From mboxrd@z Thu Jan  1 00:00:00 1970
Path: main.gmane.org!not-for-mail
From: Edi Weitz <edi@agharta.de>
Newsgroups: gmane.emacs.help
Subject: Re: delete text block with regexp
Date: Mon, 17 Nov 2003 01:32:14 +0100
Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org
Message-ID: <877k1zj0mp.fsf@bird.agharta.de>
References: <bp7eub$uf4$04$1@news.t-online.com> <873ccogor2.fsf@emacswiki.org>
	<jwvd6brubk3.fsf-monnier+gnu.emacs.help@vor.iro.umontreal.ca>
Reply-To: edi@agharta.de
NNTP-Posting-Host: deer.gmane.org
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: sea.gmane.org 1069029947 13634 80.91.224.253 (17 Nov 2003 00:45:47 GMT)
X-Complaints-To: usenet@sea.gmane.org
NNTP-Posting-Date: Mon, 17 Nov 2003 00:45:47 +0000 (UTC)
Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Mon Nov 17 01:45:45 2003
Return-path: <help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org>
Original-Received: from monty-python.gnu.org ([199.232.76.173])
	by deer.gmane.org with esmtp (Exim 3.35 #1 (Debian))
	id 1ALXWT-0002KS-00
	for <geh-help-gnu-emacs@m.gmane.org>; Mon, 17 Nov 2003 01:45:45 +0100
Original-Received: from localhost ([127.0.0.1] helo=monty-python.gnu.org)
	by monty-python.gnu.org with esmtp (Exim 4.24)
	id 1ALYTZ-0002Ba-Dy
	for geh-help-gnu-emacs@m.gmane.org; Sun, 16 Nov 2003 20:46:49 -0500
Original-Path: shelby.stanford.edu!newsfeed.stanford.edu!news.tele.dk!news.tele.dk!small.news.tele.dk!fu-berlin.de!uni-berlin.de!trane.agharta.DE!not-for-mail
Original-Newsgroups: gnu.emacs.help
Original-Lines: 24
Original-NNTP-Posting-Host: trane.agharta.de (62.159.208.82)
Original-X-Trace: news.uni-berlin.de 1069029134 56216017 62.159.208.82 (16 [15706])
Mail-Copies-To: never
User-Agent: Gnus/5.1002 (Gnus v5.10.2) Emacs/21.3 (gnu/linux)
Cancel-Lock: sha1:nuCZgj8YEkxR/bZd25C4ZqFHge4=
Original-Xref: shelby.stanford.edu gnu.emacs.help:118356
Original-To: help-gnu-emacs@gnu.org
X-BeenThere: help-gnu-emacs@gnu.org
X-Mailman-Version: 2.1.2
Precedence: list
List-Id: Users list for the GNU Emacs text editor  <help-gnu-emacs.gnu.org>
List-Unsubscribe: <http://mail.gnu.org/mailman/listinfo/help-gnu-emacs>,
	<mailto:help-gnu-emacs-request@gnu.org?subject=unsubscribe>
List-Archive: <http://mail.gnu.org/pipermail/help-gnu-emacs>
List-Post: <mailto:help-gnu-emacs@gnu.org>
List-Help: <mailto:help-gnu-emacs-request@gnu.org?subject=help>
List-Subscribe: <http://mail.gnu.org/mailman/listinfo/help-gnu-emacs>,
	<mailto:help-gnu-emacs-request@gnu.org?subject=subscribe>
Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org
Xref: main.gmane.org gmane.emacs.help:14297
X-Report-Spam: http://spam.gmane.org/gmane.emacs.help:14297

On Sun, 16 Nov 2003 23:42:37 GMT, Stefan Monnier <monnier@iro.umontreal.ca> wrote:

>> The critical part is that "." matches anything but a newline.
>> Therefore use "\(.\|\n\)" for any character or a newline.
>
> Beware: such a regexp tends to suffer from the "regexp stack
> overflow" problem.  Better use \(.*\n\)*.* which is equivalent but
> uses a lot less stack space.
>
> Sadly, to understand why you need to understand details of how the
> regexp matching happens to be implemented in Emacs.

Shouldn't a good regex implementation be able to optimize the problem
away in simple cases like this? I've written a regex engine for Common
Lisp which does transformations like (Perl syntax)

  <regex>*   ->   (?:<regex'>*<regex>)?
  <regex>+   ->   <regex'>*<regex>

if <regex> includes register groups and is of fixed length. <regex'>
is an equivalent regular expression but without the register
groups. I'm pretty sure Perl does something similar.

Edi.