From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.help Subject: Re: How are regexen implemented in Emacs? Date: Mon, 12 Dec 2022 16:19:19 -0500 Message-ID: References: <87a63see6m.fsf@mbork.pl> <877cywe8w9.fsf@mbork.pl> <875yege53t.fsf@mbork.pl> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="11250"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Cc: help-gnu-emacs@gnu.org To: Marcin Borkowski Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Mon Dec 12 22:20:02 2022 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 1p4qDS-0002jP-8T for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 12 Dec 2022 22:20:02 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1p4qCv-0000Qz-4g; Mon, 12 Dec 2022 16:19:29 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1p4qCt-0000QM-GP for help-gnu-emacs@gnu.org; Mon, 12 Dec 2022 16:19:27 -0500 Original-Received: from mailscanner.iro.umontreal.ca ([132.204.25.50]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1p4qCr-0004Sd-Mb for help-gnu-emacs@gnu.org; Mon, 12 Dec 2022 16:19:27 -0500 Original-Received: from pmg2.iro.umontreal.ca (localhost.localdomain [127.0.0.1]) by pmg2.iro.umontreal.ca (Proxmox) with ESMTP id DAFD7804C0; Mon, 12 Dec 2022 16:19:23 -0500 (EST) Original-Received: from mail01.iro.umontreal.ca (unknown [172.31.2.1]) by pmg2.iro.umontreal.ca (Proxmox) with ESMTP id F014180712; Mon, 12 Dec 2022 16:19:20 -0500 (EST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=iro.umontreal.ca; s=mail; t=1670879961; bh=GwvzjAhwKVD4Upw+JbFN8S6tKPWMIU4GxQJX3aqhLE0=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=fVbOQaLf2YOKQHlDbhARnRJTX+wRlRvra4uC6d37/pAeY8K4iL83LFFiVasgxSbcd CXPz2WNEaQNCKDvM0Tc08MdkSw6yUunL+YS/Mlcv3sDfCNJkbusfL2NM3erfwPbEA9 UuMtQUcq5TQTGPhGgIv71PwWnXP+8TZFvr5pnAKqWbyh8kayWaCw3aIvVhvrpmhIwk AT5yKaMyxD32tjnCX6vsB/cogUvjCzTUOBgvxzR5U1scUrm5FSD2w9WbF/YyeZs8S6 YNTBEO9AZqLNamOGM1Hom7vzHPo37CSe3BY2bazRCt4+K0XNjbqrCRYT7ZaKwQX7fV dVrfcOGdgpjTw== Original-Received: from pastel (unknown [45.72.193.52]) by mail01.iro.umontreal.ca (Postfix) with ESMTPSA id C96061201BF; Mon, 12 Dec 2022 16:19:20 -0500 (EST) In-Reply-To: <875yege53t.fsf@mbork.pl> (Marcin Borkowski's message of "Mon, 12 Dec 2022 21:31:34 +0100") Received-SPF: pass client-ip=132.204.25.50; envelope-from=monnier@iro.umontreal.ca; helo=mailscanner.iro.umontreal.ca X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 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-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:141691 Archived-At: > The linked article sounded a bit like "only idiots implement regexen > in the naive way", and I was pretty sure Emacs devs are not idiots - but > now I understand the reasons better. I fully agree that it doesn't make sense to *start* with a backtracking implementation, yes. But once you've invested in one, it's harder to move to something better. This said, it *would* be better. Not only in terms of eliminating the pathological blow ups, but it also offers opportunity to get new functionality, such as the ability to capture the state of a regexp match at a specific buffer position (so you can perform a multiline regexp match one line at a time). It could also make it much more reasonable to add the possibility to run ELisp code from within the regexp match engine (e.g. add a \p(NAME) entry which calls the NAME ELisp function). Stefan