Re: Timer variable binding

[Johan Andersson <johan.rejeep@gmail.com>]

Of course. Obvious now that you say it. Lexical binding it is. Thanks very
much for the answers!
On Jan 7, 2014 10:57 PM, "Nicolas Richard" <theonewiththeevillook@yahoo.fr>
wrote:

> > let (my-var=10) -> run-at-time -> *magic* -> callback-function
> > Looks to me like this should work? But why doesn't it? ;)
>
> By the time the callback is called, the let form is long gone. The
> callback-function is stored in some place (namely, in a timer structure in
> the global variable timer-list) and then, after some time, another piece of
> emacs code calls that function. At that moment, there's no more let binding.
>
> Why it works with lexical binding is because the lambda is made into a
> closure, which then knows what the symbol my-var is.
>
> In a buffer where lexical-binding is t, you can try evalling
> (setq foobar (let ((my-var 0)) (lambda () (incf my-var) (message "my-var:
> %s" my-var))))
> the answer will be:
> (closure ((my-var . 0) t) nil (setq my-var (1+ my-var)) (message "my-var:
> %s" my-var))
> if you now call (funcall foobar), you'll get "my-var: 1"
> and now, evalling foobar gives:
> (closure ((my-var . 1) t) nil (setq my-var (1+ my-var)) (message "my-var:
> %s" my-var))
> This is magic !
>
> Doing the same without lex-bind will give you a lambda, then an error,
> then the same lambda.
>
> --
>
> Nico.
>
>