kotlinlang #arrow

Any update on this? https://github.com/arrow-kt/arrow/issues/2668 This is a pretty serious spec violation in my opinion. We don't want users to become dependent on this behavior.

Satyam Agarwal

05/01/2022, 11:44 AM

Hi, Another question. I have two lists, List<A>, and List<B>, and I want to pass them through Ior to perform actions based on if they are empty or not. Only sensible logic I’ve been able to get to so far, is,

Ior.fromNullables(Nel.fromList(list1).getOrElse { null }, Nel.fromList(list2),getOrElse { null})

This is obviously not good, as

Nel<A>?

effectively means

List<A>

, so i can just

list1.isEmpty() && list2.isEmpty

to cover

Ior

cases. However, what I want is

Nel

after checking the states. Is there something better that can be done here ? Pattern matching on

Option<Nel<A>> to Option<Nel<B>>

also doesn’t work. I can’t say for example

when exp is Pair<Some, None>

Robert Kittilsen

05/03/2022, 12:29 AM

Hi everyone! 👋 😄 I’ve just started to use Arrow and I’ve come across this situation where I’m not totally sure what I’m supposed to do or what is best practice. I have this function in a file service:

fun getSignedUrl(fileName: String): Either<FileError, URL>

in which I

Either.catch

a generation of a signed URL and

mapLeft

for a potential

FileError.SignedUrlError

. In another service I have a function that looks like this:

fun getReports(): Either<GeneralError, List<Report>>

. In this I’m mapping through each report and replacing filenames with a call to

getSignedUrl

. I want to do it eagerly and go left on first fail. In the end I’m folding into a HttpResponse like this:

fun <BODY> Either<GeneralError, BODY>.toResponse(): HttpResponse<BODY>

As you can see I have two different Error objects and nested Either’s. The only solution I’ve found without changing

FileError.SignedUrlError

into

GeneralError

is something like this:

fun <OUTER_TYPE, INNER_TYPE, ERROR_TYPE> Collection<OUTER_TYPE>.mapEitherReturningFirstLeft(block: (item: OUTER_TYPE) -> Either<ERROR_TYPE, INNER_TYPE>): Either<ERROR_TYPE, List<INNER_TYPE>> =
    this.map { item ->
        block(item).fold(
            ifRight = { it },
            ifLeft = { return it.left() }
        )
    }.right()

This doesn’t seem optimal. Any suggestions or thoughts will be much appreciated! 🤩

julian

05/03/2022, 1:40 AM

Hi, @simon.vergauwen. Thanks for your blog post on

Effect

. It all made sense to me, except for this:

Only when
fold
is called it will create a
Continuation
and run the computation, this means
Effect
can encode
side-effects
as
pure values
.

What does pure values mean? I know what a pure function is, but I don't think I've ever come across pure values.

genovich

05/04/2022, 4:34 PM

Hello colleagues! I’ve just found that implementations of

raceN()

probably not handling exceptions in a right way. According to the conversation I had a year ago, it seems to me that if one of functions will throw an exception, then another will not be cancelled. Do you have an idea how to check such behaviour?

Jose Antonio Jimenez

05/06/2022, 10:41 AM

Currently i am having this error:

> Failed to query the value of task ':kspKotlin' property 'options'.
   > Could not resolve all files for configuration ':kspKotlinProcessorClasspath'.
      > Could not find io.arrow-kt:arrow-optics-ksp-plugin:1.0.1.
        Required by:
            project :

