; Can we accumulate the potatoes in this dish?
; ------------------------------
; The Little Lisper 3rd Edition
; Chapter 6
; Exercise 9
; Common Lisp
; http://t...content-available-to-author-only...r.com/thelittlelisper
; http://t...content-available-to-author-only...t.com/2010/06/little-lisper-chapter-6-oh-my-gawd-its.html
; http://t...content-available-to-author-only...t.com/2010/06/little-lisper.html
; ------------------------------
(setf l1 '((fried potatoes)(baked (fried)) tomatoes))
(setf l2 '(((chili) chili (chili))))
(setf l3 '())
(setf lat1 '(chili and hot)) 
(setf lat2 '(baked fried)) 
(setf a 'fried)
; ------------------------------

(defun add1 (a)
  (+ 1 a))

(defun occur (a lat)
  (cond
   ((null lat) 0)
   (t (cond
       ((eq (car lat) a)
        (add1 (occur a (cdr lat))))
       (t (occur a (cdr lat)))))))

(print (occur 'a '(a b c d c (b a))))

(defun occur (a lat acc)
  (cond
   ((null lat) acc)
   (t (cond
       ((eq (car lat) a)
        (occur a (cdr lat) (add1 acc)))
       (t (occur a (cdr lat) acc))))))

(print (occur 'a '(a b c d c (b a)) 0))

(defun occur (a lat acc)
  (cond
   ((null lat) acc)
   (t (occur a (cdr lat) 
             (cond 
              ((eq (car lat) a)
               (add1 acc))
              (t acc))))))

(print (occur 'a '(a b c d c (b a)) 0))

;The original value for acc is 0