From 8cd81bed92e9a699b63db2b78a7a094294bd3d9d Mon Sep 17 00:00:00 2001
From: Cody Allen <cody.allen@one.verizon.com>
Date: Fri, 6 Nov 2015 08:57:44 -0500
Subject: [PATCH 1/2] Add Show[Set]

---
 core/src/main/scala/cats/std/set.scala         |  9 +++++++++
 tests/src/test/scala/cats/tests/SetTests.scala | 17 +++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/core/src/main/scala/cats/std/set.scala b/core/src/main/scala/cats/std/set.scala
index 0f759ad795..ab5a5cbc2e 100644
--- a/core/src/main/scala/cats/std/set.scala
+++ b/core/src/main/scala/cats/std/set.scala
@@ -1,6 +1,8 @@
 package cats
 package std
 
+import cats.syntax.show._
+
 trait SetInstances extends algebra.std.SetInstances {
   implicit val setInstance: Foldable[Set] with MonoidK[Set] =
     new Foldable[Set] with MonoidK[Set] {
@@ -25,4 +27,11 @@ trait SetInstances extends algebra.std.SetInstances {
     }
 
     implicit def setMonoid[A]: Monoid[Set[A]] = MonoidK[Set].algebra[A]
+
+  implicit def setShow[A:Show]: Show[Set[A]] = new Show[Set[A]] {
+    def show(fa: Set[A]): String = {
+      val elements = fa.toIterator.map(_.show).mkString(", ")
+      s"Set($elements)"
+    }
+  }
 }
diff --git a/tests/src/test/scala/cats/tests/SetTests.scala b/tests/src/test/scala/cats/tests/SetTests.scala
index fc5a29541b..571b238b0b 100644
--- a/tests/src/test/scala/cats/tests/SetTests.scala
+++ b/tests/src/test/scala/cats/tests/SetTests.scala
@@ -11,4 +11,21 @@ class SetTests extends CatsSuite {
 
   checkAll("Set[Int]", FoldableTests[Set].foldable[Int, Int])
   checkAll("Foldable[Set]", SerializableTests.serializable(Foldable[Set]))
+
+  test("show"){
+    Set(1, 1, 2, 3).show should === ("Set(1, 2, 3)")
+    Set.empty[String].show should === ("Set()")
+
+    forAll { fs: Set[String] =>
+      fs.show should === (fs.toString)
+    }
+  }
+
+  test("show keeps separate entries for items that map to identical strings"){
+    implicit val intShow: Show[Int] = Show.show(_ => "1")
+    // an implementation implemented as set.map(_.show).mkString(", ") would
+    // only show one entry in the result instead of 3, because Set.map combines
+    // duplicate items in the codomain.
+    Set(1, 2, 3).show should === ("Set(1, 1, 1)")
+  }
 }

From 736eb84d63c5076c90f7aec9dbc6d368a83b6cab Mon Sep 17 00:00:00 2001
From: Cody Allen <cody.allen@one.verizon.com>
Date: Fri, 6 Nov 2015 09:07:02 -0500
Subject: [PATCH 2/2] Clean up show implementation for Set

---
 core/src/main/scala/cats/std/set.scala | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/core/src/main/scala/cats/std/set.scala b/core/src/main/scala/cats/std/set.scala
index ab5a5cbc2e..1efeff8350 100644
--- a/core/src/main/scala/cats/std/set.scala
+++ b/core/src/main/scala/cats/std/set.scala
@@ -29,9 +29,7 @@ trait SetInstances extends algebra.std.SetInstances {
     implicit def setMonoid[A]: Monoid[Set[A]] = MonoidK[Set].algebra[A]
 
   implicit def setShow[A:Show]: Show[Set[A]] = new Show[Set[A]] {
-    def show(fa: Set[A]): String = {
-      val elements = fa.toIterator.map(_.show).mkString(", ")
-      s"Set($elements)"
-    }
+    def show(fa: Set[A]): String =
+      fa.toIterator.map(_.show).mkString("Set(", ", ", ")")
   }
 }