stdc.stdlib;
 
+import clox.util;
+
 auto GROW_CAPACITY(size_t capacity) => capacity < 8 ? 8 : capacity * 2;
 auto GROW_ARRAY(T)(T* ptr, size_t oldCount, size_t newCount) => cast(T*)reallocate(ptr, T.sizeof * oldCount, T.sizeof * newCount);
 auto FREE_ARRAY(T)(T* ptr, size_t oldCount) => reallocate!T(ptr, T.sizeof * oldCount, 0);
@@ -29,9 +31,14 @@ version(D_BetterC) {} else {
 		import std.demangle;
 		BackTraceBuilder* btb = cast(BackTraceBuilder*)data;
 		if(func){
-			string funcStr = func.to!string.demangle;
-			btb.funcStack ~= funcStr;
-			btb.lineStack ~= lineno;
+			import std.string;
+			try{
+				btb.fileStack ~= filename.to!string;
+				btb.funcStack ~= func.to!string.demangle.stripLeft("nothrow ").stripLeft("@nogc ");
+				btb.lineStack ~= lineno;
+			} catch(Exception){
+				assert(0);
+			}
 		}
 		return 0;
 	}
@@ -41,10 +48,14 @@ version(D_BetterC) {} else {
 	}
 
 	struct BackTraceBuilder{
+		string[] fileStack;
 		string[] funcStack;
 		int[] lineStack;
 		string toString() const{
-			return zip(funcStack, lineStack).map!"'\t' ~ a[0] ~ ` : ` ~ a[1].to!string".join("\n");
+			import clox.util, std.format;
+			return zip(fileStack, lineStack, funcStack).map!(a =>
+				'\t' ~ colour!("%s", Colour.Yellow).format(a[0]) ~ colour!(`:`, Colour.Black) ~ colour!("%d", Colour.Cyan).format(a[1]) ~ ' ' ~ a[2]
+			).join("\n");
 		}
 	}
 	BackTraceBuilder createBacktrace(int skip = 1) nothrow{
@@ -62,7 +73,7 @@ version(D_BetterC) {} else {
 	ulong totalAllocs, totalReallocs, totalFrees;
 	ulong totalAllocBytes, totalFreedBytes;
 	static ~this(){
-		stderr.writefln("Allocs: %d (%d bytes), Reallocs: %d, Frees: %d (%d bytes)", totalAllocs, totalAllocBytes, totalReallocs, totalFrees, totalFreedBytes);
+		stderr.writefln(colour!("Allocs: %d (%,d bytes), Reallocs: %d, Frees: %d (%,d bytes)", Colour.Black), totalAllocs, totalAllocBytes, totalReallocs, totalFrees, totalFreedBytes);
 		if(totalAllocBytes > totalFreedBytes){
 			stderr.writefln("Leaked %d bytes!".lightRed.to!string, totalAllocBytes - totalFreedBytes);
 
@@ -123,8 +134,17 @@ void freeObject(Obj* object){
 	final switch(object.type){
 		case Obj.Type.String:
 			Obj.String* str = cast(Obj.String*)object;
-			FREE_ARRAY!char(str.chars.ptr, str.chars.length + 1);
-			FREE!(Obj.String)(cast(Obj.String*)object);
+			FREE_ARRAY(str.chars.ptr, str.chars.length + 1);
+			FREE(str);
+			break;
+		case Obj.Type.Function:
+			Obj.Function* func = cast(Obj.Function*)object;
+			func.chunk.free();
+			FREE(func);
+			break;
+		case Obj.Type.NativeFunction:
+			Obj.NativeFunction* func = cast(Obj.NativeFunction*)object;
+			FREE(func);
 			break;
 		case Obj.Type.None: assert(0);
 	}
diff --git a/src/clox/obj.d b/src/clox/obj.d
index 1a4bada..f0abd7e 100644
--- a/src/clox/obj.d
+++ b/src/clox/obj.d
@@ -2,14 +2,15 @@ module clox.object;
 
 import core.stdc.stdio;
 
+import clox.chunk;
+import clox.container.table;
 import clox.memory;
 import clox.value;
 import clox.vm;
-import clox.container.table;
 
 struct Obj{
 	enum Type{
-		None, String,
+		None, String, Function, NativeFunction
 	}
 	Type type;
 	Obj* next;
@@ -19,17 +20,27 @@ struct Obj{
 		static if(type != Type.None)
 			assert(this.type == type);
 		static if(type == Type.String) return cast(String*)&this;
+		static if(type == Type.Function) return cast(Function*)&this;
+		static if(type == Type.NativeFunction) return cast(NativeFunction*)&this;
 		static if(type == Type.None) return &this;
 	}
 
 	int print(const char* strFmt = `"%s"`) const{
 		final switch(type){
-			case Type.String: return printf(strFmt, asString.chars.ptr); break;
+			case Type.String: return printf(strFmt, asString.chars.ptr);
+			case Type.Function:
+				Function* func = asFunc;
+				if(func.name !is null)
+					return printf("<fn %s/%d>", func.name.chars.ptr, func.arity);
+				return printf("<script>");
+			case Type.NativeFunction: return printf("<native fn>");
 			case Type.None: assert(0);
 		}
 	}
 
 	String* asString() const pure => as!(Type.String);
+	Function* asFunc() const pure => as!(Type.Function);
+	NativeFunction* asNativeFunc() const pure => as!(Type.NativeFunction);
 
 	private static T* allocateObject(T)(){
 		Obj* object = reallocate!Obj(null, 0, T.sizeof);
@@ -81,17 +92,49 @@ struct Obj{
 		}
 	}
 
