save-buffer like save-excursion

save-buffer like save-excursion

[Matthew Flaschen]

Is there a command like save-excursion that only saves the buffer?  I
have several functions that must set-buffer temporarily, then do things
that change point.  I always want these point changes, but if set-buffer
changed the buffer (not necessarily true), I want to reverse that change.

So, is there already a command for this?

Matt Flaschen

Re: save-buffer like save-excursion

[Harald Hanche-Olsen]

+ Matthew Flaschen <matthew.flaschen@gatech.edu>:

| Is there a command like save-excursion that only saves the buffer?  I
| have several functions that must set-buffer temporarily, then do things
| that change point.  I always want these point changes, but if set-buffer
| changed the buffer (not necessarily true), I want to reverse that change.
|
| So, is there already a command for this?

You are aware of the difference between set-buffer and
swith-to-buffer, I presume?  Even if a function does set-buffer, at
the end of an interactive command you are back in the buffer you had.
So there may not be a need to do what you want at all.

On the other hand, if you want to temporarily change the buffer within
a function, you can use macro like this one:

(defmacro with-saved-buffer (&rest command)
  (let ((cur (make-symbol "cur")))
   `(let ((,cur (current-buffer)))
     (unwind-protect
	 (progn ,@command)
       (set-buffer ,cur)))))

and use it like

  (with-saved-buffer
   (set-buffer "blah")
   ...)
  ;; here, the buffer is back to what it was

The unwind-protect in there is not necessary in the case where an
error brings you back to the interactive top-level.  But if your code
performs a non-local exit for some reason, it's essential.

-- 
* Harald Hanche-Olsen     <URL:http://www.math.ntnu.no/~hanche/>
- It is undesirable to believe a proposition
  when there is no ground whatsoever for supposing it is true.
  -- Bertrand Russell

Re: save-buffer like save-excursion

[Matthew Flaschen]

Harald Hanche-Olsen wrote:
> + Matthew Flaschen <matthew.flaschen@gatech.edu>:
> 
> | Is there a command like save-excursion that only saves the buffer?  I
> | have several functions that must set-buffer temporarily, then do things
> | that change point.  I always want these point changes, but if set-buffer
> | changed the buffer (not necessarily true), I want to reverse that change.
> |
> | So, is there already a command for this?
> 
> You are aware of the difference between set-buffer and
> swith-to-buffer, I presume?

I think so.  set-buffer doesn't change the UI, only the working buffer.

  Even if a function does set-buffer, at
> the end of an interactive command you are back in the buffer you had.

Right...but I'd like to preserve the buffer within interactive commands.

> So there may not be a need to do what you want at all.
> 
> On the other hand, if you want to temporarily change the buffer within
> a function, you can use macro like this one:

> (defmacro with-saved-buffer (&rest command)
>   (let ((cur (make-symbol "cur")))
>    `(let ((,cur (current-buffer)))
>      (unwind-protect
> 	 (progn ,@command)
>        (set-buffer ,cur)))))
> 
> and use it like
> 
>   (with-saved-buffer
>    (set-buffer "blah")
>    ...)
>   ;; here, the buffer is back to what it was


Right, thanks.  I'll probably use something similar, or just do it
manually (depending on how often it's necessary).  I might also be able
to avoid the issue neatly just by calling set-buffer again in the client
code.  I was just wondering if there was already something, so I
wouldn't be wasting my time.

> The unwind-protect in there is not necessary in the case where an
> error brings you back to the interactive top-level.

I think that's the case for me.  But I won't have any errors anyway! My
code is tested. ;)

Matt Flaschen

Re: save-buffer like save-excursion

[Stefan Monnier]

> Is there a command like save-excursion that only saves the buffer?  I
> have several functions that must set-buffer temporarily, then do things
> that change point.  I always want these point changes, but if set-buffer
> changed the buffer (not necessarily true), I want to reverse that change.

> So, is there already a command for this?

with-current-buffer (or save-current-buffer).


        Stefan

Re: save-buffer like save-excursion

[Matthew Flaschen]

Stefan Monnier wrote:
>> Is there a command like save-excursion that only saves the buffer?  I
>> have several functions that must set-buffer temporarily, then do things
>> that change point.  I always want these point changes, but if set-buffer
>> changed the buffer (not necessarily true), I want to reverse that change.
> 
>> So, is there already a command for this?
> 
> with-current-buffer (or save-current-buffer)

Thanks.  I'll refactor the code (again)

Matt

Re: save-buffer like save-excursion

[Harald Hanche-Olsen]

+ Stefan Monnier <monnier@iro.umontreal.ca>:

| with-current-buffer (or save-current-buffer).

Duh.  Another wheel reinvented (in my earlier post in the thread).

-- 
* Harald Hanche-Olsen     <URL:http://www.math.ntnu.no/~hanche/>
- It is undesirable to believe a proposition
  when there is no ground whatsoever for supposing it is true.
  -- Bertrand Russell

Re: save-buffer like save-excursion

[Matthew Flaschen]

Harald Hanche-Olsen wrote:
> + Stefan Monnier <monnier@iro.umontreal.ca>:
> 
> | with-current-buffer (or save-current-buffer).
> 
> Duh.  Another wheel reinvented (in my earlier post in the thread).

Anytime I work on something in emacs I have the overwhelmingly feeling
it's already been done.  Half the time I turn out to be right.  The
naming conventions seem totally arbitrary, so even with apropos and
everything it's hard to find the function you want.

Maybe I should ask again about the main project I'm working on.  Has an
ed emulator already been made for emacs?

Matthew Flaschen

Re: save-buffer like save-excursion

[Stefan Monnier]

>> + Stefan Monnier <monnier@iro.umontreal.ca>:
>> 
>> | with-current-buffer (or save-current-buffer).
>> 
>> Duh.  Another wheel reinvented (in my earlier post in the thread).

> Anytime I work on something in emacs I have the overwhelmingly feeling
> it's already been done.  Half the time I turn out to be right.  The
> naming conventions seem totally arbitrary, so even with apropos and
> everything it's hard to find the function you want.

> Maybe I should ask again about the main project I'm working on.  Has an
> ed emulator already been made for emacs?

I suspect some part of it might be included in viper.


        Stefan

Re: save-buffer like save-excursion

[Matthew Flaschen]

Stefan Monnier wrote:
>>> + Stefan Monnier <monnier@iro.umontreal.ca>:
>>>
>>> | with-current-buffer (or save-current-buffer).
>>>
>>> Duh.  Another wheel reinvented (in my earlier post in the thread).
> 
>> Anytime I work on something in emacs I have the overwhelmingly feeling
>> it's already been done.  Half the time I turn out to be right.  The
>> naming conventions seem totally arbitrary, so even with apropos and
>> everything it's hard to find the function you want.
> 
>> Maybe I should ask again about the main project I'm working on.  Has an
>> ed emulator already been made for emacs?
> 
> I suspect some part of it might be included in viper.

I don't think so.  As far as I can tell, ed is almost nothing like vi.
Reviewing the Viper manual just now, I see no reference to ed.  Glad to
be corrected, though.

Matt Flaschen