functions with bindings

code/code.go

@@ -35,6 +35,8 @@ const (
 	OpCall
 	OpReturnValue
 	OpReturn
+	OpGetLocal
+	OpSetLocal
 )
 
 type Definition struct {
@@ -67,6 +69,8 @@ var definitions = map[Opcode]*Definition{
 	OpCall:          {"OpCall", []int{}},
 	OpReturnValue:   {"OpReturnValue", []int{}},
 	OpReturn:        {"OpReturn", []int{}},
+	OpGetLocal:      {"OpGetLocal", []int{1}},
+	OpSetLocal:      {"OpSetLocal", []int{1}},
 }
 
 func Lookup(op byte) (*Definition, error) {
@@ -98,6 +102,8 @@ func Make(op Opcode, operands ...int) []byte {
 		switch width {
 		case 2:
 			binary.BigEndian.PutUint16(instruction[offset:], uint16(o))
+		case 1:
+			instruction[offset] = byte(o)
 		}
 		offset += width
 	}
@@ -151,6 +157,9 @@ func ReadOperands(def *Definition, ins Instructions) ([]int, int) {
 		switch width {
 		case 2:
 			operands[i] = int(ReadUint16(ins[offset:]))
+		case 1:
+			operands[i] = int(ReadUint8(ins[offset:]))
+
 		}
 
 		offset += width
@@ -162,3 +171,7 @@ func ReadOperands(def *Definition, ins Instructions) ([]int, int) {
 func ReadUint16(ins Instructions) uint16 {
 	return binary.BigEndian.Uint16(ins)
 }
+
+func ReadUint8(ins Instructions) uint8 {
+	return ins[0]
+}

code/code_test.go

@@ -10,6 +10,7 @@ func TestMake(t *testing.T) {
 	}{
 		{OpConstant, []int{65534}, []byte{byte(OpConstant), 255, 254}},
 		{OpAdd, []int{}, []byte{byte(OpAdd)}},
+		{OpGetLocal, []int{255}, []byte{byte(OpGetLocal), 255}},
 	}
 
 	for _, tt := range test {
@@ -30,13 +31,15 @@ func TestMake(t *testing.T) {
 func TestInstructions(t *testing.T) {
 	instructions := []Instructions{
 		Make(OpAdd),
+		Make(OpGetLocal, 1),
 		Make(OpConstant, 2),
 		Make(OpConstant, 65535),
 	}
 
 	expected := `0000 OpAdd
-0001 OpConstant 2
-0004 OpConstant 65535
+0001 OpGetLocal 1
+0003 OpConstant 2
+0006 OpConstant 65535
 `
 
 	concatted := Instructions{}
@@ -49,13 +52,14 @@ func TestInstructions(t *testing.T) {
 	}
 }
 
-func TestOperands(t *testing.T) {
+func TestReadOperands(t *testing.T) {
 	tests := []struct {
 		op        Opcode
 		operands  []int
 		bytesRead int
 	}{
 		{OpConstant, []int{65535}, 2},
+		{OpGetLocal, []int{255}, 1},
 	}
 
 	for _, tt := range tests {

compiler/compiler.go

@@ -193,8 +193,13 @@ func (c *Compiler) Compile(node ast.Node) error {
 		if err != nil {
 			return err
 		}
+
 		symbol := c.symbolTable.Define(node.Name.Value)
-		c.emit(code.OpSetGlobal, symbol.Index)
+		if symbol.Scope == GlobalScope {
+			c.emit(code.OpSetGlobal, symbol.Index)
+		} else {
+			c.emit(code.OpSetLocal, symbol.Index)
+		}
 
 	case *ast.Identifier:
 		symbol, ok := c.symbolTable.Resolve(node.Value)
@@ -202,7 +207,11 @@ func (c *Compiler) Compile(node ast.Node) error {
 			return fmt.Errorf("undefined varible %s", node.Value)
 		}
 
-		c.emit(code.OpGetGlobal, symbol.Index)
+		if symbol.Scope == GlobalScope {
+			c.emit(code.OpGetGlobal, symbol.Index)
+		} else {
+			c.emit(code.OpGetLocal, symbol.Index)
+		}
 
 	case *ast.StringLiteral:
 		str := &object.String{Value: node.Value}
@@ -268,9 +277,10 @@ func (c *Compiler) Compile(node ast.Node) error {
 			c.emit(code.OpReturn)
 		}
 
