shapeless_and_applicative_functor1.scala

  import scalaz.ValidationNel

  trait Validation[A] {
    def validate(a: A): ValidationNel[ValidationError, A]
  }

  object Validation {
    implicit def validation[A](implicit a: Validation[A]): Validation[A] = a

    // Inspired from shapeless docs
    def createInstance[A](f: A => ValidationNel[ValidationError, A]): Validation[A]  = {
      a => f(a)
    }

    implicit class Validator[A](a: A) {
      def validate(implicit validator: Validation[A]): ValidationNel[ValidationError, A] =
        validator validate a
    }

    sealed trait ValidationError

    object ValidationError {
      case class InvalidValue(msg: String) extends ValidationError
    // Bla
    }
  }