(defun find_route(source destination)
  (let* ((remaining_nodes (list (make_node source nil 0)))
          (knowledge (get_world_knowledge))
          (solution (breadth_first_search remaining_nodes 
                                          destination knowledge)))
   (print_route solution)))


;; assumes that the route is of the form:
;; (total_distance (city1 city2 distance1) (city2 city3 distance2) ... )
(defun print_route (route)
  (terpri)
  (princ "distance: ")
  (if (null route)
    (progn (princ "infinity")
           (terpri))
    (progn (princ (car route))
           (princ " km")
           (terpri)))
 (princ "route:")
 (terpri)
 (if (null route)
     (princ "none")
   (mapcar #'print_segment (cdr route)))
 (values))

(defun print_segment (segment)
  (princ (first segment))
  (princ " to ")
  (princ (second segment))
  (princ ", ")
  (princ (third segment))
  (princ " km")
  (terpri))


(defun make_node(city parent distance)
 (list city parent distance))

(defun node_city (node)
  (first node))

(defun node_parent (node)
  (second node))

(defun node_distance (node)
  (third node))