Re: [Haskell-cafe] Problems with type families

9 Jul 2015

      On 07/08/2015 11:30 PM, Silvio Frischknecht wrote:
...
Anyway a workaround would be.
class SignalT t e
     where
         transform :: e -> t -> TFunIn t e -> TFunOut t e
instance (
     SignalT t1 e,
     SignalT t2 e,
     TFunOut t2 e ~ TFunIn t1 e
     ) => SignalT (ComposeT t1 t2) e
     where
         transform _ _ x =
             (transform (undefined :: e) (undefined :: t1))
             (transform (undefined :: e) (undefined :: t2))
             (x :: TFunIn (ComposeT t1 t2) e)
I got it! This solution is nice for me, and helped me to understand how 
to tell the compiler about the `e` type.
Thank you Silvio!

-- 
Leza Morais Lutonda, Lemol-C
http://lemol.github.io

50 Aniversario de la Cujae. Inaugurada por Fidel el 2 de diciembre de 1964  http://cujae.edu.cu