;; set a pointer to the cons cell, then dereference it as a pointer,
;; and bang the new value in the given offset
Hmm... so the fix was to "cast" the immutable cons cell to a mutable cons cell? Glad it works, but I was kind of hoping to learn that the immutable cons cell thing was workable for Arc. I guess I should read up on the MzScheme decision to make it immutable and see what pros/cons are associated with it.