ShapelessEnum

shapelessenum.scala

// A safer ADT+shapeless alternative ...
//
object ShapelessEnumDemo extends App {
  // ADT as an enumeration. Barely any more boilerplate ...
  sealed trait WeekDay
  object WeekDay {
    val Mon, Tue, Wed, Thu, Fri, Sat, Sun = new WeekDay {}
    val values: Set[WeekDay] = Values
  }

  import WeekDay._

  def isWorkingDay(d: WeekDay) = ! (d == Sat || d == Sun)

  assert((WeekDay.values filter isWorkingDay) == Set(Mon, Tue, Wed, Thu, Fri))

  // ... the payoff ...

  def isWeekend(d: WeekDay) = d match {
    case Sat | Sun => true
    case _ => false // compile time non-exhaustive match warning/error without this case
  }

  assert(!isWeekend(Mon)) // 
}