proposal #4095: add Applicative instance for Either

[Ross Paterson]

On Mon, May 31, 2010 at 10:18:11AM -0700, Iavor Diatchki wrote:
> Are there any uses of this instance that are not related to error
> handing?  If not, I would propose that we avoid prolonging the
> confusing use of "Either" for error handling and define a separate
> type with properly labelled constructors, to be used as "Maybe" but
> with multiple reasons for failure.

We could do that, but Either would still be there, and the question of
what instances it should have would remain.  Would it really help to
withold the obvious instances?