isintegral.scala

    type Va[A] = Validation[String, A]
    type VaNel[A] = ValidationNel[String, A]

    import shapeless._, contrib.scalaz._, syntax.std.tuple._
    import syntax.std.function._, ops.function._
    import shapeless.ops.hlist._

    // for Kleisli and its >=>
    implicit val vaBinding = new Bind[Va] {
      def map[A, B](fa: Va[A])(f: A => B): Va[B] = fa.map(f)

      def bind[A, B](fa: Va[A])(f: A => Va[B]): Va[B] = {
        import scalaz.Validation.FlatMap._
        fa.flatMap(f)
      }
    }

    type Vali[A, B] = Kleisli[Va, A, B]

    val isIntegral = (msg: String) => Vali[Option[String], Option[Int]] {
      case None => none[Int].success
      case Some(x: String) =>
        Try(x.toInt) match {
          case Success(i) => Some(i).success
          case _ => msg.failure
        }
    }