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admit weaker typeclass instances for OptionT when the wrapped Functor… #569

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merged 6 commits into from
Oct 27, 2015
Merged

admit weaker typeclass instances for OptionT when the wrapped Functor… #569

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fa0427e
admit weaker typeclass instances for OptionT when the wrapped Functor…
stew Oct 15, 2015
a6ed967
define OptionT ap in terms of flatMap, we can't have a separate Appli…
stew Oct 15, 2015
99c11b3
remove ap from OptionT
stew Oct 16, 2015
14f4ac3
Update OptionTTests.scala
stew Oct 18, 2015
c5ffd02
Test OptionT Functor
Oct 27, 2015
760b4c4
Merge pull request #3 from ceedubs/optiont-functor-test
stew Oct 27, 2015
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19 changes: 14 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 @@ -114,19 +114,28 @@ object OptionT extends OptionTInstances {
}
}

// TODO create prioritized hierarchy for Functor, Monad, etc
trait OptionTInstances {
implicit def optionTMonad[F[_]:Monad]: Monad[OptionT[F, ?]] =
new Monad[OptionT[F, ?]] {
trait OptionTInstances1 {
implicit def optionTFunctor[F[_]:Functor]: Functor[OptionT[F, ?]] =
new Functor[OptionT[F, ?]] {
override def map[A, B](fa: OptionT[F, A])(f: A => B): OptionT[F, B] =
fa.map(f)
}
}

trait OptionTInstances extends OptionTInstances1 {
implicit def optionTMonadCombine[F[_]](implicit F: Monad[F]): MonadCombine[OptionT[F, ?]] =
new MonadCombine[OptionT[F, ?]] {
def pure[A](a: A): OptionT[F, A] = OptionT.pure(a)

def flatMap[A, B](fa: OptionT[F, A])(f: A => OptionT[F, B]): OptionT[F, B] =
fa.flatMap(f)

override def map[A, B](fa: OptionT[F, A])(f: A => B): OptionT[F, B] =
fa.map(f)
}

override def empty[A]: OptionT[F,A] = OptionT(F.pure(None))
override def combine[A](x: OptionT[F,A], y: OptionT[F,A]): OptionT[F,A] = x orElse y
}
implicit def optionTEq[F[_], A](implicit FA: Eq[F[Option[A]]]): Eq[OptionT[F, A]] =
FA.on(_.value)
}
13 changes: 9 additions & 4 deletions tests/src/test/scala/cats/tests/OptionTTests.scala
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Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
package cats.tests

import cats.{Id, Monad}
import cats.data.{OptionT, Xor}
import cats.laws.discipline.{MonadTests, SerializableTests}
import cats.{Applicative, Id, Monad}
import cats.data.{OptionT, Validated, Xor}
import cats.laws.discipline.{ApplicativeTests, FunctorTests, MonadCombineTests, SerializableTests}
import cats.laws.discipline.arbitrary._
import org.scalacheck.{Arbitrary, Gen}

Expand Down Expand Up @@ -111,6 +111,11 @@ class OptionTTests extends CatsSuite {
}
}

checkAll("OptionT[List, Int]", MonadTests[OptionT[List, ?]].monad[Int, Int, Int])
checkAll("OptionT[List, Int]", MonadCombineTests[OptionT[List, ?]].monad[Int, Int, Int])
checkAll("MonadOptionT[List, ?]]", SerializableTests.serializable(Monad[OptionT[List, ?]]))

{
implicit val F = ListWrapper.functor
checkAll("Functor[OptionT[ListWrapper, ?]]", FunctorTests[OptionT[ListWrapper, ?]].functor[Int, Int, Int])
}
}