IEnumerable<T>::Pairwise extension method for C# modeled like an overload of F# Seq.pairwise<'T> (http://msdn.microsoft.com/it-it/library/ee370361.aspx).

Pairwise.cs

public static IEnumerable<TResult> Pairwise<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TSource, TResult> selector)
{
    if (source == null)
    {
        throw new ArgumentNullException("source");
    }

    if (selector == null)
    {
        throw new ArgumentNullException("selector");
    }

    using (var enumerator = source.GetEnumerator())
    {
        if (enumerator.MoveNext())
        {
            var left = enumerator.Current;

            while (enumerator.MoveNext())
            {
                var right = enumerator.Current;
                yield return selector(left, right);
                left = right;
            }
        }
    }
}