home | career | drupal | java | mac | mysql | perl | scala | uml | unix  

Scala example source code file (PlusEmpty.scala)

This example Scala source code file (PlusEmpty.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

boolean, emptylaw, equal, monad, monoid, plusempty, productplusempty

The PlusEmpty.scala Scala example source code

package scalaz

 * Universally quantified [[scalaz.Monoid]].
trait PlusEmpty[F[_]] extends Plus[F] { self =>
  def empty[A]: F[A]

  /**The composition of PlusEmpty `F` and `G`, `[x]F[G[x]]`, is a PlusEmpty */
  override def compose[G[_]]: PlusEmpty[λ[α => F[G[α]]]] =
    new CompositionPlusEmpty[F, G] {
      implicit def F = self

  /**The product of PlusEmpty `F` and `G`, `[x](F[x], G[x]])`, is a PlusEmpty */
  def product[G[_]](implicit G0: PlusEmpty[G]): PlusEmpty[λ[α => (F[α], G[α])]] =
    new ProductPlusEmpty[F, G] {
      implicit def F = self
      implicit def G = G0

  // derived functions

  def monoid[A]: Monoid[F[A]] =
    new Monoid[F[A]] {
      def append(f1: F[A], f2: => F[A]): F[A] = plus(f1, f2)
      def zero: F[A] = empty[A]

  trait EmptyLaw extends PlusLaw {
    def rightPlusIdentity[A](f1: F[A])(implicit FA: Equal[F[A]]): Boolean =
      FA.equal(plus(f1, empty[A]), f1)

    def leftPlusIdentity[A](f1: F[A])(implicit FA: Equal[F[A]]): Boolean =
      FA.equal(plus(empty[A], f1), f1)

  def plusEmptyLaw =
    new EmptyLaw {}

  val plusEmptySyntax = new scalaz.syntax.PlusEmptySyntax[F] { def F = PlusEmpty.this }

object PlusEmpty {
  @inline def apply[F[_]](implicit F: PlusEmpty[F]): PlusEmpty[F] = F

  implicit def liftPlusEmpty[M[_], N[_]](implicit M: Monad[M], P: PlusEmpty[N]): PlusEmpty[λ[α => M[N[α]]]] =
    new PlusEmpty[λ[α => M[N[α]]]] {
      def empty[A] = M.point(P.empty[A])
      def plus[A](a: M[N[A]], b: => M[N[A]]): M[N[A]] =
        M.bind(a) { a0 => M.map(b) { P.plus(a0, _) } }

Other Scala examples (source code examples)

Here is a short list of links related to this Scala PlusEmpty.scala source code file:

my book on functional programming


new blog posts


Copyright 1998-2019 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.