Add MonadUnliftIO instance for InputT

[quickdudley]

No description provided.

[judah]

Thank you for the patch. Unfortunately, I don't think it's feasible for us to support it at this time. Haskeline is a core dependency of GHC and included as part of its build. As a result, I tend to be pretty conservative about adding more dependencies to avoid increasing complexity in GHC. See in particular the recent effect of adding a dependency on exceptions: https://gitlab.haskell.org/ghc/ghc/issues/16752

As an alternative, we could consider developing a package with this change as an orphan instance. If that requires exposing InputT's constructor, maybe we could do so in a System.Console.Haskeline.Internal module, with a suitable warning about the API not being as stable. Let me know if you're interested in taking that on.

[quickdudley]

I'm willing to take that on.

[infinity0]

An alternative to exposing the constructor is to just define askUnliftIO and withRunInIO here as top-level functions. The orphan instance definition in another package can then just re-use these functions.

[judah]

Thank you for following up on this (and to @infinity0 for the suggestion)! This change looks good to me; I just have one small request for the documentation.

[judah]

Could we elaborate the comment a little more, indicating that it's intended for use with other monad transformer stacks? Maybe even call out the unliftio package explicitly as an example?

[judah]

Thanks again for this improvement!