[Haskell-cafe] automatically deriving Map and Filter on datatypes
jonathanccast at fastmail.fm
Thu Jun 5 10:40:53 EDT 2008
On 5 Jun 2008, at 1:39 AM, 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?
class Functor (f :: * -> *) where ...
PS Why isn't Functor derivable?
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