From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.devel Subject: "The starting list count" ????? Date: Mon, 3 Jan 2022 17:49:40 +0000 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="13423"; mail-complaints-to="usenet@ciao.gmane.io" To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Mon Jan 03 18:51:15 2022 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1n4RUJ-0003L5-Co for ged-emacs-devel@m.gmane-mx.org; Mon, 03 Jan 2022 18:51:15 +0100 Original-Received: from localhost ([::1]:37252 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1n4RUH-00019V-Rk for ged-emacs-devel@m.gmane-mx.org; Mon, 03 Jan 2022 12:51:13 -0500 Original-Received: from eggs.gnu.org ([209.51.188.92]:43690) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n4RSr-000095-RR for emacs-devel@gnu.org; Mon, 03 Jan 2022 12:49:45 -0500 Original-Received: from colin.muc.de ([193.149.48.1]:29520 helo=mail.muc.de) by eggs.gnu.org with smtp (Exim 4.90_1) (envelope-from ) id 1n4RSp-0007hT-3R for emacs-devel@gnu.org; Mon, 03 Jan 2022 12:49:45 -0500 Original-Received: (qmail 90075 invoked by uid 3782); 3 Jan 2022 17:49:40 -0000 Original-Received: from acm.muc.de (p4fe15534.dip0.t-ipconnect.de [79.225.85.52]) (using STARTTLS) by colin.muc.de (tmda-ofmipd) with ESMTP; Mon, 03 Jan 2022 18:49:40 +0100 Original-Received: (qmail 19318 invoked by uid 1000); 3 Jan 2022 17:49:40 -0000 Content-Disposition: inline X-Submission-Agent: TMDA/1.3.x (Ph3nix) X-Primary-Address: acm@muc.de Received-SPF: pass client-ip=193.149.48.1; envelope-from=acm@muc.de; helo=mail.muc.de X-Spam_score_int: 0 X-Spam_score: 0.0 X-Spam_bar: / X-Spam_report: (0.0 / 5.0 requ) SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.io gmane.emacs.devel:284077 Archived-At: Hello, Emacs. I'm trying to make sense of the form whose printed syntax is (1 . #1) which arises in the Emacs test suite file seq-tests.el. I'm having difficulty. The Elisp manual page "Special Read Syntax" says about it: `#N' When printing circular structures, this construct is used to represent where the structure loops back onto itself, and `N' is the starting list count: (let ((a (list 1))) (setcdr a a)) => (1 . #0) .. What does this mean, please? What does "is the starting list count" mean? There is only one "list", so what is the "list count"? Clearly the N in #N is counting something, but what? What is the meaning of (1 . #1) ? What is it about the description in the manual which is so perplexing me? Help! -- Alan Mackenzie (Nuremberg, Germany).