Problems translating Effect stack in eff-cats 2.0-RC7

ammonite.repl

Welcome to the Ammonite Repl 0.6.2
(Scala 2.11.8 Java 1.8.0_51)
@ load.plugin.ivy("com.milessabin" % "si2712fix-plugin_2.11.8" % "1.2.0")

@ load.plugin.ivy("org.spire-math" %% "kind-projector" % "0.8.0")

@ load.ivy("org.atnos" %% "eff-cats" % "2.0.0-RC7")

@ import org.atnos.eff._, all._, syntax.all._;
import org.atnos.eff._, all._, syntax.all._;
@ import cats._, data._, implicits._;
import cats._, data._, implicits._;
@ import org.atnos.eff.Interpret.Translate
import org.atnos.eff.Interpret.Translate
@   def readerToState[E, S](implicit s: State[S, ?] <= E): Translate[Reader[S, ?], E] = new Translate[Reader[S, ?], E] {
      def apply[A](fa: Reader[S, A]): Eff[E, A] =
        send(State((s: S) => (s, fa.run(s))))
    }
defined function readerToState
@ type ReadStr[E] = Member[Reader[String, ?], E]
defined type ReadStr
@ type StateStr[E] = Member[State[String, ?], E]
defined type StateStr
@ def methodWithReadEffect[E: ReadStr: _Option]: Eff[E, Unit] = ???
defined function methodWithReadEffect
@ import org.atnos.eff.Fx.prepend
import org.atnos.eff.Fx.prepend
@
def methodWithStateEffect[E: StateStr: _Option]: Eff[E, Unit] = for {_ <- methodWithReadEffect[prepend[Reader[String, ?], E]].translate(readerToState[E, String])} yield ()

cmd11.scala:1: No instance found for Member[Option, org.atnos.eff.Fx.prepend[[β$0$]cats.data.Kleisli[[A]A,String,β$0$],E]].
The effect Option is not part of the stack org.atnos.eff.Fx.prepend[[β$0$]cats.data.Kleisli[[A]A,String,β$0$],E]
 or it was not possible to determine the stack that would result from removing Option from org.atnos.eff.Fx.prepend[[β$0$]cats.data.Kleisli[[A]A,String,β$0$],E]
def methodWithStateEffect[E: StateStr: _Option]: Eff[E, Unit] = for {_ <- methodWithReadEffect[prepend[Reader[String, ?], E]].translate(readerToState[E, String])} yield ()
                                                                                              ^
Compilation Failed