/// <summary>
/// Converts matches from the specified <paramref name="parser"/> into strings.
/// </summary>
/// <typeparam name="TSource">The type of the source elements.</typeparam>
/// <typeparam name="TResult">The type of the elements that are generated from parsing the source elements.</typeparam>
/// <param name="parser">The parser from which matches will be converted into strings.</param>
/// <returns>A parser that yields strings for the matches from the specified <paramref name="parser"/>.</returns>
public static IObservableParser <TSource, string> AsString <TSource, TResult>(
this IObservableParser <TSource, TResult> parser)
{
Contract.Requires(parser != null);
Contract.Ensures(Contract.Result <IObservableParser <TSource, string> >() != null);
return(parser.Select(value => (value == null) ? null : value.ToString()));
}