Hi, regarding the (now merged) Arrow Fx Coroutines...

# arrow

[Jörg Winter]

Hi, regarding the (now merged) Arrow Fx Coroutines API, I would like to try it with 0.11.0-SNAPSHOT, specifically this monadic comprehension with Either:

suspend fun either(): Either<PersistenceError, ProcessedUser> =
  Either.fx {
    val user = !fetchUser()
    val processed = !user.process()
    processed
  }

.. so I added arrow-fx (SNAPSHOT) to my dependencies, but where does the bind-operator ! come from ? IntelliJ doesn't seem to find it.

[streetsofboston]

! is the operator fun <L,R> Either<L,R>.not(): R on the type of the receiver of the `fx`'s lambda.

It may have been deprecated, in favor of the destructuring operators.

[Jörg Winter]

Ok, mea culpa... my types were wrong, ! is working as documented now

[Jörg Winter]

it is still the not operator defined in interface BindSyntax

[simon.vergauwen]

Yes, it’s the still the same technique to expose the API but it has a different implementation now 🙂

[simon.vergauwen]

If you have any feedback we’d love to hear it 🙂

[raulraja]

We plan on replacing not for invoke so in the near future that would just be:

suspend fun foo(): Either<PersistenceError, ProcessedUser> =
  either {
    fetchUser().process()
  }

[raulraja]

because the either invoke exposed in the either block takes precedence over the suspend invoke and applies both suspend and the either comprehension

[Jörg Winter]

wow...even nicer!

[Jörg Winter]

yep, just fiddled around with Either.fx (0.11.0 snapshot).. works fine

[raulraja]

then bind, not, and others will be deprecated once we achieve this encoding

[raulraja]

no more weird operators just function application of any wrapper on its context

[raulraja]

if we achieve this it means technically you never need to use map, flatMap etc in Either

[raulraja]

just fold and either blocks

[raulraja]

same for all other datatypes since delimited continuation blocks give you direct syntax and eliminates the need for the functor and monad indirections

[raulraja]

and callback style apis

[streetsofboston]

Would we be able to call suspend functions in an either fx block, or is that reserved only for io fx blocks?

[raulraja]

you will be able to call anything anyhere

[raulraja]

since we will interleave continuation policies as if it was a monad transformer runtime without the user needing to worry about it

[raulraja]

most functions will be inlined

[simon.vergauwen]

The the tickets & projects tracking this work is already in the Arrow-core & Arrow-fx repository. You can track the efforts there, we hope to release this huge improvement to Arrow over the summer 🙂