HI Team, I see the latest stable release is 1.0.1 - https://github.com/arrow-kt/arrow/releases But I am not seeing this version in maven central repository - https://mvnrepository.com/artifact/io.arrow-kt/arrow-core-data Am I missing something?

Also can I use kotlin 1.6.10 with 1.0.1 version of arrow?

Hey Team, We are still having hard time upgrading to arrow 1.0.1. Our continuous build just fails unable to resolve the Either or any class from arrow libraries. Even though the dependencies are listed in effective pom and can see in the tree. Anybody faced this problem? Does

kotlin-maven-plugin

needs any modifications or configurations here?

I'd like to integrate arrow-optics in a multiplatform project (and this is my first try to use the arrow-optics code generator). The files I modified: build.gradle.kts

plugins {
    ...
    id("com.google.devtools.ksp") version "1.6.10-1.0.2"
}

kotlin {
    sourceSets {
        val commonMain by getting {
            dependencies {
                ...
                api("io.arrow-kt:arrow-optics:1.0.1")
            }
        ...
    }
}

dependencies {
    ksp("io.arrow-kt:arrow-optics-ksp-plugin:1.0.2-alpha.28")
}

Example.kt

...
@optics
data class Example(val p: String) {
    companion object
}

But no files are generated, the

build\generated\xxxMain

folders are created but remain empty. During the build process the corresponding tasks are executed (and I see a warning):

...
The 'ksp' configuration is deprecated in Kotlin Multiplatform projects. Please use target-specific configurations like 'kspJvm' instead.
...
Task ... kspKotlinJs UP-TO-DATE
...
Task ... kspKotlinMetadata UP-TO-DATE
...
Task ... kspKotlinJvm UP-TO-DATE
...

Do you have any idea what piece is missing? Thanks.

Hello, I'm pretty new to Kotlin but wanted to start it out implementing some things with Arrow since I got a little background in FP. Is there a structured path I could follow to learn it?

Hi! Given I have 2

Either

of type

<List<Error>, Success>>

, how could I collect both of their lefts (if both are left). My setup looks like this:

import arrow.core.Either

data class Error(val message: String)
data class Success(val data: Int)
data class SuccessSum(val success1: Success?, val success2: Success?)

fun myFunction(): Either<List<Error>, SuccessSum> {
    val responseA = someNetworkCall()
    val responseB = someNetworkCall()

    return TODO()
}


fun someNetworkCall(aGivenParameter: Int = 1): Either<List<Error>, Success> {
    TODO()
}

and I have the following possibilities regarding my return type: it can either be: • a list of errors originating from the first response • a list of errors originating from the second response • a list of errors originating from both responses •

SuccessSum

, my happy path Is there any way to check if both eithers are null and if they are, merge their left values together into one list? My happy path would then look like that:

fun myFunction(): Either<List<Error>, SuccessSum> {
    val responseA = someNetworkCall()
    val responseB = someNetworkCall()

    /* Guard Clause checking for lefts here */

    return SuccessSum(
        success1 = responseA.orNull(),
        success2 = responseB.orNull()
    )
}

That’s at least my initial idea. I guess

Validated

could be a better option but I didn’t look into it yet. Thanks in advance! 🙂

In optics, is there a way to focus on a

Either

only if it is a

Left

? I have a state that I want to modify its

Either

variable, something like:

data class State(val either: Either<Error, Something>)

And I want something like this:

State.either./*focusIfLeft()*/.modify(state) { left: Left<Error> -> Something().right() }

Is there a way to do that already or a need to define my own extension?

Is it still impossible to use Arrow Analysis to ensure that a string matches a regex expression at compiletime?

hi, i am attempting to convince my android development colleagues to embrace arrow as it has now reached v1.0.0 one really great selling point is the use of optics. sadly i cannot seem to find instructions on how to configure my gradle build file to allow my build to complete successfully is there a sample android project or documentation that explains how to correctly configure and android gradle build file(s)?

Hi everyone, I am new to Kotlin (and Arrow), and have an interest to do a project adhering to the FP paradigm. I was wondering if you guys could give pointers on how to get started. Especially: there's a lot to learn about Kotlin itself, although not everything will be relevant for FP. What Kotlin basics would you say I should get down before moving to the use of Arrow? Thanks!

The @optics ksp codegen (using

"io.arrow-kt:arrow-optics-ksp-plugin:1.0.2-alpha.42"

) seems to have a bug: if I put @optics on a data class with 3 or fewer fields it generates code with

first

,

second

,

third

which is great because arrow.core.Tuple3 has those fields. But once I hit 4 fields it starts generating code with

a

,

b

,

c

,

d

which fails because arrow..core.Tuple4 does not have those fields (it has

first

through

fourth

) -- is this a known issue? Solved

Hi I would like to know if anyone has managed to get arrow optics to work (e.g. generate code) in an Android studio project? i have been trying to achieve this for the last 4 days and failed.

