From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Chong Yidong Newsgroups: gmane.emacs.devel Subject: Re: return Date: Fri, 03 Dec 2010 16:26:08 -0500 Message-ID: <87ei9y5z0v.fsf@stupidchicken.com> References: <87hbeu7l84.fsf@stupidchicken.com> <87bp52ae9g.fsf@catnip.gol.com> <87r5dyfxmn.fsf@stupidchicken.com> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: dough.gmane.org 1291411681 8856 80.91.229.12 (3 Dec 2010 21:28:01 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Fri, 3 Dec 2010 21:28:01 +0000 (UTC) Cc: emacs-devel@gnu.org To: Miles Bader Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Dec 03 22:27:55 2010 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1POdAZ-0005rN-D1 for ged-emacs-devel@m.gmane.org; Fri, 03 Dec 2010 22:27:55 +0100 Original-Received: from localhost ([127.0.0.1]:37979 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1POdAY-000079-MK for ged-emacs-devel@m.gmane.org; Fri, 03 Dec 2010 16:27:54 -0500 Original-Received: from [140.186.70.92] (port=58406 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1POd8x-0007YQ-Vw for emacs-devel@gnu.org; Fri, 03 Dec 2010 16:26:16 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1POd8w-0005wn-AX for emacs-devel@gnu.org; Fri, 03 Dec 2010 16:26:15 -0500 Original-Received: from vm-emlprdomr-05.its.yale.edu ([130.132.50.146]:46779) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1POd8u-0005w7-S0; Fri, 03 Dec 2010 16:26:12 -0500 Original-Received: from furball (dhcp128036014088.central.yale.edu [128.36.14.88]) (authenticated bits=0) by vm-emlprdomr-05.its.yale.edu (8.14.4/8.14.4) with ESMTP id oB3LQ9kA032355 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Fri, 3 Dec 2010 16:26:09 -0500 Original-Received: by furball (Postfix, from userid 1000) id 1860C160675; Fri, 3 Dec 2010 16:26:09 -0500 (EST) In-Reply-To: <87r5dyfxmn.fsf@stupidchicken.com> (Chong Yidong's message of "Fri, 03 Dec 2010 14:46:08 -0500") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) X-Scanned-By: MIMEDefang 2.71 on 130.132.50.146 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 3) X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:133353 Archived-At: Chong Yidong writes: > You mean the performance overhead from adding an extra internal_catch? > I doubt there's a free lunch here; adding a "return" or "return-from" > mechanism would also add overhead, and that overhead would apply to > every single funcall. Still, it's a worthwhile experiment to implement > "return"/"return-from" and see how big the performance impact is. I did a quick experiment, and turns out built-in blocking is a little faster than an explicit `catch', mostly because of reduced consing. I tested with a function that runs 500,000 tight `while' loops: (defun test-loop-with-catch () (dotimes (ii 500000) (let ((ll '(1 2 3 4 5 6 7 8 9 10))) (catch 'exit (while ll (setq ll (cdr ll))))))) The run time is 1.164s, as opposed to 1.084s with the `catch' omitted. So an explicit `catch' adds about 10 percent to the run time. If I hack Fwhile to perform a catch internally, the runtime for the test function (with the `catch' omitted) is 1.057s, within the margin of error of the unhacked Emacs. This (very limited) test indicates that adding built-in support for block, return, and return-from should have little performance impact. (Though the block tags ought to use a specialized obarray instead of what cl-macs.el does, which is to intern them as "--cl-block-%s--".) Does anyone see a deeper problem with providing such functions?