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: member returns list (was: Re: To `boundp' or not to `boundp'?) Date: Wed, 02 Sep 2015 01:37:56 +0200 Message-ID: <87lhcpu2wb.fsf_-_@debian.uxu> References: <55E5C99B.3020608@yandex.ru> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1441150220 17800 80.91.229.3 (1 Sep 2015 23:30:20 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 1 Sep 2015 23:30:20 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Wed Sep 02 01:30:10 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 1ZWv0E-0000ds-KD for geh-help-gnu-emacs@m.gmane.org; Wed, 02 Sep 2015 01:30:10 +0200 Original-Received: from localhost ([::1]:59408 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWv0E-0003bf-Hp for geh-help-gnu-emacs@m.gmane.org; Tue, 01 Sep 2015 19:30:10 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:39218) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWv03-0003bK-Ay for help-gnu-emacs@gnu.org; Tue, 01 Sep 2015 19:30:00 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZWuzy-0005iO-Bm for help-gnu-emacs@gnu.org; Tue, 01 Sep 2015 19:29:59 -0400 Original-Received: from plane.gmane.org ([80.91.229.3]:45208) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWuzy-0005h8-4o for help-gnu-emacs@gnu.org; Tue, 01 Sep 2015 19:29:54 -0400 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1ZWuzu-0000RP-O0 for help-gnu-emacs@gnu.org; Wed, 02 Sep 2015 01:29:50 +0200 Original-Received: from nl106-137-244.student.uu.se ([130.243.137.244]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 02 Sep 2015 01:29:50 +0200 Original-Received: from embe8573 by nl106-137-244.student.uu.se with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 02 Sep 2015 01:29:50 +0200 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: help-gnu-emacs@gnu.org Original-Lines: 21 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: nl106-137-244.student.uu.se Mail-Copies-To: never User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux) Cancel-Lock: sha1:ga+SdfN7CHp71f1p7H3o/fB2ip0= 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:106971 Archived-At: Barry Margolin writes: > ... MEMBER, which intuitively seems like it would > just return a boolean, but actually returns the tail > of the list where the element was found. Yes, and I have wondered about that. Is it useful, perhaps with the use of `car' (?) as in: (car (member 2 '(1 2 3))) ; 2 (car (member 0 '(1 2 3))) ; nil Or is it some "leftover optimization" thing where `cdr' is faster than returning `t', and can be used the same way? Or is it something else? -- underground experts united http://user.it.uu.se/~embe8573