From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: "Pascal J. Bourguignon" Newsgroups: gmane.emacs.help Subject: Re: About self-referential object Date: Sat, 05 Jan 2013 00:40:20 +0100 Organization: Informatimago Message-ID: <87y5g8h5zv.fsf@kuiper.lan.informatimago.com> References: NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1357343121 22740 80.91.229.3 (4 Jan 2013 23:45:21 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 4 Jan 2013 23:45:21 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sat Jan 05 00:45:31 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 1TrGx5-0003P3-Sz for geh-help-gnu-emacs@m.gmane.org; Sat, 05 Jan 2013 00:45:28 +0100 Original-Received: from localhost ([::1]:55016 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TrGwq-0007rN-KE for geh-help-gnu-emacs@m.gmane.org; Fri, 04 Jan 2013 18:45:12 -0500 Original-Path: usenet.stanford.edu!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 28 Original-X-Trace: individual.net 1HMZGruLfARs6fhSJsvksQR1glSTiZjW+jjwQhFAodnHACAPoytH8cQ49BQW9OPpML Cancel-Lock: sha1:ZTlhZjcxN2FlN2YwMjAzMTY1MjJkNWY1MWIwMjhhZjI0NWIwMGFmYQ== sha1:yrR6bAzZCrGuedVxsei/TZl27xY= Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwAQMAAABtzGvEAAAABlBMVEUAAAD///+l2Z/dAAAA oElEQVR4nK3OsRHCMAwF0O8YQufUNIQRGIAja9CxSA55AxZgFO4coMgYrEDDQZWPIlNAjwq9 033pbOBPtbXuB6PKNBn5gZkhGa86Z4x2wE67O+06WxGD/HCOGR0deY3f9Ijwwt7rNGNf6Oac l/GuZTF1wFGKiYYHKSFAkjIo1b6sCYS1sVmFhhhahKQssRjRT90ITWUk6vvK3RsPGs+M1RuR mV+hO/VvFAAAAABJRU5ErkJggg== X-Accept-Language: fr, es, en User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) Original-Xref: usenet.stanford.edu gnu.emacs.help:196145 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:88450 Archived-At: Xue Fuqiao writes: > I have a question about self-referential object: > > (setq foo '(nil)) > => (nil) > (setcar foo foo) > => (#0) > > It is an infinite recursion. What does the `#0' mean here? Can anybody help? Thanks. It means you've commited the sacrilege of modifying a literal value! If you modify a mutable cons cell, everything works as expected: *** Welcome to IELM *** Type (describe-mode) for help. ELISP> (setq print-circle t) t ELISP> (setq foo (cons nil nil)) (nil) ELISP> (setcar foo foo) #1=(#1#) ELISP> -- __Pascal Bourguignon__ http://www.informatimago.com/ A bad day in () is better than a good day in {}.