protected function performOperationOnExpressionEngine($operation, $number)
    {
        $this->currentOperation = $operation;
        if (is_array($number)) {
            foreach ($number as $actualNumber) {
                $this->{$operation}($actualNumber);
            }
        } else {
            $this->addToHistory($operation, $number);
            $this->setCurrentValue($this->expressionEngine->{$operation}($this->getCurrentValue(), $number));
        }
    }