code: public static String operatorToString(int op) {
          String result = operatorNames.get(op);
          if (result == null)
              throw new IllegalArgumentException("Invalid operator: " + op);
          return result;
      }
docs: Returns the string name for this operator.
  @param op the token type, e.g. {@link Token#ADD} or {@link Token#TYPEOF}
  @return the source operator string, such as "+" or "typeof"