#lang scheme

(define (sum-all-v1 nums)
  (cond [(cons? nums) (+ (first nums) (sum-all-v1 (rest nums)))]
        [(empty? nums) 0]))


(define (sum-all-v2 nums)
  (sum-all-helper nums 0))

(define (sum-all-helper nums-remaining sum-so-far)
  (cond [(cons? nums-remaining) (sum-all-helper
                                 (rest nums-remaining)
                                 (+ sum-so-far (first nums-remaining)))]
        [(empty? nums-remaining) sum-so-far]))

;; foldr:
;; combine: a rule to combine the accumulator ("so-far" variable)
;;          with the first thing in the list.
;; base-case: the initial accumulator value.
(define (my-foldr combine base-case data)
  (letrec ([my-foldr-helper 
            (lambda (data-remaining result-so-far)
              (cond [(cons? data-remaining) (my-foldr-helper
                                             (rest data-remaining)
                                             (combine result-so-far (first data-remaining)))]
                    [(empty? data-remaining) result-so-far]))])
    
    (my-foldr-helper data base-case)))




(define (sum-all-v3 nums)
   (foldl + 0 nums))

#:(define (grow-fires lof)
  (foldl (lambda (f rr) (cons (grow-fire f) rr)) empty lof))