(define (counting-sort! fortuita sortita max)
  (let ((numerata (make-vector max 0)))
    (loop count ((for x i (in-vector fortuita)))
          (vector-set! numerata x (+ (vector-ref numerata x) 1))
          (count))
    (loop leq ((for x i (in-vector numerata 1)))
          (vector-set! numerata i (+ x (vector-ref numerata (- i 1))))
          (leq))
    (loop sort ((for x i (in-vector-reverse fortuita)))
          (let ((count-index (- (vector-ref numerata x) 1)))
            (vector-set! sortita count-index x)
            (vector-set! numerata x count-index))
          (sort))))

(let* ((fortuita (vector 6 0 2 0 1 3 4 6 1 3 2))
       (sortita (make-vector (vector-length fortuita))))
  (let ((max (+ (apply max (vector->list fortuita)) 1)))
    (counting-sort! fortuita sortita max)
    sortita))

;;; #(0 0 1 1 2 2 3 3 4 6 6)