/usr/share/emacs/site-lisp/chess/chess-puzzle.el is in emacs-chess 2.0b6-1.1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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;;
;; A special kind of display that merely autosaves the game
;;
(require 'chess-game)
(require 'chess-random)
(require 'chess-database)
(defgroup chess-puzzle nil
"A mode for playing games from a database of puzzles."
:group 'chess)
(defcustom chess-puzzle-auto-next nil
"If non-nil, move to the next puzzle once the position is won."
:type 'boolean
:group 'chess-puzzle)
(defvar chess-puzzle-indices nil)
(defvar chess-puzzle-position nil)
(make-variable-buffer-local 'chess-puzzle-indices)
(make-variable-buffer-local 'chess-puzzle-position)
(chess-message-catalog 'english
'((bad-game-read . "Error reading game at position %d")
(end-of-puzzles . "There are no more puzzles in this collection")))
;;;###autoload
(defun chess-puzzle (file &optional index)
"Pick a random puzzle from FILE, and solve it against the default engine.
The spacebar in the display buffer is bound to `chess-puzzle-next',
making it easy to go on to the next puzzle once you've solved one."
(interactive "fRead chess puzzles from: ")
(let* ((database (chess-database-open file))
(objects (and database (chess-session)))
(engine (car objects))
(display (cadr objects)))
(when database
(if engine
(chess-engine-set-option engine 'resign nil))
(with-current-buffer display
(chess-game-set-data (chess-display-game nil) 'database database)
(if chess-puzzle-auto-next
(chess-game-add-hook (chess-display-game nil)
'chess-puzzle-handler display))
(define-key (current-local-map) [? ] 'chess-puzzle-next)
(define-key (current-local-map) [??] 'chess-puzzle-show-solution)
(let ((count (chess-database-count database)))
(setq chess-puzzle-indices (make-vector count nil))
(dotimes (i count)
(aset chess-puzzle-indices i i))
(random t)
(chess-shuffle-vector chess-puzzle-indices)
(setq chess-puzzle-position 0))
(chess-game-run-hooks (chess-display-game display) 'disable-autosave)
(chess-puzzle-next)))))
(defun chess-puzzle-next ()
"Play the next puzzle in the collection, selected randomly."
(interactive)
(let* ((game (chess-display-game nil))
(database (chess-game-data game 'database))
(index chess-puzzle-position)
next-game)
(if (= index (length chess-puzzle-indices))
(chess-message 'end-of-puzzles)
;; setup and load the next puzzle position
(setq chess-puzzle-position (1+ chess-puzzle-position))
(if (null (setq next-game
(chess-database-read database
(aref chess-puzzle-indices index))))
(chess-error 'bad-game-read (aref chess-puzzle-indices index))
(chess-display-set-game nil next-game 0)
(chess-game-set-data game 'my-color (chess-game-side-to-move game 0))
(dolist (key '(database database-index database-count))
(chess-game-set-data game key (chess-game-data next-game key)))
(let ((chess-display-handling-event nil))
(chess-game-run-hooks game 'orient))))))
(defun chess-puzzle-show-solution ()
(interactive)
(let ((game (chess-display-game nil)))
(when game
(let ((bm (chess-pos-epd (chess-game-pos game 0) 'bm))
(pv (chess-pos-epd (chess-game-pos game 0) 'pv)))
(when (or bm pv)
(message "Best move %s %s%s"
(if (zerop (chess-game-index game)) "is" "would have been")
(chess-ply-to-string (car bm))
(if pv
(concat ", predicted variation "
(chess-var-to-algebraic pv))
"")))))))
(defun chess-puzzle-handler (game display event &rest args)
(if (and (eq event 'move)
(chess-game-over-p game))
(with-current-buffer display
(chess-puzzle-next))))
(provide 'chess-puzzle)
;;; chess-puzzle.el ends here
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