2 abstract class Rexp

     3 abstract class Rexp

     3 

     4 

     4 case object NULL extends Rexp

     5 case object NULL extends Rexp

     5 case object EMPTY extends Rexp

     6 case object EMPTY extends Rexp

     6 case class CHAR(c: Char) extends Rexp

     7 case class CHAR(c: Char) extends Rexp