(define $mickey'
  (lambda [$cs]
    (match cs (list char)
      {[<snoc $z <snoc $y <snoc $x (& <snoc _ _> $hs)>>>
        {@(mickey' hs) c#, x y z}]
       [_ cs]})))

(define $mickey (lambda [$s] (pack (mickey' (unpack s)))))

(mickey "10000000000")