A way for interactive to modify a let-bound variable?

A way for interactive to modify a let-bound variable?

[Kaushal Modi]

Hi,

The below snippet will of course not work but I would like to achive
something like that:

(defun my-dummy-fn ()
  (let (msg)
    (interactive (progn
                   (if (use-region-p)
                       (setq msg "Region")
                     (setq msg "No region"))
                   nil))
    (message msg)))


This is a very simplified example. But I need to change a let-bound
variable in the interactive form based on some condition and then use that
variable in the defun body.

Is that possible?

--
Kaushal Modi

RE: A way for interactive to modify a let-bound variable?

[Drew Adams]

> (defun my-dummy-fn ()
>   (let (msg)
>     (interactive (progn
>                    (if (use-region-p)
>                        (setq msg "Region")
>                      (setq msg "No region"))
>                    nil))
>     (message msg)))
> 
> This is a very simplified example. But I need to change a let-bound
> variable in the interactive form based on some condition and then use that
> variable in the defun body.  Is that possible?

No. The only thing available in the defun body that comes from
the `interactive' form is its return value, which is the list of
arguments passed to the function.

Show or explain what you are really trying to do. IOW, this sounds
like an X-Y problem: you are asking about your try at a solution
instead of asking about your actual problem.

(You can of course use `let' _inside_ `interactive', but it is not
clear what you are trying to do, so I hesitate to guess what
code might help.)

Re: A way for interactive to modify a let-bound variable?

[Michael Heerdegen]

Drew Adams <drew.adams@oracle.com> writes:

> (You can of course use `let' _inside_ `interactive', but it is not
> clear what you are trying to do, so I hesitate to guess what
> code might help.)

Yes, moving it inside is what he wants, I think.

Kaushal, don't hesitate to use whatever elisp you like in `interactive',
nothing special here.  Just be sure your expression returns the list of
arguments.

But the interactive form must look like (interactive ...), else it is
not recognized as such.


Michael.

Re: A way for interactive to modify a let-bound variable?

[Kaushal Modi]

This is the actual function I want to optimize (Reference:
http://thread.gmane.org/gmane.emacs.help/109025/focus=109137 ).

(defun modi/advice-region-or-whole (orig-fun &rest args)
  (interactive (if (use-region-p)
                   (list (region-beginning) (region-end))
                 (list (point-min) (point-max))))
  (prog1
      (apply orig-fun args) ; this defun NEEDS to return this form's value
    (when (and (called-interactively-p 'interactive) ; duplication of
condition
               (not (use-region-p)))                           ;
      (message "Executed %s on the whole buffer."
               (propertize (symbol-name this-command)
                           'face 'font-lock-function-name-face)))))

This is an :around advice function and it needs to return the (apply
orig-fun args) value.

> You can of course use `let' _inside_ `interactive'

If I move the let form inside interactive, the let form needs to return the
list required for interactive. Then how would I return the (apply ..) value?

Eventually I want something like below that actually works:

(defun modi/advice-region-or-whole (orig-fun &rest args)
  (let (msg)
    (interactive (if (use-region-p)
                     (list (region-beginning) (region-end))
                   (setq msg (format "Executed %s on the whole buffer."
                                     (propertize (symbol-name this-command)
                                                 'face
'font-lock-function-name-face)))
                   (list (point-min) (point-max))))
    (prog1
        (apply orig-fun args)
      (when msg
        (message msg)))))

Re: A way for interactive to modify a let-bound variable?

[Michael Heerdegen]

Kaushal Modi <kaushal.modi@gmail.com> writes:

> This is an :around advice function and it needs to return the (apply
> orig-fun args) value.

FWIW, for the side effect you want, a :before advice is still
sufficient.

>
> > You can of course use `let' _inside_ `interactive'
>
> If I move the let form inside interactive, the let form needs to
> return the list required for interactive. Then how would I return the
> (apply ..)  value?

