Hi, I try to apply the new Raise functionality to some new code. Does this look like a correct way to use it? Trying to instantiate HttpClient and WsHttpClient in a safe way using either, catch and Raise DSL. Any feedback is appreciated.

I've just run into an interesting problem related to

raise()

. The code in my next message references different

catch()

functions, and their return type and semantic is different as well. How should I refactor the second

eagerEffect {}

call to make it execute

fold()

in the background?

Call for users and use cases for new Arrow website 🗣️ The Arrow team is currently working on a revamped website (to be announced soon), and as part of it we would like to show how our ecosystem is used in practical settings. If you are using Arrow and want to contribute to this new website, we would love to hear from you! Anything from a logo of your company as user to a description to how you use Arrow in particular is welcome. 🎙️ If you want to contribute but are not a fan of writing, I’m more than happy to sit down with you, have a friendly chat, and then write everything down. If you (and your employer) are happy with the result, we’ll then place it in our new Use cases section. 🙏 Thanks in advance for all your help!

What am I doing wrong with

Raise<R>

, how should I use it in "real" code? My problem is: 1. I've found that very often I want to know the root cause of an error - so I've reinvented the

cause

mechanism of exceptions 😐 2. I've found that by handling

raise()

-d errors, the contextual information is lost at the top level, where I maybe want to log a stack trace for easier investigation of the problem. Do you have some practical advice for using it? Maybe my head has just "stuck" thinking only by exceptions 🙂 Thanks.

is there

import arrow.core.memoize

for

suspend fun

?

is there arrow ktor call adapter? like there used to be, or maybe there still is, Retrofit adapter or

Either
    .catch { httpClient.get("") }
    .map { it.body() }

is enough?

Funny, I thought that when using

context(Raise<...>)

requires

suspend fun

since all side-effects should be

suspend fun

... am I wrong?

Hi is it possible to employ

arrow.retrofit.adapter.either.ResponseE

in retrofit calls as follows:-

@FormUrlEncoded
    @POST(OAUTH2_TOKENS_URL_PATH)
    suspend fun accessToken(
        @HeaderMap headers: Map<String, String> = emptyMap(),
        @FieldMap(encoded = true) fields: Map<String, String>
    ) : ResponseE<CallError, AccessTokenResponse>

where

CallError

is

arrow.retrofit.adapter.either.networkhandling.CallError

as when i execute my android application I recieve a kotlin serialisation error stating no serialiser can be found for CallError do i have to supply my own custom version of CallError that is annotated as @Serializable? I am using this version of Arrow

api platform('io.arrow-kt:arrow-stack:1.1.5')
api 'io.arrow-kt:arrow-core'
api 'io.arrow-kt:arrow-core-retrofit'

It's confirmed that multi-platform context receivers won't be available before Kotlin 2.0.

If I have:

fun foo() = effect {
  raise(DomainError)
}

fun bar() = effect {
  val context = ....
  val result = foo().bind()
}

data class WrappedError(val context: Context, val error: DomainError)

// elsewhere
bar().fold({ e -> // I need e to be WrappedError but I can only get the context in bar() ... and foo() raises DomainErrors w/o the context. }) { ... }

Is there a way to somehow map the error for the fold?

I'm trying to seperate this into a function outside the

effect { }

block processing the request:

val formParameters =
    catch({ call.receiveParameters() }) { e -> raise(GenericRequestFailure(e.message ?: "")) }

but I can't since I don't have a Raise<> context (and I need the ApplicationCall as the receiver), do I just have to create another effect { } block for it and then use

bind()

or is there a better way? It seems like

Either.catch...

is deprecated... (and doesn't have a raise function?)

Hi, is it possible to do something like this on Arrow ?

either {
    

   val changeType: String

    if (changeType == "do nothing") {
       //leave early, this is not an error
        return Either.Right("leave early)
    }
    ..do some complicated logic and leave
     "quit".right()
  }

about piping. is piping, with dedicated operators etc., required only in languages that don’t support extension functions? for example: F#

let f = [ 1; 2; 3; 4; 5 ] |> List.map (fun x -> x * 2) |> List.map string

Kotlin

fun f() = listOf(1, 2, 3, 4, 5).map { it * 2 }.map(Int::toString)

it’s much nicer looking in Kotlin because

map

is en extension function. same goes for

.let {}

,

.apply {}

etc.

