Dependent pattern matching in Scala or just a GADT?

gistfile1.scala

trait Dep[T]

trait Pack[T] {
  val dep: Dep[T]
  val t: T
}

object Pack {
  def apply[T](d: Dep[T], t0: T) =
    new Pack[T] { val dep = d ; val t = t0 }

  def unapply[T](p: Pack[T]): Option[(Dep[T], T)] = Some(p.dep, p.t)
}

object IntDep extends Dep[Int]

object StringDep extends Dep[String]

def depMatch[T](d: Dep[T], t: T): Option[(T, T)] =
  Pack(d, t) match {
    case Pack(IntDep, i)    => Some((i, i*2))    // t refined to Int
    case Pack(StringDep, s) => Some((s, s+"!"))  // t refined to String
    case _ => None
  }

depMatch(IntDep, 23)       // 46
depMatch(StringDep, "foo") // "foo!"