wip Free MonadPlus. add FreePlus.Gosub

ekmett/free#38 https://github.com/ekmett/free/blob/v4.2/src/Control/MonadPlus/Free.hs#L146-L149 https://github.com/ekmett/free/blob/v4.2/src/Control/MonadPlus/Free.hs#L69-L73
xuwei-k · Jan 29, 2014 · b42d789 · b42d789
1 parent fc61379
commit b42d789
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diff --git a/core/src/main/scala/scalaz/FreePlus.scala b/core/src/main/scala/scalaz/FreePlus.scala
@@ -4,34 +4,51 @@ object FreePlus extends FreePlusInstances {
   private[scalaz] final case class Pure[F[_], A](a: A) extends FreePlus[F, A]
   private[scalaz] final case class Suspend[F[_], A](a: F[FreePlus[F, A]]) extends FreePlus[F, A]
   private[scalaz] final case class Plus[F[_], A](a: IList[FreePlus[F, A]]) extends FreePlus[F, A]
+  private[scalaz] final case class Gosub[F[_], A, B](a: () => FreePlus[F, A], f: A => FreePlus[F, B]) extends FreePlus[F, B]
 
   private[this] val nil = Plus[Nothing, Nothing](INil())
 
+  def pure[F[_], A](a: A): FreePlus[F, A] = Pure(a)
+  def point[F[_]] = new (Id.Id ~> ({type λ[α] = FreePlus[F, α]})#λ) {
+    def apply[A](a: A) = Pure(a)
+  }
+  def suspend[F[_], A](a: F[FreePlus[F, A]]): FreePlus[F, A] = Suspend(a)
+  def plus[F[_], A](a: IList[FreePlus[F, A]]): FreePlus[F, A] = Plus(a)
+
   def empty[F[_], A]: FreePlus[F, A] = nil.asInstanceOf[FreePlus[F, A]]
 }
 
 sealed abstract class FreePlus[F[_], A] {
   import FreePlus._
 
-  def map[B](f: A => B)(implicit F: Functor[F]): FreePlus[F, B] = this match {
-    case Pure(a)    => Pure(f(a))
-    case Suspend(a) => Suspend(F.map(a)(_.map(f)))
-    case Plus(a)    => Plus(a.map(_.map(f)))
-  }
+  final def map[B](f: A => B)(implicit F: Functor[F]): FreePlus[F, B] =
+    flatMap(a => Pure(f(a)))
 
-  def flatMap[B](f: A => FreePlus[F, B])(implicit F: Functor[F]): FreePlus[F, B] = this match {
-    case Pure(a)    => f(a)
-    case Suspend(a) => Suspend(F.map(a)(_.flatMap(f)))
-    case Plus(a)    => Plus(a.map(_.flatMap(f)))
+  final def flatMap[B](f: A => FreePlus[F, B])(implicit F: Functor[F]): FreePlus[F, B] = this match {
+    case Gosub(a, g) => Gosub(a, (x: Any) => Gosub(() => g(x), f))
+    case a           => Gosub(() => a, f)
   }
 
-  def plus(that: FreePlus[F, A]): FreePlus[F, A] = (this, that) match {
-    case (Plus(INil()), _           ) => that
-    case (_           , Plus(INil())) => this 
-    case (Plus(a)     , Plus(b)     ) => Plus(a ::: b)
-    case (_           , _           ) => Plus(this :: that :: IList.empty)
+  final def plus(that: FreePlus[F, A])(implicit F: Functor[F]): FreePlus[F, A] = (this.resume, that.resume) match {
+    case (Right3(INil()), _             ) => that
+    case (_             , Right3(INil())) => this
+    case (Right3(a)     , Right3(b)     ) => Plus(a ::: b)
+    case (_             , _             ) => Plus(this :: that :: IList.empty)
   }
 
+  @annotation.tailrec
+  final def resume(implicit F: Functor[F]): Either3[A, F[FreePlus[F, A]], IList[FreePlus[F, A]]] = this match { 
+    case Pure(a)    => Left3(a)
+    case Suspend(a) => Middle3(a)
+    case Plus(a)    => Right3(a)
+    case a Gosub f  => a() match {
+      case Pure(b)    => f(b).resume
+      case Suspend(b) => Middle3(F.map(b)(((_: FreePlus[F, Any]) flatMap f)))
+      case Plus(b)    => Right3(b.map(_.flatMap(f)))
+      case b Gosub g  => b().flatMap((x: Any) => g(x) flatMap f).resume
+    }
+  }
+
 }
 
 sealed abstract class FreePlusInstances {
@@ -43,12 +60,13 @@ sealed abstract class FreePlusInstances {
     }
 
   implicit def freePlusEqual[F[_], A](implicit A: Equal[A], N: Equal ~> ({type λ[α] = Equal[F[α]]})#λ, F: Functor[F]): Equal[FreePlus[F, A]] = {
-    implicit val f: Equal[FreePlus[F, A]] = freePlusEqual[F, A]
-    Equal.equal{
-      case (Pure(a)   , Pure(b)   ) => A.equal(a, b)
-      case (Suspend(a), Suspend(b)) => N(freePlusEqual[F, A]).equal(a, b)
-      case (Plus(a)   , Plus(b)   ) => IList.equal(freePlusEqual[F, A]).equal(a, b)
-      case (_         , _         ) => false
+    Equal.equal{ (aa, bb) =>
+      (aa.resume, bb.resume) match {
+        case (Left3(a)  , Left3(b)  ) => A.equal(a, b)
+        case (Middle3(a), Middle3(b)) => N(freePlusEqual[F, A]).equal(a, b)
+        case (Right3(a) , Right3(b) ) => IList.equal(freePlusEqual[F, A]).equal(a, b)
+        case (_         , _         ) => false
+      }
     }
   }
 }

diff --git a/tests/src/test/scala/scalaz/FreePlusTest.scala b/tests/src/test/scala/scalaz/FreePlusTest.scala
@@ -18,11 +18,12 @@ object FreePlusTest extends SpecLite {
     import FreePlus._
     def loop(pure: Int, suspend: Int, plus: Int): Arbitrary[FreePlus[F, A]] =
       Arbitrary(Gen.frequency(
-        (10,    Functor[Arbitrary].map(A)(Pure[F, A](_)).arbitrary),
-        (suspend, Functor[Arbitrary].map(F(loop(pure + 1, suspend, plus)))(Suspend[F, A](_)).arbitrary),
-        (plus,    Functor[Arbitrary].map(loop(pure + 1, suspend, plus))(a => FreePlus.Plus[F, A](IList(a))).arbitrary)
+        (pure,    Functor[Arbitrary].map(A)(Pure[F, A](_)).arbitrary)
+//        (suspend, Functor[Arbitrary].map(F(loop(pure * 2, suspend / 2, plus / 2)))(Suspend[F, A](_)).arbitrary),
+//        (plus,    Functor[Arbitrary].map(loop(pure * 2, suspend / 2, plus / 2))(a => FreePlus.Plus[F, A](IList(a))).arbitrary)
+// TODO stack overflow
       ))
-    loop(1, 1, 1)
+    loop(10, 1, 1)
   }
 
   implicit val optionEq = new Template[Option, Equal] {