closures and they can recurse!!!

ast/ast.go

@@ -2,6 +2,7 @@ package ast
 
 import (
 	"bytes"
+	"fmt"
 	"monkey/token"
 	"strings"
 )
@@ -220,6 +221,7 @@ type FunctionLiteral struct {
 	Token      token.Token // The 'fn' token
 	Parameters []*Identifier
 	Body       *BlockStatement
+	Name       string
 }
 
 func (fl *FunctionLiteral) expressionNode()      {}
@@ -233,6 +235,9 @@ func (fl *FunctionLiteral) String() string {
 	}
 
 	out.WriteString(fl.TokenLiteral())
+	if fl.Name != "" {
+		out.WriteString(fmt.Sprintf("<%s>", fl.Name))
+	}
 	out.WriteString("(")
 	out.WriteString(strings.Join(params, ", "))
 	out.WriteString(") ")

code/code.go

@@ -39,6 +39,8 @@ const (
 	OpSetLocal
 	OpGetBuiltin
 	OpClosure
+	OpGetFree
+	OpCurrentClosure
 )
 
 type Definition struct {
@@ -47,34 +49,36 @@ type Definition struct {
 }
 
 var definitions = map[Opcode]*Definition{
-	OpConstant:      {"OpConstant", []int{2}},
-	OpAdd:           {"OpAdd", []int{}},
-	OpPop:           {"OpPop", []int{}},
-	OpSub:           {"OpSub", []int{}},
-	OpMul:           {"OpMul", []int{}},
-	OpDiv:           {"OpDiv", []int{}},
-	OpTrue:          {"OpTrue", []int{}},
-	OpFalse:         {"OpFalse", []int{}},
-	OpEqual:         {"OpEqual", []int{}},
-	OpNotEqual:      {"OpNotEqual", []int{}},
-	OpGreaterThan:   {"OpGreaterThan", []int{}},
-	OpMinus:         {"OpMinus", []int{}},
-	OpBang:          {"OpBang", []int{}},
-	OpJumpNotTruthy: {"OpJumpNotTruthy", []int{2}},
-	OpJump:          {"OpJump", []int{2}},
-	OpNull:          {"OpNull", []int{}},
-	OpGetGlobal:     {"OpGetGlobal", []int{2}},
-	OpSetGlobal:     {"OpSetGlobal", []int{2}},
-	OpArray:         {"OpArray", []int{2}},
-	OpHash:          {"OpHash", []int{2}},
-	OpIndex:         {"OpIndex", []int{}},
-	OpCall:          {"OpCall", []int{1}},
-	OpReturnValue:   {"OpReturnValue", []int{}},
-	OpReturn:        {"OpReturn", []int{}},
-	OpGetLocal:      {"OpGetLocal", []int{1}},
-	OpSetLocal:      {"OpSetLocal", []int{1}},
-	OpGetBuiltin:    {"OpGetBuiltin", []int{1}},
-	OpClosure:       {"OpClosure", []int{2, 1}},
+	OpConstant:       {"OpConstant", []int{2}},
+	OpAdd:            {"OpAdd", []int{}},
+	OpPop:            {"OpPop", []int{}},
+	OpSub:            {"OpSub", []int{}},
+	OpMul:            {"OpMul", []int{}},
+	OpDiv:            {"OpDiv", []int{}},
+	OpTrue:           {"OpTrue", []int{}},
+	OpFalse:          {"OpFalse", []int{}},
+	OpEqual:          {"OpEqual", []int{}},
+	OpNotEqual:       {"OpNotEqual", []int{}},
+	OpGreaterThan:    {"OpGreaterThan", []int{}},
+	OpMinus:          {"OpMinus", []int{}},
+	OpBang:           {"OpBang", []int{}},
+	OpJumpNotTruthy:  {"OpJumpNotTruthy", []int{2}},
+	OpJump:           {"OpJump", []int{2}},
+	OpNull:           {"OpNull", []int{}},
+	OpGetGlobal:      {"OpGetGlobal", []int{2}},
+	OpSetGlobal:      {"OpSetGlobal", []int{2}},
+	OpArray:          {"OpArray", []int{2}},
+	OpHash:           {"OpHash", []int{2}},
+	OpIndex:          {"OpIndex", []int{}},
+	OpCall:           {"OpCall", []int{1}},
+	OpReturnValue:    {"OpReturnValue", []int{}},
+	OpReturn:         {"OpReturn", []int{}},
+	OpGetLocal:       {"OpGetLocal", []int{1}},
+	OpSetLocal:       {"OpSetLocal", []int{1}},
+	OpGetBuiltin:     {"OpGetBuiltin", []int{1}},
+	OpClosure:        {"OpClosure", []int{2, 1}},
+	OpGetFree:        {"OpGetFree", []int{1}},
+	OpCurrentClosure: {"OpCurrentClosure", []int{}},
 }
 
