I created an example app for my upcoming Arrow tal...

# arrow

[Attila Domokos]

I created an example app for my upcoming Arrow talks leveraging EitherT<ForIO> extensively. I really like the code I have, however, some people are lost with monad transformers. I tried to dummy down the example to use IO<Either<A, B>, however, the code is not very attractive. Check out the functions run using EitherT and run2 using IO<Either> types. Why do I need to call unsafeRunSync in function run2 to call that code? Does flatMap invalidate the fx context? https://github.com/adomokos/kotlin-sandbox/blob/ad/io-either/src/main/kotlin/sandbox/explorer/App.kt#L65-L98

[simon.vergauwen]

Hey,
Awesome to hear you’re using Arrow Fx with MTL. I wrote the Concurrent instances for EitherT a while ago, they should be released soon.

Anyhow, it’s hard to see what’s going on. You should be able to call ! for those `IO`s within that IO.fx block, but I am unsure what is going on with the transaction block. It seems to be missing in the EitherT alternative

[Jannis]

At https://github.com/adomokos/kotlin-sandbox/blob/ad/io-either/src/main/kotlin/sandbox/explorer/App.kt#L76
you probably need to call traverse followed by bind().flatten() on the either, because you cannot bind inside Either.flatMap as you are technically no longer in fx comprehension scope.

[Jannis]

The first unsafeRunSync is probably as already mentioned because transaction messes with scope, it should work unless transaction introduces suspend or something

[simon.vergauwen]

You can extract IO<Either<E, A>> from EitherT by simply calling value() that way you can still use EitherT nested in functions or only in places where you wants it’s powers over IO<Either<E, A>> but you can perfectly mix-and-match them.

[raulraja]

I’m not sure if you are on time to use the Bifunctor IO snapshot on your examples but if you are that will show more power than any EitherT transformers.

[Attila Domokos]

Can I see some code sample of Bifunctor IO?

[raulraja]

https://github.com/arrow-kt/arrow/compare/0.11.0/bio

[raulraja]

If you are meeting with Simon he can also share more info them but that branch shows how IO has now two type args and additional combinators

[Attila Domokos]

I'll ask him about it! Thanks!