Re: [Haskell-cafe] automatically deriving Map and Filter on datatypes etc.

Thomas Davie wrote:

Even deriving an instance of Functor seems rather implausable, what should it do for

data Wierd a b = Nil | A a (Wierd a b) | B b (Wierd a b)

Should fmap's function argument operate on 'a's, 'b's, or both?

But for many datatypes it is quite natural. Just google for "theory of containers". Ciao, Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de