chirlo

object SUG_Monads {

  trait Functor[F[_]] {
    def map[A, B](fa: F[A])(f: A => B): F[B]

    def distribute[A, B](fab: F[(A, B)]): (F[A], F[B]) =
      (map(fab)(_._1), map(fab)(_._2))

    def codistribute[A, B](e: Either[F[A], F[B]]): F[Either[A, B]] =
      e fold (map(_)(Left(_)), map(_)(Right(_)))

chirlo

object ch6_new_state {

  object State {
    def unit[S, A](a: A): State[S, A] = State(s => (a, s))

    def sequence[S, A](fs: List[State[S, A]]): State[S, List[A]] =
      fs.foldRight(unit[S, List[A]](List[A]()))((x, y) => x.map2(y)(_ :: _))

    def get[S]: State[S, S] = State(s => (s, s))

chirlo

sealed trait Result
case object X extends Result
case object O extends Result
case object Tie extends Result

object Game {
  type Player = (Result, Set[Int])

  private val emptySet: Set[Int] = Set()
  private val availableSquares = (1 to 9).toSet