Merge pull request #1354 from vectos/fristi/add-ior-monoid

Add semigroup instance for Ior

Author: non

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

@@ -140,6 +140,10 @@ private[data] sealed abstract class IorInstances extends IorInstances0 {
     def show(f: A Ior B): String = f.show
   }
 
+  implicit def catsDataSemigroupForIor[A: Semigroup, B: Semigroup]: Semigroup[Ior[A, B]] = new Semigroup[Ior[A, B]] {
+    def combine(x: Ior[A, B], y: Ior[A, B]) = x.append(y)
+  }
+
   implicit def catsDataMonadForIor[A: Semigroup]: Monad[A Ior ?] with RecursiveTailRecM[A Ior ?] = new Monad[A Ior ?] with RecursiveTailRecM[A Ior ?] {
     def pure[B](b: B): A Ior B = Ior.right(b)
     def flatMap[B, C](fa: A Ior B)(f: B => A Ior C): A Ior C = fa.flatMap(f)

tests/src/test/scala/cats/tests/IorTests.scala

@@ -2,7 +2,8 @@ package cats
 package tests
 
 import cats.data.Ior
-import cats.laws.discipline.{BifunctorTests, TraverseTests, MonadTests, SerializableTests, CartesianTests}
+import cats.kernel.laws.GroupLaws
+import cats.laws.discipline.{BifunctorTests, CartesianTests, MonadTests, SerializableTests, TraverseTests}
 import cats.laws.discipline.arbitrary._
 import org.scalacheck.Arbitrary._
 
@@ -20,6 +21,9 @@ class IorTests extends CatsSuite {
   checkAll("Traverse[String Ior ?]", SerializableTests.serializable(Traverse[String Ior ?]))
   checkAll("? Ior ?", BifunctorTests[Ior].bifunctor[Int, Int, Int, String, String, String])
 
+  checkAll("Semigroup[Ior[A: Semigroup, B: Semigroup]]", GroupLaws[Ior[List[Int], List[Int]]].semigroup)
+  checkAll("SerializableTest Semigroup[Ior[A: Semigroup, B: Semigroup]]", SerializableTests.serializable(Semigroup[Ior[List[Int], List[Int]]]))
+
   test("left Option is defined left and both") {
     forAll { (i: Int Ior String) =>
       (i.isLeft || i.isBoth) should === (i.left.isDefined)