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Up: 11 積木問題の状態空間の生成
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現在の状態から可能な次の状態のリストを作りだすために，まず
possible-statesという関数を作る．
possible-statesは，現在の状態state，
移動するブロックおよびそのブロックを載せる対象
のリストdestを与えて次の状態の
リストを返すとする．
> s
((a on table) (b on c) (c on table) (d on a))
> (possible-states 'd s '(b table))
(((d on b) (a on table) (b on c) (c on table))
((d on table) (a on table) (b on c) (c on table)))
> (possible-states 'b s '(d table))
(((b on d) (a on table) (c on table) (d on a))
((b on table) (a on table) (c on table) (d on a)))
> (possible-states 'a s '(b d))
(((a on b) (b on c) (c on table) (d on a))
((a on d) (b on c) (c on table) (d on a)))
> (possible-states 'a s '(b d table))
(((a on b) (b on c) (c on table) (d on a))
((a on d) (b on c) (c on table) (d on a))
((a on table) (b on c) (c on table) (d on a)))
> (possible-states 'b s '(b d table))
(((b on b) (a on table) (c on table) (d on a))
((b on d) (a on table) (c on table) (d on a))
((b on table) (a on table) (c on table) (d on a)))
> (possible-states 'c s '(b d table))
(((c on b) (a on table) (b on c) (d on a))
((c on d) (a on table) (b on c) (d on a))
((c on table) (a on table) (b on c) (d on a)))
> (possible-states 'a s '(a b c d table))
(((a on a) (b on c) (c on table) (d on a))
((a on b) (b on c) (c on table) (d on a))
((a on c) (b on c) (c on table) (d on a))
((a on d) (b on c) (c on table) (d on a))
((a on table) (b on c) (c on table) (d on a)))
> (possible-states 'b s '(a b c d table))
(((b on a) (a on table) (c on table) (d on a))
((b on b) (a on table) (c on table) (d on a))
((b on c) (a on table) (c on table) (d on a))
((b on d) (a on table) (c on table) (d on a))
((b on table) (a on table) (c on table) (d on a)))
> (possible-states 'c s '(a b c d table))
(((c on a) (a on table) (b on c) (d on a))
((c on b) (a on table) (b on c) (d on a))
((c on c) (a on table) (b on c) (d on a))
((c on d) (a on table) (b on c) (d on a))
((c on table) (a on table) (b on c) (d on a)))
> (possible-states 'd s '(a b c d table))
(((d on a) (a on table) (b on c) (c on table))
((d on b) (a on table) (b on c) (c on table))
((d on c) (a on table) (b on c) (c on table))
((d on d) (a on table) (b on c) (c on table))
((d on table) (a on table) (b on c) (c on table)))
> (possible-states 'table s '(a b c d table))
(((table on a) (a on table)
(b on c) (c on table) (d on a))
((table on b) (a on table)
(b on c) (c on table) (d on a))
((table on c) (a on table)
(b on c) (c on table) (d on a))
((table on d) (a on table)
(b on c) (c on table) (d on a))
((table on table) (a on table)
(b on c) (c on table) (d on a)))
(defun possible-states (block state dest)
(let*
((current (assoc block state))
(other (remove current state)))
(node-remove
current
(mapcar
#'(lambda (d)
(cons (list block 'on d) other))
dest))))
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