code.delx.au - gnu-emacs-elpa/blob - chess-fen.el

   1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   2 ;;
   3 ;; Convert a chess position to/from FEN notation
   4 ;;
   5 ;; FEN notation encodes a chess position using a simple string.  The
   6 ;; format is:
   7 ;;
   8 ;;   POSITION SIDE FLAGS
   9 ;;
  10 ;; The POSITION gives all eight ranks, by specifying a letter for each
  11 ;; piece on the position, and a number for any intervening spaces.
  12 ;; Trailing spaces need not be counted.  Uppercase letters signify
  13 ;; white, and lowercase black.  For example, if your position only had
  14 ;; a black king on d8, your POSITION string would be:
  15 ;;
  16 ;;   3k////////
  17 ;;
  18 ;; For the three spaces (a, b and c file), the black king, and then
  19 ;; all the remaining ranks (which are all empty, so their spaces can
  20 ;; be ignored).
  21 ;;
  22 ;; The SIDE is w or b, to indicate whose move it is.
  23 ;;
  24 ;; The FLAGS can contain K, Q, k or q, to signify whether the white or
  25 ;; black king can still castle on the king or queen side.  You can
  26 ;; also have coordinates, such as e4, a5, to specify which pawns may
  27 ;; be captured by en passant.
  28 ;;
  29 ;; The starting chess position always looks like this:
  30 ;;
  31 ;;   rnbqkbnr/pppppppp/////PPPPPPPP/RNBQKBNR/ w KQkq -
  32 ;;
  33 ;; And in "full" mode (where all spaces are accounted for):
  34 ;;
  35 ;;   rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq -
  36 ;;
  37 ;; It may also have the current game sequence appended, but this
  38 ;; relate to the game, not the position.
  39 ;;
  40
  41 (defun chess-fen-to-pos (fen)
  42   "Convert a FEN-like notation string to a chess position."
  43   (assert (stringp fen))
  44   (let ((i 0) (l (length fen))
  45         (rank 0) (file 0) (c ?0)
  46         (position (chess-pos-create t))
  47         error (space-count 0))
  48     (setq c (aref fen i))
  49     (while (and (null error)
  50                 (/= c ? ) (< i l))
  51       (cond
  52        ((= c ?/)
  53         (setq file 0 rank (1+ rank)))
  54        ((and (>= c ?1) (<= c ?9))
  55         (setq file (+ file (- c ?0))))
  56        ((memq (upcase c) '(?K ?Q ?B ?N ?R ?P))
  57         (chess-pos-set-piece position (chess-rf-to-index rank file) c)
  58         (setq file (1+ file)))
  59        (t
  60         (setq error t)))
  61       (setq i (1+ i) c (aref fen i)))
  62     (if (= (aref fen i) ? )
  63         (setq i (1+ i)))
  64     (if (memq (aref fen i) '(?b ?w))
  65         (progn
  66           (chess-pos-set-side-to-move position (= (aref fen i) ?w))
  67           (setq i (+ i 2)))
  68       (setq error t))
  69     (setq c (aref fen i))
  70     (while (and (null error)
  71                 (< space-count 2) (< i l))
  72       (cond
  73        ((= c ?-))
  74        ((= c ? ) (setq space-count (1+ space-count)))
  75        ((= c ?K) (chess-pos-set-can-castle position ?K t))
  76        ((= c ?Q) (chess-pos-set-can-castle position ?Q t))
  77        ((= c ?k) (chess-pos-set-can-castle position ?k t))
  78        ((= c ?q) (chess-pos-set-can-castle position ?q t))
  79        ((and (>= c ?a) (<= c ?h))
  80         (chess-pos-set-en-passant position (chess-coord-to-index
  81                                             (substring fen i (+ i 2))))
  82         (setq i (1+ i)))
  83        (t
  84         (setq error t)))
  85       (setq i (1+ i) c (and (< i l) (aref fen i))))
  86     (unless error
  87       position)))
  88
  89 (defun chess-pos-to-fen (position &optional full)
  90   "Convert a chess POSITION to FEN-like notation.
  91 If FULL is non-nil, represent trailing spaces as well."
  92   (assert (vectorp position))
  93   (let ((blank 0) (str "") output)
  94     (dotimes (rank 8)
  95       (dotimes (file 8)
  96         (let ((p (chess-pos-piece position (chess-rf-to-index rank file))))
  97           (if (= p ? )
  98               (setq blank (1+ blank))
  99             (if (> blank 0)
 100                 (setq str (concat str (int-to-string blank)) blank 0))
 101             (setq str (concat str (char-to-string p))))))
 102       (if (and full (> blank 0))
 103           (setq str (concat str (int-to-string blank))))
 104       (setq blank 0 str (concat str "/")))
 105     (setq str (if (chess-pos-side-to-move position)
 106                   (concat str " w ")
 107                 (concat str " b ")))
 108     (if (chess-pos-can-castle position ?K)
 109         (setq str (concat str "K") output t))
 110     (if (chess-pos-can-castle position ?Q)
 111         (setq str (concat str "Q") output t))
 112     (if (chess-pos-can-castle position ?k)
 113         (setq str (concat str "k") output t))
 114     (if (chess-pos-can-castle position ?q)
 115         (setq str (concat str "q") output t))
 116     (if output
 117         (setq str (concat str " "))
 118       (setq str (concat str "- ")))
 119     (let ((index (chess-pos-en-passant position)))
 120       (if index
 121           (concat str (chess-index-to-coord index))
 122         (concat str "-")))))
 123
 124 (provide 'chess-fen)
 125
 126 ;;; chess-fen.el ends here