Add Either/Validated Parallel instance

Author: Luka Jacobowitz

core/src/main/scala/cats/instances/parallel.scala

@@ -0,0 +1,19 @@
+package cats.instances
+
+import cats.data.Validated
+import cats.kernel.Semigroup
+import cats.syntax.either._
+import cats.{Applicative, Monad, Parallel, ~>}
+
+
+trait ParallelInstances {
+  implicit def parEitherValidated[E: Semigroup] = new Parallel[Either[E, ?], Validated[E, ?]] {
+    def applicative: Applicative[Validated[E, ?]] = Validated.catsDataApplicativeErrorForValidated
+
+    def sequential(implicit M: Monad[Either[E, ?]]): Validated[E, ?] ~> Either[E, ?] =
+      λ[Validated[E, ?] ~> Either[E, ?]](_.toEither)
+
+    def parallel(implicit M: Monad[Either[E, ?]]): Either[E, ?] ~> Validated[E, ?] =
+      λ[Either[E, ?] ~> Validated[E, ?]](_.toValidated)
+  }
+}

core/src/main/scala/cats/syntax/all.scala

@@ -30,6 +30,7 @@ trait AllSyntax
     with MonoidSyntax
     with OptionSyntax
     with OrderSyntax
+    with ParallelSyntax
     with PartialOrderSyntax
     with ProfunctorSyntax
     with ReducibleSyntax