From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Emanuel Berg via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: [External] : Re: Appending lists Date: Sun, 20 Jun 2021 22:42:00 +0200 Message-ID: <87tulsfeuf.fsf@zoho.eu> References: <20210617074843.GD16310@tuxteam.de> <87r1gy3f70.fsf@zoho.eu> <20210619065703.GB29866@tuxteam.de> <87fsxdzgl9.fsf@zoho.eu> <87im28gvsx.fsf@zoho.eu> Reply-To: Emanuel Berg 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="38974"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:hqd4uCpic40KLAFFGjtYDGYGm7o= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Sun Jun 20 22:42:47 2021 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 1lv4HH-0009yP-UW for geh-help-gnu-emacs@m.gmane-mx.org; Sun, 20 Jun 2021 22:42:47 +0200 Original-Received: from localhost ([::1]:48662 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lv4HG-0008KA-An for geh-help-gnu-emacs@m.gmane-mx.org; Sun, 20 Jun 2021 16:42:46 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:32830) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lv4Go-0008K1-TX for help-gnu-emacs@gnu.org; Sun, 20 Jun 2021 16:42:18 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:46148) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lv4Gm-0000W1-OO for help-gnu-emacs@gnu.org; Sun, 20 Jun 2021 16:42:18 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1lv4Gh-0009H7-Rs for help-gnu-emacs@gnu.org; Sun, 20 Jun 2021 22:42:11 +0200 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-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 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" Xref: news.gmane.io gmane.emacs.help:131115 Archived-At: Jean Louis wrote: > But then I can use the previously defined variables to > define a new one: > > (setq appended (append list-a list-b)) ⇒ (1 2 3 a b c) > > and nothing changed in those: > > list-a ⇒ (1 2 3) > list-b ⇒ (a b c) Actually `append' can also be trouble because the last list isn't copied, the new list just has a cdr somewhere to it - yes, to the actual list. Try this: (setq list-head '(1)) ; (1) (setq list-tail '(2 3 4)) ; (2 3 4) (setq whole-list (append list-head list-tail)) ; (1 2 3 4) (setcdr list-tail '(3.5 4)) ; (3.5 4) whole-list ; (1 2 3.5 4) See that "whole-list" changed even tho we did it with `setq', append, and didn't mention it... I don't know why append does this, either to speed things up or it has something to do with the car/cdr dynamic, maybe it is considered safe enough to move the car out of action with an actual copy ... -- underground experts united https://dataswamp.org/~incal