Letting hooks?

Letting hooks?

[Eric Abrahamsen]

I'm trying to temporarily add a function to a hook within the space of
one function. I've tried a bunch of stuff and nothing's worked properly,
and I suspect I'm just doing the Wrong Thing. Everything I've tried has
been along the lines of:

--8<---------------cut here---------------start------------->8---
(defun my-function ()
  (let ((grommet-created-hook
	 (push my-hook-function
	       grommet-created-hook)))
    (create-grommet)))
--8<---------------cut here---------------end--------------->8---

I've tried it with append and copy-sequence, everything blows up in
different ways.

Is this simply the wrong approach, or have I just not tried the right
commands? All advice appreciated!

Eric


-- 
GNU Emacs 24.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.24.10)
 of 2012-06-06 on pellet

Re: Letting hooks?

[Tassilo Horn]

Eric Abrahamsen <eric@ericabrahamsen.net> writes:

Hi Eric,

> (defun my-function ()
>   (let ((grommet-created-hook
> 	 (push my-hook-function
> 	       grommet-created-hook)))
>     (create-grommet)))

I think `push' is definitively a bad idea, cause it changes
`grommet-created-hook' global value, too.  And `my-hook-function' has to
be quoted.

  (let ((grommet-created-hook
         (cons 'my-hook-function grommet-created-hook)))
    (create-grommet))

should do the trick.

Bye,
Tassilo

Re: Letting hooks?

[Stefan Monnier]

>   (let ((grommet-created-hook
>          (cons 'my-hook-function grommet-created-hook)))
>     (create-grommet))

This will often work, indeed, and is fairly elegant.
For some hooks where the buffer-localness is used/modified within
create-grommet, you may prefer:

  (unwind-protect
      (progn
        (add-hook 'grommet-created-hook 'my-hook-function)
        (create-grommet))
    (remove-hook 'grommet-created-hook 'my-hook-function))


-- Stefan

Re: Letting hooks?

[Eric Abrahamsen]

On Fri, Jun 08 2012, Stefan Monnier wrote:

>>   (let ((grommet-created-hook
>>          (cons 'my-hook-function grommet-created-hook)))
>>     (create-grommet))
>
> This will often work, indeed, and is fairly elegant.
> For some hooks where the buffer-localness is used/modified within
> create-grommet, you may prefer:
>
>   (unwind-protect
>       (progn
>         (add-hook 'grommet-created-hook 'my-hook-function)
>         (create-grommet))
>     (remove-hook 'grommet-created-hook 'my-hook-function))

Thanks, I'll give this a shot as well. I was seeing very weird behavior
with Tassilo's solution – so strange that I'm assuming I've done
something elsewhere to cause it, but I haven't yet figured out what.

These are org-mode capture hooks I'm working with, and I was finding
that on a fresh start of emacs, before org was loaded (which *ought* to
mean before my own code was loaded at all), the `grommet-created-hook'
(actually `org-capture-before-finalize-hook') was already initialized to
`my-hook-function'.

Specifically: I could start emacs fresh, run describe-variable on
`org-capture-before-finalize-hook', and it would tell me the value was
(my-hook-function), but otherwise treated it as an unknown variable (ie
the docstring didn't show up, all that).

After loading org (which also loads my code, as I'm modifying a local
branch of the org codebase), describe-variable describes the hook
properly, and reports it as empty, but actually running my code (using
the cons method above) doesn't add my function to the hook.

All that seems like crazy talk me. I haven't had time to do the whole
"emacs -Q" song and dance, but I don't see anything that could be
initializing `org-capture-before-finalize-hook' before the org code is
loaded, and `my-hook-function' only exists in one place, in the one file
that's part of my local org branch.

Anyway, I'm going to dunk my head in a bucket and come back to this
later.

Thanks!
Eric

-- 
GNU Emacs 24.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.24.10)
 of 2012-06-06 on pellet