From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: [External] : Re: Appending lists Date: Sun, 20 Jun 2021 18:09:52 -0400 Message-ID: References: <20210617074843.GD16310@tuxteam.de> <87r1gy3f70.fsf@zoho.eu> <20210619065703.GB29866@tuxteam.de> <87fsxdzgl9.fsf@zoho.eu> <87im28gvsx.fsf@zoho.eu> Reply-To: Stefan Monnier Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="34962"; 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:OrACEBCM+cZ+/QYxpNhITFNlZGM= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Mon Jun 21 00:10:26 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 1lv5e5-0008y4-Ql for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 21 Jun 2021 00:10:25 +0200 Original-Received: from localhost ([::1]:51436 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lv5e4-0000vq-Sd for geh-help-gnu-emacs@m.gmane-mx.org; Sun, 20 Jun 2021 18:10:24 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:46056) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lv5dk-0000vS-ER for help-gnu-emacs@gnu.org; Sun, 20 Jun 2021 18:10:04 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:54740) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lv5di-0007Lf-Cw for help-gnu-emacs@gnu.org; Sun, 20 Jun 2021 18:10:04 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1lv5df-0008Rs-Np for help-gnu-emacs@gnu.org; Mon, 21 Jun 2021 00:09:59 +0200 X-Injected-Via-Gmane: http://gmane.org/ 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:131119 Archived-At: > ;; (setq completion-ignored-extensions > ;; (nconc completion-ignored-extensions '(".bcf" ".elc" ".run.xml")) ) > can be changed into (should be changed, since the above makes > no difference - ?) it can be changed into > (nconc completion-ignored-extensions '(".bcf" ".run.xml")) That will fail to do what you want if `completion-ignored-extensions` was empty just before executing the code. And it will have undesirable side effects if `completion-ignored-extensions` happened to hold a list some parts of which are also used elsewhere, e.g. if it was by a code such as (setq completion-ignored-extensions '("some" "constant" "list")) Since you probably don't perform this operation inside a tight loop where performance could be significant I'd recommend you just use `append` instead. > ;; (let ((modes (list > ;; '("\\.bal\\'" . balance-mode) > ;; '("\\.grm\\'" . sml-mode) > ;; '("\\.lu\\'" . lua-mode) > ;; '("\\.nqp\\'" . perl-mode) > ;; '("\\.php\\'" . html-mode) > ;; '("\\.pic\\'" . nroff-mode) > ;; '("\\.pl\\'" . prolog-mode) > ;; '("\\.sed\\'" . conf-mode) > ;; '("\\.service\\'" . conf-mode) > ;; '("\\.tex\\'" . latex-mode) > ;; '("\\.xr\\'" . conf-xdefaults-mode) > ;; '("*" . text-mode) ))) > ;; (setq auto-mode-alist (nconc modes auto-mode-alist)) ) > > might as well be > > (nconc (list > '("\\.bal\\'" . balance-mode) > '("\\.grm\\'" . sml-mode) > '("\\.lu\\'" . lua-mode) > '("\\.nqp\\'" . perl-mode) > '("\\.php\\'" . html-mode) > '("\\.pic\\'" . nroff-mode) > '("\\.pl\\'" . prolog-mode) > '("\\.sed\\'" . conf-mode) > '("\\.service\\'" . conf-mode) > '("\\.tex\\'" . latex-mode) > '("\\.xr\\'" . conf-xdefaults-mode) > '("*" . text-mode) ) > auto-mode-alist) Here `nconc` is a safe replace for `append` because indeed the first arg is a list you just constructed by `list` so you know for sure it's not shared with anything else. But the second above code is just an expensive no-op because your `nconc` will modify its first argument and not its second, so it will construct a new list, will add the content of `auto-mode-alist` to its end and then throw away the result. Here's another way you could write the code: (setq auto-mode-alist `(("\\.bal\\'" . balance-mode) ("\\.grm\\'" . sml-mode) ("\\.lu\\'" . lua-mode) ("\\.nqp\\'" . perl-mode) ("\\.php\\'" . html-mode) ("\\.pic\\'" . nroff-mode) ("\\.pl\\'" . prolog-mode) ("\\.sed\\'" . conf-mode) ("\\.service\\'" . conf-mode) ("\\.tex\\'" . latex-mode) ("\\.xr\\'" . conf-xdefaults-mode) ("*" . text-mode) ,@auto-mode-alist)) -- Stefan