I feel stupid.. is there no way to do `Either.left...

# arrow

[Emil Kantis]

I feel stupid.. is there no way to do Either.leftOrNull()? For instance if I have a List<Either<A,B>> and want to map that into a List<A>?

[Emil Kantis]

Ah, okay.. Partially figured it out. Now just gotta turn it into some nicer code.. 🙂

val unpackedProblems = problems.mapNotNull {
      when (it) {
         is Either.Left -> it.value
         else -> null
      }
   }

[Satyam Agarwal]

Either<List<A>> would be nicer though.

[Satyam Agarwal]

Then you can take you rrrors all the way to the end

[Ivan Lorenz]

Maybe you are looking for an accumulating errors use case? Then you can enter ValidatedNel<A, B> :

val unpackedProblems = problems
 .map { it.toValidatedNel() }
 .sequenceValidated()
 .tapInvalid { //consume your NonEmptyList of A typed errors }

[Emil Kantis]

Thanks @Ivan Lorenz, that looks a lot more like what I should be doing 🙂

results
      .map { it.toValidatedNel() }
      .sequenceValidated()
      .tap { generateResultEmail(it) }
      .tapInvalid { generateProblemEmails(it) }