Added Free instance for Id (typelevel#2383)

catostrophe · Sep 15, 2018 · 2e3a50e · 2e3a50e
1 parent b5b8f8d
commit 2e3a50e
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Showing 2 changed files with 37 additions and 16 deletions.
diff --git a/free/src/main/scala/cats/free/Free.scala b/free/src/main/scala/cats/free/Free.scala
@@ -292,21 +292,9 @@ object Free extends FreeInstances {
   def match_[F[_], G[_], A](fa: Free[F, A])(implicit F: Functor[F], I: InjectK[G, F]): Option[G[Free[F, A]]] =
     fa.resume.fold(I.prj(_), _ => None)
 
-  /**
-   * `Free[S, ?]` has a monad for any type constructor `S[_]`.
-   */
-  implicit def catsFreeMonadForFree[S[_]]: Monad[Free[S, ?]] =
-    new Monad[Free[S, ?]] with StackSafeMonad[Free[S, ?]] {
-      def pure[A](a: A): Free[S, A] = Free.pure(a)
-      override def map[A, B](fa: Free[S, A])(f: A => B): Free[S, B] = fa.map(f)
-      def flatMap[A, B](a: Free[S, A])(f: A => Free[S, B]): Free[S, B] = a.flatMap(f)
-    }
+  implicit def catsFreeMonadForId: Monad[Free[Id, ?]] = catsFreeMonadForFree[Id]
 
-  implicit def catsFreeDeferForFree[S[_]]: Defer[Free[S, ?]] =
-    new Defer[Free[S, ?]] {
-      def defer[A](fa: => Free[S, A]): Free[S, A] =
-        Free.defer(fa)
-    }
+  implicit def catsFreeDeferForId: Defer[Free[Id, ?]] = catsFreeDeferForFree[Id]
 }
 
 private trait FreeFoldable[F[_]] extends Foldable[Free[F, ?]] {
@@ -343,7 +331,26 @@ private trait FreeTraverse[F[_]] extends Traverse[Free[F, ?]] with FreeFoldable[
   override final def map[A, B](fa: Free[F, A])(f: A => B): Free[F, B] = fa.map(f)
 }
 
-sealed private[free] abstract class FreeInstances {
+sealed private[free] abstract class FreeInstances extends FreeInstances1 {
+
+  /**
+   * `Free[S, ?]` has a monad for any type constructor `S[_]`.
+   */
+  implicit def catsFreeMonadForFree[S[_]]: Monad[Free[S, ?]] =
+    new Monad[Free[S, ?]] with StackSafeMonad[Free[S, ?]] {
+      def pure[A](a: A): Free[S, A] = Free.pure(a)
+      override def map[A, B](fa: Free[S, A])(f: A => B): Free[S, B] = fa.map(f)
+      def flatMap[A, B](a: Free[S, A])(f: A => Free[S, B]): Free[S, B] = a.flatMap(f)
+    }
+
+  implicit def catsFreeDeferForFree[S[_]]: Defer[Free[S, ?]] =
+    new Defer[Free[S, ?]] {
+      def defer[A](fa: => Free[S, A]): Free[S, A] =
+        Free.defer(fa)
+    }
+}
+
+sealed private[free] abstract class FreeInstances1 {
 
   implicit def catsFreeFoldableForFree[F[_]](
     implicit

diff --git a/free/src/test/scala/cats/free/FreeSuite.scala b/free/src/test/scala/cats/free/FreeSuite.scala
@@ -15,6 +15,13 @@ class FreeSuite extends CatsSuite {
 
   implicit val iso = SemigroupalTests.Isomorphisms.invariant[Free[Option, ?]]
 
+  Monad[Free[Id, ?]]
+  implicitly[Monad[Free[Id, ?]]]
+
+  checkAll("Free[Id, ?]", DeferTests[Free[Id, ?]].defer[Int])
+  checkAll("Free[Id, ?]", MonadTests[Free[Id, ?]].monad[Int, Int, Int])
+  checkAll("Monad[Free[Id, ?]]", SerializableTests.serializable(Monad[Free[Id, ?]]))
+
   checkAll("Free[Option, ?]", DeferTests[Free[Option, ?]].defer[Int])
   checkAll("Free[Option, ?]", MonadTests[Free[Option, ?]].monad[Int, Int, Int])
   checkAll("Monad[Free[Option, ?]]", SerializableTests.serializable(Monad[Free[Option, ?]]))
@@ -224,7 +231,14 @@ object FreeSuite extends FreeSuiteInstances {
     freeEq[Function0, A]
 }
 
-sealed trait FreeSuiteInstances {
+sealed trait FreeSuiteInstances extends FreeSuiteInstances1 {
+
+  implicit def freeIdArbitrary[A](implicit A: Arbitrary[A]): Arbitrary[Free[Id, A]] = freeArbitrary[Id, A]
+
+  implicit def freeIdEq[A](implicit SA: Eq[A]): Eq[Free[Id, A]] = freeEq[Id, A]
+}
+
+sealed trait FreeSuiteInstances1 {
   val headOptionU = λ[FunctionK[List,Option]](_.headOption)
 
   private def freeGen[F[_], A](maxDepth: Int)(implicit F: Arbitrary[F[A]], A: Arbitrary[A]): Gen[Free[F, A]] = {