Data.IntMap: intersection function not sufficiently polymorphic

[Axel Simon]

Hi,

the function

intersectionWith :: (a -> b -> a) -> IntMap a -> IntMap b -> IntMap a

in Data.IntMap creates a map of elements that occur in both maps. This
function can and should return a map of an arbitrary third type:

intersectionWith :: (a -> b -> c) -> IntMap a -> IntMap b -> IntMap c

This also applies to Data.IntMap.intersectionWithKey. Oddly enough, this
is already fixed in Data.Map.

Discussion period one week?!

Cheers,
Axel.