/// <summary>
/// Evaluates the <paramref name="expr" /> into a <see cref="Double" /> value.
/// </summary>
/// <param name="expr">The <see cref="String" /> to evaluate.</param>
/// <returns>The <paramref name="expr" /> as a <see cref="Double" />.</returns>
public static double? Evaluate(string expr)
{
var multi = expr.Split('+').Select(Convert.ToDouble).ToList();
Operation operation = new BinaryAddOperation(multi[0], multi[1]);
for (var i = 2; i < multi.Count; i++)
{
operation = operation.Add(new UnaryAddOperation(multi[i]));
}
return Convert.ToDouble(operation.Operand().ToString());
}
