void Expression::evaluate(vector<Expression> seq)
{
    map <string, int> subs;

    for (Expression exp : seq)
    {
        if (exp.get_type() == assignment && exp.check())
        {
            vector<Token> expression_tokens = exp.get_postfix();
            subs[expression_tokens[0].get_token()] = expression_tokens[1].value();
        }
    }

    for (Expression exp : seq)
    {
        bool success = true;

        if (exp.check())
        {
            if (exp.get_type() != assignment)
            {
                stack<double> number;
                double result;
                for (int i = 0; i < postfix.size(); ++i)
                {
                    if (postfix[i].get_type() == integer)
                    {
                        number.push(postfix[i].value());
                    }
                    else if (postfix[i].get_type() == op && !number.empty())
                    {
                        double operand1, operand2;
                        string theOperator = postfix[i].get_token();
                        operand1 = number.top();
                        number.pop();
                        operand2 = number.top();
                        number.pop();
                        result = eval(operand1, operand2, theOperator);
                        number.push(result);
                    }
                    else if (postfix[i].get_type() == letter)
                    {
                        if (subs.count(tokenized[i].get_token()) != 0)
                        {
                            number.push(subs[tokenized[i].get_token()]);
                        }
                        else
                        {
                            success = false;
                            break;
                        }
                    }
                }
                while (!number.empty())
                {
                    evaluation.push_back(number.top());
                    number.pop();
                }
            }

        }
        else
        {
            success = false;
        }

        if (!success)
        {
            cout << exp.get_orignal() << "could not be evaluated!" << endl;
        }
    }
}