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Re: match-string debugging problem
From: |
Pascal Bourguignon |
Subject: |
Re: match-string debugging problem |
Date: |
10 Mar 2005 18:06:52 +0100 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 |
Stephen Berman <Stephen.Berman@gmx.net> writes:
> There seems to be something about match-string that I don't
> understand. Here is an example of the kind of code I'm working with:
>
> (defvar mystring1 "+++++ ")
> (defvar mystring2 " ~~~~~")
> (defun mystring-list ()
> (interactive)
> (with-current-buffer (get-buffer-create "*test*")
> (switch-to-buffer "*test*")
> (dotimes (num 5)
> (insert mystring1 "test" (int-to-string (1+ num)) mystring2 "\n"))
> (goto-char (point-min))
> (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
--
__Pascal Bourguignon__ http://www.informatimago.com/
Until real software engineering is developed, the next best practice
is to develop with a dynamic system that has extreme late binding in
all aspects. The first system to really do this in an important way
is Lisp. -- Alan Kay