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From: Swami Tota Ram Shankar <tota_...@india.com>
Newsgroups: gnu.emacs.help,comp.lang.lisp,comp.emacs,gnu.emacs,comp.lang.scheme
Subject: Re: Nested mapcar* application and possibly some variation of Y combinator
Date: Fri, 26 Aug 2011 01:18:07 -0700 (PDT)
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On Aug 26, 12:24=A0am, Swami Tota Ram Shankar <tota_...@india.com>
wrote:
> On Aug 26, 12:07=A0am, Barry Fishman <barry_fish...@acm.org> wrote:
>
>
>
> > On 2011-08-25 11:44:17 EDT, Barry Fishman wrote:
>
> > > On 2011-08-25 11:09:20 EDT, Barry Fishman wrote:
> > > And maybe, since this function is only useful processing trees:
>
> > > (defun maptree (fun tree)
> > > =A0 (lexical-let ((sfun nil)
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 (afun fun))
> > > =A0 =A0 (setq sfun #'(lambda (x)
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0(if (sequencep x)
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0(mapcar sfun x)
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0(funcall afun x))))
> > > =A0 =A0 (funcall sfun tree)))
>
> > I thought I was done with this, but at 3 AM I woke up thinking,
> > "This no longer requires a closure", =A0so it can be simplified to:
>
> This means that you dont have a strong enough intuition about the
> lexical closures. I studied it a year ago in connection with
> javascript. Javascript has scope chaining. In C you can create a local
> scope using {}, but this is not the case in javascript. All the
> variables from the outside are visible inside unless over-ridden by a
> local redefinition. This is called scope chaining. In JS, lexical
> scoping means, that functions create their environment (scope) ie
> symbol-value pairs in the table when they are defined and not when
> they are executed. I guess, I need someone to discuss with slightly
> different elementary series of examples to make it clear and crisp. It
> shall help the author also.

useful link on lexical closures

http://c2.com/cgi/wiki?LexicalClosure

>
> > (defun maptree (func tree)
> > =A0 (let ((sfunc nil))
> > =A0 =A0 (setq sfunc (lambda (x)
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (if (sequencep x)
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (mapcar sfunc x)
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (funcall func x))))
> > =A0 =A0 (funcall sfunc tree)))
>
> > --
> > Barry Fishman