12.0.2 next-statesの定義

Next: 12.0.3 goal-searchの定義 Up: 12 迷路問題における状態空間の生成 Previous: 12.0.1 node-equalの定義

12.0.2 next-statesの定義

次に，壁の無い方向を調べて，next-statesを作るとすれば，

(defun position-name (p)
  (intern
   (concat 
    "p"
    (+ 1 (round (car p))
       (* 5 (round (cadr p))))))
  )

(defun next-dirs (state)
  (let* ((v (robot-position state))
         (sym (position-name v)))
    (set- '(n w s e)
          (get (position-name v) 'walls))))

(defun next-state (dir state)
  (let ((v (robot-position state)))
    (case
        dir
      (n (list 'robot 'at (v+ '(0 -1) v)))
      (w (list 'robot 'at (v+ '(-1 0) v)))
      (s (list 'robot 'at (v+ '(0 1) v)))
      (e (list 'robot 'at (v+ '(1 0) v))))))

(defun next-states (state)
  (let ((dirs (next-dirs state))
        result)
    (dolist
        (d dirs)
      (setq result
            (cons (next-state d state)
                  result)))
    result))

となって，場所ベクトルからシンボルを取り出し，シンボルから壁の無い方向を集合演算で取り出すというような形で計算をする．

> (next-states '(robot at (2 2)))
((robot at (1 2)))

> (next-states '(robot at (2 3)))
((robot at (2 4)))

> (next-states '(robot at (1 3)))
((robot at (1 4)) (robot at (0 3)))

generated through LaTeX2HTML. M.Inaba 平成18年5月7日