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Refactor - #2812 sequence separate performance #2818

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merged 7 commits into from
Oct 17, 2022
Merged

Refactor - #2812 sequence separate performance #2818

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0654b0c
Refactor: Use fold to separate Sequence of Either
Khepu Sep 3, 2022
c6ec40e
Refactor: Use fold to separate Sequence of Validated
Khepu Sep 3, 2022
673bef7
Feature: Add tests for separating Either & Validated
Khepu Sep 3, 2022
bb66ed5
Chore: Evaluate sequences before assertion
Khepu Sep 3, 2022
518e099
Merge branch 'main' into refactor/2812-sequence-separate-performance
nomisRev Sep 12, 2022
0d1a1c4
Merge branch 'main' into refactor/2812-sequence-separate-performance
i-walker Oct 7, 2022
3bb9d6c
Merge branch 'main' into refactor/2812-sequence-separate-performance
i-walker Oct 7, 2022
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24 changes: 14 additions & 10 deletions arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/Sequence.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -593,23 +593,27 @@ public fun <A> Sequence<A>.salign(
* @receiver Iterable of Validated
* @return a tuple containing Sequence with [Either.Left] and another Sequence with its [Either.Right] values.
*/
public fun <A, B> Sequence<Either<A, B>>.separateEither(): Pair<Sequence<A>, Sequence<B>> {
val asep = flatMap { gab -> gab.fold({ sequenceOf(it) }, { emptySequence() }) }
val bsep = flatMap { gab -> gab.fold({ emptySequence() }, { sequenceOf(it) }) }
return asep to bsep
}
public fun <A, B> Sequence<Either<A, B>>.separateEither(): Pair<Sequence<A>, Sequence<B>> =
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IMO, the return type should be Pair<List<A>, List<B>>. Because we evaluate this sequence and return sequence is not lazy

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I do agree with that, is it something that I can change in this PR or would it be done along with other breaking changes?

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@hoc081098 that is a great point! We should probably post-pone that breaking change for Arrow 2.0. Shall we create an Arrow 2.0 ticket for the breaking change, and go ahead with these changes?

@Khepu the same improvement I commented on the Iterable.kt PR can probably be applied here too.

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Just looked into how Sequence methods are implemented in the STD. It will be a bit different so as to avoid realizing the entire sequence just to separate it. Most of the implementations included an internal class that implements a custom iterator object. I should be able to have a PoC tomorrow though!

fold(sequenceOf<A>() to sequenceOf<B>()) { (lefts, rights), either ->
when (either) {
is Left -> lefts + either.value to rights
is Right -> lefts to rights + either.value
}
}

/**
* Separate the inner [Validated] values into the [Validated.Invalid] and [Validated.Valid].
*
* @receiver Iterable of Validated
* @return a tuple containing Sequence with [Validated.Invalid] and another Sequence with its [Validated.Valid] values.
*/
public fun <A, B> Sequence<Validated<A, B>>.separateValidated(): Pair<Sequence<A>, Sequence<B>> {
val asep = flatMap { gab -> gab.fold({ sequenceOf(it) }, { emptySequence() }) }
val bsep = flatMap { gab -> gab.fold({ emptySequence() }, { sequenceOf(it) }) }
return asep to bsep
}
public fun <A, B> Sequence<Validated<A, B>>.separateValidated(): Pair<Sequence<A>, Sequence<B>> =
fold(sequenceOf<A>() to sequenceOf<B>()) { (invalids, valids), validated ->
when (validated) {
is Valid -> invalids to valids + validated.value
is Invalid -> invalids + validated.value to valids
}
}

public fun <E, A> Sequence<Either<E, A>>.sequence(): Either<E, List<A>> =
traverse(::identity)
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26 changes: 26 additions & 0 deletions arrow-libs/core/arrow-core/src/commonTest/kotlin/arrow/core/SequenceKTest.kt
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Expand Up @@ -307,5 +307,31 @@ class SequenceKTest : UnitSpec() {
ints.asSequence().filterOption().toList() shouldBe ints.filterOption()
}
}

"separateEither" {
checkAll(Arb.sequence(Arb.int())) { ints ->
val sequence = ints.map {
if (it % 2 == 0) it.left()
else it.right()
}

val (lefts, rights) = sequence.separateEither()

lefts.toList() to rights.toList() shouldBe ints.partition { it % 2 == 0 }
}
}

"separateValidated" {
checkAll(Arb.sequence(Arb.int())) { ints ->
val sequence = ints.map {
if (it % 2 == 0) it.invalid()
else it.valid()
}

val (invalids, valids) = sequence.separateValidated()

invalids.toList() to valids.toList() shouldBe ints.partition { it % 2 == 0 }
}
}
}
}