50 move rule

[nextchessmove]

I think that the 50-move rule isn't being applied correctly. From Wikipedia, I'm reading that:

The fifty-move rule in chess states that a player can claim a draw if no capture has been made and no pawn has been moved in the last fifty moves (for this purpose a "move" consists of a player completing a turn followed by the opponent completing a turn).

Binbo is currently looking at halfmoves instead of fullmoves:

 is_rule50(Game) ->
    case (get_halfmove(Game) < 50) of
        true  ->
            false;
        false ->
            case (get_fullmove(Game) < 75) of
                true  -> false;
                false -> true
            end
    end.

So I think it's as simple as this:

is_rule50(Game) ->
    get_halfmove(Game) >= 2 * 50.

Regarding the 75-move rule, I'm not sure it applies here. If I'm understanding the rules correctly, at 50 full moves without a pawn movement or capture (halfmove clock = 100), either player can (but does not have to) claim a draw, whereas at 75 full moves without a pawn movement or capture (halfmove clock = 150), the draw is mandatory.

Let me know if you agree, and if you'd like me to attempt a pull request with tests! Binbo is great and I'm learning a ton from it.

[DOBRO]

You are absolutely right. Something's wrong with this part of code.

I would rewrite it as:

is_rule50(Game) ->
    get_halfmove(Game) > 99.

it's slightly faster than >= 2 * 50.

Feel free to make a pull request and please don't forget to include tests, since this case is not covered so far. Thank you for diving into the library!

[DOBRO]

BTW, could you attach one or more PGNs where 50-move rule was applied? I would add them to tests also.

[nextchessmove]

Absolutely! Here's the PGN I used:

[Event "Hoogovens Open"]
[Site "Wijk aan Zee NED"]
[Date "1995.01.27"]
[EventDate "?"]
[Round "10"]
[Result "1/2-1/2"]
[White "Jan Timman"]
[Black "Christopher Lutz"]
[ECO "E59"]
[WhiteElo "?"]
[BlackElo "?"]
[PlyCount "242"]

1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.e3 O-O 5.Bd3 d5 6.Nf3 c5 7.O-O
Nc6 8.a3 Bxc3 9.bxc3 dxc4 10.Bxc4 Qc7 11.Bb5 a6 12.Bd3 e5
13.Qc2 b5 14.e4 exd4 15.cxd4 c4 16.Be2 Re8 17.d5 Ne5 18.Bb2
Nxf3+ 19.Bxf3 Bg4 20.d6 Qc6 21.Bxg4 Nxg4 22.h3 Ne5 23.Rad1 Nd7
24.Rfe1 a5 25.Bc3 f6 26.Qd2 Rxe4 27.Rxe4 Qxe4 28.Bxa5 Re8
29.Bb4 Re5 30.f3 Qe3+ 31.Qxe3 Rxe3 32.Kf2 Re8 33.f4 Kf7 34.Rd5
Rb8 35.Ke3 Ke6 36.Rd1 f5 37.g4 fxg4 38.hxg4 Nf6 39.f5+ Kd7
40.g5 Re8+ 41.Kf4 Nh5+ 42.Kg4 g6 43.fxg6 hxg6 44.Rd5 Ng7
45.Rxb5 Nf5 46.Rb7+ Ke6 47.Rc7 Rh8 48.Kf3 Rh3+ 49.Kf2 Rh2+
50.Ke1 Rh1+ 51.Kf2 Rh2+ 52.Kf1 Rh1+ 53.Kg2 Rd1 54.Kf2 Rd4
55.Ke1 Rh4 56.Kd2 Rh2+ 57.Kc3 Rh3+ 58.Kxc4 Nxd6+ 59.Kc5 Ne4+
60.Kb5 Nxg5 61.a4 Nf3 62.a5 Nd4+ 63.Kc4 Rh4 64.Bc5 Nc6 65.Kb5
Nxa5 66.Kxa5 g5 67.Kb5 g4 68.Rg7 g3 69.Rxg3 Rh1 70.Kc6 Re1
71.Bd4 Rc1+ 72.Bc3 Rd1 73.Re3+ Kf5 74.Kc5 Rd8 75.Be5 Rc8+
76.Kd5 Ra8 77.Rf3+ Kg4 78.Rf7 Ra5+ 79.Ke4 Ra4+ 80.Bd4 Kg5
81.Rg7+ Kh4 82.Ke5 Kh3 83.Rg1 Rb4 84.Be3 Rg4 85.Ra1 Kg2 86.Bf4
Rg8 87.Ra2+ Kf3 88.Ra3+ Ke2 89.Ke4 Re8+ 90.Be5 Re7 91.Ra2+ Ke1
92.Kd4 Kf1 93.Bf4 Re2 94.Ra8 Re7 95.Kd3 Kg2 96.Rf8 Re6 97.Rf7
Re8 98.Be3 Ra8 99.Bc5 Ra4 100.Ke3 Rg4 101.Bd6 Rg6 102.Rf2+ Kh3
103.Be5 Kg4 104.Ke4 Kh5 105.Bf6 Kg4 106.Rf4+ Kg3 107.Ke3 Kh3
108.Rf5 Rg3+ 109.Kf2 Rg2+ 110.Kf1 Rc2 111.Rg5 Rc4 112.Be5 Kh4
113.Rg8 Re4 114.Bg3+ Kh5 115.Kf2 Ra4 116.Kf3 Kh6 117.Be5 Rb4
118.Bf4+ Kh7 119.Rg5 Ra4 120.Kg4 Rb4 121.Kf5 Rb5+ 1/2-1/2

It's from a game referenced from Wikipedia's Fifty-move rule article, and I found the PGN here.

To get the particular FEN and move I used for the test, I ran the PGN through pgn-extract to see when the halfmove clock changed from 99 to 100:

cat test.pgn | ./pgn-extract --fencomments

Here's the PGN from the other games in the Wikipedia article:

https://www.chessgames.com/perl/nph-chesspgn?text=1&gid=1067317 https://www.chessgames.com/perl/nph-chesspgn?text=1&gid=1196357 https://www.chessgames.com/perl/nph-chesspgn?text=1&gid=1486011

[DOBRO]

All these PGNs are added to tests. Binbo 4.0.2 released with the fix. Thanks!