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;;; chess-ai.el --- A Chess playing module
;; Copyright (C) 2004 Free Software Foundation, Inc.
;; Author: Mario Lang <mlang@delysid.org>
;; This file is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;; This file is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING. If not, write to
;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Code:
(require 'chess-common)
(require 'chess-pos)
(require 'chess-ply)
(require 'cl)
(defgroup chess-ai ()
"A simple chess engine written in elisp."
:group 'chess)
(defcustom chess-ai-depth 2
"*The depth used to prune the search tree."
:group 'chess-ai
:type 'integer)
(defvar chess-pawn-value 100)
(defvar chess-knight-value 300)
(defvar chess-bishop-value 300)
(defvar chess-rook-value 500)
(defvar chess-queen-value 900)
(defvar chess-king-value 10000)
(defun chess-eval-static (position)
"Find the static score for POSITION."
(assert (vectorp position))
(let ((v 0)
(status (chess-pos-status position)))
(if (eq status :checkmate)
-64000
(if (eq status :stalemate)
v
(dotimes (i 64 (if (chess-pos-side-to-move position) v (- v)))
(let ((piece (aref position i)))
(cond
((= piece ?P) (incf v chess-pawn-value))
((= piece ?p) (decf v chess-pawn-value))
((= piece ?K) (incf v chess-king-value))
((= piece ?k) (decf v chess-king-value))
((= piece ?Q) (incf v chess-queen-value))
((= piece ?q) (decf v chess-queen-value))
((= piece ?R) (incf v chess-rook-value))
((= piece ?r) (decf v chess-rook-value))
((= piece ?B) (incf v chess-bishop-value))
((= piece ?b) (decf v chess-bishop-value))
((= piece ?N) (incf v chess-knight-value))
((= piece ?n) (decf v chess-knight-value)))))))))
(defun chess-ai-eval (position depth alpha beta &optional line)
"Evaluate POSITION using a simple AlphaBeta search algorithm using at most
DEPTH plies."
;; TBD: We do far too much consing
(if (= depth 0)
(cons (chess-eval-static position) line)
(let ((plies (chess-legal-plies
position :color (chess-pos-side-to-move position)))
(ret (cons alpha line)))
(if (= (length plies) 0)
(cons (chess-eval-static position) line)
(while plies
(let* ((tmp1 (chess-ai-eval (chess-ply-next-pos (car plies))
(1- depth) (- beta) (- alpha)
(cons (car plies) line)))
(tmp (- (car tmp1))))
(if (> tmp alpha) (setq alpha tmp
ret (cons tmp (cdr tmp1))))
(if (>= alpha beta)
(setq plies nil)
(setq plies (cdr plies)))))
ret))))
(defun chess-ai-best-move (position depth &optional func)
"Find the best move for POSITION using `chess-ai-eval' with DEPTH.
Returns (VALUE . LIST-OF-PLIES) where
VALUE is the evaluated score of the move and
LIST-OF-PLIES is the list of plies which were actually found."
(let ((res (chess-ai-eval position depth -100000 100000)))
(cons (car res)
(if (functionp func)
(mapcar func (nreverse (cdr res)))
(nreverse (cdr res))))))
;; TBD: It is somewhat strange that we need to define this variable.
(defvar chess-ai-regexp-alist nil)
(defun chess-ai-handler (game event &rest args)
(unless chess-engine-handling-event
(cond
((eq event 'initialize)
(setq chess-engine-opponent-name "Emacs AI")
t)
((eq event 'new)
(chess-engine-set-position nil))
((eq event 'move)
(when (= 1 (chess-game-index game))
(chess-game-set-tag game "White" chess-full-name)
(chess-game-set-tag game "Black" chess-engine-opponent-name))
(when (chess-game-over-p game)
(chess-game-set-data game 'active nil)))
((eq event 'post-move)
(unless (chess-game-over-p game)
(let (chess-display-handling-event)
(message "Thinking...")
(funcall chess-engine-response-handler
'move (cadr (chess-ai-best-move (chess-engine-position nil)
chess-ai-depth)))
(message "Thinking... done"))))
(t
(apply 'chess-common-handler game event args)))))
(provide 'chess-ai)
;;; chess-ai.el ends here
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