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 19:21:33 +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="27038"; 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 20:23:31 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 1n4Svb-0006qt-Lz for ged-emacs-devel@m.gmane-mx.org; Mon, 03 Jan 2022 20:23:31 +0100 Original-Received: from localhost ([::1]:37266 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1n4SvZ-0003VJ-RI for ged-emacs-devel@m.gmane-mx.org; Mon, 03 Jan 2022 14:23:29 -0500 Original-Received: from eggs.gnu.org ([209.51.188.92]:46794) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n4Stv-0002fs-8K for emacs-devel@gnu.org; Mon, 03 Jan 2022 14:21:47 -0500 Original-Received: from colin.muc.de ([193.149.48.1]:32139 helo=mail.muc.de) by eggs.gnu.org with smtp (Exim 4.90_1) (envelope-from ) id 1n4Stk-0001b6-FY for emacs-devel@gnu.org; Mon, 03 Jan 2022 14:21:46 -0500 Original-Received: (qmail 51779 invoked by uid 3782); 3 Jan 2022 19:21:34 -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 20:21:33 +0100 Original-Received: (qmail 19800 invoked by uid 1000); 3 Jan 2022 19:21:33 -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:284089 Archived-At: Hello, Stefan. On Mon, Jan 03, 2022 at 13:05:23 -0500, Stefan Monnier wrote: > > .. What does this mean, please? What does "is the starting list count" > > mean? There is only one "list", so what is the "list count"? > I'm not sure how to define it in general, but: > (let ((x (list 1 2 3 4 5 6 7))) (setf (nthcdr 5 x) (nthcdr N x)) x) > returns a list with a #N inside of it (well, for N sufficiently small > to make sense here, obviously). > AFAIK this is only used to avoid inf-looping, but if/when you actually > care about that you should use `print-circle` which additionally > preserves sharing and gives an output that's more explicit about > what's going on, and hence easier to understand (tho not necessarily > easier to read). I might have understood it now. I think (1 . #1) refers to: ----------------- --- | | | | | v v | -----------------------+-------- ---------+----------------------- | | | | | | | | | | | | | | | | | | | | | | | | | 1 | | | | | | nil | | | | | | | | | | | | | | | | | | | -------------------------------- --------------------------------- Am I right? This is an ugly thing, which surely only the most twisted of imaginations could conceive. ;-) Obviously, a depth first operation on this "list" is going to take a long time. Just as a matter of interest, this object is being passed to macroexp-strip-symbol-positions during the byte compilation of seq-tests.el. > Stefan -- Alan Mackenzie (Nuremberg, Germany).