/// <summary>
/// Applies an accumulator delegate over a sequence starting with a given seed value, yielding each intermediate result. The <paramref name="seed"/> value is the first element of the source sequence. Each element of the source sequence is only evaluated once.
/// </summary>
/// <typeparam name="TSource">The type of elements in the source sequence.</typeparam>
/// <typeparam name="TResult">The type of elements in the resulting sequence.</typeparam>
/// <param name="source">The source sequence.</param>
/// <param name="seed">The initial seed value.</param>
/// <param name="accumulator">The accumulator delegate. The first parameter passed to the accumulator delegate is the previous intermediate result; the second parameter is the current element of the source sequence.</param>
/// <returns>The results of the accumulator delegate.</returns>
public static IEnumerable <TResult> Scan <TSource, TResult>(this IEnumerable <TSource> source, TResult seed, Func <TResult, TSource, TResult> accumulator)
{
IEnumerable <TResult> scan = EnumerableSource.Defer(() =>
{
TResult current = seed;
return(source.Select(x => current = accumulator(seed, x)));
});
return(EnumerableSource.Return(seed).Concat(scan));
}
/// <summary>
/// Applies an accumulator delegate over a sequence, yielding each intermediate result. The first element of the returned sequence is the first element of the source sequence. Each element of the source sequence is only evaluated once.
/// </summary>
/// <typeparam name="T">The type of elements in the sequence.</typeparam>
/// <param name="source">The source sequence.</param>
/// <param name="accumulator">The accumulator delegate. The first parameter passed to the accumulator delegate is the previous intermediate result; the second parameter is the current element of the source sequence.</param>
/// <returns>The results of the accumulator delegate.</returns>
public static IEnumerable <T> Scan <T>(this IEnumerable <T> source, Func <T, T, T> accumulator)
{
return(EnumerableSource.Defer(() =>
{
T current = default(T);
bool currentValid = false;
return source.Select(x =>
{
if (currentValid)
{
current = accumulator(current, x);
}
else
{
currentValid = true;
current = x;
}
return current;
});
}));
}