gistfile1.scala

case class Action[S](when: (S) => Boolean,
                     then: (S) => Either[String, S],
                     name: String = "")
{
  def apply(state: S): Either[String, S] =
    if (when(state)) then(state)
    else Left(s"The system could not execute the action '$name'.")
}

case class Goal[S](actionSet: List[Action[S]], name: String = "") {
  def action(action: Action[S]) = Goal(action :: actionSet, name)

  def apply(state: S): Either[String, S] =
    scala.util.Random.shuffle(actionSet)
      .foldLeft[Either[String,S]](Left(s"The goal '$name' has no actions.")) {
      case (Left(_), action) => action(state)
      case (success, _) => success
    }
}

def a1 = Action[Int]( _ % 2 == 0,  i => Right(i + 1), "Add one to divisible by 2.")
def a2 = Action[Int]( _ % 3 == 0,  i => Right(i + 1), "Add one to divisible by 3.")
def a3 = Action[Int]( _ % 4 == 0,  i => Right(i + 2), "Add two to divisible by 4.")

def g1 = Goal[Int](List(), "Add")
def g2 = g1.action(a1)
def g3 = g2.action(a2)
def g4 = g3.action(a3)