fixed mutability

code/code.go

@@ -27,7 +27,8 @@ const (
 	OpJumpNotTruthy
 	OpJump
 	OpNull
-	OpAssign
+	OpAssignGlobal
+	OpAssignLocal
 	OpGetGlobal
 	OpSetGlobal
 	OpArray
@@ -52,6 +53,8 @@ type Definition struct {
 
 var definitions = map[Opcode]*Definition{
 	OpConstant:       {"OpConstant", []int{2}},
+	OpAssignGlobal:   {"OpAssignGlobal", []int{2}},
+	OpAssignLocal:    {"OpAssignLocal", []int{1}},
 	OpAdd:            {"OpAdd", []int{}},
 	OpPop:            {"OpPop", []int{}},
 	OpSub:            {"OpSub", []int{}},
@@ -67,7 +70,6 @@ var definitions = map[Opcode]*Definition{
 	OpJumpNotTruthy:  {"OpJumpNotTruthy", []int{2}},
 	OpJump:           {"OpJump", []int{2}},
 	OpNull:           {"OpNull", []int{}},
-	OpAssign:         {"OpAssign", []int{}},
 	OpGetGlobal:      {"OpGetGlobal", []int{2}},
 	OpSetGlobal:      {"OpSetGlobal", []int{2}},
 	OpArray:          {"OpArray", []int{2}},

compiler/compiler.go

@@ -210,13 +210,11 @@ func (c *Compiler) Compile(node ast.Node) error {
 		}
 
 		if symbol.Scope == GlobalScope {
-			c.emit(code.OpGetGlobal, symbol.Index)
+			c.emit(code.OpAssignGlobal, symbol.Index)
 		} else {
-			c.emit(code.OpGetLocal, symbol.Index)
+			c.emit(code.OpAssignLocal, symbol.Index)
 		}
 
-		c.emit(code.OpAssign)
-
 	case *ast.LetStatement:
 		symbol, ok := c.symbolTable.Resolve(node.Name.Value)
 		if !ok {

compiler/compiler_test.go

@@ -779,8 +779,7 @@ func TestAssignmentStatementScopes(t *testing.T) {
 				55,
 				[]code.Instructions{
 					code.Make(code.OpConstant, 1),
-					code.Make(code.OpGetGlobal, 0),
-					code.Make(code.OpAssign),
+					code.Make(code.OpAssignGlobal, 0),
 					code.Make(code.OpReturn),
 				},
 			},
@@ -791,48 +790,19 @@ func TestAssignmentStatementScopes(t *testing.T) {
 				code.Make(code.OpPop),
 			},
 		},
-
 		{
 			input: `
-			            fn() {
-			                let num = 55;
-			                num
-			            }
+            fn() { let num = 0; num  = 55; }
             `,
 			expectedConstants: []interface{}{
+				0,
 				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.OpClosure, 1, 0),
-				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),
+					code.Make(code.OpAssignLocal, 0),
+					code.Make(code.OpReturn),
 				},
 			},
 			expectedInstructions: []code.Instructions{
@@ -840,24 +810,6 @@ func TestAssignmentStatementScopes(t *testing.T) {
 				code.Make(code.OpPop),
 			},
 		},
-		{
-			input: `
-						let a = 0;
-						let a = a + 1;
-						`,
-			expectedConstants: []interface{}{
-				0,
-				1,
-			},
-			expectedInstructions: []code.Instructions{
-				code.Make(code.OpConstant, 0),
-				code.Make(code.OpSetGlobal, 0),
-				code.Make(code.OpGetGlobal, 0),
-				code.Make(code.OpConstant, 1),
-				code.Make(code.OpAdd),
-				code.Make(code.OpSetGlobal, 0),
-			},
-		},
 	}
 
 	runCompilerTests(t, tests)

evaluator/evaluator.go

@@ -46,9 +46,9 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 		return &object.ReturnValue{Value: val}
 
 	case *ast.AssignmentStatement:
-		ident := evalIdentifier(node.Name, env)
-		if isError(ident) {
-			return ident
+		obj := evalIdentifier(node.Name, env)
+		if isError(obj) {
+			return obj
 		}
 
 		val := Eval(node.Value, env)
@@ -56,12 +56,7 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 			return val
 		}
 
-		obj, ok := ident.(object.Mutable)
-		if !ok {
-			return newError("cannot assign to %s", ident.Type())
-		}
-
-		obj.Set(val)
+		env.Set(node.Name.Value, val)
 
 		return val
 
@@ -71,8 +66,8 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 			return val
 		}
 
-		if mutable, ok := val.(object.Mutable); ok {
-			env.Set(node.Name.Value, mutable.Clone())
+		if immutable, ok := val.(object.Immutable); ok {
+			env.Set(node.Name.Value, immutable.Clone())
 		} else {
 			env.Set(node.Name.Value, val)
 		}

object/builtins.go

@@ -146,7 +146,11 @@ var Builtins = []struct {
 
 			newElements := make([]Object, length+1, length+1)
 			copy(newElements, arr.Elements)
+			if immutable, ok := args[1].(Immutable); ok {
+				newElements[length] = immutable.Clone()
+			} else {
 				newElements[length] = args[1]
+			}
 
 			return &Array{Elements: newElements}
 		},

object/object.go

@@ -26,11 +26,10 @@ const (
 	CLOSURE_OBJ           = "CLOSURE"
 )
 
