On Functors - good coders code, great reuse

On Functors - good coders code, great reuse: "It's interesting how the term 'functor' means completely different things in various programming languages. Take C++ for example. Everyone who has mastered C++ knows that you call a class that implements operator() a functor. Now take Standard ML. In ML functors are mappings from structures to structures. Now Haskell. In Haskell functors are just homomorphisms over containers. And in Prolog functor means the atom at the start of a structure. They all are different. Let's take a closer look at each one."