Hello everyone, I bumped into something while I wa...

# arrow

[gabib]

Hello everyone, I bumped into something while I was trying to do some error accumulation with the new functions from 1.2.0.

I’m using a type alias for a NonEmptyList that looks like this typealias ApplicationErrors = NonEmptyList<ApplicationError>, however when used together with the either DSL and parZipOrAccumulate the code fails to compile.

suspend fun getDetails(param: Param): Either<ApplicationErrors, User> =
either {
parZipOrAccumulate(
{ serviceOne.getUser(param).bind() },
{ serviceTwo.getUserDetails(param).bind() },
{ serviceThree.getUserPermissions(param).bind() }
) { user, details, permissions ->
// do something with the user
}
}

If I just change the return type from Either<ApplicationErrors, User> to Either<Nel<ApplicationError>, User> everything works as expected.

I wasn’t expecting this to happen, any idea why? Thank you!

[dave08]

parZipOrAccumulate gathers the errors in a nel...

[gabib]

yes, I know, but ApplicationErrors is a typealias for a NonEmptyList<ApplicationError>

[dave08]

Oh... sorry, that's VERY strange, usually typealiases don't really exist at all in compiled code. Maybe try using Intellij's decompiler to Java and compare what it gives with and without the typealias?

[simon.vergauwen]

If I just change the return type from Either<ApplicationErrors, User> to Either<Nel<ApplicationError>, User> everything works as expected.

Wow, that is very strange 🤯 Did you ever find out what was happening here?

What Kotlin version are you on? I was out in August but Arrow 1.2.1 with Kotlin 1.9.x should get released this week