set1.scala

class SetExample extends FreeSpec with Matchers {
  val userEmail = "abc@mailinator.com"
  var sentEmailTo = "NOTSENT"

  "When the winner is selected they are immediately notified by email" in {
    SelectWinnerOfCompetition(ret(userEmail), set(sentEmailTo = _))()
    assert(sentEmailTo === userEmail)
  }

  def ret[A](a: A): Unit => A = _ => a

  // carry out some side effect i.e 'set' a value indicating the side effect occurred
  def set[A](f: A => Unit): A => Unit = f(_)
}

object SelectWinnerOfCompetition {
  type EmailAddress = String
  type SelectWinner = Unit => EmailAddress
  type SendWinnerEmail = EmailAddress => Unit

  def apply(s: SelectWinner, e: SendWinnerEmail)() = e(s())
}