clone

evaluator/evaluator.go

@@ -70,7 +70,12 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 		if isError(val) {
 			return val
 		}
-		env.Set(node.Name.Value, val)
+
+		if mutable, ok := val.(object.Mutable); ok {
+			env.Set(node.Name.Value, mutable.Clone())
+		} else {
+			env.Set(node.Name.Value, val)
+		}
 
 	case *ast.Identifier:
 		return evalIdentifier(node, env)

evaluator/evaluator_test.go

@@ -251,6 +251,7 @@ func TestAssignmentStatements(t *testing.T) {
 		{"let a = 0; a = 5; let b = 0; b = a; b;", 5},
 		{"let a = 0; a = 5; let b = 0; b = a; let c = 0; c = a + b + 5;", 15},
 		{"let a = 0; a = 5; let b = 0; b = a; let c = 0; c = a + b + 5; c;", 15},
+		{"let a = 5; let b = a; a = 0; b;", 5},
 	}
 
 	for _, tt := range tests {
@@ -474,6 +475,7 @@ func TestArrayIndexExpressions(t *testing.T) {
 	}
 
 	for _, tt := range tests {
+		t.Log(tt.input)
 		evaluated := testEval(tt.input)
 
 		integer, ok := tt.expected.(int)

examples/ fibi.monkey

@@ -0,0 +1,18 @@
+let fib = fn(n) {
+   if (n < 3) {
+     return 1
+   }
+   let a = 1
+   let b = 1
+   let c = 0
+   let i = 0
+   while (i < n - 2) {
+     c = a + b
+     b = a
+     a = c
+     i = i + 1
+   }
+   return a
+}
+
+print(fib(35))

examples/foo.monkey

@@ -1,2 +0,0 @@
-let a = 0;
-let a = a + 1;

object/object.go

@@ -29,6 +29,7 @@ const (
 // 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 {
+	Clone() Object
 	Set(obj Object)
 }
 
@@ -56,6 +57,9 @@ func (i *Integer) Inspect() string {
 func (i *Integer) Set(obj Object) {
 	i.Value = obj.(*Integer).Value
 }
+func (i *Integer) Clone() Object {
+	return &Integer{Value: i.Value}
+}
 
 type Boolean struct {
 	Value bool
@@ -67,8 +71,11 @@ func (b *Boolean) Type() ObjectType {
 func (b *Boolean) Inspect() string {
 	return fmt.Sprintf("%t", b.Value)
 }
-func (i *Boolean) Set(obj Object) {
+func (b *Boolean) Set(obj Object) {
-	i.Value = obj.(*Boolean).Value
+	b.Value = obj.(*Boolean).Value
+}
+func (b *Boolean) Clone() Object {
+	return &Boolean{Value: b.Value}
 }
 
 type Null struct{}
@@ -105,6 +112,9 @@ func (e *Error) Inspect() string {
 func (e *Error) Set(obj Object) {
 	e.Message = obj.(*Error).Message
 }
+func (e *Error) Clone() Object {
+	return &Error{Message: e.Message}
+}
 
 type Function struct {
 	Parameters []*ast.Identifier
@@ -147,6 +157,9 @@ func (s *String) Inspect() string {
 func (s *String) Set(obj Object) {
 	s.Value = obj.(*String).Value
 }
+func (s *String) Clone() Object {
+	return &String{Value: s.Value}
+}
 
 type BuiltinFunction func(args ...Object) Object
 
@@ -185,6 +198,11 @@ func (ao *Array) Inspect() 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
@@ -247,6 +265,13 @@ func (h *Hash) Inspect() 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

vm/vm.go

@@ -156,7 +156,12 @@ func (vm *VM) Run() error {
 			globalIndex := code.ReadUint16(ins[ip+1:])
 			vm.currentFrame().ip += 2
 
-			vm.globals[globalIndex] = vm.pop()
+			ref := vm.pop()
+			if mutable, ok := ref.(object.Mutable); ok {
+				vm.globals[globalIndex] = mutable.Clone()
+			} else {
+				vm.globals[globalIndex] = ref
+			}
 
 		case code.OpAssign:
 			ident := vm.pop()