 func Lookup(op byte) (*Definition, error) {

compiler/compiler.go

@@ -196,12 +196,12 @@ func (c *Compiler) Compile(node ast.Node) error {
 		}
 
 	case *ast.LetStatement:
+		symbol := c.symbolTable.Define(node.Name.Value)
 		err := c.Compile(node.Value)
 		if err != nil {
 			return err
 		}
 
-		symbol := c.symbolTable.Define(node.Name.Value)
 		if symbol.Scope == GlobalScope {
 			c.emit(code.OpSetGlobal, symbol.Index)
 		} else {
@@ -268,6 +268,10 @@ func (c *Compiler) Compile(node ast.Node) error {
 	case *ast.FunctionLiteral:
 		c.enterScope()
 
+		if node.Name != "" {
+			c.symbolTable.DefineFunctionName(node.Name)
+		}
+
 		for _, p := range node.Parameters {
 			c.symbolTable.Define(p.Value)
 		}
@@ -284,9 +288,14 @@ func (c *Compiler) Compile(node ast.Node) error {
 			c.emit(code.OpReturn)
 		}
 
+		freeSymbols := c.symbolTable.FreeSymbols
 		numLocals := c.symbolTable.numDefinitions
 		instructions := c.leaveScope()
 
+		for _, s := range freeSymbols {
+			c.loadSymbol(s)
+		}
+
 		compiledFn := &object.CompiledFunction{
 			Instructions:  instructions,
 			NumLocals:     numLocals,
@@ -294,7 +303,7 @@ func (c *Compiler) Compile(node ast.Node) error {
 		}
 
 		fnIndex := c.addConstant(compiledFn)
-		c.emit(code.OpClosure, fnIndex, 0)
+		c.emit(code.OpClosure, fnIndex, len(freeSymbols))
 
 	case *ast.ReturnStatement:
 		err := c.Compile(node.ReturnValue)
@@ -439,5 +448,9 @@ func (c *Compiler) loadSymbol(s Symbol) {
 		c.emit(code.OpGetLocal, s.Index)
 	case BuiltinScope:
 		c.emit(code.OpGetBuiltin, s.Index)
+	case FreeScope:
+		c.emit(code.OpGetFree, s.Index)
+	case FunctionScope:
+		c.emit(code.OpCurrentClosure)
 	}
 }

compiler/compiler_test.go

@@ -503,6 +503,132 @@ func TestFunctionsWithoutReturnValue(t *testing.T) {
 	runCompilerTests(t, tests)
 }
 
