Porting Arc to mzscheme 4.0 may be tricky. One big change is cons pairs are immutable, which will break lots of things in Arc. You can create mutable cons pairs with "mcons", so ac.scm will need to use that all over.
Also, "interaction-environment" needs to be replaced with "current-namespace", I think.
I haven't figured out how ac.scm will need to change to use the new module system. The mzscheme command line options also change in various ways.
