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Add EitherOps#leftMapOrKeep and EitherOps#leftFlatMapOrKeep #4638

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Merged
danicheg merged 4 commits into from
Jul 23, 2024
Merged

Add EitherOps#leftMapOrKeep and EitherOps#leftFlatMapOrKeep #4638

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e602fb4
Add EitherOps#leftMapOrKeep
danicheg Jul 20, 2024
03c055e
Add EitherOps#leftFlatMapOrKeep
danicheg Jul 20, 2024
5d74ad5
Add tests for leftMapOrKeep & leftFlatMapOrKeep
danicheg Jul 20, 2024
1ccfee3
Tweak the case in patmat
danicheg Jul 21, 2024
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12 changes: 12 additions & 0 deletions core/src/main/scala/cats/syntax/either.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -194,6 +194,12 @@ final class EitherOps[A, B](private val eab: Either[A, B]) extends AnyVal {
case r @ Right(_) => EitherUtil.leftCast(r)
}

def leftMapOrKeep[AA >: A](pf: PartialFunction[A, AA]): Either[AA, B] =
eab match {
case Left(a) => Left(pf.applyOrElse(a, identity[AA]))
case r: Right[A, B] => r
}

@deprecated("Included in the standard library", "2.1.0-RC1")
private[syntax] def flatMap[AA >: A, D](f: B => Either[AA, D]): Either[AA, D] =
eab match {
Expand All @@ -207,6 +213,12 @@ final class EitherOps[A, B](private val eab: Either[A, B]) extends AnyVal {
case r @ Right(_) => EitherUtil.leftCast(r)
}

def leftFlatMapOrKeep[AA >: A, BB >: B](pfa: PartialFunction[A, Either[AA, BB]]): Either[AA, BB] =
eab match {
case l @ Left(a) => pfa.applyOrElse(a, (_: A) => l)
case r: Right[A, B] => r
}

def compare[AA >: A, BB >: B](that: Either[AA, BB])(implicit AA: Order[AA], BB: Order[BB]): Int =
eab match {
case Left(a1) =>
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19 changes: 19 additions & 0 deletions tests/shared/src/test/scala/cats/tests/EitherSuite.scala
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Expand Up @@ -415,6 +415,25 @@ class EitherSuite extends CatsSuite {
}
}

test("leftFlatMapOrKeep consistent with leftMapOrKeep") {
forAll { (either: Either[String, Int], pf: PartialFunction[String, String]) =>
val liftedPF: PartialFunction[String, Either[String, Int]] = { case a =>
Either.left[String, Int](pf.applyOrElse(a, identity[String]))
}
assert(either.leftFlatMapOrKeep(liftedPF) === either.leftMapOrKeep(pf))
}
}

test("leftFlatMapOrKeep consistent with swap and then flatMapOrKeep") {
import cats.syntax.monad._

forAll { (either: Either[String, Int], pf: PartialFunction[String, Either[String, Int]]) =>
assert(either.leftFlatMapOrKeep(pf) === either.swap.flatMapOrKeep { case a =>
pf.applyOrElse(a, (_: String) => either).swap
}.swap)
}
}

test("raiseWhen raises when true") {
val result = Either.raiseWhen(true)("ok")
assert(result === Left("ok"))
Expand Down