monoid example.scala

object ops {

  implicit class SemigroupOps[F](val self: F)(implicit val F: Semigroup[F]) {
    def |+|(other: => F): F = F.combine(self, other)
  }
}
import ops._

trait Semigroup[A] {
  def combine(a1: A, a2: A): A
}

trait Monoid[A] extends Semigroup[A] {
  def zero: A
}

case class TeamScore(goals: Int, penalties: Int)
case class Soccer(score: TeamScore)

object Main extends App {

  implicit val intsg = new Semigroup[Int] {
    override def combine(a1: Int, a2: Int): Int = a1 + a2
  }

  implicit val teamscoremonoid = new Monoid[TeamScore] {
    override def zero: TeamScore = TeamScore(0,0)
    override def combine(a1: TeamScore, a2: TeamScore): TeamScore = TeamScore(a1.goals |+| a2.goals, a1.penalties |+| a2.penalties)
  }

  implicit val scoremonoid = new Monoid[Soccer] {
    override def zero: Soccer = Soccer(TeamScore(0,0))
    override def combine(a1: Soccer, a2: Soccer): Soccer = Soccer(a1.score |+| a2.score)
  }


  def getScores[A](scores: List[A])(implicit M: Monoid[A]): A = {
    scores.fold(M.zero)(_ |+| _)
  }

  val score = getScores(List(Soccer(TeamScore(1,0)), Soccer(TeamScore(2,1)), Soccer(TeamScore(3,2))))
  val score2 = getScores(List(TeamScore(1,0), TeamScore(2,1), TeamScore(3,2)))

  println(s"$score")
  println(s"$score2")
}