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Two chess notation grammars — a position in FEN and a game score in PGN — plus a terminal board printer in Unicode chess glyphs.

Version

0.2.4 none stated

Depends

none beyond the core

License

Artistic-2.0

Its own test suite

2 files, green

Checked

2026-09-15 against Raku++ 3.28.0 and Rakudo 2026.08

Where it lives

raku.land · source

Install it #

$ rakupp install Chess

zef install Chess writes the same store; either installer leaves the module usable by both engines.

What it is for #

Two text formats carry essentially all recorded chess. FEN describes a position in one line; PGN describes a whole game. Reading either means a grammar, and writing that grammar twice is what this distribution saves you.

There is no board representation here, no move generator and no legality checking — the grammars recognise the notation and hand back a Match.

Drawing a position #

use Chess;

show-FEN($Chess::startpos //
    'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1');

♜♞♝♛♚♝♞♜
♟♟♟♟♟♟♟♟
        
        
        
        
♙♙♙♙♙♙♙♙
♖♘♗♕♔♗♘♖

show-FEN prints and returns Nil. There is no string-producing form, and the ANSI escapes for the checkerboard are emitted unconditionally — redirect its output to a file and the escapes go into the file.

Reading a position #

use Chess;
use Chess::FEN;

my $m = Chess::FEN.parse('rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1');
say 'parsed         : ', ?$m;
say 'active-color   : ', ~$m<active-color>;
say 'castling       : ', ~$m<castling>;
say 'en-passant     : ', ~$m<en-passant>;
say 'half-move      : ', ~$m<half-move-clock>;
say 'full-move      : ', ~$m<full-move-number>;
say '';
say 'and the constant the module ships:';
say '  ', $Chess::startpos;

parsed         : True
active-color   : w
castling       : KQkq
en-passant     : -
half-move      : 0
full-move      : 1

and the constant the module ships:
  (Any)

Reading a game #

use Chess::PGN;

my $game = '1. e4 e5 2. Qh5 Nc6 3. Qxf7# 1-0';
my $m = Chess::PGN.parse($game);
say 'parsed       : ', ?$m;
say 'games        : ', $m<game>.elems;
say 'moves        : ', $m<game>[0]<move>.elems;
say 'move texts   : ', $m<game>[0]<move>.map(*.Str.trim).List.raku;
say 'adjudication : ', ~$m<game>[0]<adjudication>;
say '';
for '1. e4 e5 2. Nf3',
    '1. e8=Q Kh8 2. Qxh8# 1-0',
    '1. e4 $1 {best by test} e5 1/2-1/2',
    '1. e9 e5 1-0',
    'hello world' -> $s {
    say sprintf('%-40s -> %s', $s.raku, Chess::PGN.parse($s) ?? 'parses' !! 'no');
}

parsed       : True
games        : 1
moves        : 3
move texts   : ("1. e4 e5", "2. Qh5 Nc6", "3. Qxf7#")
adjudication : 1-0

"1. e4 e5 2. Nf3"                        -> parses
"1. e8=Q Kh8 2. Qxh8# 1-0"               -> parses
"1. e4 \$1 \{best by test} e5 1/2-1/2"   -> parses
"1. e9 e5 1-0"                           -> no
"hello world"                            -> no

Tags, castling, promotion, numeric annotation glyphs, comments and all four adjudications are handled, and the result is optional.

The one thing to know #

The where Chess::FEN.parse($fen) in show-FEN's signature checks the shape of the string, not the board. A rank that does not add up to eight squares is "valid".

use Chess::FEN;

for '44444444/8/8/8/8/8/8/8 w - - 0 1',
    '4/8/8/8/8/8/8/8 w - - 0 1',
    '8/8/8/8/8/8/8/8 w - - 0 1',
    'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq e3 99999 0' -> $fen {
    say sprintf('%-64s parses: %s', $fen.raku, ?Chess::FEN.parse($fen));
}
say '';
say 'those are, in order: a rank of 32 squares, a rank of 4,';
say 'a board with no kings at all, and a five-digit half-move clock.';

"44444444/8/8/8/8/8/8/8 w - - 0 1"                               parses: True
"4/8/8/8/8/8/8/8 w - - 0 1"                                      parses: True
"8/8/8/8/8/8/8/8 w - - 0 1"                                      parses: True
"rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq e3 99999 0"  parses: True

those are, in order: a rank of 32 squares, a rank of 4,
a board with no kings at all, and a five-digit half-move clock.

token rank { <symbol> ** 1..8 } counts symbols, never squares, so a rank may describe anywhere from one to sixty-four of them. A parameter constraint that runs a grammar reads like validation; here it is a spell-check.

A Chess::FEN match is not a validated position. If you need one, count the squares yourself.

Where the two engines differ #

Nowhere. Every position, every game and every rejection in this page was byte-identical on Raku++ and Rakudo, down to the ANSI escape bytes in the board.

Two things worth knowing that are not engine differences. show-FEN's body depends on $/ leaking out of its own signature — the where clause runs the grammar and the body reads the match object it left behind — so the parameter constraint is load-bearing and cannot be replaced with a cheaper check. And the distribution declares no auth, which is why it has no canonical raku.land path.