From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Oleksandr Gavenko Newsgroups: gmane.emacs.help Subject: Re: "defmacro" and "local variables" and "let" and "nconc" strange behaviour... Date: Sun, 13 Jan 2013 17:00:40 +0200 Organization: Oleksandr Gavenko , http://gavenkoa.users.sf.net Message-ID: <878v7x6sbr.fsf@gavenkoa.example.com> References: NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1358089272 22114 80.91.229.3 (13 Jan 2013 15:01:12 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 13 Jan 2013 15:01:12 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sun Jan 13 16:01:30 2013 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 1TuP3q-0005jd-NG for geh-help-gnu-emacs@m.gmane.org; Sun, 13 Jan 2013 16:01:22 +0100 Original-Received: from localhost ([::1]:33417 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TuP3a-0004EI-Ef for geh-help-gnu-emacs@m.gmane.org; Sun, 13 Jan 2013 10:01:06 -0500 Original-Received: from eggs.gnu.org ([208.118.235.92]:33919) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TuP3P-0004E9-Jk for help-gnu-emacs@gnu.org; Sun, 13 Jan 2013 10:01:02 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TuP3N-0006fE-Jr for help-gnu-emacs@gnu.org; Sun, 13 Jan 2013 10:00:55 -0500 Original-Received: from plane.gmane.org ([80.91.229.3]:37697) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TuP3N-0006fA-Cx for help-gnu-emacs@gnu.org; Sun, 13 Jan 2013 10:00:53 -0500 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1TuP3a-0005QI-V7 for help-gnu-emacs@gnu.org; Sun, 13 Jan 2013 16:01:06 +0100 Original-Received: from 37.229.4.200 ([37.229.4.200]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 13 Jan 2013 16:01:06 +0100 Original-Received: from gavenkoa by 37.229.4.200 with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 13 Jan 2013 16:01:06 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 26 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 37.229.4.200 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) Cancel-Lock: sha1:zJBcobAyUM0KmZfiR8U30oiSRrg= 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:88591 Archived-At: On 2013-01-13, Barry Margolin wrote: > In article , > Oleksandr Gavenko wrote: > >> I wrote simple macro: >> >> (defmacro my-filter (pred list) >> "Construct list with elements from LIST which satisfy PRED." >> (let ( (r (make-symbol "r_")) ) >> `(let ( (,r '(nil)) ) >> (mapc (lambda (item) >> (when (,pred item) >> (nconc ,r (cons item nil)))) >> ,list) >> (cdr ,r)))) >> [...] >> Why instead of '(nil) I get something else? > > Because nconc is destructively modifying its own source code. I know that nconc destructive. But how this effect '(nil) in defmacro inside `(...)? -- Best regards!