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.help Subject: Re: Lexical binding doesn't seem to be faster? Date: Fri, 08 Mar 2019 08:53:32 -0500 Message-ID: References: <20190308083055.GA20901@tuxteam.de> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="215512"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Fri Mar 08 14:54:07 2019 Return-path: Envelope-to: geh-help-gnu-emacs@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 1h2Fwt-000tsZ-5d for geh-help-gnu-emacs@m.gmane.org; Fri, 08 Mar 2019 14:54:07 +0100 Original-Received: from localhost ([127.0.0.1]:43986 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h2Fwr-0002ew-3y for geh-help-gnu-emacs@m.gmane.org; Fri, 08 Mar 2019 08:54:05 -0500 Original-Received: from eggs.gnu.org ([209.51.188.92]:46827) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h2FwX-0002dj-Dt for help-gnu-emacs@gnu.org; Fri, 08 Mar 2019 08:53:46 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h2FwV-0001wG-PQ for help-gnu-emacs@gnu.org; Fri, 08 Mar 2019 08:53:45 -0500 Original-Received: from [195.159.176.226] (port=51584 helo=blaine.gmane.org) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h2FwV-0001kc-GC for help-gnu-emacs@gnu.org; Fri, 08 Mar 2019 08:53:43 -0500 Original-Received: from list by blaine.gmane.org with local (Exim 4.89) (envelope-from ) id 1h2FwS-000tMG-Pq for help-gnu-emacs@gnu.org; Fri, 08 Mar 2019 14:53:40 +0100 X-Injected-Via-Gmane: http://gmane.org/ Cancel-Lock: sha1:jwaysl+TvHoOYmLnEbR8coCgpJc= 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: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.21 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.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.org gmane.emacs.help:119588 Archived-At: >> FWIW, the usual case where lexical-binding leads to bigger&slower code >> is when you pass a lambda-expression to another function and that >> lambda-expression has free variables (in the lexical-binding case, it >> requires building a closure which is rather costly currently, whereas in >> the dynamic-binding case it relies on the dynamic-scoping instead). > Let's see if I got that right: in those cases, the code would (most > probably!) behave differently depending on the binding regime (lexical > vs dynamic), so it would be doing quite different things in each case? Actually, in most such cases the code behaves identically in the end, but it gets there in a different way (so yes, in some cases it does behave differently). E.g. (let ((buf (current-buffer))) [...] (with-temp-buffer (mapcar (lambda (x) (with-current-buffer buf ...)) ...)) [...]) The end result will most likely be the same regardless which binding style is used, but the way to find the value of `buf` from within the lambda is different in the two cases. The difference becomes apparent if you do (advice-add 'mapcar :around (lambda (&rest orig-call) (let ((buf 42)) (apply orig-call)))) since in this case dynamic-binding will cause your `with-current-buffer` to try and use buffer 42 and signal an error (because of the name conflict, aka "variable capture"), whereas lexical-binding will be unaffected. Stefan