tofu.higherKind.Point.scala Maven / Gradle / Ivy

package tofu.higherKind
import cats.{ContravariantMonoidal, MonoidK}

/**
  * equivalent of UnitK ~> F
  * get F[A] for any given type A
  * useful for empty values or typeconstructors with phantom parameters
  * may look like a type class but is not
  * */
trait Point[F[_]] {
  def point[A]: F[A]
}

object Point {
  val unit: Point[UnitK] = new Point[UnitK] {
    def point[A]: UnitK[A] = ()
  }

  def covariant[F[+_]](fn: F[Nothing]) = new Point[F] {
    def point[A]: F[A] = fn
  }

  def contravariant[F[-_]](fn: F[Any]) = new Point[F] {
    def point[A]: F[A] = fn
  }

  def emptyK[F[_]](implicit F: MonoidK[F]): Point[F] = new Point[F] {
    def point[A]: F[A] = F.empty[A]
  }

  def contraMonoidal[F[_]](implicit F: ContravariantMonoidal[F]) = new Point[F] {
    override def point[A]: F[A] = F.trivial
  }
}