Scala example source code file (Dual.scala)

This example Scala source code file (Dual.scala) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" ^TM.

Learn more about this Scala project at its project page.

Java - Scala tags/keywords

dualinstances, dualinstances0, dualmonoid, dualsemigroup, monoid, order, semigroup, tag

The Dual.scala Scala example source code

package scalaz

object Dual extends DualInstances {
  def apply[A](a: A): (A @@ Tags.Dual) = Tag(a)
}

sealed abstract class DualInstances0 {
  implicit def dualSemigroup[F](implicit F0: Semigroup[F]): Semigroup[F @@ Tags.Dual] = new DualSemigroup[F] {
    implicit def F = F0
  }
}

sealed abstract class DualInstances extends DualInstances0 {
  implicit def dualMonoid[F](implicit F0: Monoid[F]): Monoid[F @@ Tags.Dual] = new DualMonoid[F] {
    implicit def F = F0
  }

  implicit def dualOrder[F](implicit F0: Order[F]): Order[F @@ Tags.Dual] =
    Tag subst F0.reverseOrder
}

private trait DualSemigroup[F] extends Semigroup[F @@ Tags.Dual] {
  implicit def F: Semigroup[F]
  def append(f1: F @@ Tags.Dual, f2: => F @@ Tags.Dual) = Tag(F.append(Tag.unwrap(f2), Tag.unwrap(f1)))
}

private trait DualMonoid[F] extends Monoid[F @@ Tags.Dual] with DualSemigroup[F] {
  implicit def F: Monoid[F]
  def zero = Tag(F.zero)
}