kotlinlang #arrow

IO.unit
      .continueOn(<http://Uniflowdispatcher.dispatcher.io|Uniflowdispatcher.dispatcher.io>)
      .flatMap { sideEffect() }
      .unsafeRunScoped(scope) { callback ->
         // TODO
      }

Still adding IO to the combo there is not gonna make much difference given uniflow works eagerly anyways, afaik. You’ll end up needing to unsafe run the IO to enforce the state update to happen right there, @arnaud.giuliani can confirm

kluck

03/02/2020, 1:46 PM

I can't find a unsafeRunScoped method, am I missing an arrow import? (Can't find it either on the arrow website for latest stable)

Neil

03/03/2020, 3:29 PM

New to Arrow, I'm experimenting using it to replace Exceptions. Nothing async. I've a few functions that return Either<> that are called in series by a function that also returns either. If one of the called functions returns Left is there a neat way for the parent to immediately abort and return that Left?

Jakub Pi

03/03/2020, 8:17 PM

New to Kotlin and Arrow, I'm trying to unwrap a

List<Either<Throwable, C>>

to a

List<C>

so that I can pass the cleaned up values to a function. I have a solution but it looks ugly, is there a more idiomatic way? Also welcome comments about approach. Underlying motivation is to start with unvalidated inputs and then only forward the parsed and validated values down to the domain layer which does not have side effects. I will log/handle errors in the next iteration.

.fold(listOf<C>(), {acc, e -> (e.fold({null}, {it})).let {if (it!=null) acc + it else acc}})

Gopal S Akshintala

03/04/2020, 3:15 PM

Hi! I have written CFP for GHC, using Arrow-kt. Request you all to please take few minutes to review and comment, in terms of technical-correctness, ambiguity, coherence. Help me improve and spread the word about Awesome Arrow. Thanks! 🙂 http://bit.ly/cfp-top

CLOVIS

03/06/2020, 11:25 AM

Is there a way to get notified of major updates in Arrow? (as in, when it's going to be multiplatform, what's going on with Typeproofs, etc)? This channel is very spammy so it's inconvenient to know what's going on, I'd rather have an email notification once in a while or something like that

Steven Sherry

03/08/2020, 6:44 PM

Has anyone here figured out how to get jacoco to ignore inline function coverage? I’m asking here since Arrow uses inline quite a bit (and is the cause of my uncovered inline woes) and I’m sure other people in this channel have run into it. I don’t really care if it’s “scalable”, we just have arbitrary test coverage metrics in our company and I need to massage out the lack of inline function coverage of the report that ends up getting consumed by sonarqube

dnowak

03/09/2020, 1:23 PM

Hi, I have such “nice” result:

val results: List<IO<Either<ListenerError, Unit>>> = ...

and want to convert it to

IO<Either<ListenerError, List<Unit>>>

This is what I got to achieve it:

val r = results.sequence(IO.applicative()).fix().map { l ->
    l.fix().sequence(Either.applicative()).fix().map { list ->
        list.fix()
    }
}

Is there any better/nicer way?

Nikhil

03/10/2020, 2:07 PM

Hi, sorry to bother you guys this question might be asked before but i recently joined the channel so wanted to ask, Is there any ongoing/already presented proposal (KEEP) for including the arrow or some of the FP concept from arrow in the language ? If not why? Are we trying to preserve the oops nature of the Kotlin ? Why can’t we add a dual paradigm to it? or Will arrow be served as a library always ?

Chris Kruczynski

03/10/2020, 4:46 PM

Hi! Sorry for rehashing this, but I wonder if a stream will keep all reactive characteristics when I convert a Mono to IO, and then IO back to Mono. I suppose it will as they are lazy-evaluated, but I want to double check

Gopal S Akshintala

03/12/2020, 12:14 PM

Hi, I have a requirement to make use of two typeclasses

Async<F>, ApplicativeError<S, Nel<E>>

. I achieved it as below:

interface RepoTC<F> : Async<F> {
    fun User.isUserCityValid(): Kind<F, Boolean>

    fun <S> ApplicativeError<S, Nel<ValidationError>>.userCityShouldBeValid(user: User) = fx.async {
        val cityValid = user.isUserCityValid().bind()
        if (cityValid) this@userCityShouldBeValid.just(cityValid)
        else raiseError(UserCityInvalid(user.city).nel())
    }
}

But it just doesn’t feel right, as: - It can’t be extended if I need other typeclasses. - I see

ApplicativeError

Async

hierarchy. So do I need both the TCs? I tried this, but am getting compiler errors due to clashes.

