From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Emanuel Berg Newsgroups: gmane.emacs.help Subject: Re: [External] : Re: Easy to add with push but not to the end of a list Date: Mon, 28 Nov 2022 23:45:35 +0100 Message-ID: <87a64a7l68.fsf@dataswamp.org> References: <878rju96i5.fsf@dataswamp.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="17524"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:a2as/fUwupnI3uTTwIFpVnkPmXU= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Wed Nov 30 14:45:40 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 1p0NPA-0004Ik-Oi for geh-help-gnu-emacs@m.gmane-mx.org; Wed, 30 Nov 2022 14:45:40 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1p0NOl-0004oR-GV; Wed, 30 Nov 2022 08:45:15 -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 1ozmsx-0008MA-WF for help-gnu-emacs@gnu.org; Mon, 28 Nov 2022 17:46:00 -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 1ozmsk-0000uP-Ga for help-gnu-emacs@gnu.org; Mon, 28 Nov 2022 17:45:59 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1ozmsh-0000KL-CQ for help-gnu-emacs@gnu.org; Mon, 28 Nov 2022 23:45:43 +0100 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: help-gnu-emacs@gnu.org Mail-Copies-To: never 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: -15 X-Spam_score: -1.6 X-Spam_bar: - X-Spam_report: (-1.6 / 5.0 requ) BAYES_00=-1.9, 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-Mailman-Approved-At: Wed, 30 Nov 2022 08:45:13 -0500 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:141256 Archived-At: Drew Adams wrote: >> Why is the below O(N), because of `last'? >> >> (defun push-last (elem lst) >> (let ((elem-lst (list elem))) >> (if lst >> (setcdr (last lst) elem-lst) >> (setq lst elem-lst) ) >> lst) ) > > Yes. > > (append lst (list elem)) also traverses the list > usually. Now it works at least, O(n) or not ... (defmacro push-last (elem lst) (if (and (symbolp lst) (not (symbol-value lst)) ) (list 'setq 'lst `(list ,elem)) (list 'nconc lst `(list ,elem)) )) ;; (setq lst ()) ; () ;; (push-last 1 lst) ; (1) ;; (push-last 1 lst) ; (1 1) ;; lst ; (1 1) ;; ;; (setq lst '(1 2 3 4)) ; (1 2 3 4) ;; (push-last 5 lst) ; (1 2 3 4 5) ;; (push-last 5 lst) ; (1 2 3 4 5) ;; lst ; (1 2 3 4 5 5) -- underground experts united https://dataswamp.org/~incal