From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: Patch for lookaround assertion in regexp Date: Mon, 23 Jan 2012 09:11:09 -0500 Message-ID: References: <009001ccd9c0$9bde09f0$d39a1dd0$@cfraizer.com> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: dough.gmane.org 1327327891 26439 80.91.229.12 (23 Jan 2012 14:11:31 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Mon, 23 Jan 2012 14:11:31 +0000 (UTC) Cc: t.matsuyama.pub@gmail.com, emacs-devel@gnu.org To: "Colin Fraizer" Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Mon Jan 23 15:11:27 2012 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([140.186.70.17]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1RpKcI-00087h-BU for ged-emacs-devel@m.gmane.org; Mon, 23 Jan 2012 15:11:26 +0100 Original-Received: from localhost ([::1]:38919 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RpKcH-0007Ml-JT for ged-emacs-devel@m.gmane.org; Mon, 23 Jan 2012 09:11:25 -0500 Original-Received: from eggs.gnu.org ([140.186.70.92]:35707) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RpKcC-0007Lu-0q for emacs-devel@gnu.org; Mon, 23 Jan 2012 09:11:24 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RpKc7-0005uP-Tg for emacs-devel@gnu.org; Mon, 23 Jan 2012 09:11:19 -0500 Original-Received: from ironport2-out.teksavvy.com ([206.248.154.181]:13132) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RpKc7-0005uA-RD for emacs-devel@gnu.org; Mon, 23 Jan 2012 09:11:15 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Av0EAHhpHU9MCos2/2dsb2JhbABDriSBBoFyAQEEAVYjBQsLDiYSFBgNJIgPuBqMJgSIO5pzhFc X-IronPort-AV: E=Sophos;i="4.71,556,1320642000"; d="scan'208";a="158200689" Original-Received: from 76-10-139-54.dsl.teksavvy.com (HELO pastel.home) ([76.10.139.54]) by ironport2-out.teksavvy.com with ESMTP/TLS/ADH-AES256-SHA; 23 Jan 2012 09:11:09 -0500 Original-Received: by pastel.home (Postfix, from userid 20848) id 8846258D29; Mon, 23 Jan 2012 09:11:09 -0500 (EST) In-Reply-To: <009001ccd9c0$9bde09f0$d39a1dd0$@cfraizer.com> (Colin Fraizer's message of "Mon, 23 Jan 2012 06:17:34 -0500") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.92 (gnu/linux) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 206.248.154.181 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:147845 Archived-At: > In 2009, Tomohiro Matsuyama sent a message to this list with a patch > to add lookahead/lookbehind assertions to Emacs regular expressions > (regexps). Is there any plan to incorporate this useful feature into > an official release? > [IMHO, it is incredibly useful. The only responses to Matsuyama-san's > message were positive.] I'd like to replace the current regexp engine with one that does not suffer from exponential blowup (i.e. using "Thompson's NFA"). Every feature added to the current regexp engine will make it more difficult to switch, so I'm not too thrilled at the idea of adding lookaround operators. OTOH, noone has submitted code to replace the current regexp engine, and I don't forsee I'll have the time to write it myself, so maybe I should just give up on this plan. Stefan