24 Jul
2010
24 Jul
'10
10:30 a.m.
On Sat, Jul 24, 2010 at 4:08 PM, aditya siram
I wouldn't-it was a bad example. My only point was that because of the way (>>=) is implemented for lists the order of the arguments 'a' and 'b' in 'liftM2 f a b' matters.
-deech
No, it's not. The type of liftM2 makes this clear: liftM2 :: (Monad m) => (a -> b -> r) -> m a -> m b -> m r The arguments to the function *must* come in the right order, because there is no way to match (a) with (m b) or (b) with (m a). Since liftM2 is parametrically polymorphic in (a) and (b), it can't behave differently in the case where (a = b). --Max