;; [a] -> [a]
(define shuffle
  (lambda (l)
    (let ((q (map (lambda (e) (cons (random 0 1) e)) l))
          (c (lambda (a b) (compare (car a) (car b)))))
      (map cdr (sort-by c q)))))

;; [float] -> float -> int
(define w-index
  (lambda (w n)
    (find-index
     (lambda (e)
       (< n e))
     (integrate w))))

;; [a] -> [float] -> a
(define w-choose
  (lambda (l w)
    (list-ref l (w-index w (random 0 1)))))

;; [float] -> [float]
(define normalize-sum
  (lambda (l)
    (let ((n (foldl1 + l)))
      (map
       (lambda (e)
	 (/ e n))
       l))))

;; [a] -> [float] -> a
(define p-choose
  (lambda (l p)
    (w-choose l (normalize-sum p))))

;; #[a] -> a
(define vector-choose
  (lambda (v)
    (vector-ref v (i-random 0 (vector-length v)))))