functors.scala

package eip

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

trait Pointed[F[_]] {
  def point[A](entity: => A): F[A]
}

trait PointedFunctor[F[_]] {
  val functor: Functor[F]
  val pointed: Pointed[F]

  def point[A](entity: => A): F[A] = pointed.point(entity)
  def fmap[A, B](f: A => B): F[A] => F[B] = functor.fmap(f)
}

// Examples

object FunctorList extends Functor[List] {
  def fmap[A, B](f: A => B) = (as: List[A]) => as.map(f)
}

object PointedList extends Pointed[List] {
  def point[A](entity: => A) = List(entity)
}

object PointedFunctorList extends PointedFunctor[List] {
  val functor = FunctorList
  val pointed = PointedList
}

object PointedOption extends Pointed[Option] {
  def point[A](entity: => A) = Option(entity)
}