(defun coordinates (v) (get v 'coordinates)) (defun straight-distance (node-1 node-2) (distance (coordinates node-1) (coordinates node-2))) > (straight-distance 's 'd) 3.4641016151377544 > (straight-distance 's 'a) 4.358898943540674という具合に求められる. パスの長さは,
(defun path-length (path) (if (null (rest path)) 0 (+ (straight-distance (first path) (second path)) (path-length (rest path)))))と定義できる.