Proposal: unify constant functors

[Ross Paterson]

On Mon, Apr 30, 2012 at 10:55:51AM +0100, Bas van Dijk wrote:
> On 30 April 2012 07:33, wren ng thornton <wren at freegeek.org> wrote:
> >    (1) add the Foldable and Traversable instances to base, and
> 
> +1
> 
> >    (2) deprecate transformers:Data.Functor.Constant
> 
> +1.
> 
> I assume you want to re-export Control.Applicative.Constant from
> Data.Functor.Constant and deprecate the whole module as in:
> 
> module Data.Functor.Constant
>   {-# DEPRECATED "Import Constant from Control.Applicative instead" #-}
>   ( Constant(..) ) where
> 
> import Control.Applicative

Not quite, as the one in Control.Applicative is called Const and the 
one in Data.Functor.Constant is called Constant.  I slightly prefer the
full name.  Maybe just move Data.Functor.Constant into base (removing
the copy in Control.Applicative)?