Semigroup & Monoid

Semigroup

A Semigroup has a binary operator. Below the typeclass definition :

trait Semigroup[A] {
  def combine(x: A, y: A): A
}

In this project we define the operator max which return the max between two values.

implicit val max = new Semigroup[Int] {
    override def combine(x: Int, y: Int): Int = if (x < y) x else y
  }

And the syntactical sugar :

implicit class SemigroupOps[A](x: A)(implicit semigroup: Semigroup[A]) {
    def |+|(y: A): A = semigroup.combine(x,y)
  }

Now we can call max in this way :

3 |+| 5
// Int: 5

Monoid

A Monoid extends Semigroup and has an additional value empty

trait Monoid[A] extends Semigroup[A] {
  def empty: A
  def combineAll(l: List[A]): A = l.foldLeft(empty)((x,y) => combine(x,y))
}

For example, this value allows to implement a method combineAll, which allows to apply the combine(x: A, y: A): A in the elements from the list in parameter

Run project

$ sbt
$ test