@Override
      public boolean apply(ASTNode node) {
        if (tokensToMatch.contains(node.getType())) {
          matched[0] = node.getText();
          return true;
        }

        return false;
      }
Performs a descent of the leftmost branch of a tree, stopping when either a
node with a non-null token is found or the leaf level is encountered.

@param tree
         candidate node from which to start searching

@return node at which descent stopped
ql/src/java/org/apache/hadoop/hive/ql/parse/ParseUtils.java