Kawa really doesn't like this kind of form:

(define (skip x)
    ...
    (set skip #f)
    ...)

/tmp/gen.scm:258:32: warning - type boolean is incompatible with required type function

It warns at compile-time, and fails at run-time.
(It probably shouldn't do the latter...)

So I looked at the offending code.  The attached solution is shorter,
seems cleaner, and is likely to be more efficient.
--
	--Per Bothner
xxxxxx@bothner.com   http://per.bothner.com/