Fix repl feedback

object/builtins.go

@@ -85,7 +85,7 @@ func Input(args ...Object) Object {
 // Print ...
 func Print(args ...Object) Object {
 	for _, arg := range args {
-		fmt.Println(arg.Inspect())
+		fmt.Println(arg.String())
 	}
 
 	return nil

object/object.go

@@ -34,6 +34,7 @@ type Immutable interface {
 
 type Object interface {
 	Type() ObjectType
+	String() string
 	Inspect() string
 }
 
@@ -56,6 +57,9 @@ func (i *Integer) Inspect() string {
 func (i *Integer) Clone() Object {
 	return &Integer{Value: i.Value}
 }
+func (i *Integer) String() string {
+	return i.Inspect()
+}
 
 type Boolean struct {
 	Value bool
@@ -70,6 +74,9 @@ func (b *Boolean) Inspect() string {
 func (b *Boolean) Clone() Object {
 	return &Boolean{Value: b.Value}
 }
+func (b *Boolean) String() string {
+	return b.Inspect()
+}
 
 type Null struct{}
 
@@ -79,6 +86,9 @@ func (n *Null) Type() ObjectType {
 func (n *Null) Inspect() string {
 	return "null"
 }
+func (n *Null) String() string {
+	return n.Inspect()
+}
 
 type ReturnValue struct {
 	Value Object
@@ -87,10 +97,12 @@ type ReturnValue struct {
 func (rv *ReturnValue) Type() ObjectType {
 	return RETURN_VALUE_OBJ
 }
-
 func (rv *ReturnValue) Inspect() string {
 	return rv.Value.Inspect()
 }
+func (rv *ReturnValue) String() string {
+	return rv.Inspect()
+}
 
 type Error struct {
 	Message string
@@ -105,6 +117,9 @@ func (e *Error) Inspect() string {
 func (e *Error) Clone() Object {
 	return &Error{Message: e.Message}
 }
+func (e *Error) String() string {
+	return e.Message
+}
 
 type Function struct {
 	Parameters []*ast.Identifier
@@ -115,7 +130,6 @@ type Function struct {
 func (f *Function) Type() ObjectType {
 	return FUNCTION_OBJ
 }
-
 func (f *Function) Inspect() string {
 	var out bytes.Buffer
 
@@ -133,6 +147,9 @@ func (f *Function) Inspect() string {
 
 	return out.String()
 }
+func (f *Function) String() string {
+	return f.Inspect()
+}
 
 type String struct {
 	Value string
@@ -142,11 +159,14 @@ func (s *String) Type() ObjectType {
 	return STRING_OBJ
 }
 func (s *String) Inspect() string {
-	return s.Value
+	return fmt.Sprintf("%#v", s.Value)
 }
 func (s *String) Clone() Object {
 	return &String{Value: s.Value}
 }
+func (s *String) String() string {
+	return s.Value
+}
 
 type BuiltinFunction func(args ...Object) Object
 
@@ -155,12 +175,15 @@ type Builtin struct {
 	Fn   BuiltinFunction
 }
 
-func (b Builtin) Type() ObjectType {
+func (b *Builtin) Type() ObjectType {
 	return BUILTIN_OBJ
 }
-func (b Builtin) Inspect() string {
+func (b *Builtin) Inspect() string {
 	return fmt.Sprintf("<built-in function %s>", b.Name)
 }
+func (b *Builtin) String() string {
+	return b.Inspect()
+}
 
 type Array struct {
 	Elements []Object
@@ -183,6 +206,9 @@ func (ao *Array) Inspect() string {
 
 	return out.String()
 }
+func (ao *Array) String() string {
+	return ao.Inspect()
+}
 
 type HashKey struct {
 	Type  ObjectType
@@ -242,6 +268,9 @@ func (h *Hash) Inspect() string {
 
 	return out.String()
 }
+func (h *Hash) String() string {
+	return h.Inspect()
+}
 
 func (cf *CompiledFunction) Type() ObjectType {
 	return COMPILED_FUNCTION_OBJ
@@ -249,6 +278,9 @@ func (cf *CompiledFunction) Type() ObjectType {
 func (cf *CompiledFunction) Inspect() string {
 	return fmt.Sprintf("CompiledFunction[%p]", cf)
 }
+func (cf *CompiledFunction) String() string {
+	return cf.Inspect()
+}
 
 type Closure struct {
 	Fn   *CompiledFunction
@@ -261,3 +293,6 @@ func (c *Closure) Type() ObjectType {
 func (c *Closure) Inspect() string {
 	return fmt.Sprintf("Closure[%p]", c)
 }
+func (c *Closure) String() string {
+	return c.Inspect()
+}

repl/repl.go

@@ -164,7 +164,7 @@ func (r *REPL) StartEvalLoop(in io.Reader, out io.Writer, env *object.Environmen
 		}
 
 		obj := evaluator.Eval(program, env)
-		if obj != nil {
+		if _, ok := obj.(*object.Null); !ok {
 			io.WriteString(out, obj.Inspect())
 			io.WriteString(out, "\n")
 		}
@@ -216,10 +216,12 @@ func (r *REPL) StartExecLoop(in io.Reader, out io.Writer, state *VMState) {
 			return
 		}
 
-		stackTop := machine.LastPoppedStackElem()
-		io.WriteString(out, stackTop.Inspect())
+		obj := machine.LastPoppedStackElem()
+		if _, ok := obj.(*object.Null); !ok {
+			io.WriteString(out, obj.Inspect())
 			io.WriteString(out, "\n")
 		}
+	}
 }
 
 func (r *REPL) Run() {