From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Christopher Dimech Newsgroups: gmane.emacs.help Subject: Re: Cycle Org Shift Select Date: Tue, 10 Nov 2020 11:17:22 +0100 Message-ID: References: <87pn4mgufa.fsf@web.de> <20201110080829.GA11023@tuxteam.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="40445"; mail-complaints-to="usenet@ciao.gmane.io" Cc: help-gnu-emacs@gnu.org To: tomas@tuxteam.de Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Nov 10 11:19:28 2020 Return-path: Envelope-to: geh-help-gnu-emacs@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 1kcQkJ-000APD-CJ for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 10 Nov 2020 11:19:27 +0100 Original-Received: from localhost ([::1]:48240 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kcQkH-00058X-2F for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 10 Nov 2020 05:19:25 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:33078) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kcQiR-00056L-PV for help-gnu-emacs@gnu.org; Tue, 10 Nov 2020 05:17:31 -0500 Original-Received: from mout.gmx.net ([212.227.15.15]:38491) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kcQiP-0001zD-Cf for help-gnu-emacs@gnu.org; Tue, 10 Nov 2020 05:17:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1605003442; bh=49niuwSbeuboneeTMW/b4ycSUbcfFdN8ZGkZ3PVn508=; h=X-UI-Sender-Class:From:To:Cc:Subject:Date:In-Reply-To:References; b=EyjzNwr67/Ik1T5/H6S3z94mMvBfBycYz65p4H7i94XFnTXNv2mwUfR+Oexn53haC MyZqlQWFo/5zO2Ki51CVJ7s+LkDG5bCzWhHyCrqu7DGOVDV766v0cu4xH/fbvtNpWU Rxf1gXTvUstpcNXSPutGKg+f6/Y0NEsXNySX+CUw= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Original-Received: from [213.165.168.94] ([213.165.168.94]) by web-mail.gmx.net (3c-app-mailcom-bs07.server.lan [172.19.170.175]) (via HTTP); Tue, 10 Nov 2020 11:17:22 +0100 Importance: normal Sensitivity: Normal In-Reply-To: <20201110080829.GA11023@tuxteam.de> X-UI-Message-Type: mail X-Priority: 3 X-Provags-ID: V03:K1:N/BMRE5fwwpfeM5UrnLjX1NIhYX9+A/R8qRxPiV7Zf+M7csFsqBdxvGEqX9d6HCZ4hUfQ pmiS2fsKJ9QXv2IhnEw4Y2qV/7nB+vq5a0SMnjvSUadCGtwYU9qBV/YUpTgI45IwroPneGDGQHA1 Et9AsAyqszD66fZ/HbW/W9UnRUSY1G+F9Or78uIsKv9QYoQPrOVQuN/5XwYmOx2XNw9Gj3pfpPj7 Hz/58EL0qcpIC6ESiU4LcMyERU7kLuiICaC9I5LXEcaz8ExQlSvpxZQe/OX946TwAgvzNOnp0GL9 TU= X-UI-Out-Filterresults: notjunk:1;V03:K0:IDasfu6kkRA=:am3h5RazBKSv9CHoZpqefA hcmhIiP4d/A13WbNRSaFsvcj7HeHXJ/idMRyVKZrpFDBMKsOcfY1woxwgFZEpiH6EgOiM7D0Z 0sGWPVYXrO0Vbpy9Rg5FSQpkZknkuGibIjH/TSgTJiJgZqhd7yvQ7z4s+72CiLb00F2MKgLP5 QD10bRQTZuN+thTVN4PCJpL1Q/JhFfwMEQ1aLQrfY0Xu9p0SyS5T0BL4ENZzuK/eoxY3N9e50 qPODZNombZXiV0KtYsjf9//ng5JvEsw67wy2Y2oKBp5TURWDldQ760b6urW24RJVixYCxAwpz JrPJq32P3o74UbtmB9sJiP9TMFnsbF2AERgne5H1sXVPcQd/VJTZnuRXRayDuUaXzXCvOrGmX TEApH0Y49l1E6hUsd4vgA1IztrgbBxUKUKdNPrenncwzGOk8m/zMWLy0s1j232KbULQnxP+3Z E90I6Vyz9DVmA0aK601hbrJzdwFoatIBwdDhUBaejogGdvpQoVT2ZPKGguZIPkJ5l/82hNqNS BIYwWMtzv/VNGalf2U6possgG1hqrjqSX59H/lH763TU2Vl5b2JHzJMvjbsvRMryWvrMSoqkX r4Ok/FERvFL6A= Received-SPF: pass client-ip=212.227.15.15; envelope-from=dimech@gmx.com; helo=mout.gmx.net X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/10 05:17:27 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 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-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:125170 Archived-At: Many thanks Tomas, have gone though the Elisp Manual yesterday and I am getting to understand this list Ouroboros thing. :) > Sent: Tuesday, November 10, 2020 at 9:08 AM > From: tomas@tuxteam.de > To: help-gnu-emacs@gnu.org > Subject: Re: Cycle Org Shift Select > > On Mon, Nov 09, 2020 at 11:49:33PM +0100, Christopher Dimech wrote: > > What is the meaning of the '.' in '#1=3D(nil t always . #1#)? > > This means that the last cdr in that list isn't nil, as "decent, > normal lists" (aka "proper lists") have, but a reference to something, > in this case to the list's head (#1#), which you have taken previously, > in #1=3D. Making the whole thing an Ouroboros [1]. > > In box-and-pointer-ish, the list '(nil t always) looks like so > (WARNING: psychedelic effects guaranteed when using variable-pitch > fonts. But who does that, anyway?): > > +-----+--+ +--+--+ +--+-----+ > | nil | | ---> | | | ---> | | nil | > +-----+--+ +--+--+ +--+-----+ > | | > v v > 't 'always > > Note how the list ends with a pair whose cdr is nil. > > The dot notation allows you to fill both slots of a pair (car > and cdr), thus putting something other than the "link to next" > in a cdr, creating an improper list; the reference notation > (that #...=3D and #...#) allows you to take a ref at some place > and use it later. That's what your above monster looks like > in box-and-pointer: > > +---------------------------------+ > | | > v | > +-----+--+ +--+--+ +--+--+ | > | nil | | ---> | | | ---> | | | ---+ > +-----+--+ +--+--+ +--+--+ > | | > v v > 't 'always > > > So if you run *that* list along (by doing cdr), you'll run > in circles, over and over again. That was this device's > intention, anyway, if I followed along correctly. > > Cheers > > [1] https://en.wikipedia.org/wiki/Ouroboros > - t >