From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Rusi Newsgroups: gmane.emacs.help Subject: Re: Real-life examples of lexical binding in Emacs Lisp Date: Sat, 30 May 2015 09:21:33 -0700 (PDT) Message-ID: References: <7b497693-bd08-45c0-99f4-e70836437535@googlegroups.com> <87h9qu6xh8.fsf@kuiper.lan.informatimago.com> <878uc66p53.fsf@kuiper.lan.informatimago.com> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 X-Trace: ger.gmane.org 1433003123 8315 80.91.229.3 (30 May 2015 16:25:23 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 30 May 2015 16:25:23 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sat May 30 18:25:21 2015 Return-path: Envelope-to: geh-help-gnu-emacs@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 1YyjZX-00082U-75 for geh-help-gnu-emacs@m.gmane.org; Sat, 30 May 2015 18:25:19 +0200 Original-Received: from localhost ([::1]:39954 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YyjZW-0006Ka-77 for geh-help-gnu-emacs@m.gmane.org; Sat, 30 May 2015 12:25:18 -0400 X-Received: by 10.68.195.166 with SMTP id if6mr16658374pbc.6.1433002894296; Sat, 30 May 2015 09:21:34 -0700 (PDT) X-Received: by 10.50.67.100 with SMTP id m4mr44856igt.12.1433002894240; Sat, 30 May 2015 09:21:34 -0700 (PDT) Original-Path: usenet.stanford.edu!h15no755209igd.0!news-out.google.com!kd3ni32208igb.0!nntp.google.com!h15no444696igd.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail Original-Newsgroups: gnu.emacs.help In-Reply-To: <878uc66p53.fsf@kuiper.lan.informatimago.com> Complaints-To: groups-abuse@google.com Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=117.195.43.191; posting-account=mBpa7woAAAAGLEWUUKpmbxm-Quu5D8ui Original-NNTP-Posting-Host: 117.195.43.191 User-Agent: G2/1.0 Injection-Date: Sat, 30 May 2015 16:21:34 +0000 Original-Xref: usenet.stanford.edu gnu.emacs.help:212404 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.14 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.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:104688 Archived-At: On Saturday, May 30, 2015 at 9:20:19 PM UTC+5:30, Pascal J. Bourguignon wrote: > Rusi writes: > > > On Saturday, May 30, 2015 at 6:20:13 PM UTC+5:30, Pascal J. Bourguignon wrote: > >> Rusi writes: > >> > >> > I'd say you are getting this from the wrong end. > >> > Today (2015) dynamic scoping is considered a bug > >> > >> "Bug" is too strong a word here. > >> > >> > >> > In 1960 when Lisp was invented of course people did not realize this. > >> > This is just a belated bug-fix > >> > >> It is actually in 1960 (or a few years after) when LISP was invented, > >> that people realized there was the so called "Funarg problem". During > >> the 60s this problem has been studied, several (faulty) solutions > >> proposed, and eventually the notions of lexical binding vs. dynamic > >> binding and environments were elaborated. > > > > I dont understand why the funarg problem is at issue here. > > > > If foo calls bar (not nested within foo) > > And bar references x which it does not define > > The natural expection is a 'Variable undefined' error. > > However in a dynamic scoping discipline, you will get the error if > > foo does NOT define x; else bar will get foo's private x. > > I dont see how this can be regarded as not buggy -- no need to bring in > > functional/higher-order aspects at all. > > It's not buggy, because it's the behavior of this tools. > > You cannot complain that chainsaw section arms and legs: this is the > behavior of chainsaws. Just learn how to use them for good use: section > only trees or zombies. > > > The funarg problem shows that what was wanted with the introduction of > lambda was not dynamic binding, but lexical binding, so that closures > could be created by lambda. Heh! If scope leaks in straightforward first-order code you say its what-you-ask-that-you-get -- chainsaw. If scope leaks (downward funarg) or breaks (upward funarg) you say the scoping is at fault. You're having it both ways aint you Pascal?! > > > >> Other languages such as Fortran and Algol had already something like > >> lexical binding, but it was actually as accidental as the dynamic > >> binding of LISP, and of no consequence, since in those languages it was > >> not possible to create closures anyways. > > > > There is somebody-or-other's law (sorry cant remember the reference) to the effect: > > When a language is designed from ground up it usually gets scoping right. > > When a language slowly evolves out of mere configuration into more and more > > features into full Turing-completeness, it invariably gets scoping wrong. > > Examples (in addition to Lisp): perl, python, lua and most famously javascript > > > > I conclude: > > a. Scoping is a much harder problem than appears at first blush > > b. Compiled languages tend to get it more right than interpreted > > When LISP was designed, the notion of scoping was just not considered. This much we can agree > It's the invention of LISP and the detection of the funarg problem that > made people think about it, and eventually invent lexical binding and > environments. Please see the Algol report www.masswerk.at/algol60/report.htm The notion of block is fundamental there In fact the scheme report RnRS used to to trace scheme's lineage as much to Algol as to Lisp. The Algol contribution was block structure.