Rename Gosub to FlatMapped

docs/src/main/tut/freemonad.md

@@ -477,24 +477,20 @@ If you look at implementation in cats, you will see another member of
 the `Free[_]` ADT:
 
 ```scala
-sealed abstract case class Gosub[S[_], B]() extends Free[S, B] {
-  type C
-  val a: () => Free[S, C]
-  val f: C => Free[S, B]
-}
+case class FlatMapped[S[_], B, C](c: Free[S, C], f: C => Free[S, B]) extends Free[S, B]
 ```
 
-`Gosub` represents a call to a subroutine `a` and when `a` is
+`FlatMapped` represents a call to a subroutine `c` and when `c` is
 finished, it continues the computation by calling the function `f`
-with the result of `a`.
+with the result of `c`.
 
 It is actually an optimization of `Free` structure allowing to solve a
 problem of quadratic complexity implied by very deep recursive `Free`
 computations.
 
 It is exactly the same problem as repeatedly appending to a `List[_]`.
 As the sequence of operations becomes longer, the slower a `flatMap`
-"through" the structure will be. With `Gosub`, `Free` becomes a
+"through" the structure will be. With `FlatMapped`, `Free` becomes a
 right-associated structure not subject to quadratic complexity.
 
 ## Future Work (TODO)

free/src/main/scala/cats/free/Free.scala

@@ -13,7 +13,7 @@ import cats.arrow.FunctionK
  */
 sealed abstract class Free[S[_], A] extends Product with Serializable {
 
-  import Free.{ Pure, Suspend, Gosub }
+  import Free.{ Pure, Suspend, FlatMapped }
 
   final def map[B](f: A => B): Free[S, B] =
     flatMap(a => Pure(f(a)))
@@ -23,7 +23,7 @@ sealed abstract class Free[S[_], A] extends Product with Serializable {
    * All left-associated binds are reassociated to the right.
    */
   final def flatMap[B](f: A => Free[S, B]): Free[S, B] =
-    Gosub(this, f)
+    FlatMapped(this, f)
 
   /**
    * Catamorphism. Run the first given function if Pure, otherwise,
@@ -35,8 +35,8 @@ sealed abstract class Free[S[_], A] extends Product with Serializable {
   /** Takes one evaluation step in the Free monad, re-associating left-nested binds in the process. */
   @tailrec
   final def step: Free[S, A] = this match {
-    case Gosub(Gosub(c, f), g) => c.flatMap(cc => f(cc).flatMap(g)).step
-    case Gosub(Pure(a), f) => f(a).step
+    case FlatMapped(FlatMapped(c, f), g) => c.flatMap(cc => f(cc).flatMap(g)).step
+    case FlatMapped(Pure(a), f) => f(a).step
     case x => x
   }
 
@@ -47,11 +47,11 @@ sealed abstract class Free[S[_], A] extends Product with Serializable {
   final def resume(implicit S: Functor[S]): S[Free[S, A]] Xor A = this match {
     case Pure(a) => Right(a)
     case Suspend(t) => Left(S.map(t)(Pure(_)))
-    case Gosub(c, f) =>
+    case FlatMapped(c, f) =>
       c match {
         case Pure(a) => f(a).resume
         case Suspend(t) => Left(S.map(t)(f))
-        case Gosub(d, g) => d.flatMap(dd => g(dd).flatMap(f)).resume
+        case FlatMapped(d, g) => d.flatMap(dd => g(dd).flatMap(f)).resume
       }
   }
 
@@ -98,13 +98,13 @@ sealed abstract class Free[S[_], A] extends Product with Serializable {
           S.pure(Xor.right(a))
         case Suspend(ma) =>
           S.map(ma)(Xor.right(_))
-        case Gosub(curr, f) =>
+        case FlatMapped(curr, f) =>
           curr match {
             case Pure(x) =>
               S.pure(Xor.left(f(x)))
             case Suspend(mx) =>
               S.map(mx)(x => Xor.left(f(x)))
-            case Gosub(prev, g) =>
+            case FlatMapped(prev, g) =>
               S.pure(Xor.left(prev.flatMap(w => g(w).flatMap(f))))
           }
       }
@@ -123,7 +123,7 @@ sealed abstract class Free[S[_], A] extends Product with Serializable {
     M.tailRecM(this)(_.step match {
       case Pure(a) => M.pure(Xor.right(a))
       case Suspend(sa) => M.map(f(sa))(Xor.right)
-      case Gosub(c, g) => M.map(c.foldMap(f))(cc => Xor.left(g(cc)))
+      case FlatMapped(c, g) => M.map(c.foldMap(f))(cc => Xor.left(g(cc)))
     })
 
   /**
@@ -155,7 +155,7 @@ object Free {
   private[free] final case class Suspend[S[_], A](a: S[A]) extends Free[S, A]
 
   /** Call a subroutine and continue with the given function. */
-  private[free] final case class Gosub[S[_], B, C](c: Free[S, C], f: C => Free[S, B]) extends Free[S, B]
+  private[free] final case class FlatMapped[S[_], B, C](c: Free[S, C], f: C => Free[S, B]) extends Free[S, B]
 
   /**
    * Lift a pure `A` value into the free monad.

free/src/test/scala/cats/free/FreeTests.scala

@@ -123,21 +123,21 @@ sealed trait FreeTestsInstances {
   }
 
   private def freeGen[F[_], A](maxDepth: Int)(implicit F: Arbitrary[F[A]], A: Arbitrary[A]): Gen[Free[F, A]] = {
-    val noGosub = Gen.oneOf(
+    val noFlatMapped = Gen.oneOf(
       A.arbitrary.map(Free.pure[F, A]),
       F.arbitrary.map(Free.liftF[F, A]))
 
     val nextDepth = Gen.chooseNum(1, maxDepth - 1)
 
-    def withGosub = for {
+    def withFlatMapped = for {
       fDepth <- nextDepth
       freeDepth <- nextDepth
       f <- arbFunction1[A, Free[F, A]](Arbitrary(freeGen[F, A](fDepth))).arbitrary
       freeFA <- freeGen[F, A](freeDepth)
     } yield freeFA.flatMap(f)
 
-    if (maxDepth <= 1) noGosub
-    else Gen.oneOf(noGosub, withGosub)
+    if (maxDepth <= 1) noFlatMapped
+    else Gen.oneOf(noFlatMapped, withFlatMapped)
   }
 
   implicit def freeArbitrary[F[_], A](implicit F: Arbitrary[F[A]], A: Arbitrary[A]): Arbitrary[Free[F, A]] =