public static IEnumerable<TSource> PreScan<TSource>(
	this IEnumerable<TSource> source,
	Func<TSource, TSource, TSource> transformation,
	TSource identity
)

<ExtensionAttribute>
Public Shared Function PreScan(Of TSource) ( 
	source As IEnumerable(Of TSource),
	transformation As Func(Of TSource, TSource, TSource),
	identity As TSource
) As IEnumerable(Of TSource)

public:
[ExtensionAttribute]
generic<typename TSource>
static IEnumerable<TSource>^ PreScan(
	IEnumerable<TSource>^ source, 
	Func<TSource, TSource, TSource>^ transformation, 
	TSource identity
)

[<ExtensionAttribute>]
static member PreScan : 
        source : IEnumerable<'TSource> * 
        transformation : Func<'TSource, 'TSource, 'TSource> * 
        identity : 'TSource -> IEnumerable<'TSource> 

Func<int, int, int> plus = (a, b) => a + b;
int[] values = { 1, 2, 3, 4 };
IEnumerable<int> prescan = values.PreScan(plus, 0);
IEnumerable<int> scan = values.Scan(plus; a + b);
IEnumerable<int> result = values.ZipShortest(prescan, plus);