abstract class Rexp+ −
case object ZERO extends Rexp+ −
case object ONE extends Rexp+ −
case class CHAR(c: Char) extends Rexp+ −
case class ALT(r1: Rexp, r2: Rexp) extends Rexp + −
case class SEQ(r1: Rexp, r2: Rexp) extends Rexp + −
case class STAR(r: Rexp) extends Rexp + −