Worked through <https://www.pacoworks.com/2019/12/...

# arrow

[Michael Marth]

Worked through https://www.pacoworks.com/2019/12/15/kotlin-coroutines-with-arrow-fx/ and tried to give it a shot on Android with Room (works great!) - however, I cannot get the Promise to mimic the view model lifecycle callback (as described at the end of the post):

val endPromise: Promise<ForIO, Unit> = Promise.unsafeUncancelable(IO.async()).fix()

simply does not compile.
Same for

endPromise.complete(Unit).unsafeRunAsync { }

accordigly.

fix() / unsafeRunAsync are simply not availble on the Promise instance. Any ideas?

[Jannis]

complete returns Kind<ForIO, Unit> afaik and I think you need endPromise.complete(Unit).fix().unsafeRunAsync {} fix() in this case comes from Kind<ForIO, Unit>.fix(): IO<Unit>

[Michael Marth]

Thanks, Jannis; `fix`ing it does work.

[Jannis]

Btw the fixing will sooner or later all be gone (with a compiler plugin). Right now it is a necessity to encode higher kinded types and can lead to quite a bit of confusion especially because ide's don't usually suggest it and can also take quite a while to show it as an option.

[Michael Marth]

That's good to hear - seems like the PR to natively support typeclasses in Kotlin is stuck.

[Jannis]

Well I think jb are pretty hesitant when it comes to adding features like this. Which I can understand, but it's a bit annoying for arrow. But that is also something coming as a compiler plugin. The current idea is to build a plattform for compiler plugins (arrow-meta) and build several quality of life plugins (that are hopefully not too invasive) on top of it to make arrow easier to use. This way one can also prototype some features that are added as KEEP's and test them in the wild. It's always sub-par to actual compiler support but it will be much better than nothing.