Le mer. 27 janv. 2016 à 14:29, Guillaume Bouchard < guillaum.bouchard+haskell@gmail.com> a écrit :
However I discovered the `ConstraintKinds` extension which may improve the situation.
It does, it is in fact quite easy in modern Haskell to write a typeclass analogue to a functor but which may have further constraints on the types contained. But it won't be the historic "Functor" typeclass which is ubiquitous in the Haskell packages... {-# LANGUAGE ConstraintKinds, TypeFamilies #-} module ConstrainedFunctor where import GHC.Exts (Constraint) import qualified Data.Vector.Unboxed as V class CFunctor f where type FConstraint f x :: Constraint type instance FConstraint f x = () cfmap :: (FConstraint f a, FConstraint f b) => (a -> b) -> f a -> f b instance CFunctor V.Vector where type FConstraint V.Vector x = V.Unbox x cfmap f v = V.map f v doubleVector :: V.Vector Int -> V.Vector Int doubleVector = cfmap (*2) -- Jedaï