Add Show for Option and OptionT

core/src/main/scala/cats/data/OptionT.scala

@@ -88,6 +88,8 @@ final case class OptionT[F[_], A](value: F[Option[A]]) {
 
   def toLeft[R](right: => R)(implicit F: Functor[F]): XorT[F, A, R] =
     XorT(cata(Xor.Right(right), Xor.Left.apply))
+
+  def show(implicit F: Show[F[Option[A]]]): String = F.show(value)
 }
 
 object OptionT extends OptionTInstances {
@@ -138,4 +140,7 @@ trait OptionTInstances extends OptionTInstances1 {
     }
   implicit def optionTEq[F[_], A](implicit FA: Eq[F[Option[A]]]): Eq[OptionT[F, A]] =
     FA.on(_.value)
+
+  implicit def optionTShow[F[_], A](implicit F: Show[F[Option[A]]]): Show[OptionT[F, A]] =
+    functor.Contravariant[Show].contramap(F)(_.value)
 }

core/src/main/scala/cats/std/option.scala

@@ -79,6 +79,14 @@ trait OptionInstances extends OptionInstances1 {
             if (y.isDefined) -1 else 0
         }
     }
+
+  implicit def showOption[A](implicit A: Show[A]): Show[Option[A]] =
+    new Show[Option[A]] {
+      def show(fa: Option[A]): String = fa match {
+        case Some(a) => s"Some(${A.show(a)})"
+        case None => "None"
+      }
+    }
 }
 
 trait OptionInstances1 extends OptionInstances2 {

tests/src/test/scala/cats/tests/OptionTTests.scala

@@ -111,6 +111,11 @@ class OptionTTests extends CatsSuite {
     }
   }
 
+  test("show"){
+    val xor: String Xor Option[Int] = Xor.right(Some(1))
+    OptionT[Xor[String, ?], Int](xor).show should === ("Xor.Right(Some(1))")
+  }
+
   checkAll("OptionT[List, Int]", MonadCombineTests[OptionT[List, ?]].monad[Int, Int, Int])
   checkAll("MonadOptionT[List, ?]]", SerializableTests.serializable(Monad[OptionT[List, ?]]))
 

tests/src/test/scala/cats/tests/OptionTests.scala

@@ -12,4 +12,13 @@ class OptionTests extends CatsSuite {
 
   checkAll("Option[Int] with Option", TraverseTests[Option].traverse[Int, Int, Int, Int, Option, Option])
   checkAll("Traverse[Option]", SerializableTests.serializable(Traverse[Option]))
+
+  test("show") {
+    none[Int].show should === ("None")
+    1.some.show should === ("Some(1)")
+
+    forAll { fs: Option[String] =>
+      fs.show should === (fs.toString)
+    }
+  }
 }