Move most of the chess position/board handling into its own classes.

diff --git a/Board.pm b/Board.pm
new file mode 100644 (file)
index 0000000..feb4893
--- /dev/null
+++ b/Board.pm
@@ -0,0 +1,346 @@
+#! /usr/bin/perl
+#
+# There are too many chess modules on CPAN already, so here's another one...
+#
+use strict;
+use warnings;
+
+package Board;
+
+sub new {
+       my ($class, @rows) = @_;
+       my $board = [];
+
+       for my $row (0..7) {
+               for my $col (0..7) {
+                       $board->[$row][$col] = substr($rows[$row], $col, 1);
+               }
+       }
+
+       return bless $board;
+}
+
+sub clone {
+       my ($board) = shift;
+       my $nb = [];
+
+       for my $row (0..7) {
+               for my $col (0..7) {
+                       $nb->[$row][$col] = $board->[$row][$col];
+               }
+       }
+
+       return bless $nb;
+}
+
+# Returns a new board.
+sub make_move {
+       my ($board, $from_row, $from_col, $to_row, $to_col, $promo) = @_;
+       my $move = _move_to_uci_notation($from_row, $from_col, $to_row, $to_col, $promo);
+       my $piece = $board->[$from_row][$from_col];
+       my $nb = $board->clone();
+
+       if ($piece eq '-') {
+               die "Invalid move $move";
+       }
+
+       # white short castling
+       if ($move eq 'e1g1' && $piece eq 'K') {
+               # king
+               $nb->[7][4] = '-';
+               $nb->[7][6] = $piece;
+
+               # rook
+               $nb->[7][7] = '-';
+               $nb->[7][5] = 'R';
+
+               return $nb;
+       }
+
+       # white long castling
+       if ($move eq 'e1c1' && $piece eq 'K') {
+               # king
+               $nb->[7][4] = '-';
+               $nb->[7][2] = $piece;
+
+               # rook
+               $nb->[7][0] = '-';
+               $nb->[7][3] = 'R';
+
+               return $nb;
+       }
+
+       # black short castling
+       if ($move eq 'e8g8' && $piece eq 'k') {
+               # king
+               $nb->[0][4] = '-';
+               $nb->[0][6] = $piece;
+
+               # rook
+               $nb->[0][7] = '-';
+               $nb->[0][5] = 'r';
+
+               return $nb;
+       }
+
+       # black long castling
+       if ($move eq 'e8c8' && $piece eq 'k') {
+               # king
+               $nb->[0][4] = '-';
+               $nb->[0][2] = $piece;
+
+               # rook
+               $nb->[0][0] = '-';
+               $nb->[0][3] = 'r';
+
+               return $nb;
+       }
+
+       # check if the from-piece is a pawn
+       if (lc($piece) eq 'p') {
+               # attack?
+               if ($from_col != $to_col) {
+                       # en passant?
+                       if ($board->[$to_row][$to_col] eq '-') {
+                               if ($piece eq 'p') {
+                                       $nb->[$to_row + 1][$to_col] = '-';
+                               } else {
+                                       $nb->[$to_row - 1][$to_col] = '-';
+                               }
+                       }
+               } else {
+                       if ($promo ne '') {
+                               if ($piece eq 'p') {
+                                       $piece = $promo;
+                               } else {
+                                       $piece = uc($promo);
+                               }
+                       }
+               }
+       }
+
+       # update the board
+       $nb->[$from_row][$from_col] = '-';
+       $nb->[$to_row][$to_col] = $piece;
+
+       return $nb;
+}
+
+sub _move_to_uci_notation {
+       my ($from_row, $from_col, $to_row, $to_col, $promo) = @_;
+       $promo //= "";
+       return sprintf("%c%d%c%d%s", ord('a') + $from_col, 8 - $from_row, ord('a') + $to_col, 8 - $to_row, $promo);
+}
+
+sub fen {
+       my ($board) = @_;
+       my @rows = ();
+       for my $row (0..7) {
+               my $str = join('', @{$board->[$row]});
+                $str =~ s/(-+)/length($1)/ge;
+               push @rows, $str;
+        }
+
+       return join('/', @rows);
+}
+
+sub can_reach {
+       my ($board, $piece, $from_row, $from_col, $to_row, $to_col) = @_;
+       
+       # can't eat your own piece
+       my $dest_piece = $board->[$to_row][$to_col];
+       if ($dest_piece ne '-') {
+               return 0 if (($piece eq lc($piece)) == ($dest_piece eq lc($dest_piece)));
+       }
+
+       if (lc($piece) eq 'k') {
+               return (abs($from_row - $to_row) <= 1 && abs($from_col - $to_col) <= 1);
+       }
+       if (lc($piece) eq 'r') {
+               return 0 unless ($from_row == $to_row || $from_col == $to_col);
+
+               # check that there's a clear passage
+               if ($from_row == $to_row) {
+                       if ($from_col > $to_col) {
+                               ($to_col, $from_col) = ($from_col, $to_col);
+                       }
+
+                       for my $c (($from_col+1)..($to_col-1)) {
+                               my $middle_piece = $board->[$to_row][$c];
+                               return 0 if ($middle_piece ne '-');
+                       }
+
+                       return 1;
+               } else {
+                       if ($from_row > $to_row) {
+                               ($to_row, $from_row) = ($from_row, $to_row);
+                       }
+
+                       for my $r (($from_row+1)..($to_row-1)) {
+                               my $middle_piece = $board->[$r][$to_col];
+                               return 0 if ($middle_piece ne '-');     
+                       }
+
+                       return 1;
+               }
+       }
+       if (lc($piece) eq 'b') {
+               return 0 unless (abs($from_row - $to_row) == abs($from_col - $to_col));
+
+               my $dr = ($to_row - $from_row) / abs($to_row - $from_row);
