sfen-parser.pegjs

sfen-parser.pegjs

/**
 *  Title: SFEN parser
 *  Date: 23-Jan-2014
 *  Author: Daichi Shinozaki <dsdseg@gmail.com>
 *  Demo URL: http://jsfiddle.net/dseg/QezQ7/15/
 *
 *  Note:
 *  Tested with PEG.js 0.8.0
 *  http://pegjs.majda.cz/
 *
 *  SFEN stands for 'Shogi FEN'
 *  http://www.glaurungchess.com/shogi/usi.html
 *
 *  FEN stands for 'Forsyth-Edwards Notation', a standard notation for describing a 
 *  particular board position of a chess game.
 *  http://en.wikipedia.org/wiki/Forsyth-Edwards_Notation
 * 
 * A complicated SFEN example is the following position, taken from the 3rd game of the
 * 19th Ryu-O match between Sato and Watanabe:
 *
 * 8l/1l+R2P3/p2pBG1pp/kps1p4/Nn1P2G2/P1P1P2PP/1PS6/1KSG3+r1/LN2+p3L w Sbgn3p 124
 *
 * http://live.shogi.or.jp/ryuou/kifu_archives/kifu_19/061115_watanabe-sato.html
 * http://live.shogi.or.jp/ryuou/kifu_archives/kifu_19/061115_ryuoh.kif
 */
    
/* utility function */
{
  function flatten(array) {
    var merged = [];
    return merged.concat.apply(merged, array);
  }
}

start
 = board:boardState " " side:theSideToMove " " piecesInHand:piecesInHand " " moves:moveCount { 
  var boardFlattened = flatten(board);
  var pihFlattened = flatten(piecesInHand);
  return { board:boardFlattened, side:side, piecesInHand:pihFlattened, moves:moves }
}

boardState
 = first:row rest:("/" row)+ { 
  var result = [];
  for (var i = 0; i < rest.length; i++)
    result = result.concat(rest[i][1]); // skip heading '/'
  return first.concat(result);
}

row
 = (digit:digit {
     var digitConverted = [];
     while (digit-- > 0)
       digitConverted.push(" ");
     return digitConverted;
    }
/ piece:piece)+

digit
 = [1-9]

piece
 = $(promotion? [lnsgkprbLNSGKPRB])

promotion
 = "+"

theSideToMove
 = [bw]

digit2to9
 = [2-9]

/* '-' means 'no pieces in hand' */
pieceInHand
 = [lnsgprbLNSGPRB-] 

piecesInHand
 = (p:pieceInHand count:digit2to9 {
  var pieces = [];
  while(count-- > 0)
    pieces.push(p);
  return pieces;
 }
/ pieceInHand)+

moveCount
 = integer

integer
 = integer:$[0-9]+ { return parseInt(integer); }