(do* ((i s-length (1- i))
        (previous-part nil)
        (curr-part nil)
        (curr-snake '() (cons curr-part curr-snake)))
       ((= i 0) (format t "Created snake with ~A parts.~%" s-length))
    (setf curr-part (make-instace 'snake-part :previous-part previous-part))
    (setf previous-part (curr-part)) ;; update previous-part
    )