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

[Janis Voigtlaender]

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 at tcs.inf.tu-dresden.de