need double save-excursion -- why?

need double save-excursion -- why?

[Joe Corneli]

When I run the function below on a file containing things like this:

####################################################################
\section{{ lefschetz}}      

(lefschetz number of a map)  \defn{
\item $X$ smooth compact manifold
\item $g:X\rightarrow X$ continuous
\item $G: X\rightarrow X\times X$
\item $G(x)=(x,g(x))$
\item $\#(G,\text{diagonal}(M\times M))$}

(global lefschetz number of a map: see ``lefschetz number of a map'')

(global lefschetz number: fact: smooth lefschetz fixed point theorem) \defn{
\item $X$ compact orientable manifold
\item $f:X\rightarrow X$ smooth
\item $L(f)\neq 0$
\item $f$ has a fixed point}

(lefschetz fixed point)   \defn{
\item $f:X\rightarrow X$
\item $f(x)=x$
\item $+1$ is not an eigenvalue of $df_x:T_x(X)\rightarrow T_x(X)$}
####################################################################

I don't get good results: the outermost save-excursion is ignored,
and the cursor winds up near the bottom of the document.

However, if I wrap another save-excursion around the currently
outermost one, the second one is heeded and point is restored
properly.

Can anyone tell me this is necessary?  Something like this is
documented in the Emacs Lisp Intro info file, but I don't understand
why a double layer of save-excursions is needed here.


(defun xi-grab-matching-defn-by-tagline (regexp)
"Grab the defns whose taglines contain a match for this regexp."
  (interactive "MRegex: ")
  (save-excursion
    (beginning-of-buffer) ;; start at the beginning
    (while (not (eobp))
      (let ((found (search-forward-regexp (concat "^(.*" regexp ".*)") nil t)))
        (if found
            (let* ((beg (save-excursion (beginning-of-line)
                                  (point)))
                   (end (save-excursion (end-of-line)
                                        (search-forward-regexp "^$" nil t)
                                        (beginning-of-line)
                                        (point))) ; cut right before that
                   (entry (buffer-substring beg end)))
              (save-excursion (set-buffer (get-buffer-create "CONCAT.tex"))
                              (insert entry)))
          (end-of-buffer))))))

Re: need double save-excursion -- why?

[Jesper Harder]

Joe Corneli <jcorneli@math.utexas.edu> writes:

> I don't get good results: the outermost save-excursion is ignored,
> and the cursor winds up near the bottom of the document.

You problem could be:

>     (beginning-of-buffer) ;; start at the beginning

,----[ C-h f beginning-of-buffer RET ]
| Don't use this command in Lisp programs!
| (goto-char (point-min)) is faster and avoids clobbering the mark.
`----

>           (end-of-buffer))))))

,----[ C-h f end-of-buffer RET ]
| Don't use this command in Lisp programs!
| (goto-char (point-max)) is faster and avoids clobbering the mark.
`----

Re: need double save-excursion -- why?

[Joe Corneli]

Actually, I take back what I said about needing a double
save-excursion.  The outer save-excursion doesn't seem to help after
all. What might have helped was running the function through
edebug. (Not that I figured out what the problem was, but rather it
somehow seems to fix the problem temporarily to have the edebugger
running.)  Totally confused now...