Re: library of monadic functions [was: Why no findM ? simple Cat revisited]

G'day all. On Wed, Nov 20, 2002 at 08:25:46PM +0000, Jorge Adriano wrote:

I think both versions can be very useful: findM :: (Monad m) => (a -> m Bool) -> [a] -> m (Maybe a) findM' :: (Monad m) => (a -> Bool) -> [m a] -> m (Maybe a)

I can also make a case for: findM'' :: (Monad m) => (a -> Bool) -> [m a] -> m a findM'' p [] = fail "findM'': not found" findM'' p (x:xs) = p x >>= \b -> if b then return x else findM'' p xs This goes with the philosophy that library functions shouldn't just return Maybe. Somewhere, somehow, there is a most general version of findM to be found. :-) Cheers, Andrew Bromage