Can I use arrow.core typed error classes in java?

[jeusdi]

It's not clear to if I'm able to use arrow typed error classes in java.

I've took a look on arrow typed errors documentation here.

I mean, I'm aware I'm able to import maven artifact dependency into my java project, but it's not clear to how to use its classes. Am I able to use Either, or EitherKt.

Which limitations am I going to face with?

I've played a bit, but I'm getting some compilation warnings:

	public static Either<NonEmptyList<String>, Reference> of(ReferenceUniqueIdentifier referenceUniqueIdentifier) {
		...
		return null;
	}

How could I provide an either object like Either<NonEmptyList<String>, Reference?

[serras]

I strongly recommend checking Kotlin's docs about calling Kotlin functions from Java. Whether the method is available through Either or EitherKt depends on whether it is a member or an extension method, respectively.

[nomisRev]

Doing this is extremely frustrating, this might be improved but we've never properly spend time since it would almost always also affects source -and binary compatibility.

Biggest annoyance is that due to Nothing, and the difference in how generics widen that you need to explicitly cast very often in Java. This makes is not very ideal, and if you cast incorrectly you still also end up with runtime exceptions.

[serras]

It seems that vavr is the library of choice for working with Either in Java. Maybe we should improve our compatibility with it?

[nomisRev]

Yes, ideally we provide that out-of-the-box with some popular integrations but I think we need context parameters first.

context(_: Raise<String>)
fun io.vavr.Either<String, Int>.bind(): Int =
  fold({ raise(it) }) { it }

[serras]

But isn't the goal to make it easier for Java developers to consume Arrow?

[nomisRev]

Yes, I was thinking of the opposite direction. We could provide a Java VAVR DSL that allows binding to Arrow's types, but I am unsure if the ergonomics of using Arrow overall would be okay. The variance with Nothing especially comes to mind.

A Java VAVR DSL could look like this (didn't check or test code):

class Test {
  public static arrow.core.Either<String, Integer > one() {
      return (arrow.core.Either<String, Integer >) arrow.core.Either.Right(1);
  }
  
    public static io.vavr.Either<String, Integer> two() {
      return  io.vavr.Either.right(2);
  }
  
  public static io.vavr.Either<String, Integer> example() {
    return ArrowDSL.<String, Int>vavr((scope) -> {
      Integer one = scope.bind(one());
      Integer two = scope.bind(two());
      return one + two;
    });
  }
}