cm.scala

import scalaz._, Scalaz._
 
object Main {
  trait A
  trait B
  trait AB extends A with B
 
  type ReadA[T] = Reader[A, T]
  type ReadB[T] = Reader[B, T]
  type ReadAB[T] = Reader[AB, T]
 
  val readsA: ReadA[Unit] = ().pure[ReadA]
  val readsB: ReadB[Unit] = ().pure[ReadB]

  val readsBothOptionT: OptionT[ReadAB, Unit] = {
    for {
      _ <- readsA.local[AB](x=>x).liftM[OptionT]
      _ <- readsB.local[AB](x=>x).liftM[OptionT]
    } yield ()
  }
}