private static <L> void appendYield(Tree<L> tree, List<L> yield) {
if (tree.isLeaf()) {
yield.add(tree.getLabel());
return;
}
for (Tree<L> child : tree.getChildren()) {
appendYield(child, yield);
}
}
/* Returns a list of words at the leafs of this tree gotten by
* traversing from left to right */
public List<L> getYield() {
List<L> yield = new ArrayList<L>();
appendYield(this, yield);
return yield;
}