package evaluator import( "fmt" "monkey/object" ) var builtins = map[string]*object.Builtin{ "len": &object.Builtin{ Fn: func(args ...object.Object) object.Object { if len(args) != 1 { return new_error("wrong number of arguments, got=%d, want=1", len(args)) } switch arg := args[0].(type) { case *object.String: return &object.Integer{Value: int64(len(arg.Value))} default: return new_error("argument to `len` not supported, got %s", args[0].Type()) } }, }, "puts": &object.Builtin { Fn: func(args ...object.Object) object.Object { for _, arg := range args { fmt.Println(arg.Inspect()) } return NULL // puts only print things passed into it, it does not return a value when used in a function or such. }, }, }