Hi, I don't understand what's taking place here. From Hoogle: ================= liftM2 :: Monad  m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r Promote a function to a monad, scanning the monadic arguments from left to right. For example,     liftM2 (+) [0,1] [0,2] = [0,2,1,3]     liftM2 (+) (Just 1) Nothing = Nothing ================= What does it mean to "promote a function to a monad?" It would seem that the monad values must understand the function that's being promoted, like Ints understand (+). Prelude Control.Monad> liftM2 (+) (Just 1) (Just 1) Just 2 But how does one add [0,1] and [0,2] to get [0,2,1,3]? Michael