reverse -rc (vb -w dest, vb src)                 reverse -rc (vb -w ., vb src)
{                                                         if (length == 0, { length = _ (src) })
  vb tail = alloc (T_SLICE);                     {
                                                   ;
  attach (dest, &head),                          }
  {
    reverse (dest, tail),
    {
      detach (head, tail, src),
      {
        vb head = alloc (T_LINK)
      }
    }
  };
}
/
{
  free (&tail);
}
