fixed mutability

object/builtins.go

@@ -146,7 +146,11 @@ var Builtins = []struct {
 
 			newElements := make([]Object, length+1, length+1)
 			copy(newElements, arr.Elements)
-			newElements[length] = args[1]
+			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)
 }