+	struct Function{
+		static enum myType = Type.Function;
+		Obj obj;
+		int arity;
+		Chunk chunk;
+		String* name;
+		static Function* create(){
+			Function* func = allocateObject!(typeof(this))();
+			func.arity = 0;
+			func.chunk = Chunk.init;
+			func.chunk.initialise();
+			func.name = null;
+			return func;
+		}
+	}
+
+	struct NativeFunction{
+		static enum myType = Type.NativeFunction;
+		alias Sig = Value function(int argCount, Value* args);
+		Obj obj;
+		Sig func;
+		static NativeFunction* create(Sig func){
+			Obj.NativeFunction* native = allocateObject!(typeof(this))();
+			native.func = func;
+			return native;
+		}
+	}
+
 	bool opEquals(in ref Obj rhs) const pure{
 		if(rhs.type != type)
 			return false;
 		final switch(type){
 			case Type.String: return asString.chars.ptr is rhs.asString.chars.ptr;
+			case Type.Function: return &this == &rhs;
+			case Type.NativeFunction: return &this == &rhs;
 			case Type.None: assert(0);
 		}
 	}
 	bool opCmp(in ref Obj rhs) const pure{
 		final switch(type){
 			case Type.String: return asString.chars > rhs.asString.chars;
+			case Type.Function: return false;
+			case Type.NativeFunction: return false;
 			case Type.None: assert(0);
 		}
 	}
@@ -100,6 +143,8 @@ struct Obj{
 		static string toString(Obj* obj){
 			final switch(obj.type){
 				case Type.String: return '"' ~ obj.asString.chars.idup ~ '"';
+				case Type.Function: return "Function";
+				case Type.NativeFunction: return "NativeFunction";
 				case Type.None: assert(0);
 			}
 		}
diff --git a/src/clox/parser.d b/src/clox/parser.d
index 828831c..4a2a538 100644
--- a/src/clox/parser.d
+++ b/src/clox/parser.d
@@ -14,16 +14,12 @@ import clox.vm;
 import clox.container.varint;
 
 struct Parser{
-	Compiler* compiler;
 	Token current, previous;
 	bool hadError, panicMode;
-	void initialise(Compiler* compiler){
-		this.compiler = compiler;
-	}
 	void advance(){
 		previous = current;
 		while(true){
-			current = compiler.scanner.scanToken();
+			current = scanner.scanToken();
 			if(current.type != Token.Type.Error)
 				break;
 
@@ -52,28 +48,36 @@ struct Parser{
 		expression();
 		if(vm.isREPL){
 			match(Token.Type.Semicolon);
-			compiler.emitter.emit(OpCode.Print);
+			currentCompiler.emit(OpCode.Print);
 		} else {
 			consume(Token.Type.Semicolon, "Expect ';' after expression.");
-			compiler.emitter.emit(OpCode.Pop);
+			currentCompiler.emit(OpCode.Pop);
 		}
 	}
 	void varDeclaration(){
-		long global = parseVariable("Expect variable name.");
+		int global = parseVariable("Expect variable name.");
 		if(match(Token.Type.Equal)){
 			expression();
 		} else {
-			compiler.emitter.emit(OpCode.Nil);
+			currentCompiler.emit(OpCode.Nil);
 		}
 		consume(Token.Type.Semicolon, "Expect ';' after variable declaration.");
 		defineVariable(global);
 	}
+	void funDeclaration(){
+		int global = parseVariable("Expect function name");
+		markInitialised();
+		func();
+		defineVariable(global);
+	}
 	void declaration(){
 		if(match(Token.Type.Var))
 			varDeclaration();
+		else if(match(Token.Type.Fun))
+			funDeclaration();
 		else
 			statement();
-		if(compiler.parser.panicMode)
+		if(parser.panicMode)
 			synchronise();
 	}
 	void statement(){
@@ -81,6 +85,8 @@ struct Parser{
 			printStatement();
 		} else if(match(Token.Type.If)){
 			ifStatement();
+		} else if(match(Token.Type.Return)){
+			returnStatement();
 		} else if(match(Token.Type.While)){
 			whileStatement();
 		} else if(match(Token.Type.For)){
@@ -95,7 +101,19 @@ struct Parser{
 	void printStatement(){
 		expression();
 		consume(Token.Type.Semicolon, "Expect ';' after value.");
-		compiler.emitter.emit(OpCode.Print);
+		currentCompiler.emit(OpCode.Print);
+	}
+	void returnStatement(){
+		if(currentCompiler.ftype == Compiler.FunctionType.Script){
+			error("Can't return from top-level code.");
+		}
+		if(match(Token.Type.Semicolon)){
+			currentCompiler.emitReturn();
+		} else {
+			expression();
+			consume(Token.Type.Semicolon, "Expect ';' after return value.");
+			currentCompiler.emit(OpCode.Return);
+		}
 	}
 	void ifStatement(){
 		consume(Token.Type.LeftParen, "Expect '(' after 'if'.");
@@ -103,13 +121,13 @@ struct Parser{
 		consume(Token.Type.RightParen, "Expect ')' after condition.");
 
 		int thenJump = emitJump(OpCode.JumpIfFalse);
-		compiler.emitter.emit(OpCode.Pop);
+		currentCompiler.emit(OpCode.Pop);
 		statement();
 
 		int elseJump = emitJump(OpCode.Jump);
 
 		patchJump(thenJump);
-		compiler.emitter.emit(OpCode.Pop);
+		currentCompiler.emit(OpCode.Pop);
 
 		if(match(Token.Type.Else))
 			statement();
@@ -117,18 +135,18 @@ struct Parser{
 		patchJump(elseJump);
 	}
 	void whileStatement(){
-		int loopStart = cast(int)compiler.currentChunk.code.count;
+		int loopStart = cast(int)currentCompiler.currentChunk.code.count;
 		consume(Token.Type.LeftParen, "Expect '(' after 'while'.");
 		expression();
 		consume(Token.Type.RightParen, "Expect ')' after condition.");
 
 		int exitJump = emitJump(OpCode.JumpIfFalse);
-		compiler.emitter.emit(OpCode.Pop);
+		currentCompiler.emit(OpCode.Pop);
 		statement();
 		emitLoop(loopStart);
 
 		patchJump(exitJump);
-		compiler.emitter.emit(OpCode.Pop);
+		currentCompiler.emit(OpCode.Pop);
 	}
 	void forStatement(){
 		beginScope();
@@ -141,20 +159,20 @@ struct Parser{
 			expressionStatement();
 		}
 
