From 9906480d3bc1b3d13bc16dc3958aea57debd0460 Mon Sep 17 00:00:00 2001
From: Thanh Le <lenguyenthanh@hotmail.com>
Date: Sun, 9 Jul 2023 10:48:16 +0200
Subject: [PATCH] Implement Traverse for ByColor

---
 src/main/scala/ByColor.scala          | 13 +++++++++++++
 src/test/scala/ByColorLawsTests.scala | 11 +++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 src/test/scala/ByColorLawsTests.scala

diff --git a/src/main/scala/ByColor.scala b/src/main/scala/ByColor.scala
index 7f04271a2..e9626776d 100644
--- a/src/main/scala/ByColor.scala
+++ b/src/main/scala/ByColor.scala
@@ -4,6 +4,8 @@ import cats.{ Applicative, Eq, Functor, Monoid }
 import cats.syntax.all.*
 import scala.annotation.targetName
 import alleycats.Zero
+import cats.Traverse
+import cats.Eval
 
 case class ByColor[A](white: A, black: A):
 
@@ -104,6 +106,17 @@ object ByColor:
   given Functor[ByColor] with
     def map[A, B](fa: ByColor[A])(f: A => B): ByColor[B] = fa.map(f)
 
+  given Traverse[ByColor] with
+
+    override def foldLeft[A, B](fa: ByColor[A], b: B)(f: (B, A) => B): B =
+      fa.fold(b)(f)
+
+    override def foldRight[A, B](fa: ByColor[A], lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] =
+      Eval.defer(f(fa.white, Eval.defer(f(fa.black, lb))))
+
+    def traverse[G[_]: Applicative, A, B](fa: ByColor[A])(f: A => G[B]): G[ByColor[B]] =
+      fa.traverse(f)
+
   extension [A](bc: ByColor[IterableOnce[A]]) def flatten: List[A] = bc.all.flatten
 
   extension [A](p: (A, A)) def asByColor: ByColor[A] = ByColor(p._1, p._2)
diff --git a/src/test/scala/ByColorLawsTests.scala b/src/test/scala/ByColorLawsTests.scala
new file mode 100644
index 000000000..15382287c
--- /dev/null
+++ b/src/test/scala/ByColorLawsTests.scala
@@ -0,0 +1,11 @@
+package chess
+
+import cats.laws.discipline.FunctorTests
+import munit.DisciplineSuite
+import org.scalacheck.*
+import Arbitraries.given
+import cats.laws.discipline.TraverseTests
+
+class ByColorLawsTest extends DisciplineSuite:
+  checkAll("ByColor.FunctorLaws", FunctorTests[ByColor].functor[Int, Int, String])
+  checkAll("ByColor.TraverseLaws", TraverseTests[ByColor].traverse[Int, Int, Int, Int, Option, Option])