From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Jean Louis Newsgroups: gmane.emacs.help Subject: Re: even elder races get tired of waiting Date: Mon, 22 Mar 2021 10:54:21 +0300 Message-ID: References: <87v99lr26w.fsf@zoho.eu> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="35762"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mutt/2.0.6 (2021-03-06) Cc: help-gnu-emacs@gnu.org To: Jude DaShiell Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Mon Mar 22 09:01:56 2021 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 1lOFVc-0009DR-P1 for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 22 Mar 2021 09:01:56 +0100 Original-Received: from localhost ([::1]:51958 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lOFVb-0006UI-Qu for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 22 Mar 2021 04:01:55 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:51850) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lOFS9-0004PZ-L1 for help-gnu-emacs@gnu.org; Mon, 22 Mar 2021 03:58:23 -0400 Original-Received: from stw1.rcdrun.com ([217.170.207.13]:38085) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lOFS7-0003JW-7E for help-gnu-emacs@gnu.org; Mon, 22 Mar 2021 03:58:21 -0400 Original-Received: from localhost ([::ffff:41.202.241.53]) (AUTH: PLAIN securesender, TLS: TLS1.3,256bits,ECDHE_RSA_AES_256_GCM_SHA384) by stw1.rcdrun.com with ESMTPSA id 000000000001E0AB.0000000060584E17.00003B33; Mon, 22 Mar 2021 00:58:15 -0700 Mail-Followup-To: Jude DaShiell , help-gnu-emacs@gnu.org Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=217.170.207.13; envelope-from=bugs@gnu.support; helo=stw1.rcdrun.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_PASS=-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:128498 Archived-At: * Jude DaShiell [2021-03-21 22:24]: > Use of cal with a month number and a year number to get a weekday of a > particular date can make work a little easier. How to do that? > This is for really long time periods and only inside the gregorian calendar > constraints since outside of those constraints things get really wild as a > result of compound errors. > With that weekday in mind subtracting a year when you won't land in a leap > year or adding a year when you won't land in a leap year, subtract or add > one weekday to get the correct weekday for that date in those years. If you > will land in a leap year, subtract or add two weekdays to get the correct > weekday. Modulus the weekday by 7 to keep it in whichever range you prefer > to use.. I would like to use Emacs functions to calculate the new DATE after SOME NUMBER OF DAYS from STARTING DATE. For leap years it looks like PostgreSQL isdoing it right: (defun days-from (from-date to-date) "Returns days passed from FROM-DATE to TO-DATE in format YYYY-MM-DD." (string-to-number (string-trim (shell-command-to-string (format "psql -Aqtc \"SELECT abs('%s'::date - '%s'::date)\"" to-date from-date))))) (days-from "2020-02-28" "2020-03-01") => 2 (days-from "2021-02-28" "2021-03-01") => 1