-		int loopStart = cast(int)compiler.currentChunk.code.count;
+		int loopStart = cast(int)currentCompiler.currentChunk.code.count;
 		int exitJump = -1;
 		if(!match(Token.Type.Semicolon)){
 			expression();
 			consume(Token.Type.Semicolon, "Expect ';' after loop condition.");
 			exitJump = emitJump(OpCode.JumpIfFalse);
-			compiler.emitter.emit(OpCode.Pop);
+			currentCompiler.emit(OpCode.Pop);
 		}
 
 		if(!match(Token.Type.RightParen)){
 			int bodyJump = emitJump(OpCode.Jump);
-			int incrementStart = cast(int)compiler.currentChunk.code.count;
+			int incrementStart = cast(int)currentCompiler.currentChunk.code.count;
 			expression();
-			compiler.emitter.emit(OpCode.Pop);
+			currentCompiler.emit(OpCode.Pop);
 			consume(Token.Type.RightParen, "Expect ')' after for clauses.");
 			emitLoop(loopStart);
 			loopStart = incrementStart;
@@ -166,7 +184,7 @@ struct Parser{
 
 		if(exitJump != -1){
 			patchJump(exitJump);
-			compiler.emitter.emit(OpCode.Pop);
+			currentCompiler.emit(OpCode.Pop);
 		}
 
 		endScope();
@@ -176,65 +194,89 @@ struct Parser{
 			declaration();
 		consume(Token.Type.RightBrace, "Expect '}' after block.");
 	}
+	void func(){
+		Compiler compiler;
+		compiler.initialise(Compiler.FunctionType.Function);
+		beginScope();
+
+		consume(Token.Type.LeftParen, "Expect '(' after function name.");
+		if(!check(Token.Type.RightParen)){
+			do {
+				currentCompiler.func.arity++;
+				int constant = parseVariable("Expect parameter name.");
+				defineVariable(constant);
+			} while(match(Token.Type.Comma));
+		}
+		consume(Token.Type.RightParen, "Expect ')' after parameters.");
+		consume(Token.Type.LeftBrace, "Expect '{' before function body.");
+		block();
+
+		Obj.Function* func = compiler.end();
+
+		VarUint constant = currentCompiler.makeConstant(Value.from(func));
+		currentCompiler.emit(OpCode.Constant, constant.bytes);
+	}
 
 	void patchJump(int offset){
-		long jump = compiler.currentChunk.code.count - offset - 2;
+		int jump = cast(int)currentCompiler.currentChunk.code.count - offset - 2;
 		if(jump > ushort.max)
 			error("Too much code to jump over.");
-		compiler.currentChunk.code[offset] = (jump >> 8) & 0xff;
-		compiler.currentChunk.code[offset + 1] = jump & 0xff;
+		currentCompiler.currentChunk.code[offset] = (jump >> 8) & 0xff;
+		currentCompiler.currentChunk.code[offset + 1] = jump & 0xff;
 	}
 	int emitJump(OpCode instruction){
-		compiler.emitter.emit(instruction, ubyte(0xff), ubyte(0xff));
-		return cast(int)compiler.currentChunk.code.count - 2;
+		currentCompiler.emit(instruction, ubyte(0xff), ubyte(0xff));
+		return cast(int)currentCompiler.currentChunk.code.count - 2;
 	}
 	void emitLoop(int loopStart){
-		compiler.emitter.emit(OpCode.Loop);
+		currentCompiler.emit(OpCode.Loop);
 
-		int offset = cast(int)compiler.currentChunk.code.count - loopStart + 2;
+		int offset = cast(int)currentCompiler.currentChunk.code.count - loopStart + 2;
 		if(offset > ushort.max)
 			error("Loop body too large.");
 