Hi 👋. I'm trying to use

Validated

instead

require

for validation when constructing an object.

class Probability private constructor(val value: Double) {
  companion object {
    fun create(value: Double) =
      if (value > 0.00 && value < 1.00) Probability(value).valid()
      else ValidationError.ProbabilityOutOfBounds("Probability must be between 0.00 and 1.00").invalid()
  }
}

I'm struggling to find the best way to structure it in a given context. Typical use case for `Probability`:

val fsmIdentifiers =
  listOf(
    FsmIdentifier(
      key = "first",
      mProbability = Probability(0.95),
      uProbability = Probability(0.1),
      compare = ::jaroWinklerDistance
    ),
    FsmIdentifier(
      key = "last",
      mProbability = Probability(0.99),
      uProbability = Probability(0.01),
      compare = ::jaroWinklerDistance
    ),
    FsmIdentifier(
      key = "middle",
      mProbability = Probability(0.90),
      uProbability = Probability(0.1),
      compare = ::jaroWinklerDistance
    ),
......
)

As you see, the

Probability

is created as part of the

FsmIdentifier

(and other similar identifiers). Any suggestion on how to handle the creation with

Validated

in this context cleanly, without making the code look overwhelmingly verbose?

Hello everyone. Wondering if there are any updates on this https://github.com/arrow-kt/arrow/issues/2656 ?

Hi, I'm trying to replace refined types with arrow analysis. Everything goes reasonably well (some NotImplementedErrors here and there). But I encountered:

@JvmInline
@Serializable
value class Email(val value: String) {
    init {
        pre(value.matches(emailRegex)){ "Must be a valid email" }
    }

    override fun toString(): String = value
}

which of course won't work since

You can only create Boolean expressions using basic arithmetic operations (addition, subtraction, …), comparisons, and simple Boolean operations (and, or, not). In particular, you cannot define a Boolean function and use it in a condition;

Will there be possibility of regex matching in the future or should we use a runtime solution?

Hi all, quick question: Is there a function somewhere in arrow core for turning List<A?> into List<A>? (Or something similar for Option)? In Haskell, I'd use sequence for this.

HI Team, Is

retry

function available in

Schedule

on version

1.0.0

? We are stuck at version

1.0.0

because of this issue and I am not finding

retry

We’ve just released Arrow Analysis, a plug-in for the Kotlin compiler which super-charges it with pre/post-condition checking, which can catch typical errors like accessing an element in a list without checking its length twice… and all in an extensible fashion, so you can add your own checks https://twitter.com/47deg/status/1488935292652326913

Hi! Where can I report bugs for Arrow Analysis? Seems like a great project and I'd love to use it but it crashes on my codebase.

I'm curious why this syntax was adopted:

return z.post({ it > 0 }) { "greater than 0" }

where the string is in a block, rather than a parameter. It seems less visually noisy to write as

z.post("greater than zero") { it > 0 }

- yeah it's different to require, but it seems to make more sense

I'm curious if there are any trainings available, so one can get more familiar with arrow

trying out the

Arrow-Analysis

… it’s early here but am i being dense with this error? 😅

Dumb question: Is it possible to run

Arrow-Analysis

in a separate compilation task from regular? The reason I ask is because of potentially increased compile times, which I assume would add up if you're frequently re-compiling your code to test. (Maybe this is not the case though)

I'm an FP beginner, working up my basic understanding so that I can use Arrow. Hope this is not considered off-topic, but I would like to know if what I'm doing here is a valid FP approach, or if it's my OOP experience muddying the waters.

Is there a way to get a compile-time warning or error when an

Either<E, A>

is not used? In particular, this would be great in an

either { … }

block when calling IO functions that return

Either<Error, Unit>

to prevent forgetting to call

bind()

on the result to propagate the error.

https://blog.jetbrains.com/kotlin/2022/02/kotlin-1-6-20-m1-released/ Kotlin 1.6.20 now supports multiple receivers as an experimental feature. What does this mean for Arrow when it gets fully released?

Reading Arrow Lens' docs and I'm a bit confused. Docs mention that

set

has type

A -> S -> T

, but actual

set

implementations seem to have it reversed:

S -> A -> T

. Screenshots are from: api docs Similarly main page of Arrow Optics mentions

set: A -> S -> S

, but then has an example of

playerLens.set(player, health)

. Am I reading this wrong or is this a little bug?

What's the best way to "flatMap" two or more validated nels ?

What's going on with Bow? I noticed there hasn't been a release in nearly two years. Is that an indication of weak interest in FP by developers who use Swift?