[plt-scheme] Null syntax / Conditional definition

On Sat, 18 Jun 2005, Jordan Johnson might have said:

> 
> On Saturday, June 18, 2005, at 01:17  PM, Mike wrote:
> >>|(define-syntax (OS-dep stx)
> >>|    (syntax-case stx ()
> >>|      [(_ u w m)
> >>|       (case (system-type)
> >>|         [(unix)    #'u]
> >>|         [(windows) #'w]
> >>|         [(macosx) #'m])]))
> >
> >What's the meaning of '_' in the expression after syntax-case?
> 
> Shorthand for "name of the macro", as I read it.  In the case above 
> you'd have
> 	(OS-dep (define foo 1) (define foo 2) (define foo 3))
> for example, so
> 	_	binds to OS-dep
> 	u	binds to (define foo 1)
> 	w	binds to (define foo 2)
> and
> 	m	binds to (define foo 3)
> 
> There's nothing magical about "_" AFAIK; you could just as easily put 
> some other identifier there, and it should work.  Consider:
> 
> 	(define-syntax (foo x) (syntax-case x () ((bar x) #'(cons 'bar 'x))))

Great, thanks.