cats.arrow.NaturalTransformation.scala Maven / Gradle / Ivy

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package cats
package arrow

trait NaturalTransformation[F[_], G[_]] extends Serializable { self =>
  def apply[A](fa: F[A]): G[A]

  def compose[E[_]](f: NaturalTransformation[E, F]): NaturalTransformation[E, G] =
    new NaturalTransformation[E, G] {
      def apply[A](fa: E[A]): G[A] = self.apply(f(fa))
    }

  def andThen[H[_]](f: NaturalTransformation[G, H]): NaturalTransformation[F, H] =
    f.compose(self)
}

object NaturalTransformation {
  def id[F[_]]: NaturalTransformation[F, F] =
    new NaturalTransformation[F, F] {
      def apply[A](fa: F[A]): F[A] = fa
    }
}