Re: [Haskell-cafe] pattern matching on data families constructors

25 Apr 2013


      At Thu, 25 Apr 2013 19:08:17 +0100,
Francesco Mazzoli wrote:
...
Would you expect this to work?
...
newtype DInt a = DInt a
newtype DBool a = DBool a
type family D a
type instance D Int = DInt Int
type instance D Bool = DBool Bool
a :: D a -> a
a (DInt x) = x
a (DBool x) = x
Or even better:
...
data family D a
data instance D Int = DInt1 Int | DInt2 Int
data instance D Bool = DBool Bool
a :: D a -> a
a (DInt1 x) = x
a (DInt2 x) = x
a (DBool x) = x
Francesco