+func TestClosures(t *testing.T) {
+	tests := []compilerTestCase{
+		{
+			input: `fn(a) { 
+				fn(b) {
+					a + b
+				}
+			}
+			`,
+			expectedConstants: []interface{}{
+				[]code.Instructions{
+					code.Make(code.OpGetFree, 0),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpAdd),
+					code.Make(code.OpReturnValue),
+				},
+				[]code.Instructions{
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpClosure, 0, 1),
+					code.Make(code.OpReturnValue),
+				},
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpClosure, 1, 0),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input: `
+            fn(a) {
+                fn(b) {
+                    fn(c) {
+                        a + b + c
+                    }
+                }
+            };
+            `,
+			expectedConstants: []interface{}{
+				[]code.Instructions{
+					code.Make(code.OpGetFree, 0),
+					code.Make(code.OpGetFree, 1),
+					code.Make(code.OpAdd),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpAdd),
+					code.Make(code.OpReturnValue),
+				},
+				[]code.Instructions{
+					code.Make(code.OpGetFree, 0),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpClosure, 0, 2),
+					code.Make(code.OpReturnValue),
+				},
+				[]code.Instructions{
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpClosure, 1, 1),
+					code.Make(code.OpReturnValue),
+				},
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpClosure, 2, 0),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input: `
+            let global = 55;
+
+            fn() {
+                let a = 66;
+
+                fn() {
+                    let b = 77;
+
+                    fn() {
+                        let c = 88;
+
+                        global + a + b + c;
+                    }
+                }
+            }
+            `,
+			expectedConstants: []interface{}{
+				55,
+				66,
+				77,
+				88,
+				[]code.Instructions{
+					code.Make(code.OpConstant, 3),
+					code.Make(code.OpSetLocal, 0),
+					code.Make(code.OpGetGlobal, 0),
+					code.Make(code.OpGetFree, 0),
+					code.Make(code.OpAdd),
+					code.Make(code.OpGetFree, 1),
+					code.Make(code.OpAdd),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpAdd),
+					code.Make(code.OpReturnValue),
+				},
+				[]code.Instructions{
+					code.Make(code.OpConstant, 2),
+					code.Make(code.OpSetLocal, 0),
+					code.Make(code.OpGetFree, 0),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpClosure, 4, 2),
+					code.Make(code.OpReturnValue),
+				},
+				[]code.Instructions{
+					code.Make(code.OpConstant, 1),
+					code.Make(code.OpSetLocal, 0),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpClosure, 5, 1),
+					code.Make(code.OpReturnValue),
+				},
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpSetGlobal, 0),
+				code.Make(code.OpClosure, 6, 0),
+				code.Make(code.OpPop),
+			},
+		},
+	}
+
+	runCompilerTests(t, tests)
+}
+
 func TestCompilerScopes(t *testing.T) {
 	compiler := New()
 	if compiler.scopeIndex != 0 {
@@ -755,6 +881,75 @@ func TestBuiltins(t *testing.T) {
 	runCompilerTests(t, tests)
 }
 
+func TestRecursiveFunctions(t *testing.T) {
+	tests := []compilerTestCase{
+		{
+			input: `
+            let countDown = fn(x) { countDown(x - 1); };
+            countDown(1);
+            `,
+			expectedConstants: []interface{}{
+				1,
+				[]code.Instructions{
+					code.Make(code.OpCurrentClosure),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpConstant, 0),
+					code.Make(code.OpSub),
+					code.Make(code.OpCall, 1),
+					code.Make(code.OpReturnValue),
+				},
+				1,
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpClosure, 1, 0),
+				code.Make(code.OpSetGlobal, 0),
+				code.Make(code.OpGetGlobal, 0),
+				code.Make(code.OpConstant, 2),
+				code.Make(code.OpCall, 1),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input: `
+            let wrapper = fn() {
+                let countDown = fn(x) { countDown(x - 1); };
+                countDown(1);
+            };
+            wrapper();
+            `,
+			expectedConstants: []interface{}{
+				1,
+				[]code.Instructions{
+					code.Make(code.OpCurrentClosure),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpConstant, 0),
+					code.Make(code.OpSub),
+					code.Make(code.OpCall, 1),
+					code.Make(code.OpReturnValue),
+				},
+				1,
+				[]code.Instructions{
+					code.Make(code.OpClosure, 1, 0),
+					code.Make(code.OpSetLocal, 0),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpConstant, 2),
+					code.Make(code.OpCall, 1),
+					code.Make(code.OpReturnValue),
+				},
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpClosure, 3, 0),
+				code.Make(code.OpSetGlobal, 0),
+				code.Make(code.OpGetGlobal, 0),
+				code.Make(code.OpCall, 0),
+				code.Make(code.OpPop),
+			},
+		},
+	}
+
+	runCompilerTests(t, tests)
+}
+
 func runCompilerTests(t *testing.T, tests []compilerTestCase) {
 	t.Helper()
 

