What is tech stack of HackerNews?

HN is one of the few places Arc, pg's own dialect of lisp runs in production.

Check out pg's page on arc to learn more: http://www.paulgraham.com/arc.html

This is a good place to start: http://www.paulgraham.com/hundred.html

One of the other places arc runs in production is the arc-forum: http://www.arclanguage.com/forum

Arc-language github: https://github.com/arclanguage

Arc (http://www.arclanguage.com/), I believe, running on top of Racket (https://racket-lang.org/). Unless they changed it since it was made public.

Here's a look at the actual out of data source: https://github.com/arclanguage/anarki/blob/master/lib/news.a...