Add SemigroupK and MonadCombine instances for StateT.

typelevel · Jun 17, 2016 · 96b6f4d · 96b6f4d
1 parent 8f94d13
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diff --git a/core/src/main/scala/cats/data/StateT.scala b/core/src/main/scala/cats/data/StateT.scala
@@ -135,24 +135,32 @@ object StateT extends StateTInstances {
     StateT(s => F.pure((s, a)))
 }
 
-private[data] sealed abstract class StateTInstances extends StateTInstances1 {
+private[data] sealed trait StateTInstances extends StateTInstances1 {
   implicit def catsDataMonadStateForStateT[F[_], S](implicit F0: Monad[F]): MonadState[StateT[F, S, ?], S] =
     new StateTMonadState[F, S] { implicit def F = F0 }
 
   implicit def catsDataLiftForStateT[S]: TransLift.Aux[StateT[?[_], S, ?], Applicative] =
-    new TransLift[StateT[?[_], S, ?]] {
-      type TC[M[_]] = Applicative[M]
-
-      def liftT[M[_]: Applicative, A](ma: M[A]): StateT[M, S, A] = StateT(s => Applicative[M].map(ma)(s -> _))
-    }
-
+    new StateTTransLift[S] {}
 }
 
-private[data] sealed abstract class StateTInstances1 {
+private[data] sealed trait StateTInstances1 extends StateTInstances2 {
   implicit def catsDataMonadRecForStateT[F[_], S](implicit F0: MonadRec[F]): MonadRec[StateT[F, S, ?]] =
     new StateTMonadRec[F, S] { implicit def F = F0 }
 }
 
+private[data] sealed trait StateTInstances2 extends StateTInstances3 {
+  implicit def catsDataMonadCombineForStateT[F[_], S](implicit F0: MonadCombine[F]): MonadCombine[StateT[F, S, ?]] =
+    new StateTMonadCombine[F, S] { implicit def F = F0 }
+}
+
+private[data] sealed trait StateTInstances3 {
+  implicit def catsDataMonadForStateT[F[_], S](implicit F0: Monad[F]): Monad[StateT[F, S, ?]] =
+    new StateTMonad[F, S] { implicit def F = F0 }
+
+  implicit def catsDataSemigroupKForStateT[F[_], S](implicit F0: Monad[F], G0: SemigroupK[F]): SemigroupK[StateT[F, S, ?]] =
+    new StateTSemigroupK[F, S] { implicit def F = F0; implicit def G = G0 }
+}
+
 // To workaround SI-7139 `object State` needs to be defined inside the package object
 // together with the type alias.
 private[data] abstract class StateFunctions {
@@ -195,8 +203,7 @@ private[data] sealed trait StateTMonad[F[_], S] extends Monad[StateT[F, S, ?]] {
   def flatMap[A, B](fa: StateT[F, S, A])(f: A => StateT[F, S, B]): StateT[F, S, B] =
     fa.flatMap(f)
 
-  override def map[A, B](fa: StateT[F, S, A])(f: A => B): StateT[F, S, B] =
-    fa.map(f)
+  override def map[A, B](fa: StateT[F, S, A])(f: A => B): StateT[F, S, B] = fa.map(f)
 }
 
 private[data] sealed trait StateTMonadState[F[_], S] extends MonadState[StateT[F, S, ?], S] with StateTMonad[F, S] {
@@ -213,3 +220,24 @@ private[data] sealed trait StateTMonadRec[F[_], S] extends MonadRec[StateT[F, S,
       case (s, a) => F.map(f(a).run(s)) { case (s, ab) => ab.bimap((s, _), (s, _)) }
     })
 }
+
+private[data] sealed trait StateTTransLift[S] extends TransLift[StateT[?[_], S, ?]] {
+  type TC[M[_]] = Applicative[M]
+
+  def liftT[M[_]: Applicative, A](ma: M[A]): StateT[M, S, A] = StateT(s => Applicative[M].map(ma)(s -> _))
+}
+
+private[data] sealed trait StateTSemigroupK[F[_], S] extends SemigroupK[StateT[F, S, ?]] {
+  implicit def F: Monad[F]
+  implicit def G: SemigroupK[F]
+
+  def combineK[A](x: StateT[F, S, A], y: StateT[F, S, A]): StateT[F, S, A] =
+    StateT(s => G.combineK(x.run(s), y.run(s)))
+}
+
+private[data] sealed trait StateTMonadCombine[F[_], S] extends MonadCombine[StateT[F, S, ?]] with StateTMonad[F, S] with StateTSemigroupK[F, S] with StateTTransLift[S] {
+  implicit def F: MonadCombine[F]
+  override def G: MonadCombine[F] = F
+
+  def empty[A]: StateT[F, S, A] = liftT[F, A](F.empty[A])
+}
diff --git a/tests/src/test/scala/cats/tests/StateTTests.scala b/tests/src/test/scala/cats/tests/StateTTests.scala
@@ -1,9 +1,9 @@
 package cats
 package tests
 
