From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Emanuel Berg Newsgroups: gmane.emacs.help Subject: Re: `append' vs. `nconc' Date: Thu, 31 Dec 2015 04:37:47 +0100 Message-ID: <8760zfs2yc.fsf@debian.uxu> References: <568164D8.6050700@ojkastl.de> <87io3iyr7t.fsf@debian.uxu> <87si2kezg1.fsf@mithlond.arda> <87a8osrlj4.fsf_-_@debian.uxu> <87lh8bgafa.fsf@mithlond.arda> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1451533105 21441 80.91.229.3 (31 Dec 2015 03:38:25 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 31 Dec 2015 03:38:25 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Dec 31 04:38:16 2015 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aEU44-0000UT-PM for geh-help-gnu-emacs@m.gmane.org; Thu, 31 Dec 2015 04:38:13 +0100 Original-Received: from localhost ([::1]:54538 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aEU43-0002oT-Tj for geh-help-gnu-emacs@m.gmane.org; Wed, 30 Dec 2015 22:38:11 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:34737) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aEU3t-0002ng-6n for help-gnu-emacs@gnu.org; Wed, 30 Dec 2015 22:38:02 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aEU3p-0006Hq-PI for help-gnu-emacs@gnu.org; Wed, 30 Dec 2015 22:38:01 -0500 Original-Received: from plane.gmane.org ([80.91.229.3]:49749) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aEU3p-0006Fh-IK for help-gnu-emacs@gnu.org; Wed, 30 Dec 2015 22:37:57 -0500 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1aEU3n-0000Ef-Al for help-gnu-emacs@gnu.org; Thu, 31 Dec 2015 04:37:55 +0100 Original-Received: from nl106-137-56.student.uu.se ([130.243.137.56]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 31 Dec 2015 04:37:55 +0100 Original-Received: from embe8573 by nl106-137-56.student.uu.se with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 31 Dec 2015 04:37:55 +0100 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: help-gnu-emacs@gnu.org Original-Lines: 49 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: nl106-137-56.student.uu.se Mail-Copies-To: never User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) Cancel-Lock: sha1:CkeZ3xjpI2BV6MA4peEXMns8TnM= X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 80.91.229.3 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.14 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-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:108540 Archived-At: Teemu Likonen writes: > Given the following: > > (append list1 list2 list3 last) > > (nconc list1 list2 list3 last) > > APPEND copies LIST1, LIST2 and LIST3 but not LAST. > All original lists remain untouched but LAST becomes > part of the new list returned by APPEND. I think I always used `append' as if it were (append list1 ... listn '()) probably the reason it never bit me was I never did much with the lists returned. > NCONC doesn't copy lists but modifies LIST1's, > LIST2's and LIST3's last cons's CDR to point to the > next list. NCONC returnes the joined list. Only LAST > remains untouched. OK, so for example this: (setq completion-ignored-extensions (append completion-ignored-extensions '(".bcf" ".run.xml")) ) Is better as: (nconc completion-ignored-extensions (list ".bcf" ".run.xml")) ? >> I have several appends in my source, is there >> a rule-of-thumb when to use `append' and when to >> use `nconc'? > > You can use NCONC if it's safe to modify the lists, > that is, you know where the lists come from and know > how they are used. Don't modify a list created with > '(...). Use (list ...) instead. OK. -- underground experts united http://user.it.uu.se/~embe8573