let sort_items_by_date =
List.sort
(fun i1 i2 ->
match i1.item_pubdate, i2.item_pubdate with
None, None -> 0
| Some _, None -> -1
| None, Some _ -> 1
| Some d1, Some d2 ->
compare
(Rss_date.since_epoch d2)
(Rss_date.since_epoch d2)
)