Question about `sequence` Is there a way to avoid 2 boilerpl kotlinlang #arrow

Question about `sequence`. Is there a way to avoid...

Gopal S Akshintala

12/19/2020, 6:55 AM

Question about

sequence

. Is there a way to avoid 2 boilerplate `fix()`s in the below example to get that data type? Is there any on-going development on this, now that

Kind

is being deprecated?

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val listOfOptionalNumbers: List<Either<Int, Int>> =
     listOf(1.right(), 2.right(),3.right())
val result: Either<Int, List<Int>> = 
     listOfOptionalNumbers.sequence(Either.applicative()).map { it.fix() }.fix()

Scott Christopher

12/19/2020, 11:14 AM

One option is to utilise `either.eager`:

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fun <E, A> Iterable<Either<E, A>>.sequence(): Either<E, Iterable<A>> =
    either.eager { this@sequence.map { it.bind() } }

listOf(1.right(), 2.right(), 3.right()).sequence()

Scott Christopher

12/19/2020, 11:19 AM

Or more generally:

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fun <E, A, B> Iterable<A>.traverse(f: (A) -> Either<E, B>): Either<E, Iterable<B>> =
    either.eager { this@traverse.map { f(it).bind() } }

fun <E, A> Iterable<Either<E, A>>.sequence(): Either<E, Iterable<A>> =
    this.traverse(::identity)

simon.vergauwen

12/19/2020, 11:19 AM

These methods will be added in the next version of Arrow, since we want to get rid of