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Scala example source code file (WordBerrySethi.scala)
This example Scala source code file (WordBerrySethi.scala) is included in the DevDaily.com
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The Scala WordBerrySethi.scala source code
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.util.automata
import scala.collection.{ immutable, mutable }
import mutable.{ HashSet, HashMap }
import scala.util.regexp.WordExp
/** This class turns a regexp into a NondetWordAutom using the
* celebrated position automata construction (also called Berry-Sethi or
* Glushkov)
*
* @author Burak Emir
* @version 1.0
*/
abstract class WordBerrySethi extends BaseBerrySethi {
override val lang: WordExp
import lang.{ Alt, Eps, Letter, Meta, RegExp, Sequ, Star, _labelT }
protected var labels: HashSet[_labelT] = _
// don't let this fool you, only labelAt is a real, surjective mapping
protected var labelAt: Map[Int, _labelT] = _ // new alphabet "gamma"
protected var deltaq: Array[HashMap[_labelT, List[Int]]] = _ // delta
protected var defaultq: Array[List[Int]] = _ // default transitions
protected var initials: Set[Int] = _
/** Computes <code>first(r) where the word regexp r .
*
* @param r the regular expression
* @return the computed set <code>first(r)
*/
protected override def compFirst(r: RegExp): Set[Int] = r match {
case x: Letter => Set(x.pos)
case _ => super.compFirst(r)
}
/** Computes <code>last(r) where the word regexp r .
*
* @param r the regular expression
* @return the computed set <code>last(r)
*/
protected override def compLast(r: RegExp): Set[Int] = r match {
case x: Letter => Set(x.pos)
case _ => super.compLast(r)
}
/** Returns the first set of an expression, setting the follow set along
* the way.
*
* @param fol1 ...
* @param r the regular expression
* @return the computed set
*/
protected override def compFollow1(fol1: Set[Int], r: RegExp): Set[Int] = r match {
case x: Letter => follow(x.pos) = fol1 ; Set(x.pos)
case Eps => emptySet
case _ => super.compFollow1(fol1, r)
}
/** returns "Sethi-length" of a pattern, creating the set of position
* along the way
*/
/** called at the leaves of the regexp */
protected def seenLabel(r: RegExp, i: Int, label: _labelT) {
labelAt = labelAt.updated(i, label)
this.labels += label
}
// overridden in BindingBerrySethi
protected def seenLabel(r: RegExp, label: _labelT): Int = {
pos += 1
seenLabel(r, pos, label)
pos
}
// todo: replace global variable pos with acc
override def traverse(r: RegExp): Unit = r match {
case a @ Letter(label) => a.pos = seenLabel(r, label)
case Eps => // ignore
case _ => super.traverse(r)
}
protected def makeTransition(src: Int, dest: Int, label: _labelT) {
val q = deltaq(src)
q.update(label, dest :: q.getOrElse(label, Nil))
}
protected def initialize(subexpr: Seq[RegExp]): Unit = {
this.labelAt = immutable.Map()
this.follow = HashMap()
this.labels = HashSet()
this.pos = 0
// determine "Sethi-length" of the regexp
subexpr foreach traverse
this.initials = Set(0)
}
protected def initializeAutom() {
finals = immutable.Map.empty[Int, Int] // final states
deltaq = new Array[HashMap[_labelT, List[Int]]](pos) // delta
defaultq = new Array[List[Int]](pos) // default transitions
for (j <- 0 until pos) {
deltaq(j) = HashMap[_labelT, List[Int]]()
defaultq(j) = Nil
}
}
protected def collectTransitions(): Unit = // make transitions
for (j <- 0 until pos ; val fol = follow(j) ; k <- fol) {
if (pos == k) finals = finals.updated(j, finalTag)
else makeTransition(j, k, labelAt(k))
}
def automatonFrom(pat: RegExp, finalTag: Int): NondetWordAutom[_labelT] = {
this.finalTag = finalTag
pat match {
case x: Sequ =>
// (1,2) compute follow + first
initialize(x.rs)
pos += 1
compFollow(x.rs) // this used to be assigned to var globalFirst and then never used.
// (3) make automaton from follow sets
initializeAutom()
collectTransitions()
if (x.isNullable) // initial state is final
finals = finals.updated(0, finalTag)
val delta1 = immutable.Map(deltaq.zipWithIndex map (_.swap): _*)
val finalsArr = 0 until pos map (k => finals.getOrElse(k, 0)) toArray // 0 == not final
val initialsArr = initials.toArray
val deltaArr: Array[mutable.Map[_labelT, immutable.BitSet]] =
(0 until pos map { x =>
HashMap(delta1(x).toSeq map { case (k, v) => k -> immutable.BitSet(v: _*) } : _*)
}).toArray
val defaultArr = 0 until pos map (k => immutable.BitSet(defaultq(k): _*)) toArray
new NondetWordAutom[_labelT] {
val nstates = pos
val labels = WordBerrySethi.this.labels.toList
val initials = initialsArr
val finals = finalsArr
val delta = deltaArr
val default = defaultArr
}
case z =>
automatonFrom(Sequ(z.asInstanceOf[this.lang._regexpT]), finalTag)
}
}
}
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