Still exploring monads. I don't understand why the type signature for double is OK, but not the one for iota. Michael ================= --double :: (Int a) => a -> Maybe b --double x = Just (x + x) iota :: (Int a) => a -> [b] iota  n = [1..n] --usage: [3,4,5] >>= iota --should produce [1,2,3,1,2,3,4,1,2,3,4,5]