Hurrah: I just got a forked version of arc to run on mzscheme 3.99.
http://git.hashcollision.org/arc.git
Caveats: I had to disable set-car! and set-cdr! related stuff; still thinking about how to handle that case. Just grep for 'set-car' and you'll see the portions of the code that have been commented out.
Other acts of violence done to the code: I separated parts that dealt with the runtime apart from the stuff dealing with the compile time. I got this running about five minutes ago, so this may not be quite right. :)
This cannot be done in a quick patch. If you want mutation in 3.99, you have to use mpairs -- but then you run against rest arguments being the usual immutable pairs.
