An example of using Functor

object Example3 {
  import cats.Functor
  import cats.std.list._
  import cats.std.option._
  import cats.syntax.functor._
  def mul2[F[_]: Functor](functor: F[Int]): F[Int] = functor.map(_ * 2)
  mul2(List(5, 2, 3))
  mul2(Option(2))
}