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Today's Topics:
1. Re: Custom type classes (Chadda? Fouch?)
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Message: 1
Date: Thu, 28 Jan 2016 20:14:21 +0000
From: Chadda? Fouch? <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Custom type classes
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Le mer. 27 janv. 2016 ? 14:29, Guillaume Bouchard <
[email protected]> a ?crit :
> 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)
--
Jeda?
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