-		compiler.emitter.emit(cast(ubyte)((offset >> 8) & 0xff));
-		compiler.emitter.emit(cast(ubyte)(offset & 0xff));
+		currentCompiler.emit(cast(ubyte)((offset >> 8) & 0xff));
+		currentCompiler.emit(cast(ubyte)(offset & 0xff));
 }
-	void defineVariable(long global){
-		if(compiler.scopeDepth > 0){
+	void defineVariable(int global){
+		if(currentCompiler.scopeDepth > 0){
 			markInitialised();
 			return;
 		}
-		compiler.emitter.emit(OpCode.DefineGlobal, VarUint(global).bytes);
+		currentCompiler.emit(OpCode.DefineGlobal, VarUint(global).bytes);
 	}
 	void markInitialised(){
-		compiler.locals[compiler.locals.count - 1].depth = compiler.scopeDepth;
+		if(currentCompiler.scopeDepth == 0)
+			return;
+		currentCompiler.locals[currentCompiler.locals.count - 1].depth = currentCompiler.scopeDepth;
 	}
 	void declareVariable(){
-		if(compiler.scopeDepth == 0)
+		if(currentCompiler.scopeDepth == 0)
 			return;
-		Token* name = &compiler.parser.previous;
-		for(long i = compiler.locals.count - 1; i >= 0; i--){
-			Compiler.Local* local = &compiler.locals[i];
-			if(local.depth != Compiler.Local.Uninitialised && local.depth < compiler.scopeDepth)
+		Token* name = &parser.previous;
+		for(int i = cast(int)currentCompiler.locals.count - 1; i >= 0; i--){
+			currentCompiler.Local* local = &currentCompiler.locals[i];
+			if(local.depth != currentCompiler.Local.Uninitialised && local.depth < currentCompiler.scopeDepth)
 				break;
 			if(name.lexeme == local.name.lexeme)
 				error("Already a variable with this name in this scope.");
 		}
 		addLocal(*name);
 	}
-	long parseVariable(const char* errorMessage){
+	int parseVariable(const char* errorMessage){
 		consume(Token.Type.Identifier, errorMessage);
 		declareVariable();
-		if(compiler.scopeDepth > 0)
+		if(currentCompiler.scopeDepth > 0)
 			return 0;
 		return identifierConstant(&previous);
 	}
-	long identifierConstant(Token* name){
+	int identifierConstant(Token* name){
 		Value nameVal = Value.from(Obj.String.copy(name.lexeme));
-		return compiler.emitter.makeConstant(nameVal);
+		return currentCompiler.makeConstant(nameVal);
 	}
 	void namedVariable(Token name, bool canAssign){
 		OpCode getOp, setOp;
-		long arg = resolveLocal(&name);
+		int arg = resolveLocal(&name);
 		if(arg != -1){
 			getOp = OpCode.GetLocal;
 			setOp = OpCode.SetLocal;
@@ -245,17 +287,28 @@ struct Parser{
 		}
 		if(canAssign && match(Token.Type.Equal)){
 			expression();
-			compiler.emitter.emit(setOp, VarUint(arg).bytes);
+			currentCompiler.emit(setOp, VarUint(arg).bytes);
 		} else {
-			compiler.emitter.emit(getOp, VarUint(arg).bytes);
+			currentCompiler.emit(getOp, VarUint(arg).bytes);
 		}
 	}
+	int argumentList(){
+		int argCount = 0;
+		if(!check(Token.Type.RightParen)){
+			do {
+				expression();
+				argCount++;
+			} while(match(Token.Type.Comma));
+		}
+		consume(Token.Type.RightParen, "Expect ')' after arguments.");
+		return argCount;
+	}
 
-	long resolveLocal(Token* name){
-		for(long i = compiler.locals.count - 1; i >= 0; i--){
-			Compiler.Local* local = &compiler.locals[i];
+	int resolveLocal(Token* name){
+		for(int i = cast(int)currentCompiler.locals.count - 1; i >= 0; i--){
+			currentCompiler.Local* local = &currentCompiler.locals[i];
 			if(name.lexeme == local.name.lexeme){
-				if(local.depth == Compiler.Local.Uninitialised)
+				if(local.depth == currentCompiler.Local.Uninitialised)
 					error("Can't read local variable in its own initialiser.");
 				return i;
 			}
@@ -263,16 +316,16 @@ struct Parser{
 		return -1;
 	}
 	void addLocal(Token name){
-		compiler.locals ~= Compiler.Local(name, Compiler.Local.Uninitialised);
+		currentCompiler.locals ~= currentCompiler.Local(name, currentCompiler.Local.Uninitialised);
 	}
 	void beginScope(){
-		compiler.scopeDepth++;
+		currentCompiler.scopeDepth++;
 	}
 	void endScope(){
-		assert(--compiler.scopeDepth >= 0);
-		while(compiler.locals.count > 0 && compiler.locals[compiler.locals.count - 1].depth > compiler.scopeDepth){
-			compiler.emitter.emit(OpCode.Pop);
-			compiler.locals.count--;
+		assert(--currentCompiler.scopeDepth >= 0);
+		while(currentCompiler.locals.count > 0 && currentCompiler.locals[currentCompiler.locals.count - 1].depth > currentCompiler.scopeDepth){
+			currentCompiler.emit(OpCode.Pop);
+			currentCompiler.locals.count--;
 		}
 	}
 
@@ -284,11 +337,11 @@ struct Parser{
 			return;
 		}
 		bool canAssign = precedence <= Precedence.Assignment;
-		prefixRule(compiler, canAssign);
+		prefixRule(currentCompiler, canAssign);
 		while(precedence <= ParseRule.get(current.type).precedence){
 			advance();
 			ParseFn infixRule = ParseRule.get(previous.type).infix;
-			infixRule(compiler);
+			infixRule(currentCompiler);
 		}
 		if(canAssign && match(Token.Type.Equal))
 			error("Invalid assignment target.");
diff --git a/src/clox/parserules.d b/src/clox/parserules.d
index 946d075..a446a9b 100644
--- a/src/clox/parserules.d
+++ b/src/clox/parserules.d
@@ -4,43 +4,43 @@ import clox.chunk;
 import clox.compiler;
 import clox.parser;
 import clox.scanner;
-import clox.emitter;
 import clox.value;
 import clox.object;
+import clox.container.varint;
 
 alias ParseFn = void function(Compiler* compiler, bool canAssign = false);
 
 private void grouping(Compiler* compiler, bool _){
-	compiler.parser.expression();
-	compiler.parser.consume(Token.Type.RightParen, "Expect ')' after expression.");
+	parser.expression();
+	parser.consume(Token.Type.RightParen, "Expect ')' after expression.");
 }
 private void unary(Compiler* compiler, bool _){
-	Token operator = compiler.parser.previous;
-	compiler.parser.parsePrecedence(Precedence.Unary);
+	Token operator = parser.previous;
+	parser.parsePrecedence(Precedence.Unary);
 	switch(operator.type){
-		case Token.Type.Minus: compiler.emitter.emit(OpCode.Negate); break;
-		case Token.Type.Bang:  compiler.emitter.emit(OpCode.Not); break;
+		case Token.Type.Minus: compiler.emit(OpCode.Negate); break;
+		case Token.Type.Bang:  compiler.emit(OpCode.Not); break;
 		default: assert(0);
 	}
 }
 private void binary(Compiler* compiler, bool _){
-	Token operator = compiler.parser.previous;
+	Token operator = parser.previous;
 	immutable(ParseRule)* rule = ParseRule.get(operator.type);
-	compiler.parser.parsePrecedence(cast(Precedence)(rule.precedence + 1));
+	parser.parsePrecedence(cast(Precedence)(rule.precedence + 1));
 	switch(operator.type){
-		case Token.Type.Plus:  compiler.emitter.emit(OpCode.Add); break;
-		case Token.Type.Minus: compiler.emitter.emit(OpCode.Subtract); break;
-		case Token.Type.Star:  compiler.emitter.emit(OpCode.Multiply); break;
-		case Token.Type.Slash: compiler.emitter.emit(OpCode.Divide); break;
+		case Token.Type.Plus:  compiler.emit(OpCode.Add); break;
+		case Token.Type.Minus: compiler.emit(OpCode.Subtract); break;
+		case Token.Type.Star:  compiler.emit(OpCode.Multiply); break;
+		case Token.Type.Slash: compiler.emit(OpCode.Divide); break;
 
