(moved reply to haskell-cafe) Hi Tobias, | data ConstInt a = Const Int | | Any ideas how to make 'ConstInt' an instance of class | Functor? What is wrong with: class Functor ConstInt where map f (Const n) = Const n ? /Koen. -- Koen Claessen http://www.cs.chalmers.se/~koen phone:+46-31-772 5424 mailto:koen@cs.chalmers.se ----------------------------------------------------- Chalmers University of Technology, Gothenburg, Sweden