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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.util.automata
import scala.util.regexp.{ Base }
import scala.collection.{ mutable, immutable }
// todo: replace global variable pos with acc
/** This class turns a regular expression over `A` into a
* [[scala.util.automata.NondetWordAutom]] over `A` using the celebrated
* position automata construction (also called ''Berry-Sethi'' or ''Glushkov'').
*/
@deprecated("This class will be removed", "2.10.0")
abstract class BaseBerrySethi {
val lang: Base
import lang.{ Alt, Eps, Meta, RegExp, Sequ, Star }
protected var pos = 0
// results which hold all info for the NondetWordAutomaton
protected var follow: mutable.HashMap[Int, Set[Int]] = _
protected var finalTag: Int = _
protected var finals: immutable.Map[Int, Int] = _ // final states
// constants --------------------------
final val emptySet: Set[Int] = Set()
private def doComp(r: RegExp, compFunction: RegExp => Set[Int]) = r match {
case x: Alt => (x.rs map compFirst).foldLeft(emptySet)(_ ++ _)
case Eps => emptySet
case x: Meta => compFunction(x.r)
case x: Sequ =>
val (l1, l2) = x.rs span (_.isNullable)
((l1 ++ (l2 take 1)) map compFunction).foldLeft(emptySet)(_ ++ _)
case Star(t) => compFunction(t)
case _ => throw new IllegalArgumentException("unexpected pattern " + r.getClass)
}
/** Computes `first(r)` for the word regexp `r`. */
protected def compFirst(r: RegExp): Set[Int] = doComp(r, compFirst)
/** Computes `last(r)` for the regexp `r`. */
protected def compLast(r: RegExp): Set[Int] = doComp(r, compLast)
/** Starts from the right-to-left
* precondition: pos is final
* pats are successor patterns of a Sequence node
*/
protected def compFollow(rs: Seq[RegExp]): Set[Int] = {
follow(0) =
if (rs.isEmpty) emptySet
else rs.foldRight(Set(pos))((p, fol) => {
val first = compFollow1(fol, p)
if (p.isNullable) fol ++ first
else first
})
follow(0)
}
/** Returns the first set of an expression, setting the follow set along the way.
*/
protected def compFollow1(fol1: Set[Int], r: RegExp): Set[Int] = r match {
case x: Alt => Set((x.rs reverseMap (compFollow1(fol1, _))).flatten: _*)
case x: Meta => compFollow1(fol1, x.r)
case x: Star => compFollow1(fol1 ++ compFirst(x.r), x.r)
case x: Sequ =>
x.rs.foldRight(fol1) { (p, fol) =>
val first = compFollow1(fol, p)
if (p.isNullable) fol ++ first
else first
}
case _ => throw new IllegalArgumentException("unexpected pattern: " + r.getClass)
}
/** Returns the "Sethi-length" of a pattern, creating the set of position along the way.
*/
protected def traverse(r: RegExp): Unit = r match {
// (is tree automaton stuff, more than Berry-Sethi)
case x: Alt => x.rs foreach traverse
case x: Sequ => x.rs foreach traverse
case x: Meta => traverse(x.r)
case Star(t) => traverse(t)
case _ => throw new IllegalArgumentException("unexp pattern " + r.getClass)
}
}
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