From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Newsgroups: gmane.emacs.help Subject: Re: Cycle Org Shift Select Date: Tue, 10 Nov 2020 09:08:29 +0100 Message-ID: <20201110080829.GA11023@tuxteam.de> References: <87pn4mgufa.fsf@web.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Qxx1br4bt0+wmkIi" Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="20346"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mutt/1.5.21 (2010-09-15) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Nov 10 09:09:35 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 1kcOid-0005At-G3 for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 10 Nov 2020 09:09:35 +0100 Original-Received: from localhost ([::1]:50288 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kcOic-0008Ss-Ev for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 10 Nov 2020 03:09:34 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:34240) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kcOhr-0008SV-1E for help-gnu-emacs@gnu.org; Tue, 10 Nov 2020 03:08:47 -0500 Original-Received: from mail.tuxteam.de ([5.199.139.25]:39265) by eggs.gnu.org with esmtps (TLS1.2:DHE_RSA_AES_128_CBC_SHA1:128) (Exim 4.90_1) (envelope-from ) id 1kcOho-0007uY-Fy for help-gnu-emacs@gnu.org; Tue, 10 Nov 2020 03:08:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=tuxteam.de; s=mail; h=From:In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject:To:Date; bh=mDfhsvSTVA00jUdVvglhXti1g442pIopij5mqTZ4rl4=; b=kfONXw1d+YGNIGyQ3TrJGQwGi58c5DNxzVo5PxguWDyWBfYHpIfzxKt+07dVGLkJV/4A5H4bOVIuxQgUyYt0RZtcqm+KuIsQDfXvlVM8jQi4aHV+sFx8TH25d2T6W7jlqtPHwG4BEDzKJP+Py6TukL9QXQY6tL+2eVmftJlOb3K8t6b50YBxqLxPeMkCV3dUAT+bpXY+g2bjwxVakTFUstPHJ0lLWwbg2cf8nM7+b8Bbca+ECLDzf5rRvt9JJssINmdsxoyZYNM+Sp1atIos76tPpm6rdQ5vXqQPN2lj9Wbmz48KSHRZMSdjw5Bmm6X146JX+J87DPWf5GVAlNOBmg==; Original-Received: from tomas by mail.tuxteam.de with local (Exim 4.80) (envelope-from ) id 1kcOhZ-0003Bd-Lf for help-gnu-emacs@gnu.org; Tue, 10 Nov 2020 09:08:29 +0100 Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=5.199.139.25; envelope-from=tomas@tuxteam.de; helo=mail.tuxteam.de X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/10 03:08:30 X-ACL-Warn: Detected OS = Linux 3.1-3.10 [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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:125167 Archived-At: --Qxx1br4bt0+wmkIi Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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?): +-----+--+ +--+--+ +--+-----+ =20 | nil | | ---> | | | ---> | | nil | +-----+--+ +--+--+ +--+-----+ =20 | | 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 | | ---> | | | ---> | | | ---+ +-----+--+ +--+--+ +--+--+ =20 | | 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 --Qxx1br4bt0+wmkIi Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAl+qSn0ACgkQBcgs9XrR2kaJHgCfewSgthTyVnfRw7/BjkcTsEx4 qKsAn3l3v+7MxYU8QYNQWszSTzNAQ+wf =88MG -----END PGP SIGNATURE----- --Qxx1br4bt0+wmkIi--