Multi-parameter case classes

I am trying to write a case class that can be partially applied, but get
a compile-time error when I try to case match. Here is a trivialised
example of what I am trying to do:

sealed abstract class S {

}

case object T extends S {

}

final case class U(xs: String)(ys: String) extends S {

}

object X {
  def f(s: S): Unit = s match {
    case T => Console.println("t")
    // COMPILE-TIME ERROR
    // case U(xs)(ys) => Console.println("u " + xs + " " + ys)
  }
}

How do I do what it is that I wanna do?
Cheers for any tips.

-- 
Tony Morris
http://tmorris.net/

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