what would be a way to "fork" an operation (suspend function) to a different scope with arrow-fx-coroutines? .... let's say on Android, I trigger an action from a ViewModel (using

viewModelScope

) which calls a suspend function in a Repository layer..... I want to suspend until the repo function executes, but also if the

viewModelScope

is canceled I don't wanna cancel the repository operation. I wanna tie the repository operation to an application level scope instead

nice work @simon.vergauwen @Alejandro Serrano Mena!

There were also a couple questions about Arrow Optics code generation in the last months. We currently have a KSP port of the kapt version as a SNAPSHOT on the latest version of Google’s KSP. You can find an example of how it’s set up in the linked

build.gradle.kts

. If you try it, and come across anything broken please let us know 🙂 https://github.com/arrow-kt/backend-arrow-example/blob/86e3bf459a8eda06cd41a17105f807202698cea4/build.gradle.kts#L38

I have just updated my Arrow fork to the latest

main

and when I try to build

arrow-libs

I get the error:

Project directory '/Users/lukasz/projects/arrow/arrow-libs' is not part of the build defined by settings file '/Users/lukasz/projects/arrow/settings.gradle.kts'. If this is an unrelated build, it must have its own settings file.

Hi all, I'm probably holding it wrong or/and I missed some steps in the evolution of the library I know that

CoProduct

was removed at some point, but wasn't it replaced by

Union

? Which dependency do I need to get

Union2

Union3

etc?

Hey folks, when i import my Arrow fork into IntelliJ it does not seem to be possible to run the Kotest tests directly from IntelliJ (screenshot #1 gutter icon is not displayed). As this works in other projects i assume my general IntelliJ setup + plugin is correct (see screenshot #2) Is there any further setup i need to do in IntelliJ to be able to run tests directly?

Hi, what is the “nicest” way to partially apply more than a few parameters?

Hey everyone, I'm trying to create my first plugin with Arrow Meta. If I understand it correctly, a plugin with Arrow Meta can intercept at each step of the compiler. Therefore I should be able to change the AST before any annotation processing takes places by other third party libraries, is that correct? If so, is there any example on how to achieve this? I tried something like the following, currently with no success:

val Meta.injectProperty: CliPlugin
    get() = "Inject new property" {
        meta(
            classBody(this, { true }, fun ClassBody.(c: KtClassBody): Transform<KtClassBody> {
                if (c.name?.contains("User") == true) {

                    return Transform.replace(
                        replacing = c,
                        newDeclaration = """
                            | 
                            | @ColumnInfo(name = "name")
                            | var name: String = ""
                            |
                            | @ColumnInfo(name = "nameabc")
                            | var nameABC: String = ""
                            | }""".classBody
                    )
                }
                else {
                    return Transform.empty
                }
            })
        )
    }

Hi, is there anything available for IntelliJ, so that Arrow Optics elements (the generated lenses for example) are not marked as (red) errors ? (this is from the 'backend-arrow-example')

having a little trouble getting the ksp plugin for optics: https://arrow-kt.io/docs/optics/#Gradle-kotlin

Is Arrow having something like zip function for nullable Kotlin variables? Solving this problem: https://stackoverflow.com/questions/35513636/multiple-variable-let-in-kotlin

• Hi! I just took a look at the tests for the proof plugin, but I didn't understand, what it is about. Could somebody tell me, what usecases there are for Proofs / what it does? Thx.

Hello everyone. We are thinking about starting to incorporate the Arrow Optics DSL into a substantial (100k+ loc) project. We have two questions: 1. Is there a plan or roadmap for supporting the K2/FIR compiler for Optics DSL? We are concerned about becoming heavily invested in the generated optics but unable to update our compiler or language version due to lack of support. 2. Could a tool be built for generating Kotlin source code for Optics DSL properties in case we need to "back out" of using the compiler plugin (similar to https://projectlombok.org/features/delombok)? This would give us peace of mind in the case that we cannot continue to use the plugin, we would not need to invest a huge effort in manually writing the optics. This in particular would make it much easier for me to sell Optics DSL to the team. 😉 Thanks for working on this great project!

Can I use Kotest Arrow assertions while working on Arrow itself? I'm working on a PR for the

arrow-core-retrofit

module. I added a dependency on

io.kotest.extensions:kotest-assertions-arrow

but when I try to use the

shouldBeRight

assertion the test doesn't compile with the error "Cannot access class 'arrow.core.Either'. Check your module classpath for missing or conflicting dependencies"

I have a question about the generated Optional optics for nullable fields. The laws for affine traversals state that "If you get nothing when extracting a value, then whatever you put in, the operation is no-op" (http://oleg.fi/gists/posts/2017-04-18-glassery.html#laws:affine-traversal). The generated code that I see for a nullable field is setting the value without checking if a value is present. Here's an example:

inline val TestOptics.Companion.nullable: arrow.optics.Optional<TestOptics, Int> inline get()= arrow.optics.Optional(
  getOrModify = { testOptics: TestOptics -> testOptics.`nullable`?.right() ?: testOptics.left() },
  set = { testOptics: TestOptics, value: Int -> testOptics.copy(`nullable` = value) }
)

Is the arrow Optional optic not equivalent to an affine traversal? If not, what is it equivalent to?