-		case Token.Type.BangEqual:  compiler.emitter.emit(OpCode.NotEqual); break;
-		case Token.Type.EqualEqual: compiler.emitter.emit(OpCode.Equal); break;
+		case Token.Type.BangEqual:  compiler.emit(OpCode.NotEqual); break;
+		case Token.Type.EqualEqual: compiler.emit(OpCode.Equal); break;
 
-		case Token.Type.Greater:  compiler.emitter.emit(OpCode.Greater); break;
-		case Token.Type.GreaterEqual: compiler.emitter.emit(OpCode.GreaterEqual); break;
+		case Token.Type.Greater:  compiler.emit(OpCode.Greater); break;
+		case Token.Type.GreaterEqual: compiler.emit(OpCode.GreaterEqual); break;
 
-		case Token.Type.Less: compiler.emitter.emit(OpCode.Less); break;
-		case Token.Type.LessEqual: compiler.emitter.emit(OpCode.LessEqual); break;
+		case Token.Type.Less: compiler.emit(OpCode.Less); break;
+		case Token.Type.LessEqual: compiler.emit(OpCode.LessEqual); break;
 
 		default: assert(0);
 	}
@@ -48,45 +48,49 @@ private void binary(Compiler* compiler, bool _){
 
 private void number(Compiler* compiler, bool _){
 	import core.stdc.stdlib : strtod;
-	Token token = compiler.parser.previous;
+	Token token = parser.previous;
 	double value = strtod(token.lexeme.ptr, null);
-	compiler.emitter.emitConstant(Value.from(value));
+	compiler.emitConstant(Value.from(value));
 }
 private void literal(Compiler* compiler, bool _){
-	Token token = compiler.parser.previous;
+	Token token = parser.previous;
 	switch(token.type){
-		case Token.Type.True: compiler.emitter.emit(OpCode.True); break;
-		case Token.Type.False: compiler.emitter.emit(OpCode.False); break;
-		case Token.Type.Nil: compiler.emitter.emit(OpCode.Nil); break;
+		case Token.Type.True: compiler.emit(OpCode.True); break;
+		case Token.Type.False: compiler.emit(OpCode.False); break;
+		case Token.Type.Nil: compiler.emit(OpCode.Nil); break;
 		default: assert(0);
 	}
 }
 private void strlit(Compiler* compiler, bool _){
-	Token token = compiler.parser.previous;
+	Token token = parser.previous;
 	const char[] str = token.lexeme[1 .. $-1];
 	Obj.String* strObj = Obj.String.copy(str);
-	compiler.emitter.emitConstant(Value.from(strObj));
+	compiler.emitConstant(Value.from(strObj));
 }
 private void variable(Compiler* compiler, bool canAssign){
-	compiler.parser.namedVariable(compiler.parser.previous, canAssign);
+	parser.namedVariable(parser.previous, canAssign);
 }
 private void and(Compiler* compiler, bool _){
-	int endJump = compiler.parser.emitJump(OpCode.JumpIfFalse);
+	int endJump = parser.emitJump(OpCode.JumpIfFalse);
 
-	compiler.emitter.emit(OpCode.Pop);
-	compiler.parser.parsePrecedence(Precedence.And);
+	compiler.emit(OpCode.Pop);
+	parser.parsePrecedence(Precedence.And);
 
-	compiler.parser.patchJump(endJump);
+	parser.patchJump(endJump);
 }
 private void or(Compiler* compiler, bool _){
-	int elseJump = compiler.parser.emitJump(OpCode.JumpIfFalse);
-	int endJump = compiler.parser.emitJump(OpCode.Jump);
+	int elseJump = parser.emitJump(OpCode.JumpIfFalse);
+	int endJump = parser.emitJump(OpCode.Jump);
 
-	compiler.parser.patchJump(elseJump);
-	compiler.emitter.emit(OpCode.Pop);
+	parser.patchJump(elseJump);
+	compiler.emit(OpCode.Pop);
 
-	compiler.parser.parsePrecedence(Precedence.Or);
-	compiler.parser.patchJump(endJump);
+	parser.parsePrecedence(Precedence.Or);
+	parser.patchJump(endJump);
+}
+private void call(Compiler* compiler, bool _){
+	VarUint argCount = VarUint(parser.argumentList());
+	compiler.emit(OpCode.Call, argCount.bytes);
 }
 
 
@@ -114,7 +118,7 @@ enum Precedence{
 }
 
 immutable ParseRule[Token.Type.max+1] rules = [
-	Token.Type.LeftParen     : ParseRule(&grouping, null,    Precedence.None),
+	Token.Type.LeftParen     : ParseRule(&grouping, &call,   Precedence.Call),
 	Token.Type.RightParen    : ParseRule(null,      null,    Precedence.None),
 	Token.Type.LeftBrace     : ParseRule(null,      null,    Precedence.None),
 	Token.Type.RightBrace    : ParseRule(null,      null,    Precedence.None),
diff --git a/src/clox/scanner.d b/src/clox/scanner.d
index 60667bc..e81cb43 100644
--- a/src/clox/scanner.d
+++ b/src/clox/scanner.d
@@ -22,6 +22,8 @@ struct Token {
 	int line;
 }
 
