Why does HN generate unique URL's for the 'more' pages?
I'm not sure if this question has been asked but it doesn't make a whole lot of sense to me. At least a dozen times I've hit the 'more' button to find the URL expired. Wouldn't it make more sense to have a page 2, page 3 etc?
It's called a continuation. Continuations are essentially closures being passed around to represent state (hence "fnid"), check the Wikipedia page on them for a proper, computer sciencey definition. The nature of Lisp really lends itself to continuation-based programming. Sometimes (like on HN) it's used in web applications. In the context of web applications, it's a different approach than, for example, REST/MVC. It has a few nice properties, such as easy state management. This can be very useful when a web application is an interface to a process (e.g. checkout in a web store) as opposed to CRUDA. On HN, it allows paging that "remembers" the order of things at the time you visited the first page. Reddit uses a similar mechanism. The obvious downside is that you have to keep track of all those states and if you lose them (for example because they expire), the user workflow is interrupted (hence the error message).
It's not the trendiest programming technique around these days but it's a useful tool in the toolkit of a good developer.
dchest answered more of the 'what' than why
the answer to the why is news.arc (what this site runs) is the pet example of Arc, which is pg's lisp dialect focused on making lisp web apps with continuation passing style
as such, the technical purity to the idea is more important than UX, as otherwise it would mean admitting that trying to implement pretty simple web app that passes around continuations like this is a fool's errand
(actually, arc and the ideas work great for rapid prototyping but just do not work well once you reach more than all but the smallest of scales)
Aigh, you beat me to it.
pg, please fix this. It drives me batty that after a page is open for a little while the "more" link breaks. That should never, ever, ever happen.
You can kill me, but I find it somewhat ironic that the functionality championed in the Arc Challenge is directly responsible for the most annoying bug on Hacker News. :)
This bugs me endlessly when browsing HN.
I like to open and read interesting links in new tabs, and invariably the continuations have expired when I return to HN after reading another tab. I see the expiry error many times everyday. It is a terrible user experience, even if it's a interesting technical 'solution' to paging.
I'm not sure how the patent relates to the question. The UI issue is that a user traverses to the 2nd or 3rd page of viewing, go reads some articles or whatnot, and then comes back to find that he or she cannot move onto the 4th page.
It's frustrating.
User experience > cute technical solution
I've read the bits about implementation based on continuations in various other comments.
Given that:
- the ranking of HN stories likely is in constant flux ...
- and that some users might want a consistent view of stories across multiple pages ...
- and that having .../page1-, .../page2-, .../page3-style URLs might result in some user seeing the same story presented twice in their browsing, once on page1 and then again on page2 as its rank changes ... or worse, missing a story that got promoted to page1 from page2 during a session
... do the continuations as implemented on HN present a static view of the ranked stories with a non-changing ordering (as long as links don't expire)? To do this with straight URL's one would need to present different URL links at different times to different users to get different page-2 contents reflecting what was on page2 at the time they started their HN visit. If so, that would be a feature.
Btw, for all those who are talking about continuations:
Sounds to me that this could be fixed quite easily. Why not pass both a continuation ID and a page number on the pagination links? If the continuation has expired, simply use the page number to generate a new page?
I agree with other commenters that the current way feels very broken. I get to see the "expired page" dozens of times a day because I always leave my HN tab open and follow stories in a new tab.
I have a suggestion for a hack that would make life a little more pleasant for those who do not mind running Javascript while not affecting those who want to use the site as is. The script can be implemented by the community and hosted on Git. PG can just include the script in the arc code with just a "one line change".
The JS will just fetch the initial n pages and allow easy navigation using the more button. It will be visually very similar to what we have now. If the community cares it can become much more richer in functionality. If PG refuses, at least there r enough HN users who are annoyed by this bug that we can create a Chrome plugin for HN that fixes this. I can probably write something like this myself. But probably the community can first formulate excatly what the plugin should/should not do. Does such a plugin already exist? Is it a bad idea to solve it this way? Would the additional burden on the servers be too high to be worth it?
Patent, shmatent. What currently exists SUCKS. How many users have to complain before someone gets a glimmer of a clue that MAYBE they should try ANYTHING ELSE.
Not only that, but it seems to be paginating comments at an absurdly low count, I went back to reference an old thread and I went 5 pages in before I got tired of looking for the right comment. That and I've been bitten by "expired" links three times today alone, once while I was trying to submit a comment.
It's done on purpose as a concrete example of how _not_ to code a social news aggregator.
If I were coding a site like this, I'm certain 'how to handle next page links' would be near the top of the problem list. I am also quite certain I would not pick a solution that gives an empty white page with 'link expired' on it.
Off-topic: is HN under heavy load recently? Sometimes I see recent pages cut off at around 50 comments, with the more links. Normally this would only happen at older pages where you can no longer comment.