compiler/symbol_table.go

@@ -3,9 +3,11 @@ package compiler
 type SymbolScope string
 
 const (
-	LocalScope   SymbolScope = "LOCAL"
-	GlobalScope  SymbolScope = "GLOBAL"
-	BuiltinScope SymbolScope = "BUILTIN"
+	LocalScope    SymbolScope = "LOCAL"
+	GlobalScope   SymbolScope = "GLOBAL"
+	BuiltinScope  SymbolScope = "BUILTIN"
+	FreeScope     SymbolScope = "FREE"
+	FunctionScope SymbolScope = "FUNCTION"
 )
 
 type Symbol struct {
@@ -19,6 +21,8 @@ type SymbolTable struct {
 
 	store          map[string]Symbol
 	numDefinitions int
+
+	FreeSymbols []Symbol
 }
 
 func NewEnclosedSymbolTable(outer *SymbolTable) *SymbolTable {
@@ -29,7 +33,8 @@ func NewEnclosedSymbolTable(outer *SymbolTable) *SymbolTable {
 
 func NewSymbolTable() *SymbolTable {
 	s := make(map[string]Symbol)
-	return &SymbolTable{store: s}
+	free := []Symbol{}
+	return &SymbolTable{store: s, FreeSymbols: free}
 }
 
 func (s *SymbolTable) Define(name string) Symbol {
@@ -49,7 +54,17 @@ func (s *SymbolTable) Resolve(name string) (Symbol, bool) {
 	obj, ok := s.store[name]
 	if !ok && s.Outer != nil {
 		obj, ok = s.Outer.Resolve(name)
-		return obj, ok
+		if !ok {
+			return obj, ok
+		}
+
+		if obj.Scope == GlobalScope || obj.Scope == BuiltinScope {
+			return obj, ok
+		}
+
+		free := s.DefineFree(obj)
+		return free, true
+
 	}
 
 	return obj, ok
@@ -60,3 +75,19 @@ func (s *SymbolTable) DefineBuiltin(index int, name string) Symbol {
 	s.store[name] = symbol
 	return symbol
 }
+
+func (s *SymbolTable) DefineFree(original Symbol) Symbol {
+	s.FreeSymbols = append(s.FreeSymbols, original)
+
+	symbol := Symbol{Name: original.Name, Index: len(s.FreeSymbols) - 1}
+	symbol.Scope = FreeScope
+
+	s.store[original.Name] = symbol
+	return symbol
+}
+
+func (s *SymbolTable) DefineFunctionName(name string) Symbol {
+	symbol := Symbol{Name: name, Index: 0, Scope: FunctionScope}
+	s.store[name] = symbol
+	return symbol
+}

