Hi there! I just talked with a Jetbrains rep and they said that KEEP-87 will be implemented using multiple receivers. @raulraja do you think this will work with Arrow? Is there any collaboration on this?

Has anyone an idea how to correctly setup arrow in a plain module in Android or maybe in Android at all. I have just a simple module:

apply(plugin: "kotlin")
apply(plugin: "kotlin-kapt")

sourceCompatibility = "8"
targetCompatibility = "8"

compileKotlin {
    kotlinOptions {
        jvmTarget = "1.8"
    }
}

dependencies {

    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8:$versions.kotlin")
    implementation("io.arrow-kt:arrow-core:$versions.arrow")
    implementation("io.arrow-kt:arrow-fx:$versions.arrow")

    testImplementation("junit:junit:4.13")
    testImplementation("com.google.truth:truth:$versions.truth")
    testImplementation("io.mockk:mockk:$versions.mockk")
}

This is compilable, but when I try to run a Test, I get the following exception: e: C:\Development\Projects\test\eight\android\domain\src\test\kotlin\com\eight\domain\simple\EmailAddressTest.kt: (16, 20): Cannot inline bytecode built with JVM target 1.8 into bytecode that is being built with JVM target 1.6. Please specify proper '-jvm-target' option Adding support for Java 8 language features could solve this issue. Change Java language level and jvmTarget to 8 in all modules if using a lower level. More information...

Curious to know why

either.eager {...}

seems to need explicit type arguments, while

either {...}

does not. e.g.

fun fn(): Either<Throwable, Boolean> = TODO()

suspend fun example() {
    either.eager<Throwable, Boolean> {
        val a = !fn()
        val b = !fn()
        a && b
    }
    either {
        val a = !fn()
        val b = !fn()
        a && b
    }
}

Hi all, i'm getting a

Duplicate JVM class name

error after moving to arrow 0.11.0 and Kotlin 1.4.10 when using optics. As far as I can tell this is similar to the issue @Joram Visser raised here except in my case I'm using gradle not maven. I'm struggling to debug this, because optics are compiling correctly elsewhere in the same project, and it just seems to be one data class that is now causing this error. I tried creating a new repo and reproducing but it compiles and run fine. Any suggestions on how to approach debugging this?

unwrapBody

is what you’re after

Hello. Is there a reason to not have an

Either.ifRight { rightValue -> ... }

extension? Is this an antipattern?

Any ETA on MPP arrow release?

you can call

map

and instead of returning a value, do a side-effect that returns `Unit`inside. It’s not a good pattern but that fits every use case for

ifRight

What's the best way to combine errors in List<ValidatedNel<MyError, Unit>> to ValidatedNel<MyError, Unit> ?

Is there a way to have Schedule with exponential back off for up to n times?

fun <A> policy() =
    Schedule.exponential<A>(100.milliseconds)
        .whileOutput { it.millis < 1000 }
        .or(Schedule.recurs(3))

What am I doing wrong here?

So what you’re saying is that it’s pointing in the right direction? I’ll let myself out.

I got a noob FP question : I got a app that reads messages off the wire (different types), and builds state from that (and only that), then spits out other msgs, or does some work. So two questions come to mind: 1. Where exactly do I "keep" my state? and how to I keep it immutable? Every msg will update it (add or delete something to some data structure). Do I just

fold

over the stream of msgs and my state lives in the fold? How can anything external to the fold access it? 2. How do you manage the IO, it's basically almost all IO w/ a small state-machine in the middle This is a pretty typical pattern for the finical markets.

Hi! I have an application that essentially resolves around making requests to various servers (for example, I can ask to query a specific documents to multiple servers, and they might all reply, or only a few reply, or none reply). The difficult thing is that some servers might request additional user information (for example, for some files a server might need authentication, but not for others, or it might ask the user for confirmation before doing something, or it might ask the user for their age... Or anything else). The ‘questions' from servers are usually yes/no questions, but sometimes can be more involved. Currently, the application is written like this: • ‘search' requests are functions that return flows • ‘action' requests are just suspended functions • when a server requests additional information, that function suspends and asks the user, then resumes and sends the information to the server. Since this project already uses some Arrow features (

Either

...), I'm wondering how I could go around to make it ‘more functional'. I see that functions that return flows are better than simple suspend functions returning a list because the side effect doesn't happen during the function execution but is ‘stored' within the type. I don't really see a way to do the same with ‘action' requests, apart from returning a Flow with a single value (or would you say that's good code?) If I understand, that's what

IO

was for, but since it seems like it has been replaced by

arrow-fx-coroutines

, I'd rather learn the ‘new version' The other problem is the user interaction: currently, the user interaction consists of a few suspend functions that are called deeply inside the program. This way, it's not really possible for the ‘client' of the application to use a different UI. Usually this would be solved with Dependency Injection, but the Arrow wiki implies Typeclasses can assume that role in a better way. Essentially, which steps would you take to change the architecture of this application so it's more functional? This particular project only runs on the JVM, if that changes anything, but I'd like to learn about techniques that work everywhere if that's possible. I've already went through and made all objects immutable, which should make the translation easier?

hi, Isn't there already a helper function to transform nullable to either? Something like this:

fun <A, B> A?.toEither(error: () -> B): Either<B, A> =
    this?.right() ?: error().left()

Hi all! I"m trying to use

Free

for a small test, and I'm basically following along this example in the tests: https://github.com/arrow-kt/arrow-incubator/blob/master/arrow-free-data/src/test/kotlin/arrow/free/FreeTest.kt My questions are these: • where does

.fix()

"come from", i.e. which import am I missing? •

'fx: MonadFx<FreePartialOf<ForProgram> /* = Kind<ForFree, ForProgram> */>' is deprecated. Fx will be moved to each datatype as a DSL constructor.

