G'day all.
Quoting John Meacham
newtype deriving is really great here.
It's really great, but in the case of Silliness, I wouldn't say it's great _here_. Incidentally, getting back to the original topic, the argument of using built-in functions fails for Perhaps.
Of course, to take the most advantage of this sort of thing, you want to define your own classes for some shared syntax.
Slightly contradicting myself, here's one that I use: class TestableProperty prop a | prop -> a where is :: prop -> a -> Bool data Prime = Prime instance TestableProperty Prime Integer where is Prime x = {- detail omitted -} The only problem with this is that with the fundep, you can't do this: instance (Integral i) => TestableProperty Prime i where is Prime x = {- same detail -} Cheers, Andrew Bromage