rfc: include bimap into Data.Either

[Herbert Valerio Riedel]

On 2014-04-18 at 22:54:18 +0200, Tobias Florek wrote:
> i propose to include the following functions into Data.Either.
>
>     mapLeft :: (a->b) -> Either a c -> Either b c
>     mapLeft f = bimap f id
>
>     bimap :: (a -> b) -> (c -> d) -> Either a c -> Either b d
>     bimap f g = either (Left . f) (Right . g)

as these are just specialized versions of existing functions, i.e.

  mapLeft = Control.Arrow.left

  bimap = Control.Arrow.(+++)

I'm not convinced we should add these