From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: replace-regexp Date: Sat, 08 May 2021 09:53:06 -0400 Message-ID: References: <87tunf1mz5.fsf@zoho.eu> <87v97v6mxg.fsf@gnu.org> <87wnsaz9df.fsf@zoho.eu> <877dkaytwu.fsf@zoho.eu> Reply-To: Stefan Monnier Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="9910"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:hsmemzC3h1iB0AIft5Yn+gwSvrw= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Sat May 08 15:53:43 2021 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1lfNOp-0002TK-2Y for geh-help-gnu-emacs@m.gmane-mx.org; Sat, 08 May 2021 15:53:43 +0200 Original-Received: from localhost ([::1]:40926 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lfNOo-0002YZ-5K for geh-help-gnu-emacs@m.gmane-mx.org; Sat, 08 May 2021 09:53:42 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:36282) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lfNOP-0002X2-1d for help-gnu-emacs@gnu.org; Sat, 08 May 2021 09:53:17 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:36098) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lfNOL-0003lj-Ak for help-gnu-emacs@gnu.org; Sat, 08 May 2021 09:53:15 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1lfNOJ-0001r1-JF for help-gnu-emacs@gnu.org; Sat, 08 May 2021 15:53:11 +0200 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:129563 Archived-At: >> > Maybe it has something to do with the replacement being >> > longer than the original string? >> >> That's it, I think, as this doesn't give me the error: >> >> (defun md-latex-reduce (beg end) >> (interactive "r") >> (save-excursion >> (goto-char beg) >> (while (re-search-forward "_\\(.*\\)_" end t) >> (replace-match "\\1") ))) > > And this is probably one of the reasons why most[citation needed] > tutorials, when implementing a function operating on a region, do a > ‘narrow-to-region’ first thing. > > (defun md-latex-reduce (beg end) > (interactive "r") > (save-excursion > (save-restriction > (narrow-to-region beg end) > > (goto-char (point-min)) > (while (re-search-forward "_\\(.*\\)_" nil t) > (replace-match "\\\\textit{\\1}")))) > > You might probably solve the same issue by carefully tracking the > lengthening of text — e.g. by incrementing ‘end’ by (- (length > "\\\\textit{}") (length "__")) on each iteration — or by putting a > marker at end and then passing that marker in re-search-forward. But > narrowing is easier. I recommend avoiding the use of narrowing as much as possible since it can have other undesirable effects (e.g. it changes the result of things like `syntax-ppss`). There are indeed 2 "standard" solutions: 1- start your loop at the end, moving towards the beginning. 2- use a marker to keep track of the end. You say "narrowing is easier", but using a marker is as simple as: (setq end (copy-marker end t)) so it's arguably simpler. Stefan