-// Mutable is the interface for all mutable objects which must implement
-// the Set() method which rebinds its internal value for assignment statements
-type Mutable interface {
+// Mutable is the interface for all immutable objects which must implement
+// the Clone() method used by binding names to values.
+type Immutable interface {
 	Clone() Object
-	Set(obj Object)
 }
 
 type Object interface {
@@ -54,9 +53,6 @@ func (i *Integer) Type() ObjectType {
 func (i *Integer) Inspect() string {
 	return fmt.Sprintf("%d", i.Value)
 }
-func (i *Integer) Set(obj Object) {
-	i.Value = obj.(*Integer).Value
-}
 func (i *Integer) Clone() Object {
 	return &Integer{Value: i.Value}
 }
@@ -71,9 +67,6 @@ func (b *Boolean) Type() ObjectType {
 func (b *Boolean) Inspect() string {
 	return fmt.Sprintf("%t", b.Value)
 }
-func (b *Boolean) Set(obj Object) {
-	b.Value = obj.(*Boolean).Value
-}
 func (b *Boolean) Clone() Object {
 	return &Boolean{Value: b.Value}
 }
@@ -109,9 +102,6 @@ func (e *Error) Type() ObjectType {
 func (e *Error) Inspect() string {
 	return "Error: " + e.Message
 }
-func (e *Error) Set(obj Object) {
-	e.Message = obj.(*Error).Message
-}
 func (e *Error) Clone() Object {
 	return &Error{Message: e.Message}
 }
@@ -154,9 +144,6 @@ func (s *String) Type() ObjectType {
 func (s *String) Inspect() string {
 	return s.Value
 }
-func (s *String) Set(obj Object) {
-	s.Value = obj.(*String).Value
-}
 func (s *String) Clone() Object {
 	return &String{Value: s.Value}
 }
@@ -195,14 +182,6 @@ func (ao *Array) Inspect() string {
 
 	return out.String()
 }
-func (ao *Array) Set(obj Object) {
-	ao.Elements = obj.(*Array).Elements
-}
-func (ao *Array) Clone() Object {
-	elements := make([]Object, len(ao.Elements))
-	copy(elements, ao.Elements)
-	return &Array{Elements: elements}
-}
 
 type HashKey struct {
 	Type  ObjectType
@@ -262,21 +241,10 @@ func (h *Hash) Inspect() string {
 
 	return out.String()
 }
-func (h *Hash) Set(obj Object) {
-	h.Pairs = obj.(*Hash).Pairs
-}
-func (h *Hash) Clone() Object {
-	pairs := make(map[HashKey]HashPair)
-	for k, v := range h.Pairs {
-		pairs[k] = v
-	}
-	return &Hash{Pairs: pairs}
-}
 
 func (cf *CompiledFunction) Type() ObjectType {
 	return COMPILED_FUNCTION_OBJ
 }
-
 func (cf *CompiledFunction) Inspect() string {
 	return fmt.Sprintf("CompiledFunction[%p]", cf)
 }
@@ -289,7 +257,6 @@ type Closure struct {
 func (c *Closure) Type() ObjectType {
 	return CLOSURE_OBJ
 }
-
 func (c *Closure) Inspect() string {
 	return fmt.Sprintf("Closure[%p]", c)
 }

vm/vm.go

@@ -157,22 +157,23 @@ func (vm *VM) Run() error {
 			vm.currentFrame().ip += 2
 
 			ref := vm.pop()
-			if mutable, ok := ref.(object.Mutable); ok {
-				vm.globals[globalIndex] = mutable.Clone()
+			if immutable, ok := ref.(object.Immutable); ok {
+				vm.globals[globalIndex] = immutable.Clone()
 			} else {
 				vm.globals[globalIndex] = ref
 			}
 
-		case code.OpAssign:
-			ident := vm.pop()
-			val := vm.pop()
+		case code.OpAssignGlobal:
+			globalIndex := code.ReadUint16(ins[ip+1:])
+			vm.currentFrame().ip += 2
+			vm.globals[globalIndex] = vm.pop()
 
-			obj, ok := ident.(object.Mutable)
-			if !ok {
-				return fmt.Errorf("cannot assign to %s", ident.Type())
-			}
+		case code.OpAssignLocal:
+			localIndex := code.ReadUint8(ins[ip+1:])
+			vm.currentFrame().ip += 1
 
-			obj.Set(val)
+			frame := vm.currentFrame()
+			vm.stack[frame.basePointer+int(localIndex)] = vm.pop()
 
 		case code.OpGetGlobal:
 			globalIndex := code.ReadUint16(ins[ip+1:])