Modifying a hook while it's being executed

Modifying a hook while it's being executed

[PT]

Is it safe? I haven't seen it anywhere stated explicitly.

For example, I add a hook function to pre-command-hook or  
post-command-hook which removes itself from the hook when invoked.

-- 
Using Opera's revolutionary e-mail client: http://www.opera.com/m2/

Re: Modifying a hook while it's being executed

[J. David Boyd]

PT <mailshield.gg@mailnull.com> writes:

> Is it safe? I haven't seen it anywhere stated explicitly.
>
> For example, I add a hook function to pre-command-hook or
> post-command-hook which removes itself from the hook when invoked.
>

Does it blow up emacs?  If not, then it is probably safe!

Dave

Re: Modifying a hook while it's being executed

[rgb]

J. David Boyd wrote:
> PT <mailshield.gg@mailnull.com> writes:
>
> > Is it safe? I haven't seen it anywhere stated explicitly.
> >
> > For example, I add a hook function to pre-command-hook or
> > post-command-hook which removes itself from the hook when invoked.
> >
>
> Does it blow up emacs?  If not, then it is probably safe!

At first I thought something similar, but that's not really
a valid way to view the problem.  If something else runs a
hook that would normally execute after the one you are removing
there is a potential for other hooks not to run on that command.
Something like that would not likely manifest itself in a
catastrophic way but could cause unusual behaviors that a
conscientious coder would want to avoid.

This line appears in remove-hook.

(setq hook-value (delete function (copy-sequence hook-value)))

It makes me think that a change to the hook's value will not
be visible to the present execution of the run-hooks command.
So I'd say it appears to be perfectly safe.

Re: Modifying a hook while it's being executed

[kcin]

rgb wrote:
>
> This line appears in remove-hook.
>
> (setq hook-value (delete function (copy-sequence hook-value)))
>
> It makes me think that a change to the hook's value will not
> be visible to the present execution of the run-hooks command.
> So I'd say it appears to be perfectly safe.

Yes, it seems OK. However I wonder why it is not simply

  (setq hook-value (remove function hook-value))
 
remove also returns a copy. Is there a difference?

Re: Modifying a hook while it's being executed

[Henrik Enberg]

> From: kcin@mytrashmail.com
> Date: 8 Aug 2005 13:21:13 -0700
> 
> rgb wrote:
> >
> > This line appears in remove-hook.
> >
> > (setq hook-value (delete function (copy-sequence hook-value)))
> >
> > It makes me think that a change to the hook's value will not
> > be visible to the present execution of the run-hooks command.
> > So I'd say it appears to be perfectly safe.
> 
> Yes, it seems OK. However I wonder why it is not simply
> 
>   (setq hook-value (remove function hook-value))
>  
> remove also returns a copy. Is there a difference?

`remove' is part of the cl library which isn't supposed to be used in
core Emacs.

Re: Modifying a hook while it's being executed

[David Kastrup]

Henrik Enberg <henrik.enberg@telia.com> writes:

>> From: kcin@mytrashmail.com
>> Date: 8 Aug 2005 13:21:13 -0700
>> 
>> rgb wrote:
>> >
>> > This line appears in remove-hook.
>> >
>> > (setq hook-value (delete function (copy-sequence hook-value)))
>> >
>> > It makes me think that a change to the hook's value will not
>> > be visible to the present execution of the run-hooks command.
>> > So I'd say it appears to be perfectly safe.
>> 
>> Yes, it seems OK. However I wonder why it is not simply
>> 
>>   (setq hook-value (remove function hook-value))
>>  
>> remove also returns a copy. Is there a difference?
>
> `remove' is part of the cl library which isn't supposed to be used in
> core Emacs.

remove is a compiled Lisp function in `subr'.
(remove ELT SEQ)

Return a copy of SEQ with all occurrences of ELT removed.
SEQ must be a list, vector, or string.  The comparison is done with `equal'.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

Re: Modifying a hook while it's being executed

[Henrik Enberg]

> From: David Kastrup <dak@gnu.org>
> Date: Mon, 08 Aug 2005 22:55:17 +0200
> 
> Henrik Enberg <henrik.enberg@telia.com> writes:
> 
> > `remove' is part of the cl library which isn't supposed to be used in
> > core Emacs.
> 
> remove is a compiled Lisp function in `subr'.
> (remove ELT SEQ)
> 
> Return a copy of SEQ with all occurrences of ELT removed.
> SEQ must be a list, vector, or string.  The comparison is done with `equal'.

doh, I must have been passing through a low flying crack cloud when I
wrote my previous message.

Re: Modifying a hook while it's being executed

[David Kastrup]

Henrik Enberg <henrik.enberg@telia.com> writes:

>> From: David Kastrup <dak@gnu.org>
>> Date: Mon, 08 Aug 2005 22:55:17 +0200
>> 
>> Henrik Enberg <henrik.enberg@telia.com> writes:
>> 
>> > `remove' is part of the cl library which isn't supposed to be used in
>> > core Emacs.
>> 
>> remove is a compiled Lisp function in `subr'.
>> (remove ELT SEQ)
>> 
>> Return a copy of SEQ with all occurrences of ELT removed.
>> SEQ must be a list, vector, or string.  The comparison is done with `equal'.
>
> doh, I must have been passing through a low flying crack cloud when I
> wrote my previous message.

I would not be terribly surprised if cl had its own keyword-rich
variant of remove.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum