lottery

lottery

;; here is a version with a better shuffle function. Note that the shuffle
;; function is written in a functional Lisp style. You need to read it from
;; inside to outside.
;; it uses a vector where the elements get a random double float attached.
;; The vector gets sorted by the random double floats.

;; the vector-iota function is another utility function

;; the 'domain' level LOTTERY function then is just a composition of the utility functions

(defun shuffle (v)
  (map-into v
            #'car
            (sort (map-into (make-array (length v))
                            (lambda (e)
                              (cons e (random 1.0d0)))
                            v)
                  #'<
                  :key #'cdr)))

(defun vector-iota (start end)
  "returns a vector with elements from start to end"
  (check-type start fixnum)
  (check-type end fixnum)
  (assert (>= end start) (start end))
  (let ((v (make-array (- end start -1))))
    (loop for i from start upto end do (setf (aref v (- i start)) i))
    v))

(defun lottery (&aux
                (start 1)
                (end 49))
  (sort (subseq (shuffle (vector-iota start end))
                0 6)
        #'<))