Port additional extensions

[tmcgilchrist]

https://github.com/ambiata/x/blob/306b5bb5e3e78fd13c8beba603ca3d43b4cbfec9/x-eithert/src/X/Control/Monad/Trans/Either.hs#L111-L278

[erikd]

Some of those we already have, some under then same name (firstEitherT) and others under a different name (tryEitherT in X is basically handleEitherT).

I've been using transformers-either quite a bit and have not missed any of these. My advice would be if you think you need them, cargo-cult them into the projects where you need them and only when you have used them for a while (in a couple of different projects) add them to transformers-either.

[tmcgilchrist]

Good to know you haven't really needed any of the extra pieces, I've been in other languages more recently. I pulled joinErrors :: (Functor m, Monad m) => (x -> z) -> (y -> z) -> EitherT x (EitherT y m) a -> EitherT z m a into mismi which was using it. Happy to leave it there and see if I do find another use for it.

[erikd]

I don't have any particularly string feelings, but I do thing its a good idea make sure anything we add is genuinely useful across more than one project.