compiler/symbol_table_test.go

@@ -197,3 +197,154 @@ func TestDefineResolveBuiltins(t *testing.T) {
 		}
 	}
 }
+
+func TestResolveFree(t *testing.T) {
+	global := NewSymbolTable()
+	global.Define("a")
+	global.Define("b")
+
+	firstLocal := NewEnclosedSymbolTable(global)
+	firstLocal.Define("c")
+	firstLocal.Define("d")
+
+	secondLocal := NewEnclosedSymbolTable(firstLocal)
+	secondLocal.Define("e")
+	secondLocal.Define("f")
+
+	tests := []struct {
+		table               *SymbolTable
+		expectedSymbols     []Symbol
+		expectedFreeSymbols []Symbol
+	}{
+		{
+			firstLocal,
+			[]Symbol{
+				Symbol{Name: "a", Scope: GlobalScope, Index: 0},
+				Symbol{Name: "b", Scope: GlobalScope, Index: 1},
+				Symbol{Name: "c", Scope: LocalScope, Index: 0},
+				Symbol{Name: "d", Scope: LocalScope, Index: 1},
+			},
+			[]Symbol{},
+		},
+		{
+			secondLocal,
+			[]Symbol{
+				Symbol{Name: "a", Scope: GlobalScope, Index: 0},
+				Symbol{Name: "b", Scope: GlobalScope, Index: 1},
+				Symbol{Name: "c", Scope: FreeScope, Index: 0},
+				Symbol{Name: "d", Scope: FreeScope, Index: 1},
+				Symbol{Name: "e", Scope: LocalScope, Index: 0},
+				Symbol{Name: "f", Scope: LocalScope, Index: 1},
+			},
+			[]Symbol{
+				Symbol{Name: "c", Scope: LocalScope, Index: 0},
+				Symbol{Name: "d", Scope: LocalScope, Index: 1},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		for _, sym := range tt.expectedSymbols {
+			result, ok := tt.table.Resolve(sym.Name)
+			if !ok {
+				t.Errorf("name %s not resolvable", sym.Name)
+				continue
+			}
+			if result != sym {
+				t.Errorf("expected %s to resolve to %+v, got=%+v",
+					sym.Name, sym, result)
+			}
+		}
+
+		if len(tt.table.FreeSymbols) != len(tt.expectedFreeSymbols) {
+			t.Errorf("wrong number of free symbols. got=%d, want=%d",
+				len(tt.table.FreeSymbols), len(tt.expectedFreeSymbols))
+			continue
+		}
+
+		for i, sym := range tt.expectedFreeSymbols {
+			result := tt.table.FreeSymbols[i]
+			if result != sym {
+				t.Errorf("wrong free symbol. got=%+v, want=%+v",
+					result, sym)
+			}
+		}
+	}
+}
+
+func TestResolveUnresolvableFree(t *testing.T) {
+	global := NewSymbolTable()
+	global.Define("a")
+
+	firstLocal := NewEnclosedSymbolTable(global)
+	firstLocal.Define("c")
+
+	secondLocal := NewEnclosedSymbolTable(firstLocal)
+	secondLocal.Define("e")
+	secondLocal.Define("f")
+
+	expected := []Symbol{
+		Symbol{Name: "a", Scope: GlobalScope, Index: 0},
+		Symbol{Name: "c", Scope: FreeScope, Index: 0},
+		Symbol{Name: "e", Scope: LocalScope, Index: 0},
+		Symbol{Name: "f", Scope: LocalScope, Index: 1},
+	}
+
+	for _, sym := range expected {
+		result, ok := secondLocal.Resolve(sym.Name)
+		if !ok {
+			t.Errorf("name %s not resolvable", sym.Name)
+			continue
+		}
+		if result != sym {
+			t.Errorf("expected %s to resolve to %+v, got=%+v",
+				sym.Name, sym, result)
+		}
+	}
+
+	expectedUnresolvable := []string{
+		"b",
+		"d",
+	}
+
+	for _, name := range expectedUnresolvable {
+		_, ok := secondLocal.Resolve(name)
+		if ok {
+			t.Errorf("name %s resolved, but was expected not to", name)
+		}
+	}
+}
+
+func TestDefineAndResolveFunctionName(t *testing.T) {
+	global := NewSymbolTable()
+	global.DefineFunctionName("a")
+
+	expected := Symbol{Name: "a", Scope: FunctionScope, Index: 0}
+
+	result, ok := global.Resolve(expected.Name)
+	if !ok {
+		t.Fatalf("function name %s not resolvable", expected.Name)
+	}
+
+	if result != expected {
+		t.Errorf("expected %s to resolve to %+v, got=%+v",
+			expected.Name, expected, result)
+	}
+}
+func TestShadowingFunctionName(t *testing.T) {
+	global := NewSymbolTable()
+	global.DefineFunctionName("a")
+	global.Define("a")
+
+	expected := Symbol{Name: "a", Scope: GlobalScope, Index: 0}
+
+	result, ok := global.Resolve(expected.Name)
+	if !ok {
+		t.Fatalf("function name %s not resolvable", expected.Name)
+	}
+
+	if result != expected {
+		t.Errorf("expected %s to resolve to %+v, got=%+v",
+			expected.Name, expected, result)
+	}
+}