+		numLocals := c.symbolTable.numDefinitions
 		instructions := c.leaveScope()
 
-		compiledFn := &object.CompiledFunction{Instructions: instructions}
+		compiledFn := &object.CompiledFunction{Instructions: instructions, NumLocals: numLocals}
 		c.emit(code.OpConstant, c.addConstant(compiledFn))
 
 	case *ast.ReturnStatement:
@@ -374,6 +384,8 @@ func (c *Compiler) enterScope() {
 	}
 	c.scopes = append(c.scopes, scope)
 	c.scopeIndex++
+
+	c.symbolTable = NewEnclosedSymbolTable(c.symbolTable)
 }
 
 func (c *Compiler) leaveScope() code.Instructions {
@@ -382,6 +394,8 @@ func (c *Compiler) leaveScope() code.Instructions {
 	c.scopes = c.scopes[:len(c.scopes)-1]
 	c.scopeIndex--
 
+	c.symbolTable = c.symbolTable.Outer
+
 	return instructions
 }
 

compiler/compiler_test.go

@@ -591,6 +591,80 @@ func TestFunctionCalls(t *testing.T) {
 	runCompilerTests(t, tests)
 }
 
+func TestLetStatementScopes(t *testing.T) {
+	tests := []compilerTestCase{
+		{
+			input: `
+            let num = 55;
+            fn() { num }
+            `,
+			expectedConstants: []interface{}{
+				55,
+				[]code.Instructions{
+					code.Make(code.OpGetGlobal, 0),
+					code.Make(code.OpReturnValue),
+				},
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpSetGlobal, 0),
+				code.Make(code.OpConstant, 1),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input: `
+            fn() {
+                let num = 55;
+                num
+            }
+            `,
+			expectedConstants: []interface{}{
+				55,
+				[]code.Instructions{
+					code.Make(code.OpConstant, 0),
+					code.Make(code.OpSetLocal, 0),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpReturnValue),
+				},
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 1),
+				code.Make(code.OpPop),
+			},
+		},
+		{
+			input: `
+            fn() {
+                let a = 55;
+                let b = 77;
+                a + b
+            }
+            `,
+			expectedConstants: []interface{}{
+				55,
+				77,
+				[]code.Instructions{
+					code.Make(code.OpConstant, 0),
+					code.Make(code.OpSetLocal, 0),
+					code.Make(code.OpConstant, 1),
+					code.Make(code.OpSetLocal, 1),
+					code.Make(code.OpGetLocal, 0),
+					code.Make(code.OpGetLocal, 1),
+					code.Make(code.OpAdd),
+					code.Make(code.OpReturnValue),
+				},
+			},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 2),
+				code.Make(code.OpPop),
+			},
+		},
+	}
+
+	runCompilerTests(t, tests)
+}
+
 func runCompilerTests(t *testing.T, tests []compilerTestCase) {
 	t.Helper()
 

compiler/symbol_table.go

@@ -3,7 +3,8 @@ package compiler
 type SymbolScope string
 
 const (
-	GlobalScope SymbolScope = "Global"
+	LocalScope  SymbolScope = "LOCAL"
+	GlobalScope SymbolScope = "GLOBAL"
 )
 
 type Symbol struct {
@@ -13,21 +14,31 @@ type Symbol struct {
 }
 
 type SymbolTable struct {
+	Outer *SymbolTable
+
 	store          map[string]Symbol
 	numDefinitions int
 }
 
+func NewEnclosedSymbolTable(outer *SymbolTable) *SymbolTable {
+	s := NewSymbolTable()
+	s.Outer = outer
+	return s
+}
+
 func NewSymbolTable() *SymbolTable {
 	s := make(map[string]Symbol)
 	return &SymbolTable{store: s}
 }
 
 func (s *SymbolTable) Define(name string) Symbol {
-	symbol := Symbol{
-		Name:  name,
-		Scope: GlobalScope,
-		Index: s.numDefinitions,
+	symbol := Symbol{Name: name, Index: s.numDefinitions}
+	if s.Outer == nil {
+		symbol.Scope = GlobalScope
+	} else {
+		symbol.Scope = LocalScope
 	}
+
 	s.store[name] = symbol
 	s.numDefinitions++
 	return symbol
@@ -35,5 +46,10 @@ func (s *SymbolTable) Define(name string) Symbol {
 
