2) the types are not general enough : like zip you should be able to take functions f : a->b->c instead of what intersectionWith forces you to do (f: a->b->a).

According to my documentation, the type of intersectionWith *is* (f :: a -> b -> c). On another note, with respect to my proposed change: I concede that it might be too general for some people. Here's a simpler change that I'd like: to be able to project information out of a value and modify it simultaneously, so simply alterProject :: (Maybe a -> (z, Maybe a)) -> k -> Map k a -> (z, Map k a ) for a specific key. and perhaps something similar for the min/max operations. I'd very much like to be able to do more general things than just min/max operations with this sort of generality -- hence the Alternative approach in my original proposal. Louis Wasserman wasserman.louis@gmail.com http://profiles.google.com/wasserman.louis