Add Bifoldable[Const]

typelevel · Feb 6, 2016 · 547ee87 · 547ee87
1 parent 720cc30
commit 547ee87
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diff --git a/core/src/main/scala/cats/data/Const.scala b/core/src/main/scala/cats/data/Const.scala
@@ -69,6 +69,15 @@ private[data] sealed abstract class ConstInstances extends ConstInstances0 {
     def combine(x: Const[A, B], y: Const[A, B]): Const[A, B] =
       x combine y
   }
+
+  implicit val constBifoldable: Bifoldable[Const] =
+    new Bifoldable[Const] {
+      def bifoldLeft[A, B, C](fab: Const[A, B], c: C)(f: (C, A) => C, g: (C, B) => C): C =
+        f(c, fab.getConst)
+
+      def bifoldRight[A, B, C](fab: Const[A, B], c: Eval[C])(f: (A, Eval[C]) => Eval[C], g: (B, Eval[C]) => Eval[C]): Eval[C] =
+        f(fab.getConst, c)
+    }
 }
 
 private[data] sealed abstract class ConstInstances0 extends ConstInstances1 {

diff --git a/tests/src/test/scala/cats/tests/ConstTests.scala b/tests/src/test/scala/cats/tests/ConstTests.scala
@@ -45,6 +45,9 @@ class ConstTests extends CatsSuite {
   checkAll("Const[String, Int]", ContravariantTests[Const[String, ?]].contravariant[Int, Int, Int])
   checkAll("Contravariant[Const[String, ?]]", SerializableTests.serializable(Contravariant[Const[String, ?]]))
 
+  checkAll("Const[?, ?]", BifoldableTests[Const].bifoldable[Int, Int, Int])
+  checkAll("Bifoldable[Const]", SerializableTests.serializable(Bifoldable[Const]))
+
   test("show") {
 
     Const(1).show should === ("Const(1)")