Λrrow is a library for Typed Functional Programming in Kotlin
Related to the Arrow library for Kotlin. https://arrow-kt.io/
Questions tagged [arrow-kt]
129 questions
3
votes
1 answer
Where to do Arrow.io IO.runUnsafeSync() ? ViewModel or Activity/Fragment?
I'm trying to learn the Arrow library and improve my functional programming by transitioning some of my Android Kotlin code from more imperative style to functional style. I've been doing a type of MVI programming in the application to make testing…
user1713450
- 1,307
- 7
- 18
3
votes
1 answer
What is Monad in kotlin arrow functional programming?
Can someone explain the concept of Monad in Arrow functional programming?
https://arrow-kt.io/docs/datatypes/option/
Sujin Shrestha
- 1,203
- 2
- 13
- 23
2
votes
1 answer
kotlin.NoWhenBranchMatchedException under unit testing a tailrec function with arrow-kt in the mix
I'm testing a function with an external dependency inside of a tailrec function. The function returns an Either.
When mocking this dependency, I'm providing a single mock invocation. I get the following…
Albert Scholtz
- 337
- 3
- 15
2
votes
1 answer
How use arrow-kt to convert a function taking two parameters into a function taking a pair?
I wrote this goofy tuplize function:
fun foo(x: Int, y: Int) = 3 * x + 2 * y + 1
fun tuplize(f: (T, U) -> R): ((Pair) -> R) = { (a, b): Pair -> f(a, b) }
val xs = listOf(Pair(1, 2), Pair(42, 23))
val f = tuplize(::foo)
val…
Tobias Hermann
- 9,936
- 6
- 61
- 134
2
votes
2 answers
arrow ensure doesn't make value non nullable after check
have a question about ensure function, somehow it doesn't make null safe after check in either block.
What I am doing wrong, or is there a better way to ensure that value is not null except of using !!
here is my code
suspend fun…
Victor Orlyk
- 1,454
- 2
- 15
- 27
2
votes
2 answers
Unresolved reference in Kotlin optic data class reference
Was playing a bit with arrow library for Kotlin and found this error right out of the documentation https://arrow-kt.io/docs/optics/ . What am I doing wrong?
Unresolved reference: company
the code is next, so it is not compiling due to an error in…
Victor Orlyk
- 1,454
- 2
- 15
- 27
2
votes
1 answer
Is there any reason to use suspend fun fn(...): Either instead of suspend fun fn(...): A?
I'm mulling over something regarding suspend that Arrow's documentation explains in detail: suspend () -> A offers the same guaranties as IO.
So, according to the documentation, just using suspend we are converting our impure functions into pure…
codependent
- 23,193
- 31
- 166
- 308
2
votes
1 answer
Iso generation is supported for data classes with up to 22 constructor parameters
@optics data class test( 1,2,...23) {
companion object
}
[ERROR] Iso generation is supported for data classes with up to 22 constructor parameters.
Uma Bodduluri
- 21
- 1
2
votes
1 answer
How to propage errors from nested Eithers in Arrow-kt?
I have some code that looks like this:
data class MyStrings(val a: String, val b: String)
sealed class Error {
object SpecificError0 : Error()
object SpecificError1 : Error()
object SpecificError2 : Error()
}
fun either2():…
Somaiah Kumbera
- 7,063
- 4
- 43
- 44
2
votes
2 answers
Cut pairs with empty values from map
I'd like to filter out all the pairs with empty values
val mapOfNotEmptyPairs: Map = mapOf("key" to Some("value"), "secondKey" to None)
expected:
print(mapOfNotEmptyPairs)
// {key=value}
Marcin Charęziński
- 47
- 1
- 7
2
votes
1 answer
How to compose IO functions with other effects in Kotlin Arrow FX
We often need some request validation before handling it. With arrow v 0.8 a typical message handler looked like:
fun addToShoppingCart(request: AddToShoppingCartRequest): IO> = fx {
request
.pipe…
conceptacid
- 248
- 2
- 13
2
votes
0 answers
Why use Kind instead of F
Whenever you read Arrow.kt tutorials, as they progress, they start touting as a benefit of FP that you can abstract away your types and write everything as things like fun myFun(): Kind instead of fun myFun(): IO or fun myFun():…
user1713450
- 1,307
- 7
- 18
2
votes
1 answer
Validate an object with Arrow-kt
I have an object (book), what fields should get updated by an event (author changed). Lets say the author field of the book only changes if the author has married and changed his name, but the book won't change if the author just moved to a new…
sschrass
- 7,014
- 6
- 43
- 62
2
votes
1 answer
Idiomatic Arrow
I have the following method:
internal typealias MaybeError = Either
override fun createCompany(companyDomain: CompanyDomain): MaybeError =
checkCompany(companyDomain).map { it.toEntity() }.fold({…
m0skit0
- 25,268
- 11
- 79
- 127
2
votes
1 answer
Kotlin & Arrow.io: Transactions with IO.bracketCase
I am currently playing with Arrow.io in Kotlin and I would love to use the library (together with Spring Boot) in a project at work. One problem I don't quite know how to solve correctly is transaction management. IO.bracketCase(...) seems to me…
Jascha
- 21
- 3