Example of composing Monoids from the book, "Functional Programming in Scala"

MonoidTest.scala

object ComposingMonoids {
	
	// Beginning of monoid compoisition (from FP in Scala)
	// https://github.com/pchiusano/fpinscala/.../.../17.answer.scala
	def productMonoid[A, B](A: Monoid[A], B: Monoid[B]): Monoid[(A, B)] = {
		new Monoid[(A, B)] {
			def op(x: (A,B), y: (A,B) ) = (A.op(x._1, y._1) , B.op(x._2, y._2))
			val zero = (A.zero, B.zero)
		}
	}
	val intMultiplication = new Monoid[Int] {
		def op(a1: Int, a2: Int) = a1 * a2
		val zero = 1
	}

	val concatenate = new Monoid[String] {
		def op(a1: String, a2: String) = a1 + a2
		val zero = ""
	}

	def main(args: Array[String]) = {
		val x = (100, "hello")
		val y = (200, "world")

		val result: (Int, String) = productMonoid(intMultiplication, concatenate).op(x,y)
		println("result: " + result)
		assert(result._1 == 20000)
		assert(result._2 == "helloworld")
	}