From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Eric Abrahamsen Newsgroups: gmane.emacs.help Subject: Re: replace element in list Date: Wed, 21 Nov 2018 22:04:35 -0800 Message-ID: <87va4py7f0.fsf@ericabrahamsen.net> References: <2087821187f90948d25d93c7ea475e66@openmail.cc> <87zhu1y9k1.fsf@ericabrahamsen.net> <45a3b5b6-2985-4eab-bb2c-2ad9b4459018@default> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: blaine.gmane.org 1542866595 30287 195.159.176.226 (22 Nov 2018 06:03:15 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 22 Nov 2018 06:03:15 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Nov 22 07:03:11 2018 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gPi50-0007kk-JU for geh-help-gnu-emacs@m.gmane.org; Thu, 22 Nov 2018 07:03:10 +0100 Original-Received: from localhost ([::1]:44164 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gPi76-0003xQ-Uc for geh-help-gnu-emacs@m.gmane.org; Thu, 22 Nov 2018 01:05:20 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:54844) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gPi6c-0003xH-IU for help-gnu-emacs@gnu.org; Thu, 22 Nov 2018 01:04:51 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gPi6Y-0007x0-J5 for help-gnu-emacs@gnu.org; Thu, 22 Nov 2018 01:04:50 -0500 Original-Received: from [195.159.176.226] (port=52452 helo=blaine.gmane.org) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gPi6X-0007sH-OQ for help-gnu-emacs@gnu.org; Thu, 22 Nov 2018 01:04:46 -0500 Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1gPi4N-0006zK-0H for help-gnu-emacs@gnu.org; Thu, 22 Nov 2018 07:02:31 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 24 Original-X-Complaints-To: usenet@blaine.gmane.org Cancel-Lock: sha1:dpndh9h6Qy+jjrIIrgCV5aWxNf8= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 195.159.176.226 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.21 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.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.org gmane.emacs.help:118729 Archived-At: Drew Adams writes: >> > (defun my-list-replace (obj orig new) >> > "Replaces an element in a list with something else" >> > (let* ((pos (cl-position orig obj :test 'equal)) >> > (pos (if pos pos 0)) >> > (objlen (length obj)) >> > (head (butlast obj (- objlen pos))) >> > (trail (nthcdr (+ 1 pos) obj))) >> > (append head (append new trail)))) >> >> (let ((orig '(("a" . "b") ("c" "d"))) >> (obj '("c" "d")) >> (new '(":)"))) >> (setf (nth (cl-position obj orig :test #'equal) orig) new) >> orig) > > (defun toto (xs old new) > (let ((ms (member old xs))) > (unless ms (error "%S is not in %S" old xs)) > (setcar ms new) > xs)) Old school, and proper :)