Histogram exercise to learn arrays. Example from "Common Lisp: A gentle introduction to symbolic computation"

histogram.lisp

(defvar *total-points* nil)
(defvar *hist-array* nil)

(defun record-value (n)
  (if (or (> n 10)
          (< n 0))
    (break "The supplied argument is not between 0 and 10"))
  (setf (aref *hist-array* n) (+ 1 (aref *hist-array* n)))
  (setf *total-points* (+ 1 *total-points*)))

(defun print-hist-line (n)
  (if (or (> n 10)
          (< n 0))
    (break "The supplied argument is not between 0 and 10"))
  (let ((value (aref *hist-array* n)))
    (format t "~%~2S[~3S]" n value)
    (dotimes (i value)
      (format t "*"))))

(defun print-histogram ()
  (dotimes (i 11)
    (print-hist-line i)))

(defun new-histogram (&optional (times 200))
  (setf *total-points* 0)
  (setf *hist-array* (make-array 11 :initial-element 0))
  (format t "~&Testing how well (RANDOM) works!")
  (dotimes (i times)
    (record-value (random 11)))
  (print-histogram)
  (format t "~%~%Total: ~S" times))

(new-histogram)

;;Example output
;; Testing how well (RANDOM) works!
;; 0 [20 ]********************
;; 1 [19 ]*******************
;; 2 [18 ]******************
;; 3 [19 ]*******************
;; 4 [20 ]********************
;; 5 [10 ]**********
;; 6 [14 ]**************
;; 7 [17 ]*****************
;; 8 [25 ]*************************
;; 9 [17 ]*****************
;; 10[21 ]*********************
;;
;; Total: 200

Thanks for the idea. I've made a more generic function:

https://gist.github.com/svetlyak40wt/57739e2238485a83a9d7e01dbcda09dd