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slouc/ContravariantFunctor.scala

Last active May 3, 2019 09:54
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Contravariant functor
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ContravariantFunctor.scala
case class Money(amount: Int)
// contramap: B => A => F[A] => F[B]
val contramapFn: Money => Int = (money) => money.amount
implicit val moneyOrd: Ordering[Money] = Ordering.by(contramapFn)
import scala.math.Ordered._
println(Money(13) < Money(20)) // true
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