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 17:44:01 -0500 Message-ID: <87vd3a79zi.fsf@stupidchicken.com> References: <87hbeu7l84.fsf@stupidchicken.com> <87bp52ae9g.fsf@catnip.gol.com> <87r5dyfxmn.fsf@stupidchicken.com> <87ei9y5z0v.fsf@stupidchicken.com> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: dough.gmane.org 1291416257 29206 80.91.229.12 (3 Dec 2010 22:44:17 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Fri, 3 Dec 2010 22:44:17 +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 23:44:12 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 1POeMO-0002vm-J3 for ged-emacs-devel@m.gmane.org; Fri, 03 Dec 2010 23:44:12 +0100 Original-Received: from localhost ([127.0.0.1]:50179 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1POeMO-0004r3-3D for ged-emacs-devel@m.gmane.org; Fri, 03 Dec 2010 17:44:12 -0500 Original-Received: from [140.186.70.92] (port=54345 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1POeMH-0004oe-CZ for emacs-devel@gnu.org; Fri, 03 Dec 2010 17:44:06 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1POeMG-0002Kv-DW for emacs-devel@gnu.org; Fri, 03 Dec 2010 17:44:05 -0500 Original-Received: from vm-emlprdomr-06.its.yale.edu ([130.132.50.147]:35131) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1POeMF-0002Kg-6Y; Fri, 03 Dec 2010 17:44:03 -0500 Original-Received: from furball (dhcp128036014088.central.yale.edu [128.36.14.88]) (authenticated bits=0) by vm-emlprdomr-06.its.yale.edu (8.14.4/8.14.4) with ESMTP id oB3Mi1Fr007096 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Fri, 3 Dec 2010 17:44:02 -0500 Original-Received: by furball (Postfix, from userid 1000) id 617B4160675; Fri, 3 Dec 2010 17:44:01 -0500 (EST) In-Reply-To: <87ei9y5z0v.fsf@stupidchicken.com> (Chong Yidong's message of "Fri, 03 Dec 2010 16:26:08 -0500") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) X-Scanned-By: MIMEDefang 2.71 on 130.132.50.147 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:133371 Archived-At: Chong Yidong writes: > 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? Thinking about this some more, I do see a couple of snags. First, the `dotimes' and `dolist' macros use `while' internally, so if we introduce a built-in `return' that exits from `while', it's hard to make that same `return' exit correctly from `dotimes'/`dolist'. One solution might be to introduce something like `while-noblock' and use that in `dotimes' and `dolist'. Also, block tags should have lexical scope, so in order to implement `block' properly we probably ought to wait for the lexical binding changes. I think it is currently possible to implement `return' for exiting unnamed blocks, and leave `block'/`return-from' for the future, but I dunno if doing it like that is worth our while.