Merge pull request #571 from liff/topic/subflatMap

Add transform and subflatMap to OptionT and XorT

Author: ceedubs

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

@@ -39,6 +39,12 @@ final case class OptionT[F[_], A](value: F[Option[A]]) {
         case None => F.pure(None)
       })
 
+  def transform[B](f: Option[A] => Option[B])(implicit F: Functor[F]): OptionT[F, B] =
+    OptionT(F.map(value)(f))
+
+  def subflatMap[B](f: A => Option[B])(implicit F: Functor[F]): OptionT[F, B] =
+    transform(_.flatMap(f))
+
   def getOrElse(default: => A)(implicit F: Functor[F]): F[A] =
     F.map(value)(_.getOrElse(default))
 

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

@@ -61,6 +61,12 @@ case class XorT[F[_], A, B](value: F[A Xor B]) {
   def flatMapF[AA >: A, D](f: B => F[AA Xor D])(implicit F: Monad[F]): XorT[F, AA, D] =
     flatMap(f andThen XorT.apply)
 
+  def transform[C, D](f: Xor[A, B] => Xor[C, D])(implicit F: Functor[F]): XorT[F, C, D] =
+    XorT(F.map(value)(f))
+
+  def subflatMap[AA >: A, D](f: B => AA Xor D)(implicit F: Functor[F]): XorT[F, AA, D] =
+    transform(_.flatMap(f))
+
   def map[D](f: B => D)(implicit F: Functor[F]): XorT[F, A, D] = bimap(identity, f)
 
   def leftMap[C](f: A => C)(implicit F: Functor[F]): XorT[F, C, B] = bimap(f, identity)

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

@@ -116,6 +116,18 @@ class OptionTTests extends CatsSuite {
     OptionT[Xor[String, ?], Int](xor).show should === ("Xor.Right(Some(1))")
   }
 
+  test("transform consistent with value.map") {
+    forAll { (o: OptionT[List, Int], f: Option[Int] => Option[String]) =>
+      o.transform(f) should === (OptionT(o.value.map(f)))
+    }
+  }
+
+  test("subflatMap consistent with value.map+flatMap") {
+    forAll { (o: OptionT[List, Int], f: Int => Option[String]) =>
+      o.subflatMap(f) should === (OptionT(o.value.map(_.flatMap(f))))
+    }
+  }
+
   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/XorTTests.scala

@@ -91,4 +91,16 @@ class XorTTests extends CatsSuite {
     val xort = XorT.right[Id, String, Int](10)
     xort.recoverWith { case "xort" => XorT.right[Id, String, Int](5) } should === (xort)
   }
+
+  test("transform consistent with value.map") {
+    forAll { (xort: XorT[List, String, Int], f: String Xor Int => Long Xor Double) =>
+      xort.transform(f) should === (XorT(xort.value.map(f)))
+    }
+  }
+
+  test("subflatMap consistent with value.map+flatMap") {
+    forAll { (xort: XorT[List, String, Int], f: Int => String Xor Double) =>
+      xort.subflatMap(f) should === (XorT(xort.value.map(_.flatMap(f))))
+    }
+  }
 }