lazy-option-partial-func.scala

lazy-option-partial-func.scala

trait LazyOption[+A] {
   def isDefined: Boolean
   def fold[AA >: A, B](ifSome: AA => B, ifNone: => B): B
   def orSome[AA >: A](a: => AA): AA = fold(identity[AA] _, a)
   // etc
}

object LazyOption {
  def some[A](a: => A): LazyOption[A] = new LazyOption[A] {
    lazy val a0 = a
    def isDefined = true
    def fold[AA >: A, B](ifSome: AA => B, ifNone: => B) = ifSome(a0)
  }

  def none[A]: LazyOption[A] = new LazyOption[A] {
    def isDefined = false
    def fold[AA >: A, B](ifSome: AA => B, ifNone: => B) = ifNone
  }
}

type PartialFunc[-A, +B] = (A => LazyOption[B])

object PartialFunc {
  import LazyOption._

  def compose[A, B, BB >: B, C](pf1: PartialFunc[A, B], pf2: PartialFunc[BB, C]): PartialFunc[A, C] = (a: A) => pf1(a).fold(pf2, none)
}