Generating strings from a regex

gistfile1.scala

import scala.util.regexp._
import scala.util.automata._
object MyLang extends WordExp {
  type _regexpT = RegExp
  type _labelT = MyChar
   case class MyChar(c:Char) extends Label
}

import MyLang._
object MyBerriSethi extends WordBerrySethi {
  override val lang = MyLang
}

import scala.util.Random
def generate(dfa: DetWordAutom[MyChar]) = {
  var result = ""
  var state = 0
  while (!((dfa isFinal state) && ((Random nextInt 5) == 0 || (dfa delta state isEmpty)))) {
    val nextState = Random nextInt (dfa delta state size)
    val transition = (dfa delta state).keys.toSeq(nextState)
    result += transition.c
    state = dfa next (state, transition)
  }
  result
}

// (a* | b)*
val rex = Star(Alt(Star(Letter(MyChar('a'))),Letter(MyChar('b'))))
val nfa = MyBerriSethi.automatonFrom(Sequ(rex), 1)
val dfa = new SubsetConstruction(nfa).determinize
generate(dfa)