From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Tim X Newsgroups: gmane.emacs.help Subject: Re: questioning let Date: Thu, 25 Feb 2010 08:53:35 +1100 Organization: Rapt Technologies Message-ID: <87hbp62tcw.fsf@lion.rapttech.com.au> References: <87vddmx3us.fsf@lola.goethe.zz> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: dough.gmane.org 1267051308 13227 80.91.229.12 (24 Feb 2010 22:41:48 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Wed, 24 Feb 2010 22:41:48 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Wed Feb 24 23:41:44 2010 Return-path: Envelope-to: geh-help-gnu-emacs@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 1NkPvH-0001Ct-NF for geh-help-gnu-emacs@m.gmane.org; Wed, 24 Feb 2010 23:41:40 +0100 Original-Received: from localhost ([127.0.0.1]:37010 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NkPvH-0005AD-9j for geh-help-gnu-emacs@m.gmane.org; Wed, 24 Feb 2010 17:41:39 -0500 Original-Path: news.stanford.edu!usenet.stanford.edu!news.kjsl.com!news-xfer.nntp.sonic.net!news.astraweb.com!border5.newsrouter.astraweb.com!not-for-mail Original-Newsgroups: gnu.emacs.help User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1.92 (gnu/linux) Cancel-Lock: sha1:zuZr5d65K8Qqu0h14K4hLfAOgn4= Original-Lines: 61 Original-NNTP-Posting-Host: 2e2c5433.news.astraweb.com Original-X-Trace: DXC=56OBQM>; 300RI=Qc=OLNJ2L?0kYOcDh@:a30YlQ[TC>:7; AA>@4l?M6E4CfZni<@b52NN0S4cN4d0 Original-Xref: news.stanford.edu gnu.emacs.help:177080 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:72118 Archived-At: Andreas Röhler writes: > David Kastrup wrote: >> Andreas Roehler writes: >> >>> Hi, >>> >>> behaviour of the example code below puzzles me. Would >>> expect setting of arg by external function, but inside >>> `let', recognised. But remains `1'. >>> >>> (defun arg-setting () >>> (interactive) >>> (let ((arg 1)) >>> (message "%s" arg) >>> (arg-extern arg) >>> (message "%s" arg))) >>> >>> (defun arg-extern (arg) >>> (setq arg (1- arg))) >>> >>> Any help? >> >> The argument binding in arg-extern is the innermost one and consequently >> the only affected one. If you make the function argument-less, it will >> likely work as expected by you, affecting the binding in arg-setting. >> > > > That works, thanks a lot! > However, stored in some eil.el, get a compiler warning than: > > > In arg-extern: > eil.el:9:9:Warning: reference to free variable `arg' > eil.el:9:17:Warning: assignment to free variable `arg' > > Would think a useless warning, as the compiler should know being inside a let (?) > The compiler cannot know that this function will always be called in such a way. All it knows is that at its time of definition, it is setting an argument it doesn't know anything about. > The point to note is that in a defun argument list, that argument list is essentially an implicit let. The 'arg' referenced inside your original arg-extern is not the same as the arg being referenced in the first function. this is why I suggest you change the argument name in the arg-extern function as this will make that distinction obvious. To get the value set in arg-extern returned to its caller, you would do something like (setq arg (arg-extern arg)) Tim -- tcross (at) rapttech dot com dot au