public static Enumerate <T> Where <T>(this Enumerate <T> source, Func <T, bool> filter)
{
return(source.SelectMany(t => filter(t) ? Return(t) : Empty <T>()));
}
public static Enumerate <TResult> Select <T, TResult>(this Enumerate <T> source, Func <T, TResult> selector)
{
return(source.SelectMany(a => Return(selector(a))));
}