mapN.scala

trait Functor[Box[_]] {
  def map[In, Out](boxA: Box[In])(f: In => Out): Box[Out]
}

object Functor {
  implicit val functorOption = new Functor[Option] {
    override def map[In, Out](boxA: Option[In])(f: In => Out) = boxA.map(f)
  }

  implicit val functorList = new Functor[List] {
    override def map[A, B](boxA: List[A])(f: A => B) = boxA.map(f)
  }


}

trait Semigroupal[Box[_]] {
  def product[A, B](fa: Box[A], fb: Box[B]): Box[(A, B)]
}

object Semigroupal {
  implicit val semigroupalOption = new Semigroupal[Option] {
    override def product[A, B](fa: Option[A], fb: Option[B]) = {
      (fa, fb) match {
        case (Some(a), Some(b)) => Some(a, b)
        case _ => None
      }
    }
  }
  implicit val semigroupalList = new Semigroupal[List] {
    override def product[A, B](la: List[A], lb: List[B])  : List[(A, B)] = {
      for {
        a <- la
        b <- lb
      } yield List((a, b))
    }.flatten
  }

}

val t1Int: Option[Int] = Some(5)
val t2Int: Option[Int] = Some(6)

val t1List = List(6)
val t2List = List(7)

case class MyTuple2[Box[_], T](a: Box[T], b: Box[T]) {
  def mapN(f: (T, T) => T)(implicit functor: Functor[Box], semigroupal: Semigroupal[Box]) = {
    functor.map(semigroupal.product(a, b)) { case (t1, t2) => f(t1, t2) }
  }
}

object MyTuple2 {
  implicit def t2x[Box[_],T](t: (Box[T], Box[T])) = MyTuple2(t._1, t._2)
}

import MyTuple2._
(t1Int, t2Int).mapN(_ + _)
(t1List, t2List).mapN(_ + _)