There's a
very old version at
http://arclanguage.com/, but the current codebase isn't public.
FWIW, here's the Arc code I wrote to generate a string of the form "Italicized Title - https://news.ycombinator.com/item?id=$ID - Month Year (n comments)". The variable i stands for item, which is HN's term for a post (story, comment, or poll):
(def biblioref (i)
(let mon (monthdate (date i!time) 'short)
(tostring
(if (astorypoll i)
(do (pr "*" (subst i!title "*" "\\*") "* - " (fullurl:item-url i!id)
" - " mon" (" (plural i!klive "comment") ")"))
(do (pr (fullurl:item-url i!id))
(unless (is mon (monthdate (date) 'short))
(pr " (" mon ")")))))))
Not that elegant but maybe not too bad.