Tony Morris - catamorphism with cons list

gistfile1.scala

// Church-encoded cons list
trait MyList[A] { 
  def foldRight[B]: (A => B => B) => B => B
}

object MyList {
  def nil[A]: MyList[A] = new MyList[A] {
    def foldRight[B] = 
      _ => z => z
  }  

  def cons[A](h: A)(t: MyList[A]): MyList[A] =
    new MyList[A] {
      def foldRight[A] =
        f => z => 
          f(h)(t.foldRight(f)(z))
    }

  // Mutual inverses
  def -->[A](a: List[A]): MyList[A] = 
    a.foldRight(nil[A])((a, b) => cons[A](a)(b))
  def <--[A](a: MyList[A]): List[A] = 
    a.foldRight[List[A]](a => b => a :: b)(Nil)
  // Mutual inverses
  // scala.List[A]=MyList[A]
}