object Polymorphism {
  object MixIn {
    trait Animal {
      def call: String
    }

    // mix-in trait.
    class Dog extends Animal {
      override def call: String = "ワン"
    }
    class Cat extends Animal {
      override def call: String = "ニャー"
    }
  }

  object TypeClass {
    trait Animal[A] {
      def call: String
    }

    // no mix-in.
    class Dog
    class Cat

    implicit object CallingDog extends Animal[Dog] {
      override def call: String = "ワン"
    }
    implicit object CallingCat extends Animal[Cat] {
      override def call: String = "ニャー"
    }

    def call[A: Animal](a: A) = implicitly[Animal[A]].call
  }
}

object Main extends App {
  Seq(
    (new MixIn.Dog).call,
    (new MixIn.Cat).call,
    TypeClass.call(new TypeClass.Dog),
    TypeClass.call(new TypeClass.Cat)
  ) foreach {
    println
  }
}