+               my $dc = ($to_col - $from_col) / abs($to_col - $from_col);
+
+               my $r = $from_row + $dr;
+               my $c = $from_col + $dc;
+
+               while ($r != $to_row) {
+                       my $middle_piece = $board->[$r][$c];
+                       return 0 if ($middle_piece ne '-');
+                       
+                       $r += $dr;
+                       $c += $dc;
+               }
+
+               return 1;
+       }
+       if (lc($piece) eq 'n') {
+               my $diff_r = abs($from_row - $to_row);
+               my $diff_c = abs($from_col - $to_col);
+               return 1 if ($diff_r == 2 && $diff_c == 1);
+               return 1 if ($diff_r == 1 && $diff_c == 2);
+               return 0;
+       }
+       if ($piece eq 'q') {
+               return (can_reach($board, 'r', $from_row, $from_col, $to_row, $to_col) ||
+                       can_reach($board, 'b', $from_row, $from_col, $to_row, $to_col));
+       }
+       if ($piece eq 'Q') {
+               return (can_reach($board, 'R', $from_row, $from_col, $to_row, $to_col) ||
+                       can_reach($board, 'B', $from_row, $from_col, $to_row, $to_col));
+       }
+
+       # TODO: en passant
+       if ($piece eq 'p') {
+               # black pawn
+               if ($to_col == $from_col && $to_row == $from_row + 1) {
+                       return ($dest_piece eq '-');
+               }
+               if ($to_col == $from_col && $from_row == 1 && $to_row == 3) {
+                       my $middle_piece = $board->[2][$to_col];
+                       return ($dest_piece eq '-' && $middle_piece eq '-');
+               }
+               if (abs($to_col - $from_col) == 1 && $to_row == $from_row + 1) {
+                       return ($dest_piece ne '-');
+               }
+               return 0;
+       }
+       if ($piece eq 'P') {
+               # white pawn
+               if ($to_col == $from_col && $to_row == $from_row - 1) {
+                       return ($dest_piece eq '-');
+               }
+               if ($to_col == $from_col && $from_row == 6 && $to_row == 4) {
+                       my $middle_piece = $board->[5][$to_col];
+                       return ($dest_piece eq '-' && $middle_piece eq '-');
+               }
+               if (abs($to_col - $from_col) == 1 && $to_row == $from_row - 1) {
+                       return ($dest_piece ne '-');
+               }
+               return 0;
+       }
+       
+       # unknown piece
+       return 0;
+}
+
+# Returns 'none', 'white', 'black' or 'both', depending on which sides are in check.
+# The latter naturally indicates an invalid position.
+sub in_check {
+       my $board = shift;
+       my ($black_check, $white_check) = (0, 0);
+
+       my ($wkr, $wkc, $bkr, $bkc) = _find_kings($board);
+
+       # check all pieces for the possibility of threatening the two kings
+       for my $row (0..7) {
+               for my $col (0..7) {
+                       my $piece = $board->[$row][$col];
+                       next if ($piece eq '-');
+               
+                       if (uc($piece) eq $piece) {
+                               # white piece
+                               $black_check = 1 if ($board->can_reach($piece, $row, $col, $bkr, $bkc));
+                       } else {
+                               # black piece
+                               $white_check = 1 if ($board->can_reach($piece, $row, $col, $wkr, $wkc));
+                       }
+               }
+       }
+
+       if ($black_check && $white_check) {
+               return 'both';
+       } elsif ($black_check) {
+               return 'black';
+       } elsif ($white_check) {
+               return 'white';
+       } else {
+               return 'none';
+       }
+}
+
+sub _find_kings {
+       my $board = shift;
+       my ($wkr, $wkc, $bkr, $bkc);
+
+       for my $row (0..7) {
+               for my $col (0..7) {
+                       my $piece = $board->[$row][$col];
+                       if ($piece eq 'K') {
+                               ($wkr, $wkc) = ($row, $col);
+                       } elsif ($piece eq 'k') {
+                               ($bkr, $bkc) = ($row, $col);
+                       }
+               }
+       }
+
+       return ($wkr, $wkc, $bkr, $bkc);
+}
+
+# Returns if any side is in mate.
+sub in_mate {
+       my $board = shift;
+       my $check = $board->in_check();
+       return 0 if ($check eq 'none');
+
+       # try all possible moves for the side in check
+       for my $row (0..7) {
+               for my $col (0..7) {
+                       my $piece = $board->[$row][$col];
+                       next if ($piece eq '-');
+
+                       if ($check eq 'white') {
+                               next if ($piece eq lc($piece));
+                       } else {
+                               next if ($piece eq uc($piece));
+                       }
+
+                       for my $dest_row (0..7) {
+                               for my $dest_col (0..7) {
+                                       next if ($row == $dest_row && $col == $dest_col);
+                                       next unless ($board->can_reach($piece, $row, $col, $dest_row, $dest_col));
+
+                                       my $nb = $board->clone();
+                                       $nb->[$row][$col] = '-';
+                                       $nb->[$dest_row][$dest_col] = $piece;
+                                       my $new_check = $nb->in_check();
+                                       return 0 if ($new_check ne $check && $new_check ne 'both');
+                               }
+                       }
+               }
+       }
+
+       # nothing to do; mate
+       return 1;
+}
+
+1;

