restructuring the mtl

[Ross Paterson]

On Mon, Mar 26, 2007 at 08:18:53PM +0100, Neil Mitchell wrote:
> >The plan is to split Control.Monad.Identity, Control.Monad.Trans and
> >Control.Monad.Trans.* off into a separate (portable) package.
> 
> Isn't Control.Monad.Identity very simple, very short and totally
> Haskell 98? Why can't it go in the standard MTL?

The point was to make all the above modules pure Haskell 98, leaving
a non-portable (but mostly backward-compatible) mtl package as a thin
wrapper.