tryFreeT.scala

import scalaz._
import Scalaz._
//scalaz 7.3.0-M4
object MyFreeT extends App {
  trait MyFunctor[A]
  case class Get() extends MyFunctor[Int]
  case class Put(x: Int) extends MyFunctor[String]

  type MyOps[A] = Free[MyFunctor, A]
  type MyOpT[A] = FreeT[MyFunctor, \/[Throwable, ?], A]

  val liftGet: MyOpT[Int] =
    FreeT.liftF[MyFunctor, \/[Throwable, ?], Int](Get())
  val liftPut: MyOpT[String] =
    FreeT.liftF[MyFunctor, \/[Throwable, ?], String](Put(1))

  val forComprehension = for { g <- liftGet; p <- liftPut } yield (g + 1, p)

  object interpreter extends ~>[MyFunctor, \/[Throwable, ?]] {
    override def apply[A](a: MyFunctor[A]): \/[Throwable, A] = a match {
      case Get() => 1.right
      case Put(x) => x match {
        case 0 => new Exception().left
        case 1 => "a".right
      }
    }
  }
  val kk = forComprehension.foldMap(interpreter)
  println(kk)
}