code: public static String opToStr(Token operator) {
      switch (operator) {
        case BITOR:
          return "|";
        case OR:
          return "||";
        case BITXOR:
          return "^";
        case AND:
          return "&&";
        case BITAND:
          return "&";
        case SHEQ:
          return "===";
        case EQ:
          return "==";
        case NOT:
          return "!";
        case NE:
          return "!=";
        case SHNE:
          return "!==";
        case LSH:
          return "<<";
        case IN:
          return "in";
        case LE:
          return "<=";
        case LT:
          return "<";
        case URSH:
          return ">>>";
        case RSH:
          return ">>";
        case GE:
          return ">=";
        case GT:
          return ">";
        case MUL:
          return "*";
        case DIV:
          return "/";
        case MOD:
          return "%";
        case EXPONENT:
          return "**";
        case BITNOT:
          return "~";
        case ADD:
        case POS:
          return "+";
        case SUB:
        case NEG:
          return "-";
        case ASSIGN:
          return "=";
        case ASSIGN_BITOR:
          return "|=";
        case ASSIGN_BITXOR:
          return "^=";
        case ASSIGN_BITAND:
          return "&=";
        case ASSIGN_LSH:
          return "<<=";
        case ASSIGN_RSH:
          return ">>=";
        case ASSIGN_URSH:
          return ">>>=";
        case ASSIGN_ADD:
          return "+=";
        case ASSIGN_SUB:
          return "-=";
        case ASSIGN_MUL:
          return "*=";
        case ASSIGN_EXPONENT:
          return "**=";
        case ASSIGN_DIV:
          return "/=";
        case ASSIGN_MOD:
          return "%=";
        case VOID:
          return "void";
        case TYPEOF:
          return "typeof";
        case INSTANCEOF:
          return "instanceof";
        default:
          return null;
      }
    }
docs: Converts an operator's token value (see {@link Token}) to a string
  representation.
  
  @param operator the operator's token value to convert
  @return the string representation or {@code null} if the token value is
  not an operator