rearrange builtins

object/builtin.go

@@ -0,0 +1,18 @@
+package object
+
+import "fmt"
+
+type Builtin struct {
+	Name string
+	Fn   BuiltinFunction
+}
+
+func (b *Builtin) Type() ObjectType {
+	return BUILTIN_OBJ
+}
+func (b *Builtin) Inspect() string {
+	return fmt.Sprintf("<built-in function %s>", b.Name)
+}
+func (b *Builtin) String() string {
+	return b.Inspect()
+}