Evaluation of hooks

Evaluation of hooks

[Sebastian Tennant]

Hi all,

I would like to add a function to my emacs-lisp-mode-hook so that whenever I
visit emacs source files, view-mode minor mode is enabled.

  (add-hook 'emacs-lisp-mode-hook
	  (lambda ()
	    (when (>= (compare-strings
               (buffer-file-name) 1 nil "/usr/share/emacs/" 1 nil) 17)
	      (view-mode-enable))))

With the above code in my ~/.emacs, I get the following message at startup:

  >: Wrong type argument: stringp, nil

but apart from this the startup process is unaffected, and the function is
successfully added to my emacs-lisp-mode-hook, as you can see:

((lambda nil
   (when
       (>
	(compare-strings
	 (buffer-file-name)
	 0 nil "/usr/share/emacs/" 0 nil)
	18)
     (view-mode-enable))))

Needless to say the hook doesn't work, i.e., view-mode is not enabled when I
visit files whose full name begins /usr/share/emacs/.

The condition itself works fine, but just not as a hook.  I have tried quoting
the function (buffer-file-name) but this did not improve things.

Any help much appreciated.

TIA

sdt

Re: Evaluation of hooks

[Tom Breton]

Sebastian Tennant <sebyte@smolny.plus.com> writes:

> Hi all,
> 
> I would like to add a function to my emacs-lisp-mode-hook so that whenever I
> visit emacs source files, view-mode minor mode is enabled.
> 
>   (add-hook 'emacs-lisp-mode-hook
> 	  (lambda ()
> 	    (when (>= (compare-strings
>                (buffer-file-name) 1 nil "/usr/share/emacs/" 1 nil) 17)
> 	      (view-mode-enable))))
> 
> With the above code in my ~/.emacs, I get the following message at startup:
> 
>   >: Wrong type argument: stringp, nil

I doubt that has anything to do with hooks.
 
> but apart from this the startup process is unaffected, and the function is
> successfully added to my emacs-lisp-mode-hook, as you can see:
> 
> ((lambda nil
>    (when
>        (>
> 	(compare-strings
> 	 (buffer-file-name)
> 	 0 nil "/usr/share/emacs/" 0 nil)
> 	18)
>      (view-mode-enable))))

Nope, that doesn't work either ... sometimes.

Try it in a few different buffers - especially those like *Article*
that aren't visiting a file.  The result is different depending on
what buffer you try it in.

The bug seems to be that when `buffer-file-name' does not return a
string, `compare-strings' justifiably barfs.

-- 
Tom Breton, the calm-eyed visionary
Ho ho ho, Merry Whatever!

Re: Evaluation of hooks

[Sebastian Tennant]

Tom Breton <tehom@REMOVEpanNOSPAMix.com> wrote:

> Sebastian Tennant <sebyte@smolny.plus.com> wrote:
> 
> > Hi all,
> > 
> > I would like to add a function to my emacs-lisp-mode-hook so that whenever
> > I visit emacs source files, view-mode minor mode is enabled.
> > 
> >   (add-hook 'emacs-lisp-mode-hook
> > 	  (lambda ()
> > 	    (when (>= (compare-strings
> >                (buffer-file-name) 1 nil "/usr/share/emacs/" 1 nil) 17)
> > 	      (view-mode-enable))))
> > 
> > With the above code in my ~/.emacs, I get the following message at startup:
> > 
> >   >=: Wrong type argument: stringp, nil
> 
> I doubt that has anything to do with hooks.

It's odd though, don't you think?  I'm wondering if I should fie a bug report.

> > but apart from this the startup process is unaffected, and the function is
> > successfully added to my emacs-lisp-mode-hook, as you can see:
> > 
> > ((lambda nil
> >    (when
> >        (>
> > 	(compare-strings
> > 	 (buffer-file-name)
> > 	 0 nil "/usr/share/emacs/" 0 nil)
> > 	18)
> >      (view-mode-enable))))
> 
> Nope, that doesn't work either ... sometimes.

I've got it working (despite the aforementioned error at startup). The problem
was that (view-mode-enable) is only defined as a function *after* view-mode is
loaded.  The fix was to replace this with (view-mode 1).

sdt

Re: Evaluation of hooks

[Sebastian Tennant]

Sebastian Tennant <sebyte@smolny.plus.com> wrote:

> Tom Breton <tehom@REMOVEpanNOSPAMix.com> wrote:
>
>> Sebastian Tennant <sebyte@smolny.plus.com> wrote:
>> 
>>> Hi all,
>>> 
>>> I would like to add a function to my emacs-lisp-mode-hook so that whenever
>>> I visit emacs source files, view-mode minor mode is enabled.
>>> 
>>>   (add-hook 'emacs-lisp-mode-hook
>>> 	  (lambda ()
>>> 	    (when (>= (compare-strings
>>>                (buffer-file-name) 1 nil "/usr/share/emacs/" 1 nil) 17)
>>> 	      (view-mode-enable))))
>>> 
>>> With the above code in my ~/.emacs, I get the following message at startup:
>>> 
>>>   >=: Wrong type argument: stringp, nil
>> 
>> I doubt that has anything to do with hooks.
>
> It's odd though, don't you think?  I'm wondering if I should fie a bug report.
>
>>> but apart from this the startup process is unaffected, and the function is
>>> successfully added to my emacs-lisp-mode-hook, as you can see:
>>> 
>>> ((lambda nil
>>>    (when
>>>        (>
>>> 	(compare-strings
>>> 	 (buffer-file-name)
>>> 	 0 nil "/usr/share/emacs/" 0 nil)
>>> 	18)
>>>      (view-mode-enable))))
>> 
>> Nope, that doesn't work either ... sometimes.
>
> I've got it working (despite the aforementioned error at startup). The problem
> was that (view-mode-enable) is only defined as a function *after* view-mode is
> loaded.  The fix was to replace this with (view-mode 1).

And I've now realised why I'm getting the error at startup.  As we all know, a
*scratch* buffer is created by default at startup and is by definition not
visitng a file.  This is what was causing the problem.

Adding the following line before the (when ...) condition fixes this and the
hook is now functioning perfectly.

  (unless (not (buffer-file-name))
    ...)

sdt

Re: Evaluation of hooks

[Cameron Desautels]

On Mon, Dec 26, 2005 at 10:07:16PM +0000, Sebastian Tennant wrote:
> Adding the following line before the (when ...) condition fixes this and the
> hook is now functioning perfectly.
> 
>   (unless (not (buffer-file-name))
>     ...)

I suppose this is a bit nit-picky, but you may as well make it

  (if (buffer-file-name)
    ...)

instead of using both ``unless'' and ``not''.
-- 
Cameron Desautels <cam@apt2324.com>


Someday, we'll look back on this, laugh nervously, and change the
subject.

Re: Evaluation of hooks

[Sebastian Tennant]

Cameron Desautels <cam@apt2324.com> wrote:

> On Mon, Dec 26, 2005 at 10:07:16PM +0000, Sebastian Tennant wrote:
>> Adding the following line before the (when ...) condition fixes this and the
>> hook is now functioning perfectly.
>> 
>>   (unless (not (buffer-file-name))
>>     ...)
>
> I suppose this is a bit nit-picky, but you may as well make it
>
>   (if (buffer-file-name)
>     ...)
>
> instead of using both ``unless'' and ``not''.

I suppose so, but should code be compact or human readable?
In this context, where the hook is written with file visiting buffers in mind,
I think it is clearer to say "unless the buffer is not visiting a file..."

sdt