Arc runs on mzscheme which turned into Racket. The last official release of Arc requires an older release of mzscheme from before lists were immutable. There is

Arc runs on mzscheme which turned into Racket. The last official release of Arc requires an older release of mzscheme from before lists were immutable. There is a community-maintained fork called Anarki [1] that runs on modern Racket. [1] - http://arclanguage.github.io/ http://arclanguage.github.io/