Scala - Understanding folds on an Either type

Asked Jul 18 '19 at 09:48

Active Jul 18 '19 at 09:48

Viewed 214 times

I am trying to understand a fold example.

val rowStream: Stream[IO, Rows] = ...

rowStream.fold(Right(()): Either[RowError, Unit]) {
    case (Right(_), b) =>
        // completely succeed here
        //b.rows... etc
    case (Left(_), _) =>
        // Fail with Left(RowError)
}

In the case (Right(_), b) => what is b? Shouldn't it just be passing Right() as the case? and how is b allowed to be passed in the case?
Am I correct to say that the Right(()) passed by the fold is the folds initial value, set to a Right of Unit?

asked Jul 18 '19 at 09:48

Chris

1

is `Stream` the one in the Scala standard library? – mfirry Jul 18 '19 at 10:15
1

It looks like a `fs2.Stream` ... – Valy Dia Jul 18 '19 at 10:54
What exactly did you tried to achieve? - `fold` will accumulate all the elements in your **Stream**, in that case `b` means each element in the **Stream**. – Luis Miguel Mejía Suárez Jul 18 '19 at 12:05

Scala - Understanding folds on an Either type

0 Answers0