+Scanner scanner;
+
 bool isDigit(char c) => c >= '0' && c <= '9';
 bool isAlpha(char c) => (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_';
  
diff --git a/src/clox/util.d b/src/clox/util.d
index 8970a60..f9e9051 100644
--- a/src/clox/util.d
+++ b/src/clox/util.d
@@ -2,6 +2,7 @@ module clox.util;
 
 import core.stdc.stdio;
 import core.stdc.stdlib;
+import core.stdc.string;
 import std.functional : ctEval;
 
 enum Colour : string{
@@ -12,10 +13,10 @@ string colour(string text, string r, string g, string b)() => ctEval!("\033[38;2
 
 extern(C) int isatty(int);
 
-static char* readFile(const char* path) {
-	FILE* file = path.fopen("rb");
+static char[] readFile(const(char)[] path){
+	FILE* file = path.ptr.fopen("rb");
 	if(file == null){
-		stderr.fprintf("Could not open file \"%s\".\n", path);
+		stderr.fprintf("Could not open file \"%s\".\n", path.ptr);
 		return null;
 	}
 	scope(exit)
@@ -29,7 +30,7 @@ static char* readFile(const char* path) {
 	size_t bytesRead = fread(buffer, char.sizeof, fileSize, file);
 	buffer[bytesRead] = '\0';
 
-	return buffer;
+	return buffer[0 .. bytesRead];
 }
 
 char* readStdin(){
@@ -52,4 +53,6 @@ char* readStdin(){
 	return buffer;
 }
 
+const(char)[] parse(const char* cstr) => cstr[0 .. cstr.strlen];
+
 
diff --git a/src/clox/vm.d b/src/clox/vm.d
index f31d65b..fb5522b 100644
--- a/src/clox/vm.d
+++ b/src/clox/vm.d
@@ -9,70 +9,87 @@ import clox.object;
 import clox.value;
 import clox.object;
 import clox.compiler;
+import clox.scanner;
 import clox.memory;
-import clox.container.stack;
 import clox.container.table;
 import clox.container.varint;
 
 VM vm;
 
 struct VM{
-	Chunk* chunk;
-	ubyte* ip;
-	Stack!Value stack;
+	Value[1024] stack;
+	Value* stackTop;
+	CallFrame[256] frames;
+	uint frameCount;
 	Table globals;
 	Table strings;
 	Obj* objects;
 	bool isREPL;
+	debug(printCode) bool printCode;
+	debug(traceExec) bool traceExec;
 	enum InterpretResult{ Ok, CompileError, RuntimeError }
+	struct CallFrame{
+		Obj.Function* func;
+		ubyte* ip;
+		Value* slots;
+	}
 	void initialise(){
-		stack.initialise();
 		strings.initialise();
 		globals.initialise();
+		stackTop = &stack[0];
+
+		defineNative("clock", (int argCount, Value* args){
+			import core.stdc.time;
+			return Value.from(cast(double)clock() / CLOCKS_PER_SEC);
+		});
 	}
 	void free(){
 		freeObjects();
 		strings.free();
 		globals.free();
-		stack.free();
+	}
+	void push(Value v){
+		*(stackTop++) = v;
+	}
+	Value pop(){
+		return *(--stackTop);
 	}
 	InterpretResult interpret(const char* source){
-		Chunk cnk;
-		cnk.initialise();
-		scope(exit)
-			cnk.free();
+		scanner.initialise(source);
 		Compiler compiler;
-		if(!compiler.compile(source, &cnk))
+		compiler.initialise(Compiler.FunctionType.Script);
+		Obj.Function* func = compiler.compile();
+		if(func is null)
 			return InterpretResult.CompileError;
-		this.chunk = &cnk;
-		this.ip = cnk.code.ptr;
+		push(Value.from(func));
+		call(func, 0);
 		return run();
 	}
 	void runtimeError(Args...)(const char* format, Args args){
 		fprintf(stderr, format, args);
 		fputs("\n", stderr);
-
-		size_t instruction = ip - chunk.code.ptr - 1;
-		uint line = chunk.lines[instruction];
-		fprintf(stderr, "[line %d] in script\n", line);
+		printStackTrace();
 	}
 	InterpretResult run(){
-		debug(traceExec){
-			printHeader(chunk);
+		CallFrame* frame = &frames[frameCount - 1];
+		ref ip() => frame.ip;
+		ref chunk() => frame.func.chunk;
+		debug(traceExec) if(traceExec){
+			printHeader(&chunk());
 		}
 		ubyte readByte() => *ip++;
 		ushort readShort(){
 			ip += 2;
 			return (ip[-2] << 8) | ip[-1];
 		}
-		long readVarUint(){
+		int readVarUint(){
 			VarUint vi = VarUint.read(ip);
 			ip += vi.len;
 			return vi.i;
 		}
 		Value readConstant() => chunk.constants[readVarUint()];
 		Obj.String* readString() => readConstant().asObj.asString;
-		Value peek(int distance = 0) => stack.top[-1 - distance];
+		Value peek(int distance = 0) => stackTop[-1 - distance];
 		bool checkBinaryType(alias type)() => peek(0).isType(type) && peek(1).isType(type);
 		bool checkSameType()() => peek(0).type == peek(1).type;
 		int binaryOp(string op, alias check, string checkMsg, alias pre)(){
@@ -80,32 +97,34 @@ struct VM{
 				runtimeError(checkMsg.ptr);
 				return 1;
 			}
-			auto b = stack.pop().as!pre;
-			auto a = stack.pop().as!pre;
-			stack ~= Value.from(mixin("a", op, "b"));
+			auto b = pop().as!pre;
+			auto a = pop().as!pre;
+			push(Value.from(mixin("a", op, "b")));
 			return 0;
 		}
 		while(true){
-			debug(traceExec){
-				disassembleInstruction(chunk, ip - chunk.code.ptr);
-				printf(" ");
-				foreach(slot; stack.live){
-					printf("");
-					slot.print();
-					printf(colour!(", ", Colour.Black).ptr);
+			debug(traceExec) if(traceExec){
+				disassembleInstruction(&chunk(), ip - chunk.code.ptr);
+				printf(colour!(" [", Colour.Black).ptr);
+				for(Value* v = stack.ptr+1; v < stackTop; v++){
+					printf(" ");
+					v.print();
+					if(v+1 < stackTop)
+						printf(colour!(",", Colour.Black).ptr);
+					printf(" ");
 				}
-				printf("\n");
+				printf(colour!("]\n", Colour.Black).ptr);
 			}
 			OpCode instruction;
 			opSwitch: final switch(instruction = cast(OpCode)readByte()){
 				case OpCode.Constant:
 					Value constant = readConstant();
-					stack ~= constant;
+					push(constant);
 					break;
-				case OpCode.Nil:   stack ~= Value.nil; break;
-				case OpCode.True:  stack ~= Value.from(true); break;
-				case OpCode.False: stack ~= Value.from(false); break;
-				case OpCode.Pop:   stack.pop(); break;
+				case OpCode.Nil:   push(Value.nil); break;
+				case OpCode.True:  push(Value.from(true)); break;
+				case OpCode.False: push(Value.from(false)); break;
+				case OpCode.Pop:   pop(); break;
 
