/// <summary>
 /// Returns a future to indicate whether the specified value
 /// is yielded by the data-source.
 /// </summary>
 /// <typeparam name="TSource">The type of data to be yielded</typeparam>
 /// <param name="source">The data-source</param>
 /// <param name="value">The value to detect from the data-source, checked with the default comparer</param>
 public static IFuture <bool> Contains <TSource>(this IDataProducer <TSource> source, TSource value)
 {
     return(source.Contains(value, EqualityComparer <TSource> .Default));
 }