Stylianos Gakis

05/09/2022, 12:27 PM

Hey people! We’ve been having a discussion regarding using Either and what should go on Left and what on Right with my team. There are some things that we feel are up to interpretation so we’d love to hear more from people inside this community. The discussion is currently taking place here and since our repository is public we have the perk of sharing it here with others directly 😅 For people who don’t want to follow the link, I’ll try and ask the question here, but the main question is be this for those who do. Do you usually treat your Either lefts as all the unknown things that could go wrong (Network error, some exception happening etc.) and the rights as the known results, whether that’s the “success” case, or if it’s a known “failed” result that you know can happen. Or do you put the known “failed” result on the left as well along with all the unknown errors, exceptions etc ? To try to explain with an example, let’s say that we have a function:

fun getLoginResult(): Success|WrongPassword|NetworkError

Would you map this to

Either<NetworkError,Success|WrongPassword>

Either<NetworkError|WrongPassword,Success>

? I also understand that both can work, technically one could flip Right and Left too, but we’re trying to see what the “convention” is to try and conform to whatever feels more standard. Feel free to respond here or there, either works for us, but probably here so that other people can benefit in the future.

Marko Novakovic

05/09/2022, 12:33 PM

how to use

Flow

and

Either

? is having

Flow<Either<A, B>>

a good option? also, are there any plans for some monadic streaming Flow-like API?

👍 1

bloder

05/10/2022, 11:15 PM

Hi all! Thank you for

Effect

feature, really cool how I can type all my effects and play with them purely, one doubt about it: Are we thinking in explore more about Algebraic Effects and bring its concept to this implementation?

👋 1

Oliver Eisenbarth

05/14/2022, 4:36 PM

Hi @simon.vergauwen. 👋 I get Either and Validated and I've learned, that Kotlin suspend is better than having IO wrappers. What's the benefit of

effect

? Please explain it to me like I'm five. 🙂

alightgoesout

05/15/2022, 5:07 PM

Is there a plan to add a a function on

Effect

leftIfNull

for

Either

? Right now I do:

effect {
    ensureNotNull(someEffect.bind()) { SomeError("…") }
}

which seems verbose

Pavel

05/16/2022, 7:26 AM

Hi, since we are all talking about

Effect

I would have one question too. Is it possible to compose multiple `Effect`s? For example:

fun test(): Effect<X, Int> = effect {
    1
}

fun test2(num: Int): Effect<X, Int> = effect {
    num + 1
}

(test().flatMap { num -> test2(num) }): Effect<X, Int>

than_

05/16/2022, 9:14 AM

Hi, I'm playing with the effects and I found out that

sealed interface DomainError
object SomeDomainError: DomainError

fun foo(): Effect<DomainError, Unit> = TODO()
fun bar(): Effect<SomeDomainError, Unit> = TODO()

fun baz() = effect<DomainError, Unit> {
    foo().bind()
    bar().bind()
}

the problem is I cannot bind result of

bar

even though

SomeDomainError

is a

DomainError

. Is this known limitation, oversight, or weirdness on my side 🙂 ?

