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: How to mapcar or across a list? Date: Thu, 16 Jul 2015 00:21:06 +0200 Message-ID: <87fv4pukod.fsf@nl106-137-147.student.uu.se> References: <87io9lmb4z.fsf@mbork.pl> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1436998983 25542 80.91.229.3 (15 Jul 2015 22:23:03 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 15 Jul 2015 22:23:03 +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 Jul 16 00:22:55 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 1ZFV4o-0000jE-BT for geh-help-gnu-emacs@m.gmane.org; Thu, 16 Jul 2015 00:22:54 +0200 Original-Received: from localhost ([::1]:37680 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFV4n-0000Ov-Lo for geh-help-gnu-emacs@m.gmane.org; Wed, 15 Jul 2015 18:22:53 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:48640) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFV4d-0000Oq-BH for help-gnu-emacs@gnu.org; Wed, 15 Jul 2015 18:22:44 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFV4Z-0005Fv-B3 for help-gnu-emacs@gnu.org; Wed, 15 Jul 2015 18:22:43 -0400 Original-Received: from plane.gmane.org ([80.91.229.3]:40525) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFV4Z-0005FX-4i for help-gnu-emacs@gnu.org; Wed, 15 Jul 2015 18:22:39 -0400 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1ZFV4W-0000d1-VD for help-gnu-emacs@gnu.org; Thu, 16 Jul 2015 00:22:37 +0200 Original-Received: from nl106-137-156.student.uu.se ([130.243.137.156]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 16 Jul 2015 00:22:36 +0200 Original-Received: from embe8573 by nl106-137-156.student.uu.se with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 16 Jul 2015 00:22:36 +0200 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: help-gnu-emacs@gnu.org Original-Lines: 45 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: nl106-137-156.student.uu.se Mail-Copies-To: never User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux) Cancel-Lock: sha1:kJEZJPYkNkn4JussMWto8vDjqEk= 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:105744 Archived-At: Marcin Borkowski writes: > so here's my problem: I have a list of Boolean > values, and I want to `mapcar' an `or' across it > (IOW, I want to test whether at least one of them is > true). Of course, (apply #'or my-list) does not > work. Of course, I can (cl-reduce (lambda (x y) (or > x y)) my-list) -- but is there a better method? "Better" I don't know, but how about using your new-found skills with the backquote? (`or' itself should be used, of course.) (setq boolean-list-1 '(t nil nil nil t nil nil)) (setq boolean-list-2 '(nil nil nil nil nil nil nil)) (eval `(or ,@boolean-list-1)) ; t (eval `(or ,@boolean-list-2)) ; nil > BTW, my-list doesn't really exist: it is a result of > `mapcar'ing a function taking some value and > yielding a Boolean value, so bonus points if the > method does not process the whole list. Check. It is a consequence of using `or', which is "short circuited" as it is called in other languages, perhaps in Lisp too - I've read "conditional evaluation" as well in AI books, but perhaps that is something else. Anyway: (or t undefined) ; t (or undefined t) ; error: (void-variable undefined) in eval To verify, append "undefined" to "boolean-list-1" (no error) - but, there will be an error (the same as above) if appended to "boolean-list-2"! ... I suppose now would be a good time for you to hand over them points! -- underground experts united http://user.it.uu.se/~embe8573