Wednesday, October 10, 2007

Announcing Planet Factor

I put together an Atom/RSS aggregator in Factor. It is running live on the experimental HTTP server. Parroting the idea behind Planet Lisp, now there's Planet Factor.

It took me about an hour of work in total to put this together. Most of the parts were already there - Chris Double's Atom/RSS library, which uses Daniel Ehrenberg's XML library is the cornerstone here, and of course the HTTP server itself.

A thread fetches the feeds every 30 minutes. Entries are then concatenated and sorted by date, and stored in a global variable. The Planet Factor web app together with the news box on the Factor home page access this variable and present the results in a nice way.

The Planet Factor source is relatively short. (And on a somewhat related note, that pastebin is a Factor web app too...) This is my favorite part:
    dup [
dup "Fetching " diagnostic
dup news-get feed-entries
swap "Done fetching " diagnostic
] parallel-map

Ignoring the diagnostic message logging, you basically have
[ news-get ] parallel-map

Where news-get makes a network connection, downloads the XML and parses it. While the XML parsing is not parallelized, the network I/O is. Not many languages make it this easy to fire off overlapping I/O operations...


Anonymous said...

Is there a feed for Factor Planet? Maybe I'm not looking hard enough, but I not seeing one...

Slava Pestov said...

It's coming soon. For now you just have to subscribe to the individual feeds.

Sam said...

You can add mine if you wish:

There is an associated RSS feed at

Sekenre said...

Seems to break IE7 if you go to and view the page source it just shows </html>. Works fine in Firefox on the same machine.