;; This is a recursive breadth-first search example from the book

(setf (get 's 'neighbors) '(a d)
      (get 'a 'neighbors) '(s b d)
      (get 'b 'neighbors) '(a c e)
      (get 'c 'neighbors) '(b)
      (get 'd 'neighbors) '(s a e)
      (get 'e 'neighbors) '(b d f)
      (get 'f 'neighbors) '(e))

(setf goal 'f)

(defun bsolve (initial)
	(bsolve1 (list  (list initial initial))))

(defun bsolve1 (queue)
	(if (goal-recognizer (caar queue))
	    (values (caar queue) (cdar queue))
	    (bsolve1 (append (cdr queue)
                             (expand-path (car queue))))))

(defun goal-recognizer (state)
	(if (eql state goal) t nil))

(defun expand-path (path)
	(print path)
	(mapcar #'(lambda (new-node) (cons new-node path))
        (remove-if #'(lambda (neighbor) (member neighbor path))
                        (get (first path) 'neighbors))))