interface RepoTC2<F, S> : Async<F>, ApplicativeError<S, Nel<ValidationError>> {
    fun User.isUserCityValid(): Kind<F, Boolean>

    fun userCityShouldBeValid(user: User) = fx.async {
        val cityValid = user.isUserCityValid().bind()
        if (cityValid) just(cityValid)
        else raiseError(UserCityInvalid(user.city).nel())
    }
}

Can I achieve it just by using Async itself?

udalov

03/13/2020, 12:57 PM

Hi Arrow team! I'm trying to compile arrow with Kotlin 1.4 and getting the following error from `:arrow-core-data:kaptKotlin`:

Caused by: org.jetbrains.kotlin.kapt3.base.util.KaptBaseError: Exception while annotation processing
        at org.jetbrains.kotlin.kapt3.base.AnnotationProcessingKt.doAnnotationProcessing(annotationProcessing.kt:84)
        at org.jetbrains.kotlin.kapt3.base.AnnotationProcessingKt.doAnnotationProcessing$default(annotationProcessing.kt:35)
        at org.jetbrains.kotlin.kapt3.base.Kapt.kapt(Kapt.kt:45)
        ... 26 more
Caused by: java.lang.NullPointerException: e.localizedMessage must not be null
        at arrow.common.utils.AbstractProcessor.processElementDoc(AbstractProcessor.kt:75)
        at arrow.common.utils.AbstractProcessor.processDocs(AbstractProcessor.kt:101)
        at arrow.common.utils.AbstractProcessor.process(AbstractProcessor.kt:107)
        at org.jetbrains.kotlin.kapt3.base.incremental.IncrementalProcessor.process(incrementalProcessors.kt)
        at org.jetbrains.kotlin.kapt3.base.ProcessorWrapper.process(annotationProcessing.kt:147)
        at com.sun.tools.javac.processing.JavacProcessingEnvironment.callProcessor(JavacProcessingEnvironment.java:794)
        <...>

Have you met something similar and maybe you know how to workaround this problem?

dnowak

03/13/2020, 4:33 PM

Hi, does anyone have experience with Arrow and Spring Cloud Sleuth? We use IO a lot and we need to somehow pass the Sleuth context via IO.

Daniele Bartorilla

03/13/2020, 8:59 PM

Hi, i'm having trouble generating optics for a simple internal sealed class. For example:

@optics
internal sealed class X {

    data class Y(val foo: String): X()

    object Z: X()

    companion object
}

The issue is that the generated extensions are internal:

'public' member exposes its 'internal' receiver type Companion

. Am i doing something wrong?

Ahmed Ibrahim

03/14/2020, 10:56 AM

How can I combine two eithers into a third that's a result of a suspend function? I tried Either.applicative.map, but apparently the combine block doesn't allow a suspend function to be executed, what's the best way to tackle that?

Either.applicative().map(sectionsResult, sectionsResult.map(this::gatherAllSaleIds)) {
                    (sections: List<SalesSectionsQuery.SalesSection>, saleIds: List<SaleId>) ->
// This is a suspend function   remoteSalesDataSource.sales(AFFILIATE, saleIds)
            }

marc0der

03/14/2020, 11:09 AM

Hi, all. As many of you know I am in the process of translating the Scala Red Book into Kotlin (aka, the Orange Book). I am progressing well and am currently at work on Chapter 9 about writing a purely function parsing library. I have run across the first constraint in the language where I would need input from my Arrow friends! Here is the problem: I need to declare an interface that has nested type parameters (which Kotlin does not support). This is how it looks in Scala:

trait Parsers[ParseError, Parser[+_]] {
  def run[A](p: Parser[A])(input: String): Either[ParseError, A]
  def char(c: Char): Parser[Char]
}

The problem of course comes when declaring the type constructor

Parser[+_]

, and when you subsequently try to use a

Parser

without the type constructor present, we get an error on the

char

parser declaration to the effect of "_type arguments not allowed for type parameters"_. I was hoping that I could use

Kind

to solve this problem but not sure how to go about it. Any help would be greatly appreciated!

🙌 5

🔝 3

:arrow: 5

pakoito

03/15/2020, 2:17 AM

either make something that works for Applicative so it works for both and any other implementation; or make 2 functions, one for either and the other for validated

bmarinovic

03/15/2020, 5:44 PM

Just starting to learn Kotlin. I'm coming from a FP Scala background, so I'm curious what is usual technology stack that FP-side of Kotlin community uses, i.e. what backend FW, what DB library, do you use coroutines or Futures, etc?

pakoito

03/16/2020, 11:12 AM

I believe we made them execute in order in the latest revision. In any case I wouldn’t trust

mapN

to execute in order. If order matters, then use

flatMap

Steven Sherry

03/17/2020, 1:37 PM

I’m finding myself doing a bunch of validations on an unknown number of items and I end up with a