diff --git a/Position.pm b/Position.pm
new file mode 100644 (file)
index 0000000..7bdb913
--- /dev/null
+++ b/Position.pm
@@ -0,0 +1,110 @@
+#! /usr/bin/perl
+#
+# There are too many chess modules on CPAN already, so here's another one...
+#
+use strict;
+use warnings;
+
+require 'Board.pm';
+
+package Position;
+
+# Takes in a FICS style 12-type position.
+sub new {
+       my ($class, $str) = @_;
+       my $pos = {};
+       my (@x) = split / /, $str;
+
+       # TODO: Not all of this stuff really belongs in this module.
+       $pos->{'board'} = Board->new(@x[1..8]);
+       $pos->{'toplay'} = $x[9];
+       $pos->{'ep_file_num'} = $x[10];
+       $pos->{'white_castle_k'} = $x[11];
+       $pos->{'white_castle_q'} = $x[12];
+       $pos->{'black_castle_k'} = $x[13];
+       $pos->{'black_castle_q'} = $x[14];
+       $pos->{'time_to_100move_rule'} = $x[15];
+       $pos->{'player_w'} = $x[17];
+       $pos->{'player_b'} = $x[18];
+       $pos->{'player_w'} =~ s/^[IG]M//;
+       $pos->{'player_b'} =~ s/^[IG]M//;
+       $pos->{'move_num'} = $x[26];
+       if ($x[27] =~ /([a-h][1-8])-([a-h][1-8])/) {
+               $pos->{'last_move_uci'} = $1 . $2;
+       } else {
+               $pos->{'last_move_uci'} = undef;
+       }
+       $pos->{'last_move'} = $x[29];
+
+       bless $pos, $class;
+       return $pos;
+}
+
+sub fen {
+       my $pos = shift;
+
+       # the board itself
+       my $fen = $pos->{'board'}->fen();
+
+       # white/black to move
+       $fen .= " ";
+       $fen .= lc($pos->{'toplay'});
+
+       # castling
+       my $castling = "";
+       $castling .= "K" if ($pos->{'white_castle_k'} == 1);
+       $castling .= "Q" if ($pos->{'white_castle_q'} == 1);
+       $castling .= "k" if ($pos->{'black_castle_k'} == 1);
+       $castling .= "q" if ($pos->{'black_castle_q'} == 1);
+       $castling = "-" if ($castling eq "");
+       # $castling = "-"; # chess960
+       $fen .= " ";
+       $fen .= $castling;
+
+       # en passant
+       my $ep = "-";
+       if ($pos->{'ep_file_num'} != -1) {
+               my $col = $pos->{'ep_file_num'};
+               my $nep = (qw(a b c d e f g h))[$col];
+
+               if ($pos->{'toplay'} eq 'B') {
+                       $nep .= "3";
+               } else {
+                       $nep .= "6";
+               }
+
+               #
+               # Showing the en passant square when actually no capture can be made
+               # seems to confuse at least Rybka. Thus, check if there's actually
+               # a pawn of the opposite side that can do the en passant move, and if
+               # not, just lie -- it doesn't matter anyway. I'm unsure what's the
+               # "right" thing as per the standard, though.
+               #
+               if ($pos->{'toplay'} eq 'B') {
+                       $ep = $nep if ($col > 0 && substr($pos->{'board'}[4], $col-1, 1) eq 'p');
+                       $ep = $nep if ($col < 7 && substr($pos->{'board'}[4], $col+1, 1) eq 'p');
+               } else {
+                       $ep = $nep if ($col > 0 && substr($pos->{'board'}[3], $col-1, 1) eq 'P');
+                       $ep = $nep if ($col < 7 && substr($pos->{'board'}[3], $col+1, 1) eq 'P');
+               }
+       }
+       $fen .= " ";
+       $fen .= $ep;
+
+       # half-move clock
+       $fen .= " ";
+       $fen .= $pos->{'time_to_100move_rule'};
+
+       # full-move clock
+       $fen .= " ";
+       $fen .= $pos->{'move_num'};
+
+       return $fen;
+}
+
+sub to_json_hash {
+       my $pos = shift;
+       return { %$pos, board => undef, fen => $pos->fen() };
+}
+
+1;

