(defmacro concatenate-vectors (vectors)
  `(let ((%n 0))
     (labels ((%concatenate-vectors (acc vector-list)
                (if (= (length vector-list) 0)
                    acc
                    (progn
                      (setf %n (+ %n (length (nth 0 vector-list))))
                      (%concatenate-vectors (concatenate 'vector acc (nth 0 vector-list))
                                            (subseq vector-list 1))))))
         (%concatenate-vectors #() ,vectors))))