Functor test

functor.scala

trait Functor[M[_]] {
  def map[A, B](ma: M[A], f: A => B): M[B]
  def lift[A, B](f: A => B): M[A] => M[B]
}

object Functor {
  
  def apply[F[_] : Functor]: Functor[F] = implicitly[Functor[F]]
  
  implicit val optionIsFunctor = new Functor[Option] {
    override def map[A, B](ma: Option[A], f: A => B): Option[B] = ma.map(f)
    override def lift[A, B](f: A => B): Option[A] => Option[B] = ma => ma.map(f)
  }
  
  object ops {
    def map[F[_] : Functor, A, B](fa: F[A], f: A => B): F[B] = Functor[F].map(fa, f)
    def lift[F[_] : Functor, A, B](f: A => B): F[A] => F[B] = Functor[F].lift(f)
  }
}

import Functor._
import Functor.ops._

val double: Int => Int = _ * 2 
println(Functor.optionIsFunctor.map(Some(1), double).get)
println(Functor[Option].map(Some(1), double).get)
val optional: Option[Int] = Some(1)
println(map(optional, double).get)

val f: Option[Int] => Option[Int] = lift(double)
println(f(optional))