LISP help! Candy machine dispenser [duplicate] - lisp

Question

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Lisp randomize and using two functions to pull from list into another
(2 answers)
Closed 8 years ago.
Hey guys I'm new here and I was wondering if you guys can give me any help. I'm creating a candy machine that dispense colors randomly.I've ran this code and it goes on for 7 times for (get-candy gummy-bear) but it should go for 4 times till nil.
So heres my code:
;;; function get-candy
(defun get-candy (machine)
(funcall machine))
;;; variable colors
(defvar *colors* '(red blue green brown yellow purple))
;;; function generate-candy-supply
(defun generate-candy-supply (num)
(if (= 0 num)
(cons (nth (+ 1 (random (- (length *colors*) 1))) *colors*) *colors* )
(generate-candy-supply (- num 1))))
;;; function candy-machine
(defun candy-machine (candy)
(function
(lambda ()
(prog1 (car candy)
(setq candy (cdr candy))))))
;;; variable gummy-bear
(defvar *gummy-bear*
(candy-machine (generate-candy-supply 4)))
;;; variable easter-egg
(defvar *easter-egg*
(candy-machine (generate-candy-supply 6)))
And the sample run should look like this:
[1]> (load 'candy.lisp)
;; Loading file candy.lisp ...
;; Loaded file candy.lisp
T
[2]> (get-candy *gummy-bear*)
BLUE
[3]> (get-candy *gummy-bear*)
BROWN
[4]> (get-candy *gummy-bear*)
YELLOW
[5]> (get-candy *gummy-bear*)
YELLOW
[6]> (get-candy *gummy-bear*)
NIL
[7]> (get-candy *easter-egg*)
BLUE
[8]> (get-candy *easter-egg*)
BROWN
[9]> (get-candy *easter-egg*)
GREEN
[10]> (get-candy *easter-egg*)
BROWN
[11]> (get-candy *easter-egg*)
YELLOW
[12]> (get-candy *easter-egg*)
BLUE
[13]> (get-candy *easter-egg*)
NIL

Answer 1

Your problem is the function generate-candy-supply. It has two branches depending on num. If it is not 0 you recurse with (1- num) and do nothing else. When num is 0 you return a list starting with a random element of *colors* followed by the elements of *colors*. This will always yield a list with exactly 7 elements.
I'll leave it at this for now, so you can have a try at figuring a solution out. Feel free to ask further questions in the comments.