I see in

arrow-meta

there is a plugin which provides a macro called

@Given()

From the tests, it seems to be roughly identical to Scala 3's

given

+

using

where you say "This function requires some type

Foo

to have a value provided in the context/scope" Is this sort of like an implementation of the Multiple Receivers proposal as a compiler plugin? https://github.com/arrow-kt/arrow-meta/blob/8f9e80bfbbcb12c16f025bc5ca7d69cbeeec08[…]gin/src/test/kotlin/arrow/meta/plugins/typeclasses/GivenTest.kt

Quick theoretical question: I have code which is parsing a GraphQL query into its AST, and then transforming that into a more specific "AST" (really just nested Kotlin dataclasses) Would this be something that

lenses

would be beneficial to for performance purposes, rather than creating an entire new AST object?

If any Gradle wizard has any idea about the following issue that’d be great 🙏 https://kotlinlang.slack.com/archives/C8UK6RTHU/p1641303439037300.

I’m just starting to work with arrow I use

<kotlin.version>1.5.31</kotlin.version>

but when I use

<dependency>
            <groupId>io.arrow-kt</groupId>
            <artifactId>arrow-core</artifactId>
            <version>0.12.1</version>
        </dependency>

        <dependency>
            <groupId>io.arrow-kt</groupId>
            <artifactId>arrow-fx</artifactId>
            <version>0.12.1</version>
        </dependency>

it leads to a warning that there are multiple koltin jars

Anyone using Arrow on Android? How you use it? Please share your experience

Why does

Either.bifoldMap

take a

Monoid

argument, when the monoid basically does no work, since

bifoldMap

always combines the mapped values of the

Either

with

empty

, where the result of that combination is know ahead of time to always be the same as the mapped values. In other words, why jump through the hoop of combining a value with

empty

, when we know the result will always be the same original value?

Looks like https://arrow-kt.io/docs/meta/ is raising a

404

. In case it hasn't already been reported...

IIRC

either

blocks with a for/while and a bind should do it

I could see arrow-fx is using Kotlin

suspend

to replace IO tell apart codes w/o side effects, while thing I could not get is how to enforce it for dependencies? the impure code from dependency will not have

suspend

in the function definition, which means we could always use them in a “safe” environment?

does anyone know what I’m missing with this compilation error?

Kotlin: Supertypes of the following classes cannot be resolved. Please make sure you have the required dependencies in the classpath:
    class arrow.core.Either, unresolved supertypes: arrow.Kind

I have function that returns an

Either

fun getConfigVersion(configId: ConfigId, versionId: ConfigVersionId): Either<DomainError, PIConfigVersion> {
        val configVersion = configVersionRepository.findByPiConfigModel_ProfileIdAndVersion(configId.id, versionId.id)
        return configVersion?.right() ?: NoVersionsFound("No ConfigVersion found for Config ${configId.id} and version ${versionId.id}").left()
    }

There are some strange things in readme from GitHub: 1. In Λrrow Core + Λrrow Optics we add Λrrow Meta 2. There are ways to add Core + something one. But if I want to use Optics and Fx at the same time?

Hi people have you ever encountered this error

kotlin.NoWhenBranchMatchedException: null
	at arrow.core.computations.EitherEffect$DefaultImpls.bind(either.kt:20) ~[arrow-core-jvm-1.0.1.jar:?]

I am using the either monad comprehension block and the bind extension function but maybe I am missing something. I am using arrow version 1.0.1 Basically I have few interface with suspended methods, and one interface exposing a method not suspended (and using jooq in the implementation to handle transactions)

interface Repository {
  suspend fun getBy(userId: UserId): Either<Error, List<DomainObject>>
  suspend fun update(obj: DomainObject) : Either<ErrorResult, Unit>
}

class TransactionMgmt(private val dslContext: DSLContext) {

    fun <T> transaction(
        block: () -> Either<Error, T>
    ): Either<ErrorResult, T> ...

interface Observer {

    suspend fun onExpired(obj: DomainObject): Either<ErrorResult, Unit>
}

class ExpireUseCase(
    private val repository: Repository,
    private val transactionMgmt: TransactionMgmt,
    private val observer: Observer
) : UseCase<Request, Response> {
    override suspend fun execute(request: Request): Either<Error, Response> =
        repository.getBy(request.userId)
            .flatMap { obj ->
                updateAndNotify(obj)
            }

    private suspend fun updateAndNotify(objs: List<DomainObject>): Either<Error, Response> {
        return objs.fold(initial) { acc, obj ->
            transactionMgmt.transaction {
                runBlocking {
                    expire(obj, acc)
                }
            }
        }
    }

    private suspend fun expire(
        obj: DomainObject,
        acc: Either<Error, Response>
    ): Either<Error, Response> = either {
        val expiredObj = obj.copy(status = EXPIRED)
        repository.update(expiredObj).bind()
        observer.onExpired(expiredObj).bind()
        Response(acc.bind().count + 1)
    }

    private val initial: Either<Error, Response> = Response(0).right()
}

Basically I am getting that error in the method

private suspend fun expire(
        obj: DomainObject,
        acc: Either<Error, Response>
    ): Either<Error, Response> = either {
        val expiredObj = obj.copy(status = EXPIRED)
        repository.update(expiredObj).bind()
        observer.onExpired(expiredObj).bind()
        Response(acc.bind().count + 1)
    }

Sorry for the very long post, and maybe I am missing something really stupid but I cannot see it. (this is a similar version of the actual code I am using, I cannot post the original one)