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Gavin Bisesi
@Daenyth
I'm not sure there's a typeclass describing unfold
Ivano Pagano
@ivanopagano
I guess not, indeed
I guess this means that I may stop searching
Rob Norris
@tpolecat
List is already traversable … what is your intent?
Gavin Bisesi
@Daenyth
@tpolecat I think he wants def unfoldWhatever[F[_]: Foldable, G[_]: ?Unfoldable?, A](as: F[A]): G[A] ( @ivanopagano is that right)
something something recursion schemes?
Greg Pfeil
@sellout
đź‘€
Rob Norris
@tpolecat
Haha
We don’t have such a thing but you can do it with Foldable and MonoidK
JsonFn
@JsonFn
When trying Applicative example e.g. Applicative[List].product(List(3), List(4)).flatten It throws No implicit view available from (Int, Int) => scala.collection.GenTraversableOnce[B]. How can I create GenTraversableOnce? The only way is to create a new such instance? for instance new GenTraversableOnce { ... }
Fabio Labella
@SystemFw
that's a red herring
Rob Norris
@tpolecat
What is your intent? The product is a List of pairs of Int.
Fabio Labella
@SystemFw
there no implicit views needed in cats, you must be getting flatten from collections
Rob Norris
@tpolecat
If you want a list of Int you can flatMap the pairs to lists.
Fabio Labella
@SystemFw
random info: Applicative cannot flatten, you need monad. you can use syntax and do (List(3), List(4)).product
or mapN and many other things
JsonFn
@JsonFn
@SystemFw no wonder. my fault. thanks for the advice.
Soren
@srnb_gitlab

wonder why you'd want F[A] => F[Boolean] instead of A => F[Boolean] tho

@oleg-py I'm checking the state of whether creating a Resource[F, ?] failed or not

So I want to use dropWhileF(_.attemptT.isLeft)
then take the head on it
Jakub Kozłowski
@kubukoz

We don’t have such a thing but you can do it with Foldable and MonoidK

MonoidK or Alternative?

Soren
@srnb_gitlab
@Daenyth On the usage of fs2, how should I get the head from the stream? Is calling compile in the middle of my program ok?
Jakub Kozłowski
@kubukoz
it's fine (stream.head.compile.lastOrError should do it)
Gavin Bisesi
@Daenyth
Sure. You can .head.compile.last and get F[Option[A]]
Jakub Kozłowski
@kubukoz
or that yeah
Gavin Bisesi
@Daenyth
But if your F[A] is a resource you don't want this
because you've lost release
Jakub Kozłowski
@kubukoz
I think he doesn't have a resource since there's a List[A] mentioned forget it, I can't read again today
Soren
@srnb_gitlab
Yeah, I need the first Resource[F, Connection[F]] that doesn't encounter an error
Gavin Bisesi
@Daenyth
that's a bit trickier
and when I say a bit... massively
uh
how about
Jakub Kozłowski
@kubukoz
hmm
Soren
@srnb_gitlab
It's a List[ServerEndpoint] that I'm trying to find the first valid one
Jakub Kozłowski
@kubukoz
stream.head.compile.resource.last.flatMap(_.sequence)
not sure but according to my knowledge resource might help there
Gavin Bisesi
@Daenyth
val operation = connRes.use(stuff)
Stream.retry(connRes, ...)
oh I see, you don't have Resource, you have List[A] and A => Resource ?
that seems easier
Soren
@srnb_gitlab
Yes
Gavin Bisesi
@Daenyth
Hmm, the failure handling is a little trickier though
like
you can't just return a Resource
Soren
@srnb_gitlab
I have List[ServerEndpoint], ServerEndpoint => Resource[F, Connection[F]], and I want the first Resource[F, Connection[F]] that doesn't fail to connect
Gavin Bisesi
@Daenyth
because in order to make sure you didn't fail you need to run acquire
so since you need to run acquire you should take your use as an input 
val getFirstResult =
  Stream.emits(inputs)
    .evalMap(resourceFor(input).use(operation).attempt)
    .dropWhile(_.isLeft)
    .take(1)
Soren
@srnb_gitlab
operation is a function passed in, correct?
Gavin Bisesi
@Daenyth

if you want to find the first working resource, acquire, and keep it open, that sucks, and is harder - please see my blog post on concurrent resource caching and adapt for your needs. https://gist.github.com/Daenyth/28243952f1fcfac6e8ef838040e8638e

operation is a function passed in, correct?

Yes