functor.scala

import scalaz._, Scalaz._

sealed trait MyOption[+A]

case class MySome[A](value: A) extends MyOption[A]

case object MyNone extends MyOption[Nothing]

object MyOption {
  implicit object MyOptionFunctor extends Functor[MyOption] {
    def map[A, B](m: MyOption[A])(f: A => B) = m match {
      case MySome(a) => MySome(f(a))
      case MyNone => MyNone
    }
  }
}

object Main extends App {
  val m: MyOption[String] = MySome("1234")
  assert(m.map(_.length) == MySome(4))
  def f[F[_]: Functor](m: F[String]) = m map (_.toInt)
  assert(f(m) == MySome(1234))
}