Evidence that a typeclass instance does not exist for a type. You probably don't want to use this.

NoImplicitFor.scala

trait Show[A] {
  def show(a: A): String
}

object Show {
  implicit val stringShow: Show[String] = new Show[String] {
    def show(a: String) = a
  }
}

trait NoImplicitFor[F[_], A]

sealed trait LowPriorityNoImplicitFor {
  implicit def lowPriorityNoImplicitFor[F[_], A]: NoImplicitFor[F, A] = new NoImplicitFor[F, A] {}
}

object NoImplicitFor extends LowPriorityNoImplicitFor {
  implicit def ambiguousPriorityNoImplicitFor1[F[_], A](implicit ev: F[A]): NoImplicitFor[F, A] = new NoImplicitFor[F, A] {}
  implicit def ambiguousPriorityNoImplicitFor2[F[_], A](implicit ev: F[A]): NoImplicitFor[F, A] = new NoImplicitFor[F, A] {}
}

object Test {
  implicitly[NoImplicitFor[Show, Int]]

  // doesn't compile
  //implicitly[NoImplicitFor[Show, String]]
}