object FreeASTs { import FreeADTs._ val prg: Free[Dialog,Unit] = for { x <- Ask("What's your first name?") _ <- Tell(s"Hi, $x") y <- Ask("What's your last name?") _ <- Tell(s"Hello $x $y!!!") } yield() }

object FreeInterp { import FreeADTs._ object DialogConsole extends (Dialog ~> Id) { def apply[A](da: Dialog[A]): Id[A] = da match { case Ask(p) => println(p); readLine case Tell(s) => println(s) } } type WF[A] = Map[String,String] => A type Tester[A] = WriterT[WF,List[String],A] implicit val testerMonad = WriterT.writerTMonad[WF,List[String]] def testerToWriter[A](f: Map[String,String] => (List[String],A)) = WriterT[WF,List[String],A](f) object DialogTester extends (Dialog ~> Tester) { def apply[A](da: Dialog[A]): Tester[A] = da match { case Ask(p) => testerToWriter {m => (List(),m(p))} case Tell(s) => testerToWriter {m => (List(s),())} } } }

object SimpleFree extends App { import FreeASTs._ import FreeInterp._ //prg.foldMapRec(DialogConsole)
 prg.foldMapRec(DialogTester).run( Map("What's your first name?" -> "Johnny", "What's your last name?" -> "Foo") )._1.map(println) }