further improvements

internal/builtins/builtins.go

@@ -7,7 +7,7 @@ import (
 )
 
 // Builtins ...
-var Builtins = map[string]*object.Builtin{
+var Builtins = map[string]object.Builtin{
 	"len":       {Name: "len", Fn: Len},
 	"input":     {Name: "input", Fn: Input},
 	"print":     {Name: "print", Fn: Print},
@@ -58,7 +58,7 @@ var Builtins = map[string]*object.Builtin{
 }
 
 // BuiltinsIndex ...
-var BuiltinsIndex []*object.Builtin
+var BuiltinsIndex []object.Builtin
 
 func init() {
 	var keys []string