Proposal: merge either into transformers

Erik de Castro Lopo mle+hs at
Mon Jan 2 18:58:18 UTC 2017

Edward Kmett wrote:

> I sympathize. If you feel the need for those combinators, you can talk to
> Ross to try to get him to add them to the library.

Where/how is transformers even maintained. The github mirror at:

offers no clue.

> (Well, secondEitherT is already fmap, of course.)

Yes, still a little embarrased about that :).

> When the ExceptT API was crafted, it pretty much
> tried to follow the API of the rest of transformers, and didn't really take
> any of the extra combinators we had in the either package into account. =/

That was unfortunate.

> You might have a hard time getting the last one adopted, though, due to the
> dependency on exceptions taking the API into "non-standard" territory.

What is the problem here, the `Exception` constraint, the `MonadCatch`
constraint or both?

> Unfortunately, even if Ross adds them, I have no way to supply them in
> transformers-compat when used with middle versions of transformers that
> have ExceptT, but not those combinators, so the compatibility hack I offer
> will suffer a bit.

Can't be done even with CPP?

Erik de Castro Lopo

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