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: Appending lists Date: Tue, 15 Jun 2021 02:46:54 +0200 Message-ID: <87zgvs2bup.fsf@zoho.eu> References: <4tl1yvylvg1fxx5eefjs9mnk.1623688568572@email.android.com> <87o8c8l32h.fsf@posteo.net> Reply-To: Emanuel Berg Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="18840"; 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:ts8IKGDIlFrK/RVlSm4Zjfmc7ec= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Jun 15 02:47:38 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 1lsxEv-0004iz-Ot for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 15 Jun 2021 02:47:37 +0200 Original-Received: from localhost ([::1]:57638 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lsxEu-0001G6-RM for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 14 Jun 2021 20:47:36 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:33414) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lsxES-0001Fj-NH for help-gnu-emacs@gnu.org; Mon, 14 Jun 2021 20:47:08 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:52278) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lsxEQ-0004sJ-Se for help-gnu-emacs@gnu.org; Mon, 14 Jun 2021 20:47:08 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1lsxEO-0003xy-UT for help-gnu-emacs@gnu.org; Tue, 15 Jun 2021 02:47:04 +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:130826 Archived-At: Alexandr Vityazev wrote: > (defvar newlist '()) > (append `(,city ,district) newlist) Okay, but I think (list city district) looks better... And no need for a default value if one sets it the line after IMO. Also, one would try not to mix abstract and applied names too much, but I get it it was to demonstrate `append'. But since newlist is nil I don't know how much of a demo it is, actually. Hm... (to the OP: an empty list is '() or (list) or nil, so when something actually _is_ an empty list '() (and not just something to indicate false, for instance) is a good way of putting it since that's what an empty list looks like, almost. this is neat as it works the other way around as well, i.e. a non-empty list is interpreted as non-nil, so you can check for a non-empty list e.g. like this (when lst ... ) useful with recursion (e.g., tail-recursion, with the empty list as the non-recursive/base case) but also here and there in general, I'd say...) Also check out `nconc' (nconc '(1 2 3) '(4 5) '(6)) ; (1 2 3 4 5 6) - if this works for you, use it (nconc '(1 2 3) '(4 5) 6 ) ; (1 2 3 4 5 . 6) - see, last "list" isn't a list! There was a trick with nconc, you could reverse a list in constant time, right? I think that was it but that's all I remember. -- underground experts united https://dataswamp.org/~incal