On Mon, Apr 30, 2012 at 01:33:39AM -0400, wren ng thornton wrote:
Hello all,
I recently (re)noticed the following duplication:
base:Control.Applicative newtype Const a b = Const { getConst :: a } instance Functor (Const m) where... instance Monoid m => Applicative (Const m) where...
transformers:Data.Functor.Constant newtype Constant a b = Constant { getConstant :: a } instance Functor (Constant a) where... instance Foldable (Constant a) where... instance Traversable (Constant a) where... instance (Monoid a) => Applicative (Constant a) where...
I don't see any reason for this redundancy. I propose we:
(1) add the Foldable and Traversable instances to base, and (2) deprecate transformers:Data.Functor.Constant
Why do it this way? For backwards compatibility? It seems to me it would be much more consistent to remove the one in Control.Applicative and have all the fundamental functor combinators in one place. -Brent