Add ByColor.traverseReduce

lichess-org · Jul 10, 2023 · edbd99d · edbd99d
1 parent 920c286
commit edbd99d
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diff --git a/src/main/scala/ByColor.scala b/src/main/scala/ByColor.scala
@@ -89,6 +89,9 @@ case class ByColor[A](white: A, black: A):
   def traverse[F[_], B](f: A => F[B]): Applicative[F] ?=> F[ByColor[B]] =
     (f(white), f(black)).mapN(ByColor(_, _))
 
+  def traverseReduce[F[_], B, C](f: A => F[B])(r: (B, B) => C): Applicative[F] ?=> F[C] =
+    (f(white), f(black)).mapN(r)
+
 object ByColor:
   inline def fill[A](a: A): ByColor[A]          = ByColor(a, a)
   inline def fromPair[A](p: (A, A)): ByColor[A] = ByColor(p._1, p._2)

diff --git a/src/test/scala/ByColorTest.scala b/src/test/scala/ByColorTest.scala
@@ -119,3 +119,7 @@ class ByColorTest extends ScalaCheckSuite:
   test("traverse"):
     forAll: (bc: ByColor[Int], f: Int => Option[String]) =>
       bc.traverse(f).map(_.all) == bc.all.traverse(f)
+
+  test("traverseReduce == traverse.map.reduce"):
+    forAll: (bc: ByColor[Int], f: Int => Option[String], r: (String, String) => Long) =>
+      bc.traverseReduce(f)(r) == bc.traverse(f).map(_.reduce(r))