[Haskell-beginners] Map on Nested Lists

Hi, I'm trying to write a generalization of the map function that operates on nested lists, e.g. [[a]] or [[[a]]]. (It should map all elements of type a (not list) with f) I was thinking of something along these lines: mapN f *list of type [a] (where a is not a list type)* = map f l mapN f l = (mapN f (head l)):(mapN f (tail l)) Any suggestions about how to go about this? Many thanks, Ben -- Ben Derrett Department of Mathematics MIT Class of 2012 bderrett@mit.edu