* @param operator   an operator
     * @param tag        a tree tag
     * @param left       type of left hand side
     * @param right      type of right hand side
     */
    int checkOperator(DiagnosticPosition pos,
                       OperatorSymbol operator,
                       int tag,
                       Type left,
                       Type right) {
        if (operator.opcode == ByteCodes.error) {
            log.error(pos,
                      "operator.cant.be.applied",
                      treeinfo.operatorName(tag),
                      left + "," + right);
        }
        return operator.opcode;
    }