 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
+	}
+
 	return obj, ok
 }

compiler/symbol_table_test.go

@@ -14,6 +14,10 @@ func TestDefine(t *testing.T) {
 			Scope: GlobalScope,
 			Index: 1,
 		},
+		"c": {Name: "c", Scope: LocalScope, Index: 0},
+		"d": {Name: "d", Scope: LocalScope, Index: 1},
+		"e": {Name: "e", Scope: LocalScope, Index: 0},
+		"f": {Name: "f", Scope: LocalScope, Index: 1},
 	}
 
 	global := NewSymbolTable()
@@ -27,6 +31,30 @@ func TestDefine(t *testing.T) {
 	if b != expected["b"] {
 		t.Errorf("expected b=%+v, got=%+v", expected["b"], b)
 	}
+
+	firstLocal := NewEnclosedSymbolTable(global)
+
+	c := firstLocal.Define("c")
+	if c != expected["c"] {
+		t.Errorf("expected c=%+v, got=%+v", expected["c"], c)
+	}
+
+	d := firstLocal.Define("d")
+	if d != expected["d"] {
+		t.Errorf("expected d=%+v, got=%+v", expected["d"], d)
+	}
+
+	secondLocal := NewEnclosedSymbolTable(firstLocal)
+
+	e := secondLocal.Define("e")
+	if e != expected["e"] {
+		t.Errorf("expected e=%+v, got=%+v", expected["e"], e)
+	}
+
+	f := secondLocal.Define("f")
+	if f != expected["f"] {
+		t.Errorf("expected f=%+v, got=%+v", expected["f"], f)
+	}
 }
 
 func TestResolveGlobal(t *testing.T) {
@@ -57,3 +85,84 @@ func TestResolveGlobal(t *testing.T) {
 		}
 	}
 }
+
+func TestResolveLocal(t *testing.T) {
+	global := NewSymbolTable()
+	global.Define("a")
+	global.Define("b")
+
+	local := NewEnclosedSymbolTable(global)
+	local.Define("c")
+	local.Define("d")
+
+	expected := []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},
+	}
+
+	for _, sym := range expected {
+		result, ok := local.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)
+		}
+	}
+}
+
+func TestResolveNestedLocal(t *testing.T) {
+	global := NewSymbolTable()
+	global.Define("a")
+	global.Define("b")
+
+	firstLocal := NewEnclosedSymbolTable(global)
+	firstLocal.Define("c")
+	firstLocal.Define("d")
+
+	secondLocal := NewEnclosedSymbolTable(global)
+	secondLocal.Define("e")
+	secondLocal.Define("f")
+
+	tests := []struct {
+		table           *SymbolTable
+		expectedSymbols []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},
+			},
+		},
+		{
+			secondLocal,
+			[]Symbol{
+				Symbol{Name: "a", Scope: GlobalScope, Index: 0},
+				Symbol{Name: "b", Scope: GlobalScope, Index: 1},
+				Symbol{Name: "e", Scope: LocalScope, Index: 0},
+				Symbol{Name: "f", 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)
+			}
+		}
+	}
+}

object/object.go

@@ -36,6 +36,7 @@ type Integer struct {
 
 type CompiledFunction struct {
 	Instructions code.Instructions
+	NumLocals    int
 }
 
 func (i *Integer) Type() ObjectType {

vm/frame.go

@@ -0,0 +1,20 @@
+package vm
+
+import (
+	"monkey/code"
+	"monkey/object"
+)
+
+type Frame struct {
+	fn          *object.CompiledFunction
+	ip          int
+	basePointer int
+}
+
+func NewFrame(fn *object.CompiledFunction, basePointer int) *Frame {
+	return &Frame{fn: fn, ip: -1, basePointer: basePointer}
+}
+
+func (f *Frame) Instructions() code.Instructions {
+	return f.fn.Instructions
+}

vm/vm.go

@@ -15,19 +15,6 @@ var Null = &object.Null{}
 var True = &object.Boolean{Value: true}
 var False = &object.Boolean{Value: false}
 