 				case OpCode.Jump:
 					ushort offset = readShort();
@@ -123,11 +142,11 @@ struct VM{
 
 				case OpCode.GetLocal:
 					long slot = readVarUint();
-					stack ~= stack[slot];
+					push(frame.slots[slot]);
 					break;
 				case OpCode.SetLocal:
 					long slot = readVarUint();
-					stack[slot] = peek(0);
+					frame.slots[slot] = peek(0);
 					break;
 				case OpCode.GetGlobal:
 					Obj.String* name = readString();
@@ -136,12 +155,12 @@ struct VM{
 						runtimeError("Undefined variable '%s'.", name.chars.ptr);
 						return InterpretResult.RuntimeError;
 					}
-					stack ~= value;
+					push(value);
 					break;
 				case OpCode.DefineGlobal:
 					Obj.String* name = readString();
 					globals.set(name, peek(0));
-					stack.pop();
+					pop();
 					break;
 				case OpCode.SetGlobal:
 					Obj.String* name = readString();
@@ -164,14 +183,14 @@ struct VM{
 						break opSwitch;
 				}
 
-				static foreach(k, op; [ OpCode.Add: "+", OpCode.Subtract: "-", OpCode.Multiply: "*", OpCode.Divide: "-" ]){
+				static foreach(k, op; [ OpCode.Add: "+", OpCode.Subtract: "-", OpCode.Multiply: "*", OpCode.Divide: "/" ]){
 					case k:
 						static if(k == OpCode.Add){
 							if(checkBinaryType!(Obj.Type.String)){
-								Obj.String* b = stack.pop().asObj.asString;
-								Obj.String* a = stack.pop().asObj.asString;
+								Obj.String* b = pop().asObj.asString;
+								Obj.String* a = pop().asObj.asString;
 								Obj.String* result = Obj.String.concat(a, b);
-								stack ~= Value.from(result);
+								push(Value.from(result));
 								break opSwitch;
 							}
 						}
@@ -181,24 +200,98 @@ struct VM{
 				}
 
 				case OpCode.Not:
-					stack ~= Value.from(stack.pop().isFalsey);
+					push(Value.from(pop().isFalsey));
 					break;
 				case OpCode.Negate:
 					if(!peek(0).isType(Value.Type.Number)){
 						runtimeError("Operand must be a number.");
 						return InterpretResult.RuntimeError;
 					}
-					stack ~= Value.from(-stack.pop().asNumber);
+					push(Value.from(-pop().asNumber));
 					break;
 				case OpCode.Print:
-					stack.pop().print("%s");
+					pop().print("%s");
 					printf("\n");
 					break;
+
+				case OpCode.Call:
+					int argCount = readVarUint();
+					if(!callValue(peek(argCount), argCount))
+						return InterpretResult.RuntimeError;
+					frame = &frames[frameCount - 1];
+					break;
 				case OpCode.Return:
-					return InterpretResult.Ok;
+					Value result = pop();
+					vm.frameCount--;
+					if(vm.frameCount == 0){
+						pop();
+						return InterpretResult.Ok;
+					}
+					stackTop = frame.slots;
+					push(result);
+					frame = &vm.frames[vm.frameCount - 1];
+					break;
 			}
 		}
 		assert(0);
 	}
+
+	bool call(Obj.Function* func, int argCount){
+		if(argCount != func.arity){
+			runtimeError("Expected %d arguments but got %d.", func.arity, argCount);
+			return false;
+		}
+		if(frameCount == frames.length){
+			runtimeError("Stack overflow.");
+			return false;
+		}
+		CallFrame* frame = &frames[frameCount++];
+		frame.func = func;
+		frame.ip = func.chunk.code.ptr;
+		frame.slots = stackTop - argCount - 1;
+		return true;
+	}
+	bool callValue(Value callee, int argCount){
+		if(callee.isType(Value.Type.Obj)){
+			Obj* obj = callee.asObj;
+			final switch(obj.type){
+				case Obj.Type.Function:
+					return call(obj.asFunc, argCount);
+				case Obj.Type.NativeFunction:
+					Obj.NativeFunction* native = obj.asNativeFunc;
+					Value result = native.func(argCount, vm.stackTop - argCount);
+					vm.stackTop -= argCount + 1;
+					push(result);
+					return true;
+				case Obj.Type.String: break;
+				case Obj.Type.None: assert(0);
+			}
+		}
+		runtimeError("Can only call functions and classes.");
+		return false;
+	}
+
+	void printStackTrace(){
+		for(int i = vm.frameCount - 1; i >= 0; i--){
+			CallFrame* frame = &frames[i];
+			Obj.Function* func = frame.func;
+			size_t instruction = frame.ip - func.chunk.code.ptr - 1;
+			fprintf(stderr, "[line %d] in ", func.chunk.lines[instruction]);
+			if(func.name is null){
+				fprintf(stderr, "script\n");
+			} else {
+				fprintf(stderr, "%s()\n", func.name.chars.ptr);
+			}
+		}
+	}
+
+	void defineNative(const(char)[] name, Obj.NativeFunction.Sig func){
+		push(Value.from(Obj.String.copy(name)));
+		push(Value.from(Obj.NativeFunction.create(func)));
+		globals.set(stack[0].asObj.asString, vm.stack[1]);
+		pop();
+		pop();
+	}
+
 }
 
