8-Puzzle: Invoking the Search

(defun make-initial-state (tiles)

(make-state

:tiles tiles

:actions '()))

(defun goal-state-p (state)

(equal (state-tiles state) '(1 2 3 4 5 6 7 8 0)))

(defun next-states (state)

(remove NIL

(list (move-blank state :UP)

(move-blank state :DOWN)

(move-blank state :LEFT)

(move-blank state :RIGHT))))

(defun move-blank (state dir)

(let ((blank-pos (state-blank-pos state))

(new-pos (state-new-pos state dir)))

(cond

((null new-pos) NIL)

(T (let ((new-state (copy-state-deeply state)))

(state-swap-pos new-state blank-pos new-pos)

(state-add-action new-state dir)

new-state)))))

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