-type Frame struct {
-	fn *object.CompiledFunction
-	ip int
-}
-
-func NewFrame(fn *object.CompiledFunction) *Frame {
-	return &Frame{fn: fn, ip: -1}
-}
-
-func (f *Frame) Instructions() code.Instructions {
-	return f.fn.Instructions
-}
-
 type VM struct {
 	constants []object.Object
 
@@ -42,7 +29,7 @@ type VM struct {
 
 func New(bytecode *compiler.Bytecode) *VM {
 	mainFn := &object.CompiledFunction{Instructions: bytecode.Instructions}
-	mainFrame := NewFrame(mainFn)
+	mainFrame := NewFrame(mainFn, 0)
 
 	frames := make([]*Frame, MaxFrames)
 	frames[0] = mainFrame
@@ -220,13 +207,15 @@ func (vm *VM) Run() error {
 			if !ok {
 				return fmt.Errorf("calling non-function")
 			}
-			frame := NewFrame(fn)
+			frame := NewFrame(fn, vm.sp)
 			vm.pushFrame(frame)
+			vm.sp = frame.basePointer + fn.NumLocals
 
 		case code.OpReturnValue:
 			returnValue := vm.pop()
-			vm.popFrame()
-			vm.pop()
+
+			frame := vm.popFrame()
+			vm.sp = frame.basePointer - 1
 
 			err := vm.push(returnValue)
 			if err != nil {
@@ -234,14 +223,32 @@ func (vm *VM) Run() error {
 			}
 
 		case code.OpReturn:
-			vm.popFrame()
-			vm.pop()
+			frame := vm.popFrame()
+			vm.sp = frame.basePointer - 1
 
 			err := vm.push(Null)
 			if err != nil {
 				return err
 			}
 
+		case code.OpSetLocal:
+			localIndex := code.ReadUint8(ins[ip+1:])
+			vm.currentFrame().ip += 1
+
+			frame := vm.currentFrame()
+
+			vm.stack[frame.basePointer+int(localIndex)] = vm.pop()
+
+		case code.OpGetLocal:
+			localIndex := code.ReadUint8(ins[ip+1:])
+			vm.currentFrame().ip += 1
+
+			frame := vm.currentFrame()
+
+			err := vm.push(vm.stack[frame.basePointer+int(localIndex)])
+			if err != nil {
+				return err
+			}
 		}
 	}
 

vm/vm_test.go

@@ -379,6 +379,16 @@ func TestFirstClassFunctions(t *testing.T) {
         let returnsOne = fn() { 1; };
         let returnsOneReturner = fn() { returnsOne; };
         returnsOneReturner()();
+        `,
+			expected: 1,
+		},
+		{
+			input: `
+        let returnsOneReturner = fn() {
+            let returnsOne = fn() { 1; };
+            returnsOne;
+        };
+        returnsOneReturner()();
         `,
 			expected: 1,
 		},
@@ -386,3 +396,55 @@ func TestFirstClassFunctions(t *testing.T) {
 
 	runVmTests(t, tests)
 }
+
+func TestCallingFunctionsWithBindings(t *testing.T) {
+	tests := []vmTestCase{
+		{
+			input: `
+        let one = fn() { let one = 1; one };
+        one();
+        `,
+			expected: 1,
+		},
+		{
+			input: `
+        let oneAndTwo = fn() { let one = 1; let two = 2; one + two; };
+        oneAndTwo();
+        `,
+			expected: 3,
+		},
+		{
+			input: `
+        let oneAndTwo = fn() { let one = 1; let two = 2; one + two; };
+        let threeAndFour = fn() { let three = 3; let four = 4; three + four; };
+        oneAndTwo() + threeAndFour();
+        `,
+			expected: 10,
+		},
+		{
+			input: `
+        let firstFoobar = fn() { let foobar = 50; foobar; };
+        let secondFoobar = fn() { let foobar = 100; foobar; };
+        firstFoobar() + secondFoobar();
+        `,
+			expected: 150,
+		},
+		{
+			input: `
+        let globalSeed = 50;
+        let minusOne = fn() {
+            let num = 1;
+            globalSeed - num;
+        }
+        let minusTwo = fn() {
+            let num = 2;
+            globalSeed - num;
+        }
+        minusOne() + minusTwo();
+        `,
+			expected: 97,
+		},
+	}
+
+	runVmTests(t, tests)
+}