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feat: add Alternative instance for OptionT #4028

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feat: add Alternative instance for OptionT #4028

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18 changes: 13 additions & 5 deletions core/src/main/scala/cats/data/OptionT.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -393,14 +393,14 @@ sealed abstract private[data] class OptionTInstances0 extends OptionTInstances1
implicit val F = F0
}

implicit def catsDataAlternativeForOptionT[F[_]](implicit F0: Monad[F]): Alternative[OptionT[F, *]] =
new OptionTAlternative[F] { implicit val F = F0 }

implicit def catsDataContravariantMonoidalForOptionT[F[_]](implicit
F0: ContravariantMonoidal[F]
): ContravariantMonoidal[OptionT[F, *]] =
new OptionTContravariantMonoidal[F] { implicit val F = F0 }

implicit def catsDataMonoidKForOptionT[F[_]](implicit F0: Monad[F]): MonoidK[OptionT[F, *]] =
new OptionTMonoidK[F] { implicit val F = F0 }

implicit def catsDataSemigroupForOptionT[F[_], A](implicit F0: Semigroup[F[Option[A]]]): Semigroup[OptionT[F, A]] =
new OptionTSemigroup[F, A] { implicit val F = F0 }

Expand All @@ -417,8 +417,8 @@ sealed abstract private[data] class OptionTInstances0 extends OptionTInstances1
}

sealed abstract private[data] class OptionTInstances1 extends OptionTInstances2 {
implicit def catsDataSemigroupKForOptionT[F[_]](implicit F0: Monad[F]): SemigroupK[OptionT[F, *]] =
new OptionTSemigroupK[F] { implicit val F = F0 }
implicit def catsDataMonoidKForOptionT[F[_]](implicit F0: Monad[F]): MonoidK[OptionT[F, *]] =
new OptionTMonoidK[F] { implicit val F = F0 }

implicit def catsDataEqForOptionT[F[_], A](implicit F0: Eq[F[Option[A]]]): Eq[OptionT[F, A]] =
new OptionTEq[F, A] { implicit val F = F0 }
Expand All @@ -428,6 +428,9 @@ sealed abstract private[data] class OptionTInstances1 extends OptionTInstances2
}

sealed abstract private[data] class OptionTInstances2 extends OptionTInstances3 {
implicit def catsDataSemigroupKForOptionT[F[_]](implicit F0: Monad[F]): SemigroupK[OptionT[F, *]] =
new OptionTSemigroupK[F] { implicit val F = F0 }

implicit def catsDataFoldableForOptionT[F[_]](implicit F0: Foldable[F]): Foldable[OptionT[F, *]] =
new OptionTFoldable[F] { implicit val F = F0 }

Expand Down Expand Up @@ -566,6 +569,11 @@ private[data] trait OptionTMonoidK[F[_]] extends MonoidK[OptionT[F, *]] with Opt
def empty[A]: OptionT[F, A] = OptionT.none[F, A]
}

private[data] trait OptionTAlternative[F[_]]
extends Alternative[OptionT[F, *]]
with OptionTMonad[F]
with OptionTMonoidK[F] {}

sealed private[data] trait OptionTEq[F[_], A] extends Eq[OptionT[F, A]] {
implicit def F: Eq[F[Option[A]]]

Expand Down
7 changes: 7 additions & 0 deletions tests/src/test/scala/cats/tests/OptionTSuite.scala
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Expand Up @@ -125,13 +125,19 @@ class OptionTSuite extends CatsSuite {
checkAll("OptionT[ListWrapper, Int]", MonoidKTests[OptionT[ListWrapper, *]].monoidK[Int])
checkAll("MonoidK[OptionT[ListWrapper, *]]", SerializableTests.serializable(MonoidK[OptionT[ListWrapper, *]]))

checkAll("OptionT[ListWrapper, Int]", AlternativeTests[OptionT[ListWrapper, *]].monoidK[Int])
checkAll("Alternative[OptionT[ListWrapper, *]]",
SerializableTests.serializable(Alternative[OptionT[ListWrapper, *]])
)

Monad[OptionT[ListWrapper, *]]
FlatMap[OptionT[ListWrapper, *]]
Applicative[OptionT[ListWrapper, *]]
Apply[OptionT[ListWrapper, *]]
Functor[OptionT[ListWrapper, *]]
MonoidK[OptionT[ListWrapper, *]]
SemigroupK[OptionT[ListWrapper, *]]
Alternative[OptionT[ListWrapper, *]]
}

{
Expand Down Expand Up @@ -529,6 +535,7 @@ class OptionTSuite extends CatsSuite {

SemigroupK[OptionT[List, *]]
MonoidK[OptionT[List, *]]
Alternative[OptionT[List, *]]

Functor[OptionT[List, *]]
Monad[OptionT[List, *]]
Expand Down