[Haskell-cafe] Is it possible to represent such polymorphism?

[Victor Gorokgov]

02.10.2011 19:55, David Barbour пишет:
> Use TypeFamilies.
>
>
> {-# LANGUAGE TypeFamilies #}
> ...
> type family FType a :: *
> type instance FType Char = Float
> type instance FType Double = Int
>
> class ExampleClass a where
> f :: a -> FType a
>

Better to include type in class.

class ExampleClass a where
type FType a
f :: a -> FType a

instance ExampleClass Char where
type FType Char = Float
f char = ...