From 7249b4d63a72eb7fc1391e1a8106fb602f94c56a Mon Sep 17 00:00:00 2001
From: Cody Allen <ceedubs@gmail.com>
Date: Tue, 17 Nov 2015 08:09:24 -0500
Subject: [PATCH] Add PartialOrder and Eq instances for XorT

Fixes #664.
---
 core/src/main/scala/cats/data/XorT.scala      | 36 ++++++++++++++++---
 .../src/test/scala/cats/tests/XorTTests.scala | 15 ++++++++
 2 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/core/src/main/scala/cats/data/XorT.scala b/core/src/main/scala/cats/data/XorT.scala
index d5a3828568..5bc5669bbe 100644
--- a/core/src/main/scala/cats/data/XorT.scala
+++ b/core/src/main/scala/cats/data/XorT.scala
@@ -156,10 +156,9 @@ private[data] abstract class XorTInstances extends XorTInstances1 {
   }
   */
 
-  implicit def xorTEq[F[_], L, R](implicit e: Eq[F[L Xor R]]): Eq[XorT[F, L, R]] =
-    // TODO Use Eq.instance on next algebra upgrade
-    new Eq[XorT[F, L, R]] {
-      def eqv(x: XorT[F, L, R], y: XorT[F, L, R]): Boolean = e.eqv(x.value, y.value)
+  implicit def xorTOrder[F[_], L, R](implicit F: Order[F[L Xor R]]): Order[XorT[F, L, R]] =
+    new XorTOrder[F, L, R] {
+      val F0: Order[F[L Xor R]] = F
     }
 
   implicit def xorTShow[F[_], L, R](implicit sh: Show[F[L Xor R]]): Show[XorT[F, L, R]] =
@@ -200,6 +199,11 @@ private[data] abstract class XorTInstances1 extends XorTInstances2 {
     new XorTFoldable[F, L] {
       val F0: Foldable[F] = F
     }
+
+  implicit def xorTPartialOrder[F[_], L, R](implicit F: PartialOrder[F[L Xor R]]): PartialOrder[XorT[F, L, R]] =
+    new XorTPartialOrder[F, L, R] {
+      val F0: PartialOrder[F[L Xor R]] = F
+    }
 }
 
 private[data] abstract class XorTInstances2 extends XorTInstances3 {
@@ -213,6 +217,11 @@ private[data] abstract class XorTInstances2 extends XorTInstances3 {
     implicit val L0 = L
     new XorTSemigroupK[F, L] { implicit val F = F0; implicit val L = L0 }
   }
+
+  implicit def xorTEq[F[_], L, R](implicit F: Eq[F[L Xor R]]): Eq[XorT[F, L, R]] =
+    new XorTEq[F, L, R] {
+      val F0: Eq[F[L Xor R]] = F
+    }
 }
 
 private[data] abstract class XorTInstances3 {
@@ -289,3 +298,22 @@ private[data] sealed trait XorTTraverse[F[_], L] extends Traverse[XorT[F, L, ?]]
   override def traverse[G[_]: Applicative, A, B](fa: XorT[F, L, A])(f: A => G[B]): G[XorT[F, L, B]] =
     fa traverse f
 }
+
+private[data] sealed trait XorTEq[F[_], L, A] extends Eq[XorT[F, L, A]] {
+  implicit def F0: Eq[F[L Xor A]]
+
+  override def eqv(x: XorT[F, L, A], y: XorT[F, L, A]): Boolean = x === y
+}
+
+private[data] sealed trait XorTPartialOrder[F[_], L, A] extends PartialOrder[XorT[F, L, A]] with XorTEq[F, L, A]{
+  override implicit def F0: PartialOrder[F[L Xor A]]
+
+  override def partialCompare(x: XorT[F, L, A], y: XorT[F, L, A]): Double =
+    x partialCompare y
+}
+
+private[data] sealed trait XorTOrder[F[_], L, A] extends Order[XorT[F, L, A]] with XorTPartialOrder[F, L, A]{
+  override implicit def F0: Order[F[L Xor A]]
+
+  override def compare(x: XorT[F, L, A], y: XorT[F, L, A]): Int = x compare y
+}
diff --git a/tests/src/test/scala/cats/tests/XorTTests.scala b/tests/src/test/scala/cats/tests/XorTTests.scala
index 485c750d20..af4ba819b9 100644
--- a/tests/src/test/scala/cats/tests/XorTTests.scala
+++ b/tests/src/test/scala/cats/tests/XorTTests.scala
@@ -5,6 +5,7 @@ import cats.functor.Bifunctor
 import cats.data.{Xor, XorT}
 import cats.laws.discipline.{BifunctorTests, FoldableTests, FunctorTests, MonadErrorTests, MonoidKTests, SerializableTests, TraverseTests}
 import cats.laws.discipline.arbitrary._
+import algebra.laws.OrderLaws
 
 class XorTTests extends CatsSuite {
   implicit val eq0 = XorT.xorTEq[List, String, String Xor Int]
@@ -17,6 +18,8 @@ class XorTTests extends CatsSuite {
   checkAll("Bifunctor[XorT[List, ?, ?]]", SerializableTests.serializable(Bifunctor[XorT[List, ?, ?]]))
   checkAll("XorT[List, Int, ?]", TraverseTests[XorT[List, Int, ?]].foldable[Int, Int])
   checkAll("Traverse[XorT[List, Int, ?]]", SerializableTests.serializable(Traverse[XorT[List, Int, ?]]))
+  checkAll("XorT[List, String, Int]", OrderLaws[XorT[List, String, Int]].order)
+  checkAll("Order[XorT[List, String, Int]]", SerializableTests.serializable(Order[XorT[List, String, Int]]))
 
   {
     implicit val F = ListWrapper.foldable
@@ -30,6 +33,18 @@ class XorTTests extends CatsSuite {
     checkAll("Functor[XorT[ListWrapper, Int, ?]]", SerializableTests.serializable(Functor[XorT[ListWrapper, Int, ?]]))
   }
 
+  {
+    implicit val F = ListWrapper.partialOrder[String Xor Int]
+    checkAll("XorT[ListWrapper, String, Int]", OrderLaws[XorT[ListWrapper, String, Int]].partialOrder)
+    checkAll("PartialOrder[XorT[ListWrapper, String, Int]]", SerializableTests.serializable(PartialOrder[XorT[ListWrapper, String, Int]]))
+  }
+
+  {
+    implicit val F = ListWrapper.eqv[String Xor Int]
+    checkAll("XorT[ListWrapper, String, Int]", OrderLaws[XorT[ListWrapper, String, Int]].eqv)
+    checkAll("Eq[XorT[ListWrapper, String, Int]]", SerializableTests.serializable(Eq[XorT[ListWrapper, String, Int]]))
+  }
+
   // make sure that the Monad and Traverse instances don't result in ambiguous
   // Functor instances
   Functor[XorT[List, Int, ?]]