Boxes -- what exactly are these?

[Jason Coughlin <image.soe.clarkson.edu!jk0@uunet.uu.net>]

I saw an implementation of boxes that looks like this:

(define box (lambda (x) (cons x #f)))
(define unbox (lambda (x) (car x)))
(define set-box! (lambda (x v) (set-car! x v)))

Is the point akin to a pointer in C?  ie, so you could have args that
"changed" (call by variable)?

Is this an OK defn of boxes?

-- 
Jason Coughlin ( jk0@sun.soe.clarkson.edu , jk0@clutx )
"Every jumbled pile of person has a thinking part that wonders what the
part that isn't thinking isn't thinking of." - They Might Be Giants