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: Re: "The starting list count" ????? Date: Mon, 3 Jan 2022 21:03:33 +0000 Message-ID: References: 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="34835"; mail-complaints-to="usenet@ciao.gmane.io" Cc: emacs-devel@gnu.org To: Stefan Monnier Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Mon Jan 03 22:04:33 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 1n4UVN-0008tI-8d for ged-emacs-devel@m.gmane-mx.org; Mon, 03 Jan 2022 22:04:33 +0100 Original-Received: from localhost ([::1]:52494 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1n4UVM-0006oP-7w for ged-emacs-devel@m.gmane-mx.org; Mon, 03 Jan 2022 16:04:32 -0500 Original-Received: from eggs.gnu.org ([209.51.188.92]:50654) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n4UUV-0005wx-1Y for emacs-devel@gnu.org; Mon, 03 Jan 2022 16:03:39 -0500 Original-Received: from colin.muc.de ([193.149.48.1]:34924 helo=mail.muc.de) by eggs.gnu.org with smtp (Exim 4.90_1) (envelope-from ) id 1n4UUS-0004wJ-Gg for emacs-devel@gnu.org; Mon, 03 Jan 2022 16:03:38 -0500 Original-Received: (qmail 19309 invoked by uid 3782); 3 Jan 2022 21:03:33 -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 22:03:33 +0100 Original-Received: (qmail 20106 invoked by uid 1000); 3 Jan 2022 21:03:33 -0000 Content-Disposition: inline In-Reply-To: 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:284101 Archived-At: Hello, Stefan. On Mon, Jan 03, 2022 at 15:38:33 -0500, Stefan Monnier wrote: > > I might have understood it now. I think (1 . #1) refers to: > No, if you see (1 . #1) then it's an error. What I actually saw was in a backtrace, after C-g'ing out of the byte compilation of set-tests.el, and was this: Debugger entered--Lisp error: (quit) copy-tree((1 . #1) t) macroexp-strip-symbol-positions((1 . #1)) byte-compile-constant((1 . #1)) byte-compile-quote('(1 . #2)) byte-compile-form('(1 . #2)) > The #1 means "the second heap object between the root and here" and in > (1 . #1) there's only one heap object. I can cope with "the second heap object", but what is "the root"? > You can have > [a b c (1 . #1)] > and > ((1 . #1)) > and > (a . (1 . #1)) > and many more, but not just > (1 . #1) Yes. Looking at seq-tests.el, it's clear the original source for it is (let ((l1 '#1=(1 . #1#))) ....) , that being the only circular list or setc[ad]r in the entire file. I'm actually feeling quite sad about the whole business. There doesn't appear to be a lot of support for circular lists in Emacs. Does that mean I have to write my own version of copy-tree (?etc.) that handles circularity? It's surely something that's already been done dozens of times. > -- Stefan -- Alan Mackenzie (Nuremberg, Germany).