jianbing

05/19/2022, 7:45 AM

Dear Arrow Core Team Please kindly help: I am using arrow-core:1.0.1 in my kotlin project. recently I upgraded kotlin version from 1.6.0 to 1.6.21 and ktor from 1.6.0 to 2.0.1, but keep arrow-core version as it is now when I am building my kotlin project from remote CICD pipeline, I constantly observed the build failures (see the attachment for full stack). several re-tries can fix this problem. But I want to know the root cause here. I cannot search out any similar case from Bing.com for rootcause. hence I have no clue what is happening around. Maybe arrow-core:1.0.1 will NOT work with latest 1.6.21 kotlin... Caused by: java.lang.IllegalArgumentException: Missing extension point: org.jetbrains.kotlin.com.intellij.documentWriteAccessGuard in container org.jetbrains.kotlin.com.intellij.core.CoreApplicationEnvironment$1@3b88f6af at org.jetbrains.kotlin.com.intellij.openapi.extensions.impl.ExtensionsAreaImpl.getExtensionPoint(ExtensionsAreaImpl.java:273) at org.jetbrains.kotlin.com.intellij.openapi.extensions.BaseExtensionPointName.getPointImpl(BaseExtensionPointName.java:28) at org.jetbrains.kotlin.com.intellij.openapi.extensions.ExtensionPointName.getExtensions(ExtensionPointName.java:38) at org.jetbrains.kotlin.com.intellij.openapi.editor.impl.DocumentImpl.assertWriteAccess(DocumentImpl.java:700) at org.jetbrains.kotlin.com.intellij.openapi.editor.impl.DocumentImpl.replaceString(DocumentImpl.java:605) at org.jetbrains.kotlin.com.intellij.openapi.editor.impl.DocumentImpl.lambda$setText$2(DocumentImpl.java:1083) at org.jetbrains.kotlin.com.intellij.openapi.command.impl.CoreCommandProcessor.executeCommand(CoreCommandProcessor.java:211) at org.jetbrains.kotlin.com.intellij.openapi.command.impl.CoreCommandProcessor.executeCommand(CoreCommandProcessor.java:177) at org.jetbrains.kotlin.com.intellij.openapi.command.impl.CoreCommandProcessor.executeCommand(CoreCommandProcessor.java:167) at org.jetbrains.kotlin.com.intellij.openapi.command.impl.CoreCommandProcessor.executeCommand(CoreCommandProcessor.java:153) at org.jetbrains.kotlin.com.intellij.openapi.editor.impl.DocumentImpl.setText(DocumentImpl.java:1088) at arrow.meta.quotes.QuoteProcessorKt$changeSource$1$1.invoke(QuoteProcessor.kt:205) at arrow.meta.quotes.QuoteProcessorKt$changeSource$1$1.invoke(QuoteProcessor.kt:203) at arrow.meta.phases.analysis.MetaFileViewProvider.getDocument(MetaFileViewProvider.kt:17) at org.jetbrains.kotlin.com.intellij.psi.AbstractFileViewProvider$VirtualFileContent.getText(AbstractFileViewProvider.java:468)

compiling failures.txt

Katarzyna

05/19/2022, 1:08 PM

Hi everyone, @marcinmoskala is currently working on book series Kotlin for developers. It will contain 3 books: 1. Kotlin Essentials 2. Functional Kotlin 3. Advanced Kotlin He thought of adding a special chapter to the Functional Kotlin concerning the Arrow Library. We are looking for someone who would write this chapter as a guest author. What do you think? Let me know, here or write to kasia@kt.academy to discuss all the details. Have a nice day 🌞

Marko Novakovic

05/20/2022, 3:01 PM

I was away from Arrow for some time and two days ago I came across

Effect

. can somebody give me concrete example where difference between

Effect

and

Either

is clear?

Łukasz Gendek

05/23/2022, 7:33 AM

Hi. Do you know why divide1 does compile and divide2 does not?

Satyam Agarwal

05/24/2022, 5:02 AM

Hei ! I was wondering what is the state of https://github.com/arrow-kt/arrow-endpoint ? Is this ready to be used ? (I haven’t browsed through the code) Looks like last tag is 0.1.1-alpha.5 from 2 days ago.

jean

05/25/2022, 8:25 AM

I have the following functions :

fun interface PatchDevice<T> {
    suspend operator fun invoke(
        deviceId: String,
        payload: T
    ): Either<Error, Action>
}

fun interface PatchDeviceAttribute<T> {
    suspend operator fun invoke(
        deviceId: String,
        payload: T
    ): Either<Error, Action>
}

suspend fun <T> save(
    patchDevice: PatchDevice<T>,
    patchDeviceAttribute: PatchDeviceAttribute<T>
) {
    either.eager<> { 
        val patchDeviceResult = patchDevice("")
    }
}

The IDE complains that

Restricted suspending functions can only invoke member or extension suspending functions on their restricted coroutine scope

when I call

patchDevice()

What should I change to make it work?

kyleg

05/25/2022, 2:59 PM

Howdy do, it's been a couple years since I've been here. Arrow has gone through so much since then (Arrow Meta wasn't even out yet, and

IO<A>

hadn't been deprecated for suspend yet!). Quick question: didn't Arrow used to have a Free/FreeMonad implementation? I can't seem to find it in the codebase or the docs now. I found a gist for creating a DSL using Arrow (written three years ago) but I can't even find annotations like

@higherkind

to import them. It looks like there used to be a module arrow-free or something based on links in the gist, but I can't find that now.

