code: private final String getOperationText(final BinaryOperation exp) {
          final String text;
  
          if (exp instanceof AdditionOperation) {
              text = " + ";
          } else if (exp instanceof SubtractionOperation) {
              text = " - ";
          } else if (exp instanceof MultiplicationOperation) {
              text = " * ";
          } else if (exp instanceof DivisionOperation) {
              text = " / ";
          } else {
              LOGGER.warn("Unsupported expression of type {}", exp.getClass());
              text = "";
          }
  
          return text;
      }
docs: Returns the text value of the received operation.
  
  @param exp
  expression containing the operation
  @return text value of the operation