;;; Prof R. Williams                            Artificial Intelligence
;;;
;;; The following implements depth-limited depth-first search for a path
;;; from a given start to any goal state in a graph.  For simplicity, no
;;; checking is done for repeated states.

(defun find-path-dldf (start goal-test successors depth-limit)
  (check-node start goal-test nil successors depth-limit)
  )

(defun check-node (node goal-test path-so-far successors dl)
  (let ((path-so-far (cons node path-so-far)))
    (cond ((funcall goal-test node) path-so-far)
	  ((zerop dl) nil)
	  (t (check-nodes (funcall successors node)
			  goal-test path-so-far successors dl))
	  )))
  
(defun check-nodes (nodes goal-test path-so-far successors dl)
  (unless (null nodes)
    (or (check-node (first nodes)
		    goal-test path-so-far successors (1- dl))
	(check-nodes (rest nodes)
		     goal-test path-so-far successors dl))
    ))