Add 'FunctionK' instance for converting TaskR to cats.IO #791

interop-cats/jvm/src/main/scala/scalaz/zio/interop/catsjvm.scala

@@ -17,6 +17,7 @@
 package scalaz.zio
 package interop
 
+import cats.arrow.FunctionK
 import cats.effect.{ Concurrent, ContextShift, ExitCase }
 import cats.{ effect, _ }
 import scalaz.zio.{ App, clock => zioClock, ZIO }
@@ -73,8 +74,8 @@ abstract class CatsInstances extends CatsInstances1 {
 
   implicit def taskEffectInstances[R](
     implicit runtime: Runtime[R]
-  ): effect.ConcurrentEffect[TaskR[R, ?]] with SemigroupK[TaskR[R, ?]] =
-    new CatsConcurrentEffect[R](runtime)
+  ): effect.ConcurrentEffect[TaskR[R, ?]] with SemigroupK[TaskR[R, ?]] with FunctionK[TaskR[R, ?], effect.IO] =
+    new CatsConcurrentEffect[R](runtime) with CatsFunctionK[R]
 
 }
 
@@ -313,3 +314,8 @@ private class CatsParApplicative[R, E] extends Applicative[ParIO[R, E, ?]] {
   final override def unit: ParIO[R, E, Unit] =
     Par(ZIO.unit)
 }
+
+private trait CatsFunctionK[R] extends FunctionK[TaskR[R, ?], effect.IO] {
+  this: effect.ConcurrentEffect[TaskR[R, ?]] =>
+  override def apply[A](fa: TaskR[R, A]): effect.IO[A] = toIO(fa)
+}