Re: syntax-case

[Lynn Winebarger <owinebar@free-expression.org>]

On Monday 19 August 2002 09:57, Lynn Winebarger wrote:
>     Does anyone else see the following behaviour (from a Petite Chez
> session) as inconsistent?
>      I was trying to figure out how you can eagerly expand macros without
> worrying about this sort of thing, and  
       this sort of thing means the dependence of a macro expansion on a
variable binding that could change.  And apparently, plain lexical variable
bindings are not in scope in a let(rec)-syntax, but global variable bindings
are.  The last email didn't include an example of the global binding working
in a let-syntax (just in define-syntax), so here's one (again from Chez):

> (define x 5)
> (let-syntax ((foo (lambda (exp)
			(syntax-case exp ()
			  ((_ y) (with-syntax ((z (datum->syntax-object (syntax _) x)))
				   (syntax (quote (z y)))))))))
      (foo 'bar))
(5 'bar)
>

      I had thought this behaviour was part of syntax-case, but now I see it's actually part
of let(rec)-syntax.  If the lexical variables were in scope in a let(rec)-syntax, macros
would have to be re-expanded every time an expression that contained them got
executed.  I'm not sure why the same criticism doesn't hold for global variable bindings,
though.

Lynn


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