diff --git a/remoteglot.pl b/remoteglot.pl
index 9301ac7939d25796dbf6407d36741e9b7a6a0029..7b650477c95d8fa6727e033ef7e413c02074100f 100755 (executable)
--- a/remoteglot.pl
+++ b/remoteglot.pl
@@ -14,6 +14,7 @@ use FileHandle;
 use IPC::Open2;
 use Time::HiRes;
 use JSON::XS;
+require 'Position.pm';
 use strict;
 use warnings;
 
@@ -115,15 +116,15 @@ while (1) {
                chomp $line;
                $line =~ tr/\r//d;
                if ($line =~ /^<12> /) {
-                       my $pos = style12_to_pos($line);
+                       my $pos = Position->new($line);
                        
                        # if this is already in the queue, ignore it
-                       next if (defined($pos_waiting) && $pos->{'fen'} eq $pos_waiting->{'fen'});
+                       next if (defined($pos_waiting) && $pos->fen() eq $pos_waiting->fen());
 
                        # if we're already chewing on this and there's nothing else in the queue,
                        # also ignore it
                        next if (!defined($pos_waiting) && defined($pos_calculating) &&
-                                $pos->{'fen'} eq $pos_calculating->{'fen'});
+                                $pos->fen() eq $pos_calculating->fen());
 
