From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Jean Louis Newsgroups: gmane.emacs.help Subject: Re: [External] : Re: Testing whether a list contains at least one non-nil element Date: Thu, 27 Oct 2022 07:53:09 +0300 Message-ID: References: <87r0yw85la.fsf@dataswamp.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="30229"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mutt/2.2.7+37 (a90f69b) (2022-09-02) Cc: "help-gnu-emacs@gnu.org" To: Drew Adams Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Thu Oct 27 06:59:42 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 1onuzW-0007f5-83 for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 27 Oct 2022 06:59:42 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1onuxq-0007vC-Ho; Thu, 27 Oct 2022 00:57:58 -0400 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 1onuxo-0007sc-Jy for help-gnu-emacs@gnu.org; Thu, 27 Oct 2022 00:57:56 -0400 Original-Received: from stw1.rcdrun.com ([217.170.207.13]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1onuxj-00043A-8S for help-gnu-emacs@gnu.org; Thu, 27 Oct 2022 00:57:52 -0400 Original-Received: from localhost ([::ffff:102.82.225.124]) (AUTH: PLAIN admin, TLS: TLS1.3,256bits,ECDHE_RSA_AES_256_GCM_SHA384) by stw1.rcdrun.com with ESMTPSA id 0000000000081D92.00000000635A0FC8.00006FE8; Wed, 26 Oct 2022 21:57:43 -0700 Mail-Followup-To: Drew Adams , "help-gnu-emacs@gnu.org" Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=217.170.207.13; envelope-from=bugs@gnu.support; helo=stw1.rcdrun.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham 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: , Original-Sender: "help-gnu-emacs" Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:140418 Archived-At: * Drew Adams [2022-10-27 06:54]: > ;; Why do the rest of this? > ;; Search for a nil, after the non-nil car? > ;; Then copy the entire list. Then delete > ;; all nils from it? Why on earth do this? > (if (memq elt list) > ^^^^ > (delq elt (copy-sequence list)) > ^^^^^^^^^^^^^ > ^^^^^^^^^ > list)) I get your reasoning. Maybe my function was not named correctly and then your logic jumps in. > You certainly don't need to remove all nils > from the list. If your list is 100,000,000 > elements long and the first element is t, why > would you want to copy the entire list and > then remove all the nils from it? Testing > the first element tells you the answer. I get the reasoning, you are right, though maybe not in the context of testing if list has at least one non nil element. I am not sure, you know is not easy to grasp all. What I know is that by testing the first element does not tell the answer if list has any non nil element: (let ((my-list '(nil nil nil nil))) (car my-list)) ⇒ nil (let ((my-list '(nil nil nil nil 1))) (car my-list)) ⇒ nil So testing the first element did not give me the answer that my-list has one non-nil element. Maybe you can show in Emacs Lisp practically how do you mean it. -- Jean Take action in Free Software Foundation campaigns: https://www.fsf.org/campaigns In support of Richard M. Stallman https://stallmansupport.org/