-import cats.kernel.std.tuple._
-import cats.laws.discipline.{CartesianTests, MonadRecTests, MonadStateTests, SerializableTests}
 import cats.data.{State, StateT}
+import cats.kernel.std.tuple._
+import cats.laws.discipline._
 import cats.laws.discipline.eq._
 import cats.laws.discipline.arbitrary._
 import org.scalacheck.Arbitrary
@@ -114,14 +114,62 @@ class StateTTests extends CatsSuite {
     got should === (expected)
   }
 
+
+  implicit val iso = CartesianTests.Isomorphisms.invariant[StateT[ListWrapper, Int, ?]](StateT.catsDataMonadForStateT(ListWrapper.monad))
+
+  {
+    // F has a Monad
+    implicit val F = ListWrapper.monad
+
+    checkAll("StateT[ListWrapper, Int, Int]", MonadStateTests[StateT[ListWrapper, Int, ?], Int].monadState[Int, Int, Int])
+    // checkAll("MonadState[StateT[ListWrapper, Int, ?], Int]", SerializableTests.serializable(MonadState[StateT[ListWrapper, Int, ?], Int]))
+    checkAll("MonadState[StateT[List, Int, ?], Int]", SerializableTests.serializable(MonadState[StateT[List, Int, ?], Int]))
+
+    Monad[StateT[ListWrapper, Int, ?]]
+    FlatMap[StateT[ListWrapper, Int, ?]]
+    Applicative[StateT[ListWrapper, Int, ?]]
+    Apply[StateT[ListWrapper, Int, ?]]
+    Functor[StateT[ListWrapper, Int, ?]]
+  }
+
+  {
+    // F has a MonadRec
+    implicit val F = ListWrapper.monadRec
+
+    checkAll("StateT[ListWrapper, Int, Int]", MonadRecTests[StateT[ListWrapper, Int, ?]].monadRec[Int, Int, Int])
+    checkAll("MonadRec[StateT[ListWrapper, Int, ?]]", SerializableTests.serializable(MonadRec[StateT[ListWrapper, Int, ?]]))
+
+    Monad[StateT[ListWrapper, Int, ?]]
+    FlatMap[StateT[ListWrapper, Int, ?]]
+    Applicative[StateT[ListWrapper, Int, ?]]
+    Apply[StateT[ListWrapper, Int, ?]]
+    Functor[StateT[ListWrapper, Int, ?]]
+  }
+
   {
-    implicit val iso = CartesianTests.Isomorphisms.invariant[StateT[Option, Int, ?]]
+    // F has a Monad and a SemigroupK
+    implicit def F = ListWrapper.monad
+    implicit def S = ListWrapper.semigroupK
 
-    checkAll("StateT[Option, Int, Int]", MonadStateTests[StateT[Option, Int, ?], Int].monadState[Int, Int, Int])
-    checkAll("MonadState[StateT[Option, Int, ?], Int]", SerializableTests.serializable(MonadState[StateT[Option, Int, ?], Int]))
+    checkAll("StateT[ListWrapper, Int, Int]", SemigroupKTests[StateT[ListWrapper, Int, ?]].semigroupK[Int])
+    checkAll("SemigroupK[StateT[ListWrapper, Int, ?]]", SerializableTests.serializable(SemigroupK[StateT[ListWrapper, Int, ?]]))
+  }
 
-    checkAll("StateT[Option, Int, Int]", MonadRecTests[StateT[Option, Int, ?]].monadRec[Int, Int, Int])
-    checkAll("MonadRec[StateT[Option, Int, ?]]", SerializableTests.serializable(MonadRec[StateT[Option, Int, ?]]))
+  {
+    // F has a MonadCombine
+    implicit def F = ListWrapper.monadCombine
+
+    checkAll("StateT[ListWrapper, Int, Int]", MonadCombineTests[StateT[ListWrapper, Int, ?]].monadCombine[Int, Int, Int])
+    checkAll("MonadCombine[StateT[ListWrapper, Int, ?]]", SerializableTests.serializable(MonadCombine[StateT[ListWrapper, Int, ?]]))
+
+    Monad[StateT[ListWrapper, Int, ?]]
+    FlatMap[StateT[ListWrapper, Int, ?]]
+    Alternative[StateT[ListWrapper, Int, ?]]
+    Applicative[StateT[ListWrapper, Int, ?]]
+    Apply[StateT[ListWrapper, Int, ?]]
+    Functor[StateT[ListWrapper, Int, ?]]
+    MonoidK[StateT[ListWrapper, Int, ?]]
+    SemigroupK[StateT[ListWrapper, Int, ?]]
   }
 
   {