;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname lect05c-accumulator) (read-case-sensitive #t) (teachpacks ((lib "world.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #t #t none #f ((lib "world.ss" "teachpack" "htdp")))))
(define (sum-all lon)
  (cond [(empty? lon) 0]
        [(cons?  lon) (+ (first lon) (sum-all (rest lon)))]))

#;(sum-all empty)
#;(sum-all (list 2 3 4 5 6 7 8 9 10 11))


(define (sum-all-v2 lon)
  (sum-all-helper lon 0))
   
   
; Return the sum of all elements in lon, plus ssf.
(define (sum-all-helper lon ssf)
  (cond [(empty? lon) ssf]
        [(cons?  lon) (sum-all-helper (rest lon) (+ (first lon) ssf)) ]))

(sum-all-v2 empty)
(sum-all-v2 (list 2 3 4 5 6 7 8 9 10 11))