                        # if we're already thinking on something, stop and wait for the engine
                        # to approve
@@ -134,7 +135,7 @@ while (1) {
                                if ($uci_assume_full_compliance) {
                                        $pos_waiting = $pos;
                                } else {
-                                       uciprint($engine, "position fen " . $pos->{'fen'});
+                                       uciprint($engine, "position fen " . $pos->fen());
                                        uciprint($engine, "go infinite");
                                        $pos_calculating = $pos;
                                }
@@ -142,7 +143,7 @@ while (1) {
                                # it's wrong just to give the FEN (the move history is useful,
                                # and per the UCI spec, we should really have sent "ucinewgame"),
                                # but it's easier
-                               uciprint($engine, "position fen " . $pos->{'fen'});
+                               uciprint($engine, "position fen " . $pos->fen());
                                uciprint($engine, "go infinite");
                                $pos_calculating = $pos;
                        }
@@ -151,7 +152,7 @@ while (1) {
                                if (defined($pos_calculating_second_engine)) {
                                        uciprint($engine2, "stop");
                                } else {
-                                       uciprint($engine2, "position fen " . $pos->{'fen'});
+                                       uciprint($engine2, "position fen " . $pos->fen());
                                        uciprint($engine2, "go infinite");
                                        $pos_calculating_second_engine = $pos;
                                }
@@ -237,7 +238,7 @@ sub handle_uci {
                if ($primary) {
                        return if (!$uci_assume_full_compliance);
                        if (defined($pos_waiting)) {
-                               uciprint($engine, "position fen " . $pos_waiting->{'fen'});
+                               uciprint($engine, "position fen " . $pos_waiting->fen());
                                uciprint($engine, "go infinite");
 
                                $pos_calculating = $pos_waiting;
@@ -246,7 +247,7 @@ sub handle_uci {
                } else {
                        $engine2->{'info'} = {};
                        my $pos = $pos_waiting // $pos_calculating;
-                       uciprint($engine2, "position fen " . $pos->{'fen'});
+                       uciprint($engine2, "position fen " . $pos->fen());
                        uciprint($engine2, "go infinite");
                        $pos_calculating_second_engine = $pos;
                }
@@ -336,193 +337,6 @@ sub parse_ids {
        }
 }
 
