/// <summary>
/// Evaluates the specified expression using this object's data.
/// </summary>
/// <param name='e'>
/// The expression to evaluate.
/// </param>
/// <returns>
/// The result of the evaluated expression.
/// </returns>
public double Evaluate(Token e)
{
double ans = e.Evaluate(this);
Variables["ans"] = ans;
return ans;
}
