[chucksmash]

Don't know how much it is still true, but HN was originally implemented in arc.

The language homepage[1] says "Arc is unfinished. It's missing things you'd need to solve some types of problems. [...] The first priority right now is the core language."

Perhaps parallelism is still pending. A Ctrl-F on the tutorial doesn't turn up any hits for "process", "thread", "parallel", or "concurrency".

[1]: http://www.arclanguage.org

[dang]

Arc has threads and HN's code relies heavily on them. Arc currently runs on Racket, though, which uses green threads, so the threadiness doesn't make it to the lower levels. Racket has other ways of doing parallelism, but as far I know they don't map as well to Arc's abstractions.