Since I cant find an email address for you just wanted to let it be known that I have an implementation of that random number generator you linked to in your code and on your blog. I still have to hammer out some bugs but it pretty much works well. Probably should build a computational expression using the State Monad to make it a bit more beautiful but for now I am happy with what I have written and wouldn't mind sharing it with you, or anyone.

I notice that fscheck's conditional expressions aren't quite lazy enough. For example, say I have

1

let prop_foo = forAll (Gen.Int) (fun a -> false ==> prop (printf "foo\n"; true))

quickCheck prop_foo will print foo 100 times before saying that the arguments were exhausted. But if the left-hand side of ==> is false, the right-hand side shouldn't be evaluated at all!

Haskell gets around this problem by its implicit laziness (to say nothing of its referential transparency). QCheck for sml requires the arguments of ==> to be functions, and achieves its laziness that way.

Actually QCheck for sml has a slightly different design from fscheck, but the authors seem to have gotten around some of the limitations you've run into. Have you looked at it?

galen