+ /** a slow and inefficient epsilon-ness checker used when constructing parse trees (see Union.epsilonForm()) */
+ public static boolean possiblyEpsilon(SequenceOrElement e) {
+ if (e instanceof Atom) return false;
+ if (e instanceof Sequence) {
+ Sequence s = (Sequence)e;
+ for(Sequence.Pos p = s.firstp(); !p.isLast(); p = p.next())
+ if (!possiblyEpsilon(p.element()))
+ return false;
+ return true;
+ }
+ if (e instanceof Union) {
+ Union u = (Union)e;
+ if (u.visiting) return true;
+ try {
+ u.visiting = true;
+ for(Sequence s : u)
+ if (possiblyEpsilon(s))
+ return true;
+ return false;
+ } finally {
+ u.visiting = false;
+ }
+ }
+ throw new Error();
+ }
+ boolean visiting = false;