On Jun 14, 2009, at 10:46 PM, Abdulaziz Ghuloum wrote:
BTW, this is not a 100% correct definition of when-bound, but ...
The more I stare at it, the more it looks correct.
Here's a more self-documenting version of the same code:
(define-syntax when-bound
(lambda (x)
(define unbound?
(let ([empty-ctxt (car (generate-temporaries '(t)))])
(lambda (id)
(let ([unbound-id
(datum->syntax empty-ctxt (syntax->datum id))])
(free-identifier=? id unbound-id)))))
(syntax-case x ()
[(_ (id) e* ...)
(if (unbound? #'id)
#'(begin)
#'(begin e* ...))])))
Aziz,,,
