Hi, I was thinking about some of my code today, and I realised that where I have an arrow in my code, A b c, the type (A b) is also a functor. The definition is (see http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Arrow.htm...): fmap = (^<<) -- Or, in long form: fmap f x = arr f <<< x Out of curiosity, and since this is a typical haskell-cafe question, does this definition of fmap hold for all arrows? And is there a wiki page somewhere that has a table of all of these Haskell type-classes (Functor, Monad, Category, Arrow, Applicative and so on), and says that if you are an instance of class A you must have some corresponding instance of B? (e.g. all Monads are Functors and Applicatives) I'm fairly certain my arrow isn't a Monad or Applicative, although of course it must be a Category, given the type-class dependency, but it would be nice when using one of these things to see what other instances you should automatically supply. Thanks, Neil.