> (trace length-cps)
(length-cps)
> (trace apply-cont)
(apply-cont)
> (length-cps '(1 4 2 7 4) (halt-cont))
|(length-cps (1 4 2 7 4) (halt-cont))
|(length-cps (4 2 7 4) (add-cont 1 (halt-cont)))
|(length-cps (2 7 4) (add-cont 1 (add-cont 1 (halt-cont))))
|(length-cps (7 4) (add-cont 1 (add-cont 1 (add-cont 1 (halt-cont)))))
|(length-cps
   (4)
   (add-cont 1 (add-cont 1 (add-cont 1 (add-cont 1 (halt-cont))))))
|(length-cps
     ()
        (add-cont 1 (add-cont 1 (add-cont 1 (add-cont 1 (add-cont 1 (halt-cont)))))))
|(apply-cont
   (add-cont 1 (add-cont 1 (add-cont 1 (add-cont 1 (add-cont 1 (halt-cont))))))
   0)
|(apply-cont (add-cont 1 (add-cont 1 (add-cont 1 (add-cont 1 (halt-cont))))) 1)
|(apply-cont (add-cont 1 (add-cont 1 (add-cont 1 (halt-cont)))) 2)
|(apply-cont (add-cont 1 (add-cont 1 (halt-cont))) 3)
|(apply-cont (add-cont 1 (halt-cont)) 4)
|(apply-cont (halt-cont) 5)
|5
5
>