Play Framework/Scala example source code file (Monoid.scala)

This example Play Framework source code file (Monoid.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Play Framework (and Scala) source code examples by using tags.

All credit for the original source code belongs to Play Framework; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Play Framework tags/keywords

a, api, b, functional, lib, library, monoid, monoidops, play, play framework, reducer

The Monoid.scala Play Framework example source code

/*
 * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
 */
package play.api.libs.functional

trait Monoid[A] {

  def append(a1: A, a2: A): A
  def identity: A

}

class MonoidOps[A](m1: A)(implicit m: Monoid[A]) {
  def |+|(m2: A): A = m.append(m1, m2)
}

/* A practical variant of monoid act/action/operator (search on wikipedia)
 * - allows to take an element A to create a B
 * - allows a prepend/append a A to a B
 * cf Reducer[JsValue, JsArray]
 */
trait Reducer[A, B] {

  def unit(a: A): B
  def prepend(a: A, b: B): B
  def append(b: B, a: A): B

}

object Reducer {
  def apply[A, B](f: A => B)(implicit m: Monoid[B]) = new Reducer[A, B] {
    def unit(a: A): B = f(a)
    def prepend(a: A, b: B) = m.append(unit(a), b)
    def append(b: B, a: A) = m.append(b, unit(a))
  }
}