Satyam Agarwal

05/27/2022, 9:05 AM

Hei Hei !! I recently bumped to arrow 1.1.2. And I was wondering the rationale behind deprecating ResultEffect. I’ve been using it in my tests a lot. ResultEffect.bind() helps a lot in providing prerequisites my tests need to assert on something. For example inserting rows in databases. Most of my operations are effectful, so I have to wrap them either in either or eagerEffect. With ResultEffect I didn’t need to use these computation blocks. Take a look at this simple test example :

import arrow.core.computations.ResultEffect.bind

@Test
fun `encrypt produces new encryption for given text and should be decrypted back `() {
    val text = "Some sensitive data :partying_face: 2020-06-27T19:11:44.095Z @#$%^&*(&^%$#@! åååå πø˜˜¶∞¢"
    val textByteArray: ByteArray = text.toByteArray()

    val firstEncryption: ByteArray = Crypto.encrypt(securityKey, textByteArray).bind()
    val secondEncryption: ByteArray = Crypto.encrypt(securityKey, textByteArray).bind()

    firstEncryption shouldNotBe secondEncryption

    val firstDecryption: ByteArray = Crypto.decrypt(securityKey, firstEncryption).bind()
    val secondDecryption: ByteArray = Crypto.decrypt(securityKey, secondEncryption).bind()

    firstDecryption shouldBe textByteArray
    secondDecryption shouldBe textByteArray
    String(firstDecryption) shouldBe text
    String(secondDecryption) shouldBe text
}

Is there some alternative, or am I forced to migrate my hundreds of tests 😅

Marko Novakovic

05/30/2022, 11:47 AM

help needed I have top level function:

suspend fun createTask(
    tasksDao: TasksDao,
    localDate: LocalDate,
    label: String,
): Either<TaskError, Unit> = either {
    ensure(label.isNotBlank()) { TaskError.EmptyLabel }
    try {
        tasksDao.createTask(localDate.year, localDate.monthNumber, localDate.dayOfMonth, label)
    } catch (e: Throwable) {
        shift(TaskError.CreationError)
    }
}

but it fails to compile for iOS target,

Task :shared:linkDebugTestIosSimulatorArm64 FAILED

happens on 1.1.2 and 1.1.3-alpha.14 works for Android error in thread

stojan

05/31/2022, 1:26 PM

https://twitter.com/trupill/status/1531621986207678464

👏🏼 1

👏 4

simon.vergauwen

05/31/2022, 2:32 PM

message has been deleted

🙌 2

❤️ 7

Moritz Lindner

06/01/2022, 8:29 PM

Hi I have a question regarding combining 2 Monads. I have the following type

Either<A, Option<B>

and want to create a

Either<A, B>

. If the Option is

None

the Either should be

Left<A>

and if it is

Some

I want the Either to be

Right<B>

. I did not find a function in the library and since MonadeTransformers are not an option I came up with the following solution:

fun <A, B> Either<A, Option<B>>.unwrapOptionOrElse(other: () -> A): Either<A, B> {
    return flatMap { option -> option.fold({ other().left() }, { it.right() }) }
}

Is this a reasonable way of handling this case or should I change something? Regards Moritz 🙂

jean

06/02/2022, 7:34 PM

I’m trying to add arrow as a dependency on an older multiplatform project but I’m running in this issue

