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 19:48:01 +0100 Message-ID: <87h9iyv4im.fsf@debian.uxu> References: <568164D8.6050700@ojkastl.de> <87io3iyr7t.fsf@debian.uxu> <87si2kezg1.fsf@mithlond.arda> <87a8osrlj4.fsf_-_@debian.uxu> <87lh8bgafa.fsf@mithlond.arda> <877fjve0x5.fsf@kuiper.lan.informatimago.com> <87wprvqnco.fsf@debian.uxu> <20151231092253.GA19900@tuxteam.de> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1451587714 21275 80.91.229.3 (31 Dec 2015 18:48:34 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 31 Dec 2015 18:48:34 +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 19:48:27 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 1aEiGv-0001Ih-FL for geh-help-gnu-emacs@m.gmane.org; Thu, 31 Dec 2015 19:48:25 +0100 Original-Received: from localhost ([::1]:56552 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aEiGu-000701-RY for geh-help-gnu-emacs@m.gmane.org; Thu, 31 Dec 2015 13:48:24 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:53359) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aEiGk-0006zf-N2 for help-gnu-emacs@gnu.org; Thu, 31 Dec 2015 13:48:15 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aEiGh-0000eA-F6 for help-gnu-emacs@gnu.org; Thu, 31 Dec 2015 13:48:14 -0500 Original-Received: from plane.gmane.org ([80.91.229.3]:50595) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aEiGh-0000dx-8W for help-gnu-emacs@gnu.org; Thu, 31 Dec 2015 13:48:11 -0500 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1aEiGd-0000zF-HY for help-gnu-emacs@gnu.org; Thu, 31 Dec 2015 19:48:07 +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 19:48:07 +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 19:48:07 +0100 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: help-gnu-emacs@gnu.org Original-Lines: 40 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: sha1:2bshNg9h0pWvmKJon0OBiPRn4s4= 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:108556 Archived-At: writes: > Side effect, the big lurking Monster for functional > programmers: > > (defvar foo 15) > > (defun monster () (setq foo 42)) > > (monster) ;; now foo is 42: Gaaah! (message "%S" > foo) > > Nconc has a side effect: after calling it, many of the > lists are changed. However, because of the potential situation with a symbol being nil or the empty list, `nconc' can't really be used only "for effect" - so it should return the list and that in turn be assigned! So a little bit of functional programming still has to be employed! (Not that the FP people has the monopoly on returning stuff tho they might think so themselves in their opium dreams.) On the other hand, `append' isn't side-effect free! (setq *digits* '(1 2 3 4 5)) (setq *chars* '(a b c d e)) (setq *appended-list* (append *digits* *chars*)) (setf (car (last *appended-list*)) 'x) (insert (format " ; %s" *appended-list*)) ; (1 2 3 4 5 a b c d x) (insert (format " ; %s" *chars*)) ; (a b c d x) Perhaps (concatenate 'list ...) is the functional function? -- underground experts united http://user.it.uu.se/~embe8573