Monoid Stuff

monoid.scala

      sealed trait Foobar
      case object Foo extends Foobar
      case object Bar extends Foobar

      case class Baz(foo: Boolean = false, bar: Boolean = false)

      implicit val bazMon: Monoid[Baz] =
        new Monoid[Baz] {
          override def zero: Baz = Baz()
          override def append(f1: Baz, f2: => Baz): Baz =
            Baz(
              f1.foo || f2.foo,
              f1.bar || f2.bar
            )
        }

      def convert
      (a: Set[Foobar])
      (implicit mon: Monoid[Baz]): Baz =
        a.foldLeft(mon.zero) {
          case (m, n) =>
            mon.append(m, n match {
              case Foo => Baz(foo = true)
              case Bar => Baz(bar = true)
            })
        }