It was running an old version of BC. I can't remember the details, but I recall that Arc was pinned to an older version of Racket and didn't benefit from impro

It was running an old version of BC. I can't remember the details, but I recall that Arc was pinned to an older version of Racket and didn't benefit from improvements to BC and then later to CS. But ... be aware that the Arc interpreter is much more dynamic than Racket, so in general normal Racket programs are more efficient than Arc programs.