-sub style12_to_pos {
-       my $str = shift;
-       my %pos = ();
-       my (@x) = split / /, $str;
-       
-       $pos{'board'} = [ @x[1..8] ];
-       $pos{'toplay'} = $x[9];
-       $pos{'ep_file_num'} = $x[10];
-       $pos{'white_castle_k'} = $x[11];
-       $pos{'white_castle_q'} = $x[12];
-       $pos{'black_castle_k'} = $x[13];
-       $pos{'black_castle_q'} = $x[14];
-       $pos{'time_to_100move_rule'} = $x[15];
-       $pos{'player_w'} = $x[17];
-       $pos{'player_b'} = $x[18];
-       $pos{'player_w'} =~ s/^[IG]M//;
-       $pos{'player_b'} =~ s/^[IG]M//;
-       $pos{'move_num'} = $x[26];
-       if ($x[27] =~ /([a-h][1-8])-([a-h][1-8])/) {
-               $pos{'last_move_uci'} = $1 . $2;
-       } else {
-               $pos{'last_move_uci'} = undef;
-       }
-       $pos{'last_move'} = $x[29];
-       $pos{'fen'} = make_fen(\%pos);
-
-       return \%pos;
-}
-
-sub make_fen {
-       my $pos = shift;
-
-       # the board itself
-       my (@board) = @{$pos->{'board'}};
-       for my $rank (0..7) {
-               $board[$rank] =~ s/(-+)/length($1)/ge;
-       }
-       my $fen = join('/', @board);
-
-       # white/black to move
-       $fen .= " ";
-       $fen .= lc($pos->{'toplay'});
-
-       # castling
-       my $castling = "";
-       $castling .= "K" if ($pos->{'white_castle_k'} == 1);
-       $castling .= "Q" if ($pos->{'white_castle_q'} == 1);
-       $castling .= "k" if ($pos->{'black_castle_k'} == 1);
-       $castling .= "q" if ($pos->{'black_castle_q'} == 1);
-       $castling = "-" if ($castling eq "");
-       # $castling = "-"; # chess960
-       $fen .= " ";
-       $fen .= $castling;
-
-       # en passant
-       my $ep = "-";
-       if ($pos->{'ep_file_num'} != -1) {
-               my $col = $pos->{'ep_file_num'};
-               my $nep = (qw(a b c d e f g h))[$col];
-
-               if ($pos->{'toplay'} eq 'B') {
-                       $nep .= "3";
-               } else {
-                       $nep .= "6";
-               }
-
-               #
-               # Showing the en passant square when actually no capture can be made
-               # seems to confuse at least Rybka. Thus, check if there's actually
-               # a pawn of the opposite side that can do the en passant move, and if
-               # not, just lie -- it doesn't matter anyway. I'm unsure what's the
-               # "right" thing as per the standard, though.
-               #
-               if ($pos->{'toplay'} eq 'B') {
-                       $ep = $nep if ($col > 0 && substr($pos->{'board'}[4], $col-1, 1) eq 'p');
-                       $ep = $nep if ($col < 7 && substr($pos->{'board'}[4], $col+1, 1) eq 'p');
-               } else {
-                       $ep = $nep if ($col > 0 && substr($pos->{'board'}[3], $col-1, 1) eq 'P');
-                       $ep = $nep if ($col < 7 && substr($pos->{'board'}[3], $col+1, 1) eq 'P');
-               }
-       }
-       $fen .= " ";
-       $fen .= $ep;
-
-       # half-move clock
-       $fen .= " ";
-       $fen .= $pos->{'time_to_100move_rule'};
-
-       # full-move clock
-       $fen .= " ";
-       $fen .= $pos->{'move_num'};
-
-       return $fen;
-}
-
-sub make_move {
-       my ($board, $from_row, $from_col, $to_row, $to_col, $promo) = @_;
-       my $move = move_to_uci_notation($from_row, $from_col, $to_row, $to_col, $promo);
-       my $piece = substr($board->[$from_row], $from_col, 1);
-       my @nb = @$board;
-
-       if ($piece eq '-') {
-               die "Invalid move $move";
-       }
-
-       # white short castling
-       if ($move eq 'e1g1' && $piece eq 'K') {
-               # king
-               substr($nb[7], 4, 1, '-');
-               substr($nb[7], 6, 1, $piece);
-               
-               # rook
-               substr($nb[7], 7, 1, '-');
-               substr($nb[7], 5, 1, 'R');
-                               
-               return \@nb;
-       }
-
-       # white long castling
-       if ($move eq 'e1c1' && $piece eq 'K') {
-               # king
-               substr($nb[7], 4, 1, '-');
-               substr($nb[7], 2, 1, $piece);
-               
-               # rook
-               substr($nb[7], 0, 1, '-');
-               substr($nb[7], 3, 1, 'R');
-                               
-               return \@nb;
-       }
-
-       # black short castling
-       if ($move eq 'e8g8' && $piece eq 'k') {
-               # king
-               substr($nb[0], 4, 1, '-');
-               substr($nb[0], 6, 1, $piece);
-               
-               # rook
-               substr($nb[0], 7, 1, '-');
-               substr($nb[0], 5, 1, 'r');
-                               
-               return \@nb;
-       }
-
-       # black long castling
-       if ($move eq 'e8c8' && $piece eq 'k') {
-               # king
-               substr($nb[0], 4, 1, '-');
-               substr($nb[0], 2, 1, $piece);
-               
-               # rook
-               substr($nb[0], 0, 1, '-');
-               substr($nb[0], 3, 1, 'r');
-                               
-               return \@nb;
-       }
-
-       # check if the from-piece is a pawn
-       if (lc($piece) eq 'p') {
-               # attack?
-               if ($from_col != $to_col) {
-                       # en passant?
-                       if (substr($board->[$to_row], $to_col, 1) eq '-') {
-                               if ($piece eq 'p') {
-                                       substr($nb[$to_row + 1], $to_col, 1, '-');
-                               } else {
-                                       substr($nb[$to_row - 1], $to_col, 1, '-');
-                               }
-                       }
-               } else {
-                       if ($promo ne '') {
-                               if ($piece eq 'p') {
-                                       $piece = $promo;
-                               } else {
-                                       $piece = uc($promo);
-                               }
-                       }
-               }
-       }
-
-       # update the board
-       substr($nb[$from_row], $from_col, 1, '-');
-       substr($nb[$to_row], $to_col, 1, $piece);
-
-       return \@nb;
-}
-
 sub prettyprint_pv {
        my ($board, @pvs) = @_;
 
@@ -537,8 +351,8 @@ sub prettyprint_pv {
        my $to_row   = row_letter_to_num(substr($pv, 3, 1));
        my $promo    = substr($pv, 4, 1);
 
