(define (shuffle l)
  (let ((v (list->vector l)))
    (let loop ((i (vector-length v))
               (r '()))
      (if (zero? i)
        r
        (let* ((x (random i))
               (in (- i 1))
               (rn (cons (vector-ref v x) r)))
          (vector-set! v x (vector-ref v in))
          (loop in rn))))))