A few questions about `Effects`: 1. Can I assume that they are what

IO

was in early versions of arrow? 2. Any advantage of using

Effect

compared to

suspended function

? 3. Where can I find some “reference” code showing how to use effects - combining small effects into larger ones, using effects in the application?

What is the current take on Kotlin's native Result vs eg Arrow Either/Try? I've used Either/Try in my previous team, about to join a team that prefer using Result instead. They seem kinda similar to me (Result needs throwables as errors which is a bit different but whatever) but then there are people that claim that Kotlin devs themselves advocate against using Result in your business code as it will catch all exceptions, which isn't really desirable (see https://stackoverflow.com/questions/70847513/when-and-how-to-use-result-in-kotlin)

Was there a plan to remove Validated in favor of Either, or did I just imagine this? Or replacing Try with Either? Something like that?

What’s with either requiring suspend? What about either.eager? Does either just require suspend so that you can use suspend functions inside of it?

Is there any better built-in options for achieving the same results as this? (Arrow 2.0, doing input validation in a function with type

EitherNel<CreateInvoiceError, A>

)

listOfNotNull(
         if (dueDate <= invoiceDate) CreateInvoiceError.InvalidDueDate(invoiceDate, dueDate) else null,
         if (rows.isEmpty()) CreateInvoiceError.NoRows else null,
      ).toNonEmptyListOrNull()?.let { raise(it) }

What’s the situation regarding multi platform? Does everything work well on iOS/Swift and the web/js/ts?

Sorry if this is off-topic, but a lot of people here have played with context receivers. If I write

interface A
interface B

context(A, B)
fun foo() { … }

can I call it like this?

class Context : A, B

with(Context()) {
    foo()
}

Said otherwise, can a single object satisfy multiple context receivers?

Is there a way to use Optics to work with KotlinX Serialization's JsonObject hierarchy? i'd like to pinpoint on certain parts of a big, very nested json and just modify it...

... it seems like it wouldn't be possible even with optics-reflect... they don't use data classes for those JsonXXX classes 😞

Trying add arrow-meta compiler plugin to my project but it just seems like nothing's working for me compileOnly "com.github.arrow-kt.arrow-meta:compiler-plugin:-SNAPSHOT" tried adding this didn't work tried every possible version tried looking at forums even chat gpt couldn't help How do I add arrow-meta to my build.gradle? I need real help here, please someone

Hello. I would like to maintain a Resource in an object with some lifecycle. Meaning the resource is acquired during instantiation of the object and should be released when done (an

onExit

method will be called). The

Rescource.use

and

resourceScope

functions only provide the resource in the lambda, however I would like to have the resource available between object initialization and

onExit

, so during the lifecycle of the object). Is there a standard way to do so? I was thinking of creating a CoroutineScope and lauching a coroutine in the

init

part, running resourceScope there and waiting for cancellation. The

onExit

method would cancel that scope. However that would mean the acquired resource would need to be defined as a

lateinit var

rather than val since the compiler does not allow initialization from within the coroutine. It also seems a bit convoluted.

class Test() {

  val scope = CoroutineScope(EmptyCoroutineContext)
  lateinit var resource: String

  init {
    scope.launch {
      resourceScope {
        resource = install({"test"}, { _,_ -> Unit })
      }
      awaitCancellation()
    }
  }

If there is a better way I would love to hear about it.

Hey folks, happy Friday! I’ve thrown together an exploratory project using Arrow 2.0 and Http4k after getting more into FP since finishing the ‘Function Programming in Kotlin’ book. If anyone could spare some time to have a quick look and provide any feedback on how I’m using Arrow whether that’s reasonable and any other places that I’m not utilising it but it could help that would be really appreciated (feel free to make a PR or just reply here). The project is a simple Http service with which you can create, get and solve simple quizzes. To use the quiz endpoints you need to register with the user endpoint and use those credentials as Basic Auth. There’s a lot of real-world input validation missing as this is just a test project. You can find it here: https://github.com/TevJ/kfp-quiz Thanks

Hi! It seems like if I have

{ "some": "json" }

and I have

JsonPath["some2"].set(json, JsonPrimitive("json2"))

it just silently doesn't do anything... I would have expected it to create the new key. Is there any way to do that?

Actually, maybe this is the behaviour of Optics? That an Optional's setter can't set what it didn't find?

Funny... even with suspendApp ( with the resource library for Ktor) and I still get things like what I posted in the thread...