From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: "Pascal J. Bourguignon" Newsgroups: gmane.emacs.help Subject: Re: Real-life examples of lexical binding in Emacs Lisp Date: Sat, 30 May 2015 17:50:16 +0200 Organization: Informatimago Message-ID: <878uc66p53.fsf@kuiper.lan.informatimago.com> References: <7b497693-bd08-45c0-99f4-e70836437535@googlegroups.com> <87h9qu6xh8.fsf@kuiper.lan.informatimago.com> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: ger.gmane.org 1433001321 12308 80.91.229.3 (30 May 2015 15:55:21 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 30 May 2015 15:55:21 +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 17:55:19 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 1Yyj6U-0005ik-H7 for geh-help-gnu-emacs@m.gmane.org; Sat, 30 May 2015 17:55:18 +0200 Original-Received: from localhost ([::1]:39755 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yyj6T-0008TB-CW for geh-help-gnu-emacs@m.gmane.org; Sat, 30 May 2015 11:55:17 -0400 Original-Path: usenet.stanford.edu!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 68 Original-X-Trace: individual.net YElJKWw6yIfEXXkzJ/xmGQ7GFkSv5KnFK0oV4BqkhqbYQ9ZJ4Z Cancel-Lock: sha1:Y2I2YjA4YTVkNzE3NzMwZGE0NzZhMzY1OGZhNjYxNmRjZDE4OGU4NA== sha1:cdeseZ5wTSJrS8NHcBGkDJfLcYo= Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwAQMAAABtzGvEAAAABlBMVEUAAAD///+l2Z/dAAAA oElEQVR4nK3OsRHCMAwF0O8YQufUNIQRGIAja9CxSA55AxZgFO4coMgYrEDDQZWPIlNAjwq9 033pbOBPtbXuB6PKNBn5gZkhGa86Z4x2wE67O+06WxGD/HCOGR0deY3f9Ijwwt7rNGNf6Oac l/GuZTF1wFGKiYYHKSFAkjIo1b6sCYS1sVmFhhhahKQssRjRT90ITWUk6vvK3RsPGs+M1RuR mV+hO/VvFAAAAABJRU5ErkJggg== X-Accept-Language: fr, es, en User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) Original-Xref: usenet.stanford.edu gnu.emacs.help:212402 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:104686 Archived-At: 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. >> 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. 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. -- __Pascal Bourguignon__ http://www.informatimago.com/ “The factory of the future will have only two employees, a man and a dog. The man will be there to feed the dog. The dog will be there to keep the man from touching the equipment.” -- Carl Bass CEO Autodesk