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Message from discussion Question about scoping
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Edi Weitz  
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 More options Sep 10 2003, 6:58 am
Newsgroups: comp.lang.lisp
From: Edi Weitz <e...@agharta.de>
Date: 10 Sep 2003 12:58:15 +0200
Local: Wed, Sep 10 2003 6:58 am
Subject: Re: Question about scoping
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On Wed, 10 Sep 2003 12:51:18 +0200, jblazi <jbl...@hotmail.com> wrote:
> A few years ago there were flame wars here as to whether Scheme was
> Lisp or not and if I remember correctly, E. said at the time that
> Scheme resembled Algol more that CL as Scheme use exclusively static
> scoping (I hope I remember correctly).  I believed him of course,
> but did not fully understand what that meant.

> Is not static (or lexical) scoping generally regarded as safer and
> better than dynamic scoping? What are the advantages of dynamic
> scoping if we do not take the simplicity of implementation into
> account?

> Please try to give a simple (idiotproof) explanation.

  * (defun foo (x) (format t "Result: ~A" (* x x)))

  FOO
  * (with-output-to-string (*standard-output*) (foo 3))

  "Result: 9"

FOO is a simple function which just prints to *STANDARD-OUTPUT*. But
because *STANDARD-OUTPUT* is dynamically scoped you can easily
"redirect" FOO's output to another stream without changing FOO.

See also

  <http://www.flownet.com/gat/specials.pdf>
  <http://cl-cookbook.sourceforge.net/io.html#redir>

Edi.


 
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