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: Fri, 09 Dec 2022 22:21:28 +0100 Message-ID: <87h6y4s27b.fsf@web.de> References: <87lenh7vrn.fsf@web.de> <87tu25d77o.fsf@gnu.org> <87h6y5pt8k.fsf@web.de> <87bkodpqnk.fsf@web.de> <87k030tlfh.fsf@web.de> <87ilike1l8.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="1382"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:H+YSs2/LputOzyptrxppM6m5knA= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Fri Dec 09 22:22:29 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 1p3kpB-00009u-6n for geh-help-gnu-emacs@m.gmane-mx.org; Fri, 09 Dec 2022 22:22:29 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1p3koV-0006HG-2Z; Fri, 09 Dec 2022 16:21:47 -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 1p3koS-0006Gl-Lf for help-gnu-emacs@gnu.org; Fri, 09 Dec 2022 16:21:44 -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 1p3koN-0006ik-Qg for help-gnu-emacs@gnu.org; Fri, 09 Dec 2022 16:21:44 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1p3koJ-0009Yr-MW for help-gnu-emacs@gnu.org; Fri, 09 Dec 2022 22:21:35 +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=0.248, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.25, 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:141534 Archived-At: Tassilo Horn writes: > This time I'm prepared and have three versions making a new binding. > Take this, Michael! :-) Wow - ok, let's see... > (let ((i 0) > (m (lambda (i) > (lambda () i))) > funs) > (while (< i 100) > (push (funcall m i) funs) > (cl-incf i)) > (mapcar #'funcall funs)) Yes, I think one can do this (the argument variable i shadows the variable of the same in the `let', but it also exists to conserve the value from the outside i so one can argue that it's ok to use the same name - it's semantically not incorrect anyway). Nice solution. > (let ((i 0) > funs) > (while (< i 100) > (let ((j i)) > (push (lambda () j) funs)) > (cl-incf i)) > (mapcar #'funcall funs)) This is the trick that is used in the implementation of `dolist': create a binding that lives only inside the evaluation of the body of the loop in one iteration step. > (let ((i 0) > funs) > (while (< i 100) > (push `(lambda () ,i) funs) > (cl-incf i)) > (mapcar #'funcall funs)) Hmm...hmm. No, we don't want to quote lambdas. When Stefan sees that he might install a patch that will make the above error (he really could do this!). Better only do that privately. > Oh, I forgot to `nreverse` funs so my Nth function returns 99-N instead. > Good enough... Ok, it still counts (but maybe backwards). Regards, Michael.