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|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Routines for manipulating chess plies
;;
;; $Revision$
;;; Commentary:
;; A ply is the differential between two positions. Or, it is the
;; coordinate transformations applied to one position in order to
;; arrive at the following position. It is also informally called "a
;; move".
;;
;; A ply is represented in Lisp using a cons cell of the form:
;;
;; (BASE-POSITION .
;; (FROM-COORD1 TO-COORD1 [FROM-COORD2 TO-COORD2] [KEYWORDS]))
;;
;; The KEYWORDS indicate special actions that are not really chess
;; moves:
;;
;; :promote PIECE ; promote pawn to PIECE on arrival
;; :resign ; a resignation causes the game to end
;; :stalemate
;; :repetition
;; :perpetual
;; :check ; check is announced
;; :checkmate
;; :draw ; a draw was offered and accepted
;; :draw-offered ; a draw was offered but not accepted
;;
;; A ply may be represented in ASCII by printing the FEN string of the
;; base position, and then printing the positional transformation in
;; algebraic notation. Since the starting position is usually known,
;; the FEN string is optional. A ply may be represented graphically
;; by moving the chess piece(s) involved. It may be rendered verbally
;; by voicing which piece is to move, where it will move to, and what
;; will happen a result of the move (piece capture, check, etc).
;;
;; Plies may be sent over network connections, postal mail, e-mail,
;; etc., so long as the current position is maintained at both sides.
;; Transmitting the base position's FEN string along with the ply
;; offers a form of confirmation during the course of a game.
;;; Code:
(require 'chess-pos)
(defgroup chess-ply nil
"Routines for manipulating chess plies."
:group 'chess)
(defsubst chess-ply-pos (ply)
(car ply))
(defsubst chess-ply-set-pos (ply position)
(setcar ply position))
(defsubst chess-ply-changes (ply)
(cdr ply))
(defsubst chess-ply-set-changes (ply changes)
(setcdr ply changes))
(defun chess-ply-has-keyword (ply &rest keywords)
(catch 'found
(dolist (keyword keywords)
(if (memq keyword (chess-ply-changes ply))
(throw found keyword)))))
(defsubst chess-ply-source (ply)
(car (chess-ply-changes ply)))
(defsubst chess-ply-target (ply)
(cadr (chess-ply-changes ply)))
(defsubst chess-ply-next-pos (ply)
(apply 'chess-pos-move (chess-pos-copy (chess-ply-pos ply))
(chess-ply-changes ply)))
(defconst chess-piece-name-table
'(("queen" . ?q)
("rook" . ?r)
("knight" . ?n)
("bishop" . ?b)))
(defun chess-ply-create-castle (position &optional long)
"Create a castling ply; this function supports Fischer Random castling."
(let* ((color (chess-pos-side-to-move position))
(king (car (chess-pos-search position (if color ?K ?k))))
(king-target (chess-rf-to-index (if color 7 0) (if long 2 6)))
(king-file (chess-index-file king))
(file (if long 0 7))
rook)
(while (funcall (if long '< '>) file king-file)
(let ((index (chess-rf-to-index (if color 7 0) file)))
(if (chess-pos-piece-p position index (if color ?R ?r))
(setq rook index file king-file)
(setq file (funcall (if long '1+ '1-) file)))))
(if (and rook
(chess-search-position position king-target (if color ?K ?k)))
(cons (chess-pos-copy position)
(list king king-target rook
(chess-rf-to-index (if color 7 0) (if long 3 5))
(if long :long-castle :castle))))))
(defun chess-ply-create (position &rest changes)
"Create a ply from the given POSITION by applying the suppiled CHANGES.
This function will guarantee the resulting ply is legal, and will also
annotate the ply with :check or other modifiers as necessary. It will
also extend castling, and will prompt for a promotion piece.
Note: Do not pass in the rook move if CHANGES represents a castling
maneuver."
(let ((ply (cons (chess-pos-copy position) changes)))
(if (null changes)
ply
;; validate that `changes' can be legally applied to the given
;; position
(when (member (car changes)
(chess-search-position position (cadr changes)
(chess-pos-piece position
(car changes))))
;; is this a castling maneuver?
(let ((color (chess-pos-side-to-move position)))
(when (and (eq (if color ?K ?k)
(chess-pos-piece position (car changes)))
(> (abs (- (chess-index-file (cadr changes))
(chess-index-file (car changes)))) 1))
(let ((kingside (> (chess-index-file (cadr changes))
(chess-index-file (car changes)))))
;; if so, add the rook moves
(nconc changes (if kingside
(list (chess-rf-to-index (if color 7 0) 7)
(chess-rf-to-index (if color 7 0) 5)
:castle)
(list (chess-rf-to-index (if color 7 0) 0)
(chess-rf-to-index (if color 7 0) 3)
:long-castle))))))
(let* ((next-pos (chess-ply-next-pos ply))
(color (chess-pos-side-to-move next-pos)))
;; is the opponent's king in check/mate or stalemate now, as
;; a result of the changes? NOTE: engines, whom we should
;; trust, may already have determine if check/checkmate
;; applies.
(let ((can-move (catch 'can-move
(dotimes (rank 8)
(dotimes (file 8)
(let* ((to (chess-rf-to-index rank file))
(piece (chess-pos-piece next-pos to)))
(when (or (eq piece ? )
(if color
(> piece ?a)
(< piece ?a)))
(if (chess-search-position next-pos
to color)
(throw 'can-move t)))))))))
(if (chess-search-position next-pos
(car (chess-pos-search
next-pos (if color ?K ?k)))
(not color))
;; yes, well is in he in checkmate?
(if can-move
(nconc changes (list :check))
(nconc changes (list :checkmate)))
;; no, but is he in stalemate?
(unless can-move
(nconc changes (list :stalemate)))))
;; is this a pawn move to the ultimate rank? if so, and we
;; haven't already been told, ask for the piece to promote
;; it to; NOTE: 'color' has the inverse meaning at this
;; point...
(if (and (= ?p (downcase (chess-pos-piece next-pos
(cadr changes))))
(= (if color 7 0)
(chess-index-rank (cadr changes))))
(let ((new-piece (completing-read
"Promote pawn to queen/rook/knight/bishop? "
chess-piece-name-table nil t "queen")))
(setq new-piece
(cdr (assoc new-piece chess-piece-name-table)))
(unless color
(setq new-piece (upcase new-piece)))
(nconc changes (list :promote new-piece)))))
;; return the annotated ply
ply))))
(defsubst chess-ply-final-p (ply)
"Return non-nil if this is the last ply of a game/variation."
(chess-ply-has-keyword ply :draw :perpetual :repetition :stalemate
:resign :checkmate))
(defun chess-legal-plies (position)
"Return a list of all legal plies in POSITION."
(let ((color (chess-pos-side-to-move position)) plies)
(dotimes (rank 8)
(dotimes (file 8)
(let* ((to (chess-rf-to-index rank file))
(piece (chess-pos-piece position to)))
(when (or (eq piece ? )
(if color
(> piece ?a)
(< piece ?a)))
(dolist (candidate (chess-search-position position to color))
(push (chess-ply-create position candidate to) plies))))))
plies))
(provide 'chess-ply)
;;; chess-ply.el ends here
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