I'm not completely sure, but I think this is a compile-time overhead. So when you type directly into the toplevel, its a O(n) overhead, but when you execute a function defined in arc, executing the function itself should be less additional overhead because it was compiled to a scheme function in the original def.
; translate fn directly into a lambda if it has ordinary
; parameters, otherwise use a rest parameter and parse it.
(define (ac-fn args body env)
; ...
