Add a universal zeroK instance for MonadError

Author: danslapman

src/main/scala/asyncstreams/Implicits.scala

@@ -2,21 +2,17 @@ package asyncstreams
 
 import asyncstreams.typeclass.ZeroK
 
-import scala.concurrent.{ExecutionContext, Future}
 import scala.language.higherKinds
 import scalaz.{Monad, MonadError, MonadPlus}
 
 object Implicits {
   object MonadErrorInstances {
-    implicit def streamMonadPlus[F[+_]: λ[`x[+_]` => MonadError[x, Throwable]] : ZeroK]: MonadPlus[AsyncStream[F, ?]] = new ASMonadPlusForMonadError[F]
-    implicit def impl[F[+_]: λ[`x[+_]` => MonadError[x, Throwable]] : ZeroK]: ASImpl[F] = new ASImplForMonadError[F]
+    implicit def streamMonadPlus[F[+_]: λ[`x[+_]` => MonadError[x, Throwable]]]: MonadPlus[AsyncStream[F, ?]] = new ASMonadPlusForMonadError[F]
+    implicit def impl[F[+_]: λ[`x[+_]` => MonadError[x, Throwable]]]: ASImpl[F] = new ASImplForMonadError[F]
+    implicit def zeroK[F[+_]](implicit me: MonadError[F, Throwable]): ZeroK[F] = new ZeroK[F] {
+      override def zero[A] = me.raiseError(new NoSuchElementException)
+    }
   }
 
   def asStateTOps[F[+_]: Monad](implicit methods: ASImpl[F]) = new ASStateTOps[F]
-
-  object ScalaFuture {
-    implicit def scalaFutureZero(implicit ec: ExecutionContext): ZeroK[Future] = new ZeroK[Future] {
-      override def zero[A]: Future[A] = Future.failed(new NoSuchElementException)
-    }
-  }
 }

src/test/scala/asyncstreams/monixTask/AsyncStreamTestsWithMonixTask.scala

@@ -14,7 +14,6 @@ import scala.concurrent.duration._
 import scalaz.syntax.monadPlus._
 
 class AsyncStreamTestsWithMonixTask extends FunSuite with Matchers {
-  import TaskZeroK.taskZeroK
   private implicit val scheduler = Scheduler.fixedPool("monix", 4)
   private def makeInfStream = AsyncStream.unfold[Task, Int](0)(_ + 1)
   private def wait[T](f: Task[T], d: FiniteDuration = 5.seconds): T = Await.result(f.runAsync, d)

src/test/scala/asyncstreams/monixTask/TaskZeroK.scala

@@ -13,7 +13,6 @@ import scalaz.syntax.monadPlus._
 
 class AsyncStreamMonadSyntaxTests extends FunSuite with Matchers {
   import Implicits.MonadErrorInstances._
-  import Implicits.ScalaFuture._
   import Implicits.asStateTOps
   private val ftInstance = asStateTOps[Future]
   import ftInstance._

src/test/scala/asyncstreams/stdFuture/AsyncStreamMonadSyntaxTests.scala

@@ -4,7 +4,6 @@ import java.util.concurrent.Executors
 
 import asyncstreams.Utils._
 import asyncstreams.{ASImpl, AsyncStream}
-import asyncstreams.Implicits.ScalaFuture._
 import asyncstreams.Implicits.MonadErrorInstances._
 import org.scalatest.{FunSuite, Matchers}
 

src/test/scala/asyncstreams/stdFuture/AsyncStreamTestsWithStandardFuture.scala

@@ -12,8 +12,6 @@ import scala.collection.mutable.ArrayBuffer
 import scalaz.syntax.monadPlus._
 
 class AsyncStreamTestsWithTwitterFuture extends FunSuite with Matchers with FutureInstances {
-  import TwitterFutureZeroK.zeroK
-
   private def wait[T](f: Future[T]): T = Await.result(f)
   private def makeInfStream = AsyncStream.unfold(0)(_ + 1)