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post.scala

trait handlersId {

  implicit val basicMathHandler = new BasicMath.Handler[Id] {
    def add(a: Int, b: Int): Id[Int] = a + b

    def subtract(a: Int, b: Int): Id[Int] = a - b

    def multiply(a: Int, b: Int): Id[Int] = a * b
  }

  implicit val highMathHandler = new HighMath.Handler[Id] {
    def power(a: Int, b: Int): Id[Int] =
      (0 until b).fold(1)((acc, _) => acc * a)
  }

}

object handlersId extends handlersId