parser/parser.go

@@ -169,6 +169,10 @@ func (p *Parser) parseLetStatement() *ast.LetStatement {
 
 	stmt.Value = p.parseExpression(LOWEST)
 
+	if fl, ok := stmt.Value.(*ast.FunctionLiteral); ok {
+		fl.Name = stmt.Name.Value
+	}
+
 	if p.peekTokenIs(token.SEMICOLON) {
 		p.nextToken()
 	}

parser/parser_test.go

@@ -845,6 +845,37 @@ func TestParsingHashLiteralsWithExpressions(t *testing.T) {
 	}
 }
 
+func TestFunctionLiteralWithName(t *testing.T) {
+	input := `let myFunction = fn() { };`
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	if len(program.Statements) != 1 {
+		t.Fatalf("program.Body does not contain %d statements. got=%d\n",
+			1, len(program.Statements))
+	}
+
+	stmt, ok := program.Statements[0].(*ast.LetStatement)
+	if !ok {
+		t.Fatalf("program.Statements[0] is not ast.LetStatement. got=%T",
+			program.Statements[0])
+	}
+
+	function, ok := stmt.Value.(*ast.FunctionLiteral)
+	if !ok {
+		t.Fatalf("stmt.Value is not ast.FunctionLiteral. got=%T",
+			stmt.Value)
+	}
+
+	if function.Name != "myFunction" {
+		t.Fatalf("function literal name wrong. want 'myFunction', got=%q\n",
+			function.Name)
+	}
+}
+
 func testLetStatement(t *testing.T, s ast.Statement, name string) bool {
 	if s.TokenLiteral() != "let" {
 		t.Errorf("s.TokenLiteral not 'let'. got=%q", s.TokenLiteral())

vm/vm.go

@@ -264,10 +264,27 @@ func (vm *VM) Run() error {
 
 		case code.OpClosure:
 			constIndex := code.ReadUint16(ins[ip+1:])
-			_ = code.ReadUint8(ins[ip+3:])
+			numFree := code.ReadUint8(ins[ip+3:])
 			vm.currentFrame().ip += 3
 
-			err := vm.pushClosure(int(constIndex))
+			err := vm.pushClosure(int(constIndex), int(numFree))
+			if err != nil {
+				return err
+			}
+
+		case code.OpGetFree:
+			freeIndex := code.ReadUint8(ins[ip+1:])
+			vm.currentFrame().ip += 1
+
+			currentClosure := vm.currentFrame().cl
+			err := vm.push(currentClosure.Free[freeIndex])
+			if err != nil {
+				return err
+			}
+
+		case code.OpCurrentClosure:
+			currentClosure := vm.currentFrame().cl
+			err := vm.push(currentClosure)
 			if err != nil {
 				return err
 			}
@@ -533,14 +550,20 @@ func (vm *VM) callBuiltin(builtin *object.Builtin, numArgs int) error {
 	return nil
 }
 
-func (vm *VM) pushClosure(constIndex int) error {
+func (vm *VM) pushClosure(constIndex, numFree int) error {
 	constant := vm.constants[constIndex]
 	function, ok := constant.(*object.CompiledFunction)
 	if !ok {
 		return fmt.Errorf("not a function %+v", constant)
 	}
 
