;; (= f (letrec [(x 1)
;;               (y 1)]
;;        (add x y)))

;; (assert (eq f 2))

(= (num-list-sum list)
   (letrec
     [(iter (lambda [list sum]
              (println list)
              (println sum)
              (println iter)
              (case list
                (null-t sum)
                (cons-t (iter (cdr list)
                              (add (car list) sum))))))]
     (iter list 0)))

(println (num-list-sum '(1 2 3 4)))

;; (assert (eq (num-list-sum '(1 2 3 4)) 10))