$ racket -f as.scm
In general, the instructions we've been steering newcomers toward are at https://sites.google.com/site/arclanguagewiki/getting-starte..., which we try to keep up-to-date. If that helps in this case.
(Once you resolve this issue I'd also recommend switching to the Nu branch described in the above link. It's a much more clean and modern implementation.)
https://github.com/Pauan/ar
I too recommend using it rather than vanilla Arc. It has many bug fixes and new features, yet is still backwards compatible.
-----