Error while evaluating property 'filteredArgumentsMap' of task ':compileKotlinMetadata'
   > Could not resolve all files for configuration ':metadataCompileClasspath'.
      > Could not resolve io.arrow-kt:arrow-core:1.1.2.
        Required by:
            project :
         > The consumer was configured to find a usage of 'kotlin-api' of a library, preferably optimized for non-jvm, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'common'. However we cannot choose between the following variants of io.arrow-kt:arrow-core:1.1.2:
             - iosArm32ApiElements-published
             - iosArm64ApiElements-published
             - iosSimulatorArm64ApiElements-published
             - iosX64ApiElements-published
             - jsApiElements-published
             - jvmApiElements-published
             - jvmRuntimeElements-published
             - linuxX64ApiElements-published
             - macosArm64ApiElements-published
             - macosX64ApiElements-published
             - mingwX64ApiElements-published
             - tvosArm64ApiElements-published
             - tvosSimulatorArm64ApiElements-published
             - tvosX64ApiElements-published
             - watchosArm32ApiElements-published
             - watchosArm64ApiElements-published
             - watchosSimulatorArm64ApiElements-published
             - watchosX64ApiElements-published
             - watchosX86ApiElements-published

this is my commonMain

val commonMain by getting {
    dependencies {
        implementation("io.arrow-kt:arrow-core:1.1.2")
        implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.1-native-mt")
    }
}

Am I missing something here? I tried to add other multiplatform dependencies like ktor, and it did not have the same issue, it compiled just fine

Daniel Wojda

06/06/2022, 9:35 AM

👋 Hello, team! I'm trying to format my code according to Contributing guide (https://github.com/arrow-kt/arrow/blob/main/CONTRIBUTING.md#requirements-to-change-an-existing-feature)

./gradlew spotlessApply

Unfortunately, the task fails with following error:

FAILURE: Build failed with an exception.

* What went wrong:
Task 'spotlessApply' not found in root project 'arrow'.

Did I miss some configuration step?

Luke

06/14/2022, 9:11 PM

Is there a function that takes a lambda with one parameter (

(T) -> R

) and another parameter of type

and returns a lambda with no parameter (

() -> R

) which when called runs the parameter lambda (

(T) -> R

) with the instance of

tavish pegram

06/17/2022, 5:37 PM

Hey y'all! I'm just starting to learn some reactive patterns and was wondering what people see the relationship between something like arrow or arrow fx and flux/mono/etc might be (and suspend)? Would you pick one over the other, or are they complementary or isomorphic?

Partho Paul

06/22/2022, 11:16 AM

Hi all, I’m new to arrows. My use case is if an exception occurs in a function, then I want to catch it and do some post processing, something like this:

fun f1(): Either<Throwable, String> {
	either {
		doSomething() //throws exception
	}
}

fun f2() {
	f1().fold(
		{
			print("you messed up")
            doErrorHandling()
		},
		{
			print("everything's fine")
		}
	)
}

fun main() {
	runCatching{
		f2()
	}
	.onSuccess {
		print("it worked")
	}
	.onFailure {
		print("Either didn't catch exception")
	}
}

When function f1() throws exception here, the code should print “you messed up” but instead it’s printing “Either didn’t catch exception”. Am I doing anything wrong here? I’m using kotlin 1.7.0 and arrow version 1.1.2 TIA

Title

Partho Paul

06/22/2022, 11:16 AM

Hi all, I’m new to arrows. My use case is if an exception occurs in a function, then I want to catch it and do some post processing, something like this:

fun f1(): Either<Throwable, String> {
	either {
		doSomething() //throws exception
	}
}

fun f2() {
	f1().fold(
		{
			print("you messed up")
            doErrorHandling()
		},
		{
			print("everything's fine")
		}
	)
}

fun main() {
	runCatching{
		f2()
	}
	.onSuccess {
		print("it worked")
	}
	.onFailure {
		print("Either didn't catch exception")
	}
}

stojan

06/22/2022, 11:28 AM

for code that throws you can use

Either.catch {}

or similar functions e.g.

