Blackjack hands for initial, in-play and split

Hand.scala

abstract class Hand {
    val cards: Seq[Card]
    def +(card: Card): Hand
    def split: List[Hand]
    lazy val scores = {
        def combinations(cards: Seq[Card]): List[Seq[Int]] = {
            if (!cards.isEmpty) {
                for (c ← combinations(cards.tail); v ← cards.head.rank.faceValues) yield v +: c
            } else List(Nil)
        }
        combinations(cards).map(_.sum).distinct.filter(_ < 22).sortWith(_ > _)
    }
    def score = {
        if (scores.isEmpty) 0
        else if ((cards.size == 2) && (scores.head == 21)) 22
        else scores.head
    }
    lazy val scoreText = score match {
        case 0  ⇒ "Bust"
        case 22 ⇒ "Blackjack"
        case _  ⇒ score.toString
    }
    override def toString = cards.reverse.mkString("(", ", ", ")") + " for " + scoreText
}
case class InitialHand(first: Card, second: Card) extends Hand {
    val cards = Seq(second, first)
    def +(card: Card) = InPlayHand(card, second, first)
    def split = List(SplitHand(first), SplitHand(second))
}
case class InPlayHand(cards: Card*) extends Hand {
    def +(card: Card) = InPlayHand(card +: cards: _*)
    def split = throw new UnsupportedOperationException
}
case class SplitHand(cards: Card*) extends Hand {
    def +(card: Card) = SplitHand(card +: cards: _*)
    def split = throw new UnsupportedOperationException
    override def score = 21.min(super.score)
}