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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") | |
} |
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