Either.catch { doSomething() }

Partho Paul

06/22/2022, 11:29 AM

@stojan had tried it as well, but it wasn’t working as I intended to. Output was same as the either block

Alejandro Serrano Mena

06/22/2022, 11:41 AM

@Partho Paul what did you try exactly? I often find the combination of

Either.catch

within an

either

block a bit confusing

you either remove the block altogether

fun f1(): Either<Throwable, String> =
	Either.catch { doSomething() }

or you need to call

bind

to make the block aware of the thing being run

fun f1(): Either<Throwable, String> {
	either {
		Either.catch { doSomething() }.bind()
	}
}

Partho Paul

06/22/2022, 11:43 AM

@Alejandro Serrano Mena I had tried the below approach with Either.catch:

fun f1(): Either<Throwable, String> {
	Either.catch {
		doSomething() //throws exception
	}
}

fun f2() {
	f1().fold(
		{
			print("you messed up")
            doErrorHandling()
		},
		{
			print("everything's fine")
		}
	)
}

fun main() {
	runCatching{
		f2()
	}
	.onSuccess {
		print("it worked")
	}
	.onFailure {
		print("Either didn't catch exception")
	}
}

Alejandro Serrano Mena

06/22/2022, 11:44 AM

note that above you are "throwing away" the either, you need to define it as

fun f1(): Either<Throwable, String> =
	Either.catch { doSomething() }

(note that I'm using

and not braces)

☝️ 3

Partho Paul

06/22/2022, 12:37 PM

@Alejandro Serrano Mena Tried using

fun f1(): Either<Throwable, String> =
	Either.catch { doSomething() }

but still not able to catch exception in f2

stojan

06/22/2022, 12:40 PM

Either.catch

is basically a `try/catch`https://github.com/arrow-kt/arrow/blob/051847de3b1d3186fc9843864aaf642a2f4a854f/ar[…]libs/core/arrow-core/src/commonMain/kotlin/arrow/core/Either.kt except if your exception is fatal e.g.: https://github.com/arrow-kt/arrow/blob/0afdd9a7cc5251cf0c50701b21ccbb5693045bde/arrow-libs/core/arrow-core/src/jvmMain/kotlin/arrow/core/NonFatal.kt#L10

Partho Paul

06/22/2022, 12:55 PM

@stojan Thanks, this helps. The Exception I was getting from f1 was LinkageError which is fatal. Tested the code with other non fatal exceptions as per @Alejandro Serrano Mena’s suggestion and it was working.

raulraja

06/22/2022, 2:51 PM

@Partho Paul I’m curious about the use case to capture a fatal ex. like in this case

LinkageError

, how did you plan to recover from it? and what leads you to this point where you care about it in user code?

Partho Paul

06/22/2022, 3:39 PM

@raulraja So for me, f1() was a db call. In my use case, I’m trying to fetch a document from db and do some action based on the data received. If I don’t receive any data or the db call fails because of any exception, then I’ll perform another set of actions. I wasn’t aware that the sdk which I’m using inside f1() will return fatal exception as the error message was misleading. Currently I don’t have anything planned for recovering from this

LinkageError

. I’m migrating a legacy codebase into a new microservice. I’ll discuss it with my colleagues if we should continue the earlier workflow or short-circuit the process. I’ll be in favour of short-circuiting as continuing the earlier workflow will make the system less reliable.

👍 2

raulraja

06/22/2022, 4:53 PM

The reason I was asking is because

LinkageError

is fatal and usually means you are missing a native library file in the path and your application should not even be running at that point. Exceptions would be some kind of local application where the user is responsible to provide the linked libraries manually but that is an odd case. Normally you can’t recover from fatal exceptions because at that point for many of them you don’t even have guarantees the VM is in a recoverable state, for example

OutOfMemoryError

👍 2

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