Re: while break and continue

[Kevin Ryde]

Matthias Koeppe <address@hidden> writes:
>
> I think you need a fresh catch tag for every invocation (not only for
> every macro expansion site) of WHILE.

I think this might do the trick.  A separate helper is an easy way to
keep the "key" binding from being exposed to the cond and body.

(define-macro (while cond . body)
  (define (while-helper proc)
    (do ((key (make-symbol "while-key")))
        ((catch key
                (lambda ()
                  (proc (lambda () (throw key #t))
                        (lambda () (throw key #f))))
                (lambda (key arg) arg)))))
  `(,while-helper (,lambda (break continue)
                    (,do ()
                        ((,not ,cond))
                      ,@body)
                    #t)))