On 06/19/2015 01:23 AM, David Johnson wrote:
You could constrain d in the type signature of SC.
{-# LANGUAGE GADTs #-}dataS e whereSC::Show d => d -> e ->S e
instanceShow e =>Show (S e) whereshow (SC x y) = show x ++ show y
Hi David, thanks for the rapid answer. But, I also want an instance for Num like: instance Num e => Show (S e) where (SC x1 y1) + (SC x2 y2) = SC (x1+x2) (y1+y2) And in the future I will want another instance that constraints to the `e` type. And the client of the library will implement his own instances or functions. So I think it wont be nice to constraint `Show d` in the type signature of the `SC` constructor. -- Leza Morais Lutonda, Lemol-C Electronic and Telecommunication Engineer Software Development and Architecture Enthusiast http://lemol.github.io 50 Aniversario de la Cujae. Inaugurada por Fidel el 2 de diciembre de 1964 http://cujae.edu.cu