How can I update map fileds. #587

I have some map fields in a Env , and a string content . Env struct is like this :

type Env struct {
    msg string
   fileds map[string]any
}

Now I want to add filed by the msg content , such as .

fileds["len"] = len(msgs)
fileds["uppper"] = uppper(msgs)

At last return the fields to the expr script caller.

How can I do that.

Thanks.

And I wonder why not provide built in much more map functions.