<- how to deal with this?

is Stream available in 1.0.0-SNAPSHOT?, i can't found it

Hi, I am new to arrow. I have been using kotlin for Android development and i wanted to explore arrow. So far I am a bit confused by many overlapping apis, there seem to be multiple ways to do the same thing and it is not clear to me how things should be used. Example IO { ... } vs IO.async().async { ... }.unsafeRunSync() vs IO.async().run { fx.async { ... }.fix().attempt().unsafeWhateverRun() }

in a reactive-ish Android app how would I use arrow to represent the state and update views as the state changes ? (I am used to reactive programming where each view "binds" to the state with combine/subscribe)

does arrow-core work w/ 1.4.x of kotlin?

With the release of

0.11.0

(or

1.1.0-SNAPSHOT

) is there any migration guide for what has changed (https://arrow-kt.io/docs/next/fx/ is not what I'm looking for, I am looking for a comparison of how things were done in previous releases versus

0.11.0

). Along with that, are there any actual code examples for the 0.11.0 / 1.1.0-SNAPSHOT releases? Again, I don't want https://arrow-kt.io/docs/next/fx/ as there are no code samples of how to do monad comprehensions, as an example. For example, take this example from @mattmoore’s blog post https://lambda.show/blog/arrow-io-monad-comprehensions-cleaner-monadic-composition... what's the equivalent syntax of this?

fun getAddressFromOrder(orderId: Int) = IO.fx {
    val order = !getOrder(orderId)
    val customer = !getCustomer(order.customerId)
    val address = !getAddress(customer.addressId)
    address
}

In general, can anyone point me to any documents, blog posts, videos, etc. that specifically cover the new syntax changes in

0.11.0

(not older versions) other than the (very spare) Arrow docs?

Related note: Is this page https://arrow-kt.io/docs/patterns/monad_comprehensions/ up to date with the 0.11.0 syntax? Looks like not.

Hello, I have an application written using kotlinx coroutines, and as a proof of concept/learning opportunity I'm thinking of porting it to arrow-fx, but I'd like to confirm that I've got some concepts straight, I wasn't able to find answers in the docs, so apologies if this is already covered somewhere. I use launch to start up long-running 'worker' Jobs, which I sometimes need to cancel and restart. Is using

ForkConnected

to start up fibers the correct abstraction? I use Channels to have different Jobs communicate. Are queues used for a similar purpose as channels? Is there an equivalent to

select

? In particular, I'd like have some behavior repeated periodically OR when a signal is received, whichever is first. Would I use a

Race

with a

Schedule

for that?

hey guys, is there any workaround for calling a suspend function inside

handleError

? I’m getting

Suspension functions can be called only within coroutine body

😞

weird. Try a clean build

Good day. I have a function which returns an Either<DomainError, Id> which i need to invoke in a loop for a few times. What would be the best way to implement this loop taking into account that when a Either.Left<DomainError> is returned then the loop should stop?

Hi Folks! I hope you are all keeping well in these COVID times. I'm nearing the end of my journey with the FP in Kotlin book (just put finishing touches on chapter 14 - Local Effects 🎉) but am in need of some help and advice from the Arrow masters. 😄 For those who haven't read the Scala red book, this chapter deals with a datatype called

ST

, short for State Token, which is a type that encapsulates local memory mutation and isolates the outside world from it.

ST

is also a

Monad

, and works very similar to the

State

monad. In my code samples while working with

ST

, I am ending up with gnarly nested

flatMap

and

map

sequences that seem so redundant and difficult to interpret for the reader. I would love to replace these nested monstrosities with neat for comprehension

fx

blocks, and I have been digging into the arrow source code to get some tips about how to achieve this. The problem is that adding

fx

binding capabilities to my own data type seems way complicated. Is there an easy way to achieve this? (or at least a guide or tutorial that instructs how to go about equipping your own data types with

fx

binding)? Hoping that someone can advise or shed some light on this. I really appreciate any help you can provide.

In Kotlin with suspend

try/catch

can safely be used to recover from exceptions. source: https://github.com/arrow-kt/arrow-fx/pull/169

does that mean that:

val result: Int = try {
  evalOn(BlockingI)) { mySuspendFun() }
} catch(t: Throwable) {
  5
}

would work?

Hei. I am seeing few issues with

evalOn

, and

coroutineContexts

. Made 2 test files to show what is happening and what I expect. https://github.com/satyamagarwal/arrow-issues/tree/master/src/test/kotlin/com/arrow/issues Can any one help me please ? feel free to take a pull and test it out.