Proposal to solve the `EitherT` problem.

[David Virebayre]

2013/8/13 Henning Thielemann <schlepptop at henning-thielemann.de>:
> Am 13.08.2013 20:31, schrieb Gabriel Gonzalez:

>> I'm still in favor of adding `EitherT` to `transformers` in addition to
>> `ErrorT`.  The only person who disagreed the last discussion was Ross,
>> so it's a matter of convincing him.

> I also prefer Ross' suggestion of Except/ExceptT.
> Using Either as a monad for me is abuse, as is defining Monad for pairs, Num
> for functions, Ord for complex numbers etc.

I find Henning Thielemann and Ross Paterson's arguments very convicing too.