1 abstract class Val

     2 case object Empty extends Val

     3 case class Char(c: Char) extends Val

     4 case class Seq(v1: Val, v2: Val) extends Val

     5 case class Left(v: Val) extends Val

     6 case class Right(v: Val) extends Val

     7 case class Stars(vs: List[Val]) extends Val

     8 case class Rec(x: String, v: Val) extends Val