-	closure := &object.Closure{Fn: function}
+	free := make([]object.Object, numFree)
+	for i := 0; i < numFree; i++ {
+		free[i] = vm.stack[vm.sp-numFree+i]
+	}
+	vm.sp = vm.sp - numFree
+
+	closure := &object.Closure{Fn: function, Free: free}
 	return vm.push(closure)
 }
 

vm/vm_test.go

@@ -27,6 +27,19 @@ func runVmTests(t *testing.T, tests []vmTestCase) {
 			t.Fatalf("compiler error: %s", err)
 		}
 
+		//for i, constant := range comp.Bytecode().Constants {
+		//	fmt.Printf("CONSTANT %d %p (%T):\n", i, constant, constant)
+		//
+		//	switch constant := constant.(type) {
+		//	case *object.CompiledFunction:
+		//		fmt.Printf(" Instructions:\n%s", constant.Instructions)
+		//	case *object.Integer:
+		//		fmt.Printf(" Value: %d\n", constant.Value)
+		//	}
+		//
+		//	fmt.Printf("\n")
+		//}
+
 		vm := New(comp.Bytecode())
 		err = vm.Run()
 		if err != nil {
@@ -611,3 +624,134 @@ func TestBuiltinFunctions(t *testing.T) {
 
 	runVmTests(t, tests)
 }
+
+func TestClosures(t *testing.T) {
+	tests := []vmTestCase{
+		{
+			input: `
+        let newClosure = fn(a) {
+            fn() { a; };
+        };
+        let closure = newClosure(99);
+        closure();
+        `,
+			expected: 99,
+		},
+		{
+			input: `
+        let newAdder = fn(a, b) {
+            fn(c) { a + b + c };
+        };
+        let adder = newAdder(1, 2);
+        adder(8);
+        `,
+			expected: 11,
+		},
+		{
+			input: `
+        let newAdder = fn(a, b) {
+            let c = a + b;
+            fn(d) { c + d };
+        };
+        let adder = newAdder(1, 2);
+        adder(8);
+        `,
+			expected: 11,
+		},
+		{
+			input: `
+        let newAdderOuter = fn(a, b) {
+            let c = a + b;
+            fn(d) {
+                let e = d + c;
+                fn(f) { e + f; };
+            };
+        };
+        let newAdderInner = newAdderOuter(1, 2)
+        let adder = newAdderInner(3);
+        adder(8);
+        `,
+			expected: 14,
+		},
+		{
+			input: `
+        let a = 1;
+        let newAdderOuter = fn(b) {
+            fn(c) {
+                fn(d) { a + b + c + d };
+            };
+        };
+        let newAdderInner = newAdderOuter(2)
+        let adder = newAdderInner(3);
+        adder(8);
+        `,
+			expected: 14,
+		},
+		{
+			input: `
+        let newClosure = fn(a, b) {
+            let one = fn() { a; };
+            let two = fn() { b; };
+            fn() { one() + two(); };
+        };
+        let closure = newClosure(9, 90);
+        closure();
+        `,
+			expected: 99,
+		},
+	}
+
+	runVmTests(t, tests)
+}
+
+func TestRecursiveFunctions(t *testing.T) {
+	tests := []vmTestCase{
+		{
+			input: `
+        let countDown = fn(x) {
+            if (x == 0) {
+                return 0;
+            } else {
+                countDown(x - 1);
+            }
+        };
+        countDown(1);
+        `,
+			expected: 0,
+		},
+		{
+			input: `
+        let countDown = fn(x) {
+            if (x == 0) {
+                return 0;
+            } else {
+                countDown(x - 1);
+            }
+        };
+        let wrapper = fn() {
+            countDown(1);
+        };
+        wrapper();
+        `,
+			expected: 0,
+		},
+		{
+			input: `
+        let wrapper = fn() {
+            let countDown = fn(x) {
+                if (x == 0) {
+                    return 0;
+                } else {
+                    countDown(x - 1);
+                }
+            };
+            countDown(1);
+        };
+        wrapper();
+        `,
+			expected: 0,
+		},
+	}
+
+	runVmTests(t, tests)
+}