Blogger - Scalaz Motivation - 8

object Monoid {
  implicit object IntMonoid extends Monoid[Int] {
    def mzero = 0
    def mappend(a: Int, b: Int) = a + b
  }

  implicit object StringMonoid extends Monoid[String] {
    def mzero = ""
    def mappend(a1: String, a2: String) = a1 + a2
  }
}

def sum[T](xs: List[T])(implicit m: Monoid[T]): T = xs.foldLeft(m.mzero)(m.mappend)

p(sum(List(1, 2, 3))) // prints ###> 6
p(sum(List("lamb", "da"))) // prints ###> lambda