diff --git a/test/all.d b/test/all.d
index a7c3542..66c016c 100755
--- a/test/all.d
+++ b/test/all.d
@@ -8,27 +8,36 @@ import std.string, std.format;
 import std.algorithm, std.range;
 
 void main(){
+
+	"./test/func.lox".match("-1\n6\n1\n");
+	"./test/bigsum.lox".match("125250\n");
+	"./test/biglocals.lox".match("125250\n");
+	"./test/simplescope.lox".match("abc\nabd\n");
+	"./test/for.lox".match("1 2 1 2 3 ".replace(' ', '\n'));
+	"./test/ifelse.lox".match("a1 b2 c3 ".replace(' ', '\n'));
+	"./test/while.lox".match("1 2  3 2 1  0 1  1 2  3 2 1  0 1 ".replace(' ', '\n'));
+
 	"./test/ops.lox".match("1\n2\n3\n4\n5\n6\n7\ntrue\nfalse\ntrue\ntrue\nhello, world\n");
 	"./test/shortcircuit.lox".match("true\nAAAA!\nAAAA!\nAAAA?\n");
-	"./test/closure.lox".match("1\n2\n");
-	"./test/scope.lox".match("global first first second first ".replace(' ', '\n').repeat(2).join("\n"));
+	/* "./test/closure.lox".match("1\n2\n"); */
+	"./test/scope.lox".match("global first first second first ".replace(' ', '\n'));
 	"./test/fib_for.lox".match(fib(6765));
 	"./test/fib_recursive.lox".match(fib(34));
-	"./test/fib_closure.lox".match(fib(34));
-	"./test/class.lox".match("The German chocolate cake is delicious!\n");
-	"./test/super.lox".match("Fry until golden brown.\nPipe full of custard and coat with chocolate.\nA method\n");
+	/* "./test/fib_closure.lox".match(fib(34)); */
+	/* "./test/class.lox".match("The German chocolate cake is delicious!\n"); */
+	/* "./test/super.lox".match("Fry until golden brown.\nPipe full of custard and coat with chocolate.\nA method\n"); */
 
 	"./test/err/invalid_syntax.lox".shouldFail(RetVal.other);
 	"./test/err/already_defined.lox".shouldFail(RetVal.other, "Already a variable with this name");
 	"./test/err/undefined_var.lox".shouldFail(RetVal.runtime, "Undefined variable");
 	"./test/err/self_ref_vardecl.lox".shouldFail(RetVal.runtime, "Undefined variable");
 	"./test/err/global_scope_return.lox".shouldFail(RetVal.other, "Can't return from top-level code");
-	"./test/err/super_outside_class.lox".shouldFail(RetVal.other, "Can't use 'super' outside of a class");
-	"./test/err/super_without_superclass.lox".shouldFail(RetVal.other, "Can't use 'super' in a class with no superclass");
+	/* "./test/err/super_outside_class.lox".shouldFail(RetVal.other, "Can't use 'super' outside of a class"); */
+	/* "./test/err/super_without_superclass.lox".shouldFail(RetVal.other, "Can't use 'super' in a class with no superclass"); */
 }
 
 enum RetVal{
-	success = 0, other = 1, runtime = 2
+	success = 0, other = 65, runtime = 70
 }
 
 string fib(uint n){
@@ -42,13 +51,13 @@ string fib(uint n){
 	}
 	return r;
 }
-auto run(string file) => [ "./lox", file ].execute;
+auto run(string file, Config.Flags f = Config.Flags.stderrPassThrough) => [ "./lox", file ].execute(null, Config(f));
 void match(string file, string correct){
 	auto res = file.run.output;
 	assert(res == correct, "Match %s failed\n-- Got --\n%s\n-- Expected --\n%s".format(file, res, correct));
 }
 void shouldFail(string file, int code = 1, string msg = null){
-	auto c = file.run;
+	auto c = file.run(Config.Flags.none);
 	assert(c.status == code, "Expected %s to fail with code %d but got %d".format(file, code, c.status));
 	assert(!msg || c.output.toLower.indexOf(msg.toLower) >= 0, "ShouldFail %s failed\n-- Got --\n%s\n-- Expected --\n%s".format(file, c.output, msg));
 	assert(c.output.indexOf("_Dmain") == -1, "ShouldFail %s got D exception\n%s".format(file, c.output));
diff --git a/test/func.lox b/test/func.lox
new file mode 100644
index 0000000..e39d745
--- /dev/null
+++ b/test/func.lox
@@ -0,0 +1,13 @@
+
+fun sub(a, b){
+	print a - b;
+}
+
+fun mul(a, b){
+	sub(a, b);
+	print a * b;
+	sub(b, a);
+}
+
+mul(2, 3);
+
diff --git a/test/scope.lox b/test/scope.lox
index 4b9eadc..7742528 100644
--- a/test/scope.lox
+++ b/test/scope.lox
@@ -14,6 +14,4 @@ fun f(){
 }
 
 f();
-print "";
-f();