Pagination/"More" uses fnids; looking at the source it's a callback, but from an HTTP client perspective it might as well be a continuation.
How do you test and debug things like that that have random URIs and function names and get GCed on a regular basis? That's what I mean when I say continuations lead to unmaintainable web apps.
I've been using this technique since 1995 and it has never once been a problem. It's an instance of programming with closures, which has been common in the Lisp world for even longer. One doesn't need to examine something represented as a closure any more than one needs to examine a particular invocation of a recursive function.
Perhaps the reason I've never had a problem is that I've been careful to use this technique in fairly restricted ways. Lisp macros are the same sort of thing. They could yield unreadable code if abused. But good programmers use them in principled ways, and when used with restraint they are clearly a net win.
Yes, I clicked the reply link on your comment from there.
I figured you had to know about this bug, since it happens to me regularly (maybe 10% of eligible comments) when I comment in active threads during standard procrastination hours. The misdirect is usually to the threads page of a user further up the comment tree, though sometimes it's to the permalink of a grandparent comment.
Seems like you're mixing up the redirects of concurrent users but never across comment hierarchies so it's not omnipresent.
The problem is that links expire at all. There are two products: HN with "link expired" and HN without "link expired". You can write the former in a highly maintainable way.
Also, even if you accept that links expire, it's not trivial to make the links not expire for a long time. You can add a lot of RAM to a single machine, but only up to a point. Supporting multiple machines is very hard, although it can be done (distributed object system). RAM is not the only problem however. The server is inevitably going to restart once in a while. Perhaps not in the literal sense of killing and restarting the mzscheme process if you're very careful, but still in the practical sense. The data structures for storing content change as you develop a web app/site, thereby invalidating old closures hanging around.
How do you test and debug things like that that have random URIs and function names and get GCed on a regular basis? That's what I mean when I say continuations lead to unmaintainable web apps.