upgraded to cats 0.8.1

build.sbt

@@ -21,13 +21,13 @@ lazy val commonSettings = Seq(
     "bintray/non" at "http://dl.bintray.com/non/maven"
   ),
   libraryDependencies ++= Seq(
-    "org.typelevel"  %% "cats"           % "0.7.2",
-    "org.typelevel"   %% "alleycats-core" % "0.1.7",
+    "org.typelevel"  %% "cats"           % "0.8.1",
+    "org.typelevel"   %% "alleycats-core" % "0.1.8",
     "com.chuusai"     %% "shapeless"      % "2.3.2",
     "org.typelevel"   %% "export-hook"    % "1.1.0",
-    "org.scalatest"   %% "scalatest"      % "3.0.0-M7" % "test",
-    "org.scalacheck"  %% "scalacheck"     % "1.12.5" % "test",
-    "org.typelevel"   %% "discipline"     % "0.4" % "test",
+    "org.scalatest"   %% "scalatest"      % "3.0.0" % "test",
+    "org.scalacheck"  %% "scalacheck"     % "1.13.4" % "test",
+    "org.typelevel"   %% "discipline"     % "0.7.2" % "test",
 
     compilerPlugin("com.milessabin" % "si2712fix-plugin" % "1.1.0" cross CrossVersion.full),
     compilerPlugin("org.spire-math" %% "kind-projector" % "0.6.3")

core/src/main/scala/cats/derived/monad.scala

@@ -19,14 +19,15 @@ object MkMonad extends MkMonad0 {
   def apply[F[_]](implicit mmf: MkMonad[F]): MkMonad[F] = mmf
 }
 
-trait MkMonad0 extends MkMonad1 {
+
+private[derived] sealed abstract class MkMonad0 extends MkMonad1 {
   implicit def withConsK[F[_]](
     implicit
     P: Cached[Pure[F]],
     C: Cached[ConsK[F]],
     E: Cached[EmptyK[F]],
     F: Cached[Foldable[F]]
-  ): MkMonad[F] = new MkMonad[F] {
+  ): MkMonad[F] = new MkMonad[F] with UnsafeTailRecM[F] {
     def pure[A](x: A): F[A] = P.value.pure(x)
 
     def flatMap[A, B](fa: F[A])(f: (A) => F[B]): F[B] = {
@@ -36,25 +37,36 @@ trait MkMonad0 extends MkMonad1 {
       }.value
     }
 
-    def tailRecM[A, B](a: A)(f: (A) => F[Either[A, B]]): F[B] = defaultTailRecM(a)(f)
   }
 }
 
 
-trait MkMonad1 {
+private[derived] sealed abstract class MkMonad1 {
   implicit def withoutConsK[F[_]](
     implicit
     P: Cached[Pure[F]],
     E: Cached[EmptyK[F]],
     F: Cached[Foldable[F]]
-  ): MkMonad[F] = new MkMonad[F] {
+  ): MkMonad[F] = new MkMonad[F] with UnsafeTailRecM[F] {
     def pure[A](x: A): F[A] = P.value.pure(x)
 
     def flatMap[A, B](fa: F[A])(f: (A) => F[B]): F[B] = {
       F.value.foldLeft[A, F[B]](fa, E.value.empty[B])((_, a) => f(a))
     }
 
-    def tailRecM[A, B](a: A)(f: (A) => F[Either[A, B]]): F[B] = defaultTailRecM(a)(f)
 
   }
+
+
+  /**
+   * todo: implement a stack safe version
+   */
+  trait UnsafeTailRecM[F[_]] extends Monad[F] {
+    override def tailRecM[A, B](a: A)(f: (A) => F[Either[A, B]]): F[B] =  flatMap(f(a)) {
+      case Right(b) => pure(b)
+      case Left(nextA) => tailRecM(nextA)(f)
+    }
+  }
 }
+
+

core/src/test/scala/cats/derived/adtdefns.scala

@@ -17,7 +17,7 @@
 package cats.derived
 
 import cats.Eq
-import org.scalacheck.Arbitrary, Arbitrary.arbitrary
+import org.scalacheck.{Cogen, Arbitrary}, Arbitrary.arbitrary
 
 object TestDefns {
   sealed trait IList[A]
@@ -27,11 +27,20 @@ object TestDefns {
   object IList {
     def fromSeq[T](ts: Seq[T]): IList[T] =
       ts.foldRight(INil[T](): IList[T])(ICons(_, _))
+
+    def toList[T](l: IList[T]): List[T] = l match {
+      case INil() => Nil
+      case ICons(h, t) => h :: toList(t)
+    }
+
   }
 
   implicit def arbIList[A:Arbitrary]: Arbitrary[IList[A]] = Arbitrary(
     arbitrary[Seq[A]].map(IList.fromSeq))
 
+  implicit def cogenIList[A:Cogen]: Cogen[IList[A]] =
+    Cogen[Seq[A]].contramap(IList.toList)
+
   sealed trait Snoc[A]
   final case class SCons[A](init: Snoc[A], last: A) extends Snoc[A]
   final case class SNil[A]() extends Snoc[A]

extra-tests/src/test/scala/cats/derived/monad.scala

@@ -16,8 +16,6 @@
 
 package cats.derived
 
-import cats.data.Xor
-import cats.laws.MonadLaws
 import cats.{Eval, Foldable}, Eval.now
 
 import alleycats.{EmptyK, ConsK, Pure}, alleycats.std.all._