code: public CALC val(String value, char decimalSeparator) {
          infix.add(new Num(value, decimalSeparator));
          return getThis();
      }
docs: Append String value to expression that will be parsed to {@link Num} with defined decimal separator
  
  
  @param value String representation of number
  @param decimalSeparator used in string representation of number
  @return