Merge pull request #998 from aaronlevin/validated-semigroupk-instance

Add SemigroupK instance for Validated + tests

Author: adelbertc

core/src/main/scala/cats/data/Validated.scala

@@ -210,9 +210,19 @@ object Validated extends ValidatedInstances with ValidatedFunctions{
   final case class Invalid[+E](e: E) extends Validated[E, Nothing]
 }
 
-
 private[data] sealed abstract class ValidatedInstances extends ValidatedInstances1 {
 
+  implicit def validatedSemigroupK[A](implicit A: Semigroup[A]): SemigroupK[Validated[A,?]] =
+    new SemigroupK[Validated[A,?]] {
+      def combineK[B](x: Validated[A,B], y: Validated[A,B]): Validated[A,B] = x match {
+        case v @ Valid(_) => v
+        case Invalid(ix) => y match {
+          case Invalid(iy) => Invalid(A.combine(ix,iy))
+          case v @ Valid(_) => v
+        }
+      }
+    }
+
   implicit def validatedMonoid[A, B](implicit A: Semigroup[A], B: Monoid[B]): Monoid[Validated[A, B]] = new Monoid[Validated[A, B]] {
     def empty: Validated[A, B] = Valid(B.empty)
     def combine(x: Validated[A, B], y: Validated[A, B]): Validated[A, B] = x combine y

tests/src/test/scala/cats/tests/ValidatedTests.scala

@@ -5,6 +5,7 @@ import cats.data.{NonEmptyList, Validated, ValidatedNel, Xor, XorT}
 import cats.data.Validated.{Valid, Invalid}
 import cats.laws.discipline.{BifunctorTests, TraverseTests, ApplicativeErrorTests, SerializableTests, CartesianTests}
 import org.scalacheck.Arbitrary._
+import cats.laws.discipline.{SemigroupKTests}
 import cats.laws.discipline.arbitrary._
 import algebra.laws.{OrderLaws, GroupLaws}
 
@@ -32,6 +33,12 @@ class ValidatedTests extends CatsSuite {
 
   checkAll("Validated[String, NonEmptyList[Int]]", GroupLaws[Validated[String, NonEmptyList[Int]]].semigroup)
 
+  {
+    implicit val L = ListWrapper.semigroup[String]
+    checkAll("Validated[ListWrapper[String], ?]", SemigroupKTests[Validated[ListWrapper[String], ?]].semigroupK[Int])
+    checkAll("SemigroupK[Validated[ListWrapper[String], ?]]", SerializableTests.serializable(SemigroupK[Validated[ListWrapper[String], ?]]))
+  }
+
   {
     implicit val S = ListWrapper.partialOrder[String]
     implicit val I = ListWrapper.partialOrder[Int]