gistfile1.cs

public static IEnumerable<TAcc> Scan<T, TAcc>(this IEnumerable<T> This, TAcc initialValue, Func<TAcc, T, TAcc> accFunc)
{
    TAcc acc = initialValue;

    foreach (var x in This)
    {
        acc = accFunc(acc, x);
        yield return acc;
    }
}