(defun nshuffle (sequence)
  (etypecase sequence
    (list  (nshuffle-list sequence))
    (array (nshuffle-array sequence))))

(defun nshuffle-list (list)
  "Shuffle the list using an intermediate vector."
  (let ((array (nshuffle-array (coerce list 'vector))))
    (declare (dynamic-extent array))
    (map-into list 'identity array)))

(defun nshuffle-array (array)
  (loop for i from (length array) downto 2
        do (rotatef (aref array (random i))
                    (aref array (1- i)))
        finally (return array)))