/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */



package scala.util.regexp

/** Basic regular expressions.
 *
 *  @author  Burak Emir
 *  @version 1.0
 */
abstract class Base
{
  type _regexpT <: RegExp

  abstract class RegExp {
    val isNullable: Boolean
  }

  object Alt {
    /** `Alt( R,R,R* )`. */
    def apply(rs: _regexpT*) =
      if (rs.size < 2) throw new SyntaxError("need at least 2 branches in Alt")
      else new Alt(rs: _*)
    // Can't enforce that statically without changing the interface
    // def apply(r1: _regexpT, r2: _regexpT, rs: _regexpT*) = new Alt(Seq(r1, r2) ++ rs: _*)
    def unapplySeq(x: Alt) = Some(x.rs)
  }

  class Alt private (val rs: _regexpT*) extends RegExp {
    final val isNullable = rs exists (_.isNullable)
  }

  object Sequ {
    /** Sequ( R,R* ) */
    def apply(rs: _regexpT*) = if (rs.isEmpty) Eps else new Sequ(rs: _*)
    def unapplySeq(x: Sequ) = Some(x.rs)
  }

  class Sequ private (val rs: _regexpT*) extends RegExp {
    final val isNullable = rs forall (_.isNullable)
  }

  case class Star(r: _regexpT) extends RegExp {
    lazy val isNullable = true
  }

  // The empty Sequ.
  case object Eps extends RegExp {
    lazy val isNullable = true
    override def ToString() = "Eps"
  }

  /** this class can be used to add meta information to regexps. */
  class Meta(r1: _regexpT) extends RegExp {
    final val isNullable = r1.isNullable
    def r = r1
  }
}
