From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: Lexical binding: why? Date: Tue, 28 May 2019 08:26:16 -0400 Message-ID: References: <20190528100850.GA5296@ACM> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="69499"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue May 28 14:26:36 2019 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1hVbBb-000Hxo-NS for ged-emacs-devel@m.gmane.org; Tue, 28 May 2019 14:26:35 +0200 Original-Received: from localhost ([127.0.0.1]:33933 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hVbBa-0004Z0-Mi for ged-emacs-devel@m.gmane.org; Tue, 28 May 2019 08:26:34 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:51123) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hVbBU-0004Yv-EL for emacs-devel@gnu.org; Tue, 28 May 2019 08:26:29 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hVbBT-0007JZ-Ix for emacs-devel@gnu.org; Tue, 28 May 2019 08:26:28 -0400 Original-Received: from [195.159.176.226] (port=55104 helo=blaine.gmane.org) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hVbBT-0007J5-CY for emacs-devel@gnu.org; Tue, 28 May 2019 08:26:27 -0400 Original-Received: from list by blaine.gmane.org with local (Exim 4.89) (envelope-from ) id 1hVbBQ-000HjN-Tz for emacs-devel@gnu.org; Tue, 28 May 2019 14:26:24 +0200 X-Injected-Via-Gmane: http://gmane.org/ Cancel-Lock: sha1:7xUlX387V8Ao/zCFUk+Msrnrm0w= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 195.159.176.226 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 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" Xref: news.gmane.org gmane.emacs.devel:237092 Archived-At: > What is the purpose of converting Lisp files to use lexical binding? The lexical-binding version of Elisp offers closures and avoidance of corner-case name clashes with higher-order functions. For this reason, we added it and we're very unlikely to remove it. In contrast the non-lexical-binding version of Elisp is now redundant/obsolete because it does not offer any feature not already available in the lexical-binding mode. So we only keep it for backward compatibility and will likely remove it in some distant future. > I always thought the idea was to speed the SW up. Not really, no. It does offer a better potential for optimization, but nobody has made any effort to take advantage of it so far. > I thus see no speedup from the use of lexical binding. That corresponds to my experience as well. When I installed the lexical-binding code, my main concern was to not impact existing code, so the fact that the new lexical-binding mode was "about as fast" was kind of a happy accident. > Have I, perhaps, made some mistake somewhere? Does anybody else see > significant speed increases through the use of lexical binding? IIRC some operation in the js2 code was significantly slowed down (in Emacs-24) by lexical-binding and then (less significantly but still significantly) sped up when the new condition-case byte-codes were introduced in 24.4 (and used by default since Emacs-25), so there are some cases, but by and large I wouldn't expect any major change. Stefan