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 23:38:57 +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="1264"; 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 22:42:29 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 1oo9ht-000Adn-NW for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 27 Oct 2022 22:42:29 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oo9h9-0005Qn-OR; Thu, 27 Oct 2022 16:41:43 -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 1oo9h7-0005MC-JE for help-gnu-emacs@gnu.org; Thu, 27 Oct 2022 16:41:41 -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 1oo9h5-0006Tt-2s for help-gnu-emacs@gnu.org; Thu, 27 Oct 2022 16:41:41 -0400 Original-Received: from localhost ([::ffff:102.85.119.94]) (AUTH: PLAIN admin, TLS: TLS1.3,256bits,ECDHE_RSA_AES_256_GCM_SHA384) by stw1.rcdrun.com with ESMTPSA id 0000000000081D92.00000000635AECFF.00004B95; Thu, 27 Oct 2022 13:41:34 -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:140437 Archived-At: * Drew Adams [2022-10-27 18:54]: > In the worst case for your code, the first element IS non-nil and > you spend forever doing useless stuff. In no case is your code as > efficient as just testing each list element, starting at the > beginning, and STOPPING as soon as you find a non-nil element. Of course I agree with the thought in general. Is it this below? (defun check-if-any-elt-is-non-nil (list) (let (there-is) (while (and list (not there-is)) (when (car list) (setq there-is t)) (setq list (cdr list))) there-is)) (check-if-any-elt-is-non-nil '(nil nil nil nil nil nil nil nil 1 nil)) ⇒ t (check-if-any-elt-is-non-nil '(nil nil nil nil nil nil nil nil nil)) ⇒ nil (benchmark 10000000 (check-if-any-elt-is-non-nil (append (list 1) (make-list 1000000 nil)))) ⇒ "Elapsed time: 0.771948s" (benchmark 10000000 (check-if-any-elt-is-non-nil (append (make-list 1000000 nil) (list 1) ))) ⇒ "Elapsed time: 0.744323s" -- Jean Take action in Free Software Foundation campaigns: https://www.fsf.org/campaigns In support of Richard M. Stallman https://stallmansupport.org/