docs: function getPiecesFromBoard(board) {
      var initialPieces = {
          white: [],
          black: []
      };
      return board.reduce(function (piecesRow, row) {
          return row.reduce(function (pieces, position) {
              if (Position.hasBlackPiece(position)) pieces.black = pieces.black.concat(position);else if (Position.hasWhitePiece(position)) pieces.white = pieces.white.concat(position);
              return pieces;
          }, piecesRow);
      }, initialPieces);
  }