From: Pascal Bourguignon <spam@mouse-potato.com>
Subject: Re: match-string debugging problem
Date: 11 Mar 2005 00:40:14 +0100 [thread overview]
Message-ID: <8764zzkr35.fsf@thalassa.informatimago.com> (raw)
In-Reply-To: mailman.3372.1110495427.32256.help-gnu-emacs@gnu.org
Stephen Berman <Stephen.Berman@gmx.net> writes:
> On 10 Mar 2005 18:06:52 +0100 Pascal Bourguignon <spam@mouse-potato.com> wrote:
>
> > Stephen Berman <Stephen.Berman@gmx.net> writes:
> >
> [...]
> >> (let ((mystring-list ()))
> >> (while (re-search-forward
> >> (concat "^" (regexp-quote mystring1) "\\(.+\\)"
> >> (regexp-quote mystring2) "$")
> >> (point-max) t)
> >> (setq mystring-list (append (list (match-string 1)) mystring-list)))
> >> (insert "\n")
> >> (setq mystring-list (reverse mystring-list))
> >> (dolist (elt mystring-list)
> >> (insert elt " ")))))
> >>
> >> After evalling this code and typing `M-x mystring-list', buffer *test*
> >> consists of these lines:
> >>
> >> +++++ test1 ~~~~~
> >> +++++ test2 ~~~~~
> >> +++++ test3 ~~~~~
> >> +++++ test4 ~~~~~
> >> +++++ test5 ~~~~~
> >> test1 test2 test3 test4 test5
> >>
> >> The last line indicates that match-string correctly matches the
> >> strings that build mystring-list. But when I step through the code
> >> with edebug, match-string always returns nil and a wrong-type-argument
> >> error is raised at the insert (since nil is not char-or-string-p).
> >> (Edebug isn't the problem: evalling first the regexp search code in
> >> *test* and then (match-string 1) also returns nil.) Because of this
> >> I'm having a hard time debugging other code that uses match-string.
> >> Can someone explain what's going on?
> >
> > re-search-forward uses global state (buffer, matched range, etc) as
> > match-data, to communicate with match-string. When you're debugging,
> > this global state is switched or modified. One could consider it a
> > bug in the debugger.
> >
> > See: match-data
> > save-match-data
> > save-excursion
> > save-buffer
>
> How do you know about this state difference?
Infered from the doc of re-search-forward, match-string and save-match-data.
> I couldn't find any
> mention of it in the documentation of the functions you mention, nor
> elsewhere in the Elisp manual (CVS version). I glanced through the
> comments in search.c but didn't see anything obviously (to me)
> relevant. If it's defined in the C source code I'd appreciate a
> pointer, even though I probably wouldn't be able to understand it at
> present.
>
> In any case, what I did find is that I can in fact track match-string
> by explicitly entering the ordinary Lisp debugger at that point. So
> putting `(debug)' before `(match-string 1)' in the above code stops
> execution there and stepping into the function by pressing `d' returns
> the matched string. So if there's a bug, then it's only in Edebug. I
> couldn't find any relevant discussion in the Edebug section of the
> manual. So at the very least, the Elisp documentation could be more
> explicit on this issue.
My guess is that either:
- Edebug matches regexp itself, and therefore erases the match-data,
(a save-match-data would be in order in Edebug), or
- Edebug changes the current buffer, and therefore when it executes
(match-string 1), this functions refers the match-data of the Edebug
buffer instead of that of the original buffer
(a save-excursion would be in order in Edebug).
I'd bet for the former, since save-excursion is more commonly used
than save-match-data... (save-excursion calls save-buffer).
--
__Pascal Bourguignon__ http://www.informatimago.com/
The rule for today:
Touch my tail, I shred your hand.
New rule tomorrow.
next prev parent reply other threads:[~2005-03-10 23:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.3303.1110470311.32256.help-gnu-emacs@gnu.org>
2005-03-10 17:06 ` match-string debugging problem Pascal Bourguignon
2005-03-10 22:27 ` Stephen Berman
[not found] ` <mailman.3372.1110495427.32256.help-gnu-emacs@gnu.org>
2005-03-10 23:40 ` Pascal Bourguignon [this message]
2005-03-11 22:18 ` Stephen Berman
2005-03-13 21:52 ` Alan Wehmann
2005-03-14 19:32 ` Stephen Berman
2005-03-10 15:18 Stephen Berman
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