From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Michael Heerdegen Newsgroups: gmane.emacs.help Subject: Re: Closures - do you understand them well? Date: Thu, 08 Dec 2022 20:53:31 +0100 Message-ID: <87h6y5pt8k.fsf@web.de> References: <87lenh7vrn.fsf@web.de> <87tu25d77o.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="35742"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:bTndrrUN1EOYFVtN9hLSMveTYkc= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Thu Dec 08 20:54:08 2022 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1p3My8-00091u-7z for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 08 Dec 2022 20:54:08 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1p3Mxm-0001cr-Ts; Thu, 08 Dec 2022 14:53:46 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1p3Mxm-0001cj-1X for help-gnu-emacs@gnu.org; Thu, 08 Dec 2022 14:53:46 -0500 Original-Received: from ciao.gmane.io ([116.202.254.214]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1p3Mxk-00048u-7K for help-gnu-emacs@gnu.org; Thu, 08 Dec 2022 14:53:45 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1p3Mxh-0008NV-R1 for help-gnu-emacs@gnu.org; Thu, 08 Dec 2022 20:53:41 +0100 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -13 X-Spam_score: -1.4 X-Spam_bar: - X-Spam_report: (-1.4 / 5.0 requ) BAYES_00=-1.9, FREEMAIL_FORGED_FROMDOMAIN=0.229, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 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-mx.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:141471 Archived-At: Tassilo Horn writes: > Shocking!!! The example is written in a way to suggest a wrong result. But don't we all rely on the behavior demonstrated from time to time? The implementation of `letrec' for example: (macroexpand-1 '(letrec ((f (lambda () f))))) ==> (let (f) (setq f (lambda nil f))) We expect that the value of F in the closure bound to F references the closure itself, not the initial value. > Common Lisp agrees: > > (let ((funs '())) > (loop for i from 1 to 3 > do (push (lambda () i) funs)) > (apply #'+ (mapcar #'funcall funs))) > ;=> 12 I guess this depends a bit on the implementation of `loop'. But I think the result is expected, yes. Don't you remember what you learned about shared environments that different places in the code have access to (including the ability to modify)? > So I guess the reason is that the `i' is not an integer but a place > where the integers 1, 2, and 3? It's a free variable in all the lambdas, and it refers to the binding in the same environment. When the `apply' call is made the binding in that environment is the one from the moment when it was last changed in the loop, and that is `4`. That's all. Michael.