Well, `let' returns the result of the evaluation of the last form, so
you have to arrange that this last form is your (apply ...), or evals to
the result of it.

> Eventually I want something like below that actually works:
>
> (defun modi/advice-region-or-whole (orig-fun &rest args)
>   (let (msg)
>     (interactive (if (use-region-p)
>                      (list (region-beginning) (region-end))
>                    (setq msg (format "Executed %s on the whole buffer."
>                                      (propertize (symbol-name this-command)
>                                                  'face
> 'font-lock-function-name-face)))
>                    (list (point-min) (point-max))))
>     (prog1
>         (apply orig-fun args)
>       (when msg
>         (message msg)))))

It may work, but that doesn't define an interactive spec for your
function, so again you change the function you want to advice, which you
wanted to avoid.


Michael.

Re: A way for interactive to modify a let-bound variable?

[Kaushal Modi]

> FWIW, for the side effect you want, a :before advice is still
> sufficient.

I ended up using :around, because I need to call (message ..) *after*
(apply orig-fun args). I need my message to be displayed last in the echo
area after whatever orig-fun could be displaying.

> Well, `let' returns the result of the evaluation of the last form, so
> you have to arrange that this last form is your (apply ...), or evals to
> the result of it.

It's a bit tricky if I put let inside interactive. If I do that, the let
form has to return the list that interactive needs. But I also need the
let-bound msg variable after calling (apply orig-fun args). So that implies
that I would need something like (interactive (let (msg) .. (apply orig-fun
args) (message msg))), which does not look right (and also does not work).

> It may work, but that doesn't define an interactive spec for your
> function, so again you change the function you want to advice, which you
> wanted to avoid.

Exactly, that does not work at all. The (interactive ..) form in there is
as good as it not being there, because it doesn't do anything if it is
wrapped in (let ..).

Re: A way for interactive to modify a let-bound variable?

[Michael Heerdegen]

Kaushal Modi <kaushal.modi@gmail.com> writes:

> It's a bit tricky if I put let inside interactive. If I do that, the let
> form has to return the list that interactive needs. But I also need the
> let-bound msg variable after calling (apply orig-fun args). So that
> implies
> that I would need something like (interactive (let (msg) .. (apply
> orig-fun
> args) (message msg))), which does not look right (and also does not work).

Eh, no, that's nonsense.  I didn't fully understand what you wanted.  It
is not possible to bind a variable in the interactive spec and refer to
it in the body.

But your last version with `prog1' is ok.  Are you happy with that one?

Michael.

Re: A way for interactive to modify a let-bound variable?

[Kaushal Modi]

> But your last version with `prog1' is ok.  Are you happy with that one?

I am happy that it works and much much better than my first version (
https://github.com/kaushalmodi/.emacs.d/blob/0b427ce554b1cade7f5fabb8ee4bfb704f6e497f/setup-files/setup-editing.el#L686-L730
).

I just wanted to go an extra mile and prevent the duplication of the
conditions.. first time in the interactive form for settings the fn args
and second time when deciding when to display the message. I just wanted to
check if the "extra optimization" I thought of was possible. So the gist
is.. what happens in interactive stays in interactive. :)

Thanks.

Re: A way for interactive to modify a let-bound variable?

[Marcin Borkowski]

On 2016-02-12, at 18:17, Michael Heerdegen <michael_heerdegen@web.de> wrote:

> Drew Adams <drew.adams@oracle.com> writes:
>
>> (You can of course use `let' _inside_ `interactive', but it is not
>> clear what you are trying to do, so I hesitate to guess what
>> code might help.)
>
> Yes, moving it inside is what he wants, I think.
>
> Kaushal, don't hesitate to use whatever elisp you like in `interactive',
> nothing special here.  Just be sure your expression returns the list of
> arguments.

My little 2cents & a plug: perhaps this could help?
http://mbork.pl/2015-09-12_A_trick_with_argument_for_interactive_call

> But the interactive form must look like (interactive ...), else it is
> not recognized as such.
>
> Michael.

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University