private void Calculate(IEnumerable<FunctionArgument> items, ref double nItems)
{
foreach (var item in items)
{
if (item.Value is IEnumerable<FunctionArgument>)
{
Calculate((IEnumerable<FunctionArgument>)item.Value, ref nItems);
}
else if (ShouldCount(item))
{
nItems++;
}
}
}