From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: "Stephen J. Turnbull" Newsgroups: gmane.emacs.devel Subject: Re: The purpose of makunbound Date: Fri, 20 Feb 2015 11:58:14 +0900 Message-ID: <87egplffw9.fsf@uwakimon.sk.tsukuba.ac.jp> References: NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 X-Trace: ger.gmane.org 1424401122 8106 80.91.229.3 (20 Feb 2015 02:58:42 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 20 Feb 2015 02:58:42 +0000 (UTC) Cc: emacs-devel@gnu.org, Stefan Monnier , Richard Stallman To: Kelly Dean Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Feb 20 03:58:32 2015 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YOdnU-00027w-24 for ged-emacs-devel@m.gmane.org; Fri, 20 Feb 2015 03:58:32 +0100 Original-Received: from localhost ([::1]:58910 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YOdnS-0000SJ-VP for ged-emacs-devel@m.gmane.org; Thu, 19 Feb 2015 21:58:30 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:44604) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YOdnP-0000SB-3L for emacs-devel@gnu.org; Thu, 19 Feb 2015 21:58:27 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YOdnL-0003I9-RS for emacs-devel@gnu.org; Thu, 19 Feb 2015 21:58:27 -0500 Original-Received: from shako.sk.tsukuba.ac.jp ([130.158.97.161]:58645) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YOdnL-0003Hb-IZ; Thu, 19 Feb 2015 21:58:23 -0500 Original-Received: from uwakimon.sk.tsukuba.ac.jp (uwakimon.sk.tsukuba.ac.jp [130.158.99.156]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by shako.sk.tsukuba.ac.jp (Postfix) with ESMTPS id B9B421C3892; Fri, 20 Feb 2015 11:58:14 +0900 (JST) Original-Received: by uwakimon.sk.tsukuba.ac.jp (Postfix, from userid 1000) id 96FD41A26E3; Fri, 20 Feb 2015 11:58:14 +0900 (JST) In-Reply-To: X-Mailer: VM undefined under 21.5 (beta34) "kale" 83e5c3cd6be6 XEmacs Lucid (x86_64-unknown-linux) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 130.158.97.161 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 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.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:183315 Archived-At: Kelly Dean writes: > The implementation does see [the two forms of unbinding] as > different, I don't understand what you mean. The unbinding is the same, and has the conventional semantics: this value can no longer be accessed by that name (== symbol). Exit from let has *additional semantics* of restoring the previous binding. The void or unbound pseudo-value is an implementation detail, useful in so-called shallow-binding implementations. You can't observe that symbol from Lisp without making an end-run around the Lisp engine (eg, via an FFI). It's uninterned so it's not possible to find it and then store it somewhere, and all slot-accessing internal functions check for it and error if it's found. > In contrast, if makunbound didn't work for let-bound or > buffer-local variables, If there's a reason for makunbound in the top-level environment, the same reason will apply to let-bound environments. I can't support your proposal to error on makunbound of let-bound variables.