SunnyCloud: 2.17 and 2.18

sicp2.17.scm

;; 2.17
(define (last-pair list)
  (if (= (cdr list) ()
      (car list)                    ;; if statement parens fixed
  (last-pair (cdr list))            ;; now it's called last-pair recursively

;; 2.18
(define (reverse list)
  (if (= (cdr list) ())               ;; if statement inserted
  (= new-list (cons (car list) ())))  ;; extra paren added for if statement
     (cons (car list) (car new-list)))

;; Think of 2.18 in terms of 2.17: if you can find the last pair of a list
;; can't you call that recursively to build a new list last-element to first?

;; Testing
(reverse (list 1 4 9 16 25))  ;; => (list 25 26 9 4 1)