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

Janis Voigtlaender voigt at tcs.inf.tu-dresden.de
Thu Jun 5 04:49:33 EDT 2008

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

Ciao, Janis.

Dr. Janis Voigtlaender
mailto:voigt at tcs.inf.tu-dresden.de

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