/** Legal as long as there is at least one item on the state's stack. */
public boolean isLegal(State state, List<ParserConstraint> constraints) {
if (state.finished) {
return false;
}
if (state.stack.size() == 0) {
return false;
}
Tree top = state.stack.peek();
if (top.label().value().equals(label)) {
// Disallow unary transitions where the label doesn't change
return false;
}
if (top.label().value().startsWith("@") && !label.equals(top.label().value().substring(1))) {
return false;
}
if (top.children().length == 1) {
Tree child = top.children()[0];
if (child.children().length == 1) {
Tree grandChild = child.children()[0];
if (grandChild.children().length == 1) {
// Three consecutive unary trees. Not legal to keep adding unaries.
// TODO: do preterminals count in that equation?
return false;
}
}
}
if (isRoot && (state.stack.size() > 1 || !state.endOfQueue())) {
return false;
}
// UnaryTransition actually doesn't care about the constraints.
// If the constraint winds up unsatisfied, we'll get stuck and
// have to do an "emergency transition" to fix the situation.
return true;
}
private boolean parseInternal() {
final int maxBeamSize = Math.max(parser.op.testOptions().beamSize, 1);
success = true;
unparsable = false;
PriorityQueue<State> beam =
new PriorityQueue<>(maxBeamSize + 1, ScoredComparator.ASCENDING_COMPARATOR);
beam.add(initialState);
// TODO: don't construct as many PriorityQueues
while (beam.size() > 0) {
// System.err.println("================================================");
// System.err.println("Current beam:");
// System.err.println(beam);
PriorityQueue<State> oldBeam = beam;
beam = new PriorityQueue<>(maxBeamSize + 1, ScoredComparator.ASCENDING_COMPARATOR);
State bestState = null;
for (State state : oldBeam) {
Collection<ScoredObject<Integer>> predictedTransitions =
parser.model.findHighestScoringTransitions(state, true, maxBeamSize, constraints);
// System.err.println("Examining state: " + state);
for (ScoredObject<Integer> predictedTransition : predictedTransitions) {
Transition transition = parser.model.transitionIndex.get(predictedTransition.object());
State newState = transition.apply(state, predictedTransition.score());
// System.err.println(" Transition: " + transition + " (" + predictedTransition.score() +
// ")");
if (bestState == null || bestState.score() < newState.score()) {
bestState = newState;
}
beam.add(newState);
if (beam.size() > maxBeamSize) {
beam.poll();
}
}
}
if (beam.size() == 0) {
// Oops, time for some fallback plan
// This can happen with the set of constraints given by the original paper
// For example, one particular French model had a situation where it would reach
// @Ssub @Ssub .
// without a left(Ssub) transition, so finishing the parse was impossible.
// This will probably result in a bad parse, but at least it
// will result in some sort of parse.
for (State state : oldBeam) {
Transition transition = parser.model.findEmergencyTransition(state, constraints);
if (transition != null) {
State newState = transition.apply(state);
if (bestState == null || bestState.score() < newState.score()) {
bestState = newState;
}
beam.add(newState);
}
}
}
// bestState == null only happens when we have failed to make progress, so quit
// If the bestState is finished, we are done
if (bestState == null || bestState.isFinished()) {
break;
}
}
List<State> bestParses;
if (beam.size() == 0) {
success = false;
unparsable = true;
debinarized = null;
finalState = null;
bestParses = Collections.emptyList();
} else {
// TODO: filter out beam elements that aren't finished
bestParses = Generics.newArrayList(beam);
Collections.sort(bestParses, beam.comparator());
Collections.reverse(bestParses);
finalState = bestParses.get(0);
debinarized = debinarizer.transformTree(finalState.stack.peek());
debinarized =
Tsurgeon.processPattern(
rearrangeFinalPunctuationTregex, rearrangeFinalPunctuationTsurgeon, debinarized);
}
return success;
}