Merge pull request #816 from notxcain/master

Traverse instance for OneAnd
typelevel · Jan 26, 2016 · acbe54e · acbe54e
2 parents d8e7e78 + 96e92b9
commit acbe54e
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diff --git a/core/src/main/scala/cats/data/OneAnd.scala b/core/src/main/scala/cats/data/OneAnd.scala
@@ -87,7 +87,7 @@ final case class OneAnd[F[_], A](head: A, tail: F[A]) {
     s"OneAnd(${A.show(head)}, ${FA.show(tail)})"
 }
 
-private[data] sealed trait OneAndInstances extends OneAndLowPriority1 {
+private[data] sealed trait OneAndInstances extends OneAndLowPriority2 {
 
   implicit def oneAndEq[A, F[_]](implicit A: Eq[A], FA: Eq[F[A]]): Eq[OneAnd[F, A]] =
     new Eq[OneAnd[F, A]]{
@@ -163,4 +163,23 @@ trait OneAndLowPriority1 extends OneAndLowPriority0 {
     }
 }
 
+trait OneAndLowPriority2 extends OneAndLowPriority1 {
+  implicit def oneAndTraverse[F[_]](implicit F: Traverse[F]): Traverse[OneAnd[F, ?]] =
+    new Traverse[OneAnd[F, ?]] {
+      def traverse[G[_], A, B](fa: OneAnd[F, A])(f: (A) => G[B])(implicit G: Applicative[G]): G[OneAnd[F, B]] = {
+        val tail = F.traverse(fa.tail)(f)
+        val head = f(fa.head)
+        G.ap2(head, tail)(G.pure(OneAnd(_, _)))
+      }
+
+      def foldLeft[A, B](fa: OneAnd[F, A], b: B)(f: (B, A) => B): B = {
+        fa.foldLeft(b)(f)
+      }
+
+      def foldRight[A, B](fa: OneAnd[F, A], lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] = {
+        fa.foldRight(lb)(f)
+      }
+    }
+}
+
 object OneAnd extends OneAndInstances
diff --git a/tests/src/test/scala/cats/tests/OneAndTests.scala b/tests/src/test/scala/cats/tests/OneAndTests.scala
@@ -4,7 +4,7 @@ package tests
 import algebra.laws.{GroupLaws, OrderLaws}
 
 import cats.data.{NonEmptyList, OneAnd}
-import cats.laws.discipline.{ComonadTests, FunctorTests, SemigroupKTests, FoldableTests, MonadTests, SerializableTests, MonoidalTests}
+import cats.laws.discipline.{ComonadTests, FunctorTests, SemigroupKTests, FoldableTests, MonadTests, SerializableTests, MonoidalTests, TraverseTests}
 import cats.laws.discipline.arbitrary.{evalArbitrary, oneAndArbitrary}
 import cats.laws.discipline.eq._
 
@@ -13,6 +13,9 @@ import scala.util.Random
 class OneAndTests extends CatsSuite {
   checkAll("OneAnd[List, Int]", OrderLaws[OneAnd[List, Int]].eqv)
 
+  checkAll("OneAnd[List, Int] with Option", TraverseTests[OneAnd[List, ?]].traverse[Int, Int, Int, Int, Option, Option])
+  checkAll("Traverse[OneAnd[List, A]]", SerializableTests.serializable(Traverse[OneAnd[List, ?]]))
+
   implicit val iso = MonoidalTests.Isomorphisms.invariant[OneAnd[ListWrapper, ?]](OneAnd.oneAndFunctor(ListWrapper.functor))
 
   // Test instances that have more general constraints