XorTStateT.scala

package org.apache.mesos.edsl

import cats.{Applicative,Functor}
import cats.data.{XorT,StateT}

package object control {
  type ErrorTStateT[F[_], S, A] = XorT[({type l[X] = StateT[F, S, X]})#l, String, A]
  def bail[F[_], S, A](msg: String)(implicit I1: Applicative[F], I2: Functor[({type l[X] = StateT[F, S, X]})#l]): ErrorTStateT[F, S, A] =
    XorT.left[({type l[X] = StateT[F, S, X]})#l, String, A](StateT.pure[F, S, String](msg))

  def state[F[_], S, A](f: (S) => (S,A))(implicit I1: Applicative[F], I2: Functor[({type l[X] = StateT[F, S, X]})#l]): ErrorTStateT[F, S, A] =
    XorT.right[({type l[X] = StateT[F, S, X]})#l,String,A](StateT.apply[F, S, A]({ s => I1.pure(f(s)) }))

}

package object test {
  import cats.free.{Trampoline}
  type TestM[A] = control.ErrorTStateT[Trampoline, Int, A]
  def bail[A](msg:String):TestM[A] = control.bail(msg)
  def state[A](f: Int => (Int,A)):TestM[A] = control.state(f)
  def get:TestM[Int] = state({ s => (s,s)})
  def put(v:Int):TestM[Unit] = state({ _ => (v,())})

  def inc: TestM[Int] =
    for {
      v <- get
      _ <- put(v + 1)
    } yield(v)

}

/*
scala> inc
res1: org.apache.mesos.edsl.test.TestM[Int] = XorT(cats.data.StateT@2e1cc1b7)

scala> inc.toEither
res2: cats.data.StateT[cats.free.Trampoline,Int,Either[String,Int]] = cats.data.StateT@2d533fef

scala> inc.toEither.run(1)
res3: cats.free.Trampoline[(Int, Either[String,Int])] = Gosub(Pure(<function1>),<function1>)

scala> inc.toEither.run(1).run
<console>:15: error: could not find implicit value for parameter S: cats.Comonad[Function0]
       inc.toEither.run(1).run
                           ^
   */