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Re: Behaviour for save-excursion

From: martin rudalics
Subject: Re: Behaviour for save-excursion
Date: Tue, 06 Oct 2009 16:44:47 +0200
User-agent: Thunderbird (Windows/20090302)

> What is the proper behaviour for save-excursion?  The emacs-lisp intro and
> the docstring seem to have slightly differing explanations - namely, the
> docstring mentions that it saves current-buffer as well as point and mark,
> and the emacs-lisp intro does not.  Based on just what it does, I'm not
> entirely sure which is correct - the following code snippet, executed in
> *scratch*, returns the "*scratch*" buffer but the buffer displayed is the
> "bar" buffer, and evaluating current-bufer afterwards returns the "bar"
> buffer.
> (progn
>   (save-excursion
>     (switch-to-buffer "bar"))
>   (current-buffer))
> Either the manual or the docstring should be changed to reflect what it
> does, but I'm not entirely sure which based on this.

Please read the Elisp manual entry on `save-excursion' which states:

     Likewise, `save-excursion' does not restore window-buffer
     correspondences altered by functions such as `switch-to-buffer'.
     One way to restore these correspondences, and the selected window,
     is to use `save-window-excursion' inside `save-excursion' (*note
     Window Configurations::).

Also the following entry from section 27.2 The Current Buffer of the
Elisp manual might provide further explanation:

     When an editing command returns to the editor command loop, the
  command loop designates the buffer displayed in the selected window as
  current, to prevent confusion: the buffer that the cursor is in when
  Emacs reads a command is the buffer that the command will apply to.
  (*Note Command Loop::.)  Therefore, `set-buffer' is not the way to
  switch visibly to a different buffer so that the user can edit it.  For
  that, you must use the functions described in *Note Displaying


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