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: Easy to add with push but not to the end of a list Date: Wed, 30 Nov 2022 20:30:24 +0100 Message-ID: <87a648kzov.fsf@dataswamp.org> References: <877czcid1d.fsf@web.de> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="39121"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:U5q+JXiVtkgFuv8KVuxd85Dlh0U= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Thu Dec 01 14:52:01 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 1p0jyr-0009r6-PW for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 01 Dec 2022 14:52:01 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1p0jyd-0001ML-4W; Thu, 01 Dec 2022 08:51:47 -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 1p0Smz-00023h-2t for help-gnu-emacs@gnu.org; Wed, 30 Nov 2022 14:30:42 -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 1p0Smw-0007XO-Ay for help-gnu-emacs@gnu.org; Wed, 30 Nov 2022 14:30:36 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1p0Smt-0002op-Bl for help-gnu-emacs@gnu.org; Wed, 30 Nov 2022 20:30:31 +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: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, 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-Mailman-Approved-At: Thu, 01 Dec 2022 08:51:45 -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:141284 Archived-At: Michael Heerdegen wrote: >> Although it is easy to add to a list using push, it >> currently looks hideous to be able to add to the end of >> a list. > > In addition to what has already been said: if you store and > update the last cdr of your list (in a variable for > example), you can add something to the end of the list in > O(1). The cost is the cost of maintaining additional data. You can write a function that does all of that automatically for you but then you are restricted to using such tailor-made functions. If you couple those functions with the data they are to manipulate you have already a small OO system with methods and members ... So use `push' and provide a "push-last" and say in the docstring it's not as fast is better ... ;;; -*- lexical-binding: t -*- ;; ;; this file: ;; https://dataswamp.org/~incal/emacs-init/list.el (defmacro push-last (elem lst) "Push ELEM to be the last element of LST. Beware that this is O(n) while `push' is O(1)." (if (and (symbolp lst) (not (symbol-value lst)) ) (list 'setq lst `(list ,elem)) (list 'nconc lst `(list ,elem)) )) -- underground experts united https://dataswamp.org/~incal