Shows how the Freenion works

XorExample.scala

import freek._
import cats.{Id,~>}
import cats.data.Xor
import cats.free.Free

object XorExample extends App{

  sealed trait Algebra[A]
  case object Good extends Algebra[Xor[Throwable,String]]
  case object Bad extends Algebra[Xor[Throwable,String]]

  type PRG[A] = (Algebra :|: FXNil)#Cop[A]

  def good: Free[PRG,Xor[Throwable,String]] = Good.freek[PRG]

  def bad: Free[PRG,Xor[Throwable,String]] = Bad.freek[PRG]

  val interpreter =  new (Algebra ~> Id){
    def apply[A](fa: Algebra[A]): A = fa match {
      case Good => Xor.Right("Good")
      case Bad  => Xor.Left(new RuntimeException("Bad"))
    }
  }


  type O = Xor[Throwable,?] :&: Bulb
  val freenionRight = for{
    str <- good.onionT[O]
  } yield str

  val onionMappedRight = freenionRight.map{ str =>
    str + " job sir!"
  }

  val freeRight = onionMappedRight.free
  println(freeRight.foldMap(Interpreter(interpreter).nat)) //Right(Good job sir!)


  val freenionLeft = for{
    str <- bad.onionT[O]
  } yield str

  val onionMappedLeft = freenionLeft.map{ str =>
    str + "this will never happen because of the Left"
  }

  val freeLeft = onionMappedLeft.free
  println(freeLeft.foldMap(Interpreter(interpreter).nat)) //Left(java.lang.RuntimeException: Bad)

}