List<ValidatedNel<E, A>>

and I’m converting that to a

ValidatedNel<E, List<A>>

. Is there a more idiomatic way of doing that? The actual flow of data is more like this:

List<A> -> List<ValidatedNel<E, B>> -> ValidatedNel<E, List<B>>

. It works, but it feels like there is probably something more “native” to arrow that would handle this kind of flow.

than_

03/17/2020, 2:26 PM

Hey, quick question. IO<A> and suspend () ->A are isomorphic does that mean that after arrow meta well be able to do for example

val useFunc: suspend (A)->B = TODO()
val releaseFunc: suspend (A)->Unit = TODO()
something.bracket(
    use = useFunc,
    release = releaseFunc
)

Archie

03/17/2020, 3:39 PM

Hi, I'm learning Arrow for Android Development and I got stuck on how to integrate arrow with ktor? How exactly can I run my suspend functions? Do I just:

suspend fun someApi(): IO<SomeObject> {
    return IO.effect {         
        ktorClient.get("<http://someendpoint.com>") 
    }
}

May I ask for some guidance?

pakoito

03/17/2020, 4:18 PM

https://www.pacoworks.com/2019/12/15/kotlin-coroutines-with-arrow-fx/

gabib

03/18/2020, 11:09 AM

Hi, I think I saw at some point something like @given in an example. Are we going to have KEEP-87 implemented with Arrow Meta?

pakoito

03/18/2020, 10:44 PM

myEither.fold({ IO.unit }, { IO.effect { susFun() } }).bind()

Gopal S Akshintala

03/19/2020, 1:09 AM

Hi, I am looking to short-circuit (with

Applicative

) + lazy call functions (with

BIO.defer

), so when

mapN

processes from left to right, first

raiseError

should halt the processing and rest of the functions shouldn’t be called, @pakoito helped me come-up with this approach, but I am facing 2 problems: 1. I am using BIO, but

raiseError

from

ApplicativeError

doesn’t return a

Kind2

, how can I get around it? 2.

IO.defer{..}

has this compiler error:

Type mismatch. Required: () → IOOf<String, ???> Found: () → Unit

for both my extension functions

raiseAnError()

and

justString()

Please help. Thanks.

@Test
  fun `IO ApplicativeError 2`() {
        val product =
                IO.applicativeError<String>().mapN(
                        IO.defer { raiseSomeError() },
                        IO.defer { justString() }
                ) {}.fix().unsafeRunSyncEither()
        
        product.fold({ assertEquals("error", it) }, {})
    }

    private fun <S> ApplicativeError<S, String>.raiseSomeError(): Kind2<S, String, Unit> {
        println("raising an error")
        return raiseError("error")
    }
    
    private fun <S> ApplicativeError<S, String>.justString(): Kind2<S, String, Unit> {
        println("This should not be printed")
        return just("just")
    }

Satyam Agarwal

03/19/2020, 4:46 PM

Hei. I see

0.10.5

release github project is all done. When its getting released 😅 I am waiting for coroutine integration so that I can make my logs nicer by attaching correlation ids to them 😄

bjonnh

03/19/2020, 10:27 PM

I'm trying to convert some old arrow code and I'm struggling with that: https://pastebin.com/DJrUavqQ

✔️ 1

kyleg

03/20/2020, 3:32 PM

Supposing I’ve got a

Ref<ForIO, MyClass>

and a

StateT<ForIO, MyClass, Unit>

, what is the best way to make these two work together (using the

StateT

to update the value wrapped in

Ref

?) I have to unpack the

Ref

, pass it into the

StateT

, and use the result to update the

Ref

. I’m not sure how to do that without

myRef.update { oldState ->
  val (newState, _) = myStateT.runM(IO.monad(), oldState).unsafeRunSync()
  newState
}

but I know the

unsafeRunSync

is the stinkiest code smell there ever was.

kartoffelsup

03/20/2020, 6:47 PM

Has someone used Arrow.fx with Jetpack Compose already? Is there a way to use it so that we only have one unsafeRunSync per Activity?

Title

kartoffelsup

03/20/2020, 6:47 PM

Has someone used Arrow.fx with Jetpack Compose already? Is there a way to use it so that we only have one unsafeRunSync per Activity?

kyleg

03/20/2020, 7:36 PM

That’s an interesting question. From what I’ve seen of Jetpack Compose, they have this @Model annotation and

+state {}

thing that are a step backwards from immutability. I’d be interested to see what people suggest, as Compose is something I’ve been playing around with, too.

raulraja

03/20/2020, 10:02 PM

We are looking into compose to provide an integration with Arrow when its design is finalised and their changes to their compiler fork make it upstream to main kotlin

🔝 1

kartoffelsup

03/20/2020, 10:05 PM

That's awesome!

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