-       my $nb = make_move($board, $from_row, $from_col, $to_row, $to_col, $promo);
-       my $piece = substr($board->[$from_row], $from_col, 1);
+       my $nb = $board->make_move($from_row, $from_col, $to_row, $to_col, $promo);
+       my $piece = $board->[$from_row][$from_col];
 
        if ($piece eq '-') {
                die "Invalid move $pv";
@@ -593,23 +407,23 @@ sub prettyprint_pv {
                my $num_total = 0;
                for my $col (0..7) {
                        for my $row (0..7) {
-                               next unless (substr($board->[$row], $col, 1) eq $piece);
-                               ++$num_total if (can_reach($board, $piece, $row, $col, $to_row, $to_col));
+                               next unless ($board->[$row][$col] eq $piece);
+                               ++$num_total if ($board->can_reach($piece, $row, $col, $to_row, $to_col));
                        }
                }
 
                # see how many of these pieces from the given row could go here
                my $num_row = 0;
                for my $col (0..7) {
-                       next unless (substr($board->[$from_row], $col, 1) eq $piece);
-                       ++$num_row if (can_reach($board, $piece, $from_row, $col, $to_row, $to_col));
+                       next unless ($board->[$from_row][$col] eq $piece);
+                       ++$num_row if ($board->can_reach($piece, $from_row, $col, $to_row, $to_col));
                }
                
                # and same for columns
                my $num_col = 0;
                for my $row (0..7) {
-                       next unless (substr($board->[$row], $from_col, 1) eq $piece);
-                       ++$num_col if (can_reach($board, $piece, $row, $from_col, $to_row, $to_col));
+                       next unless ($board->[$row][$from_col] eq $piece);
+                       ++$num_col if ($board->can_reach($piece, $row, $from_col, $to_row, $to_col));
                }
                
                # see if we need to disambiguate
@@ -624,16 +438,16 @@ sub prettyprint_pv {
                }
 
                # attack?
-               if (substr($board->[$to_row], $to_col, 1) ne '-') {
+               if ($board->[$to_row][$to_col] ne '-') {
                        $pretty .= 'x';
                }
 
                $pretty .= substr($pv, 2, 2);
        }
 
-       if (in_mate($nb)) {
+       if ($nb->in_mate()) {
                $pretty .= '#';
-       } elsif (in_check($nb) ne 'none') {
+       } elsif ($nb->in_check() ne 'none') {
                $pretty .= '+';
        }
        return ($pretty, prettyprint_pv($nb, @pvs));
@@ -768,7 +582,7 @@ sub output_screen {
                $text .= "\n\n";
        }
 
-       #$text .= book_info($pos_calculating->{'fen'}, $pos_calculating->{'board'}, $pos_calculating->{'toplay'});
+       #$text .= book_info($pos_calculating->fen(), $pos_calculating->{'board'}, $pos_calculating->{'toplay'});
 
        my @refutation_lines = ();
        if (defined($engine2)) {
@@ -872,7 +686,7 @@ sub output_json {
        my $info = $engine->{'info'};
 
        my $json = {};
-       $json->{'position'} = $pos_calculating;
+       $json->{'position'} = $pos_calculating->to_json_hash();
        $json->{'id'} = $engine->{'id'};
        $json->{'score'} = long_score($info, $pos_calculating, '');
 
@@ -920,203 +734,6 @@ sub output_json {
        rename("/srv/analysis.sesse.net/www/analysis.json.tmp", "/srv/analysis.sesse.net/www/analysis.json");
 }
 
-sub find_kings {
-       my $board = shift;
-       my ($wkr, $wkc, $bkr, $bkc);
-
-       for my $row (0..7) {
-               for my $col (0..7) {
-                       my $piece = substr($board->[$row], $col, 1);
-                       if ($piece eq 'K') {
-                               ($wkr, $wkc) = ($row, $col);
-                       } elsif ($piece eq 'k') {
-                               ($bkr, $bkc) = ($row, $col);
-                       }
-               }
-       }
-
-       return ($wkr, $wkc, $bkr, $bkc);
-}
-
-sub in_mate {
-       my $board = shift;
-       my $check = in_check($board);
-       return 0 if ($check eq 'none');
-
-       # try all possible moves for the side in check
-       for my $row (0..7) {
-               for my $col (0..7) {
-                       my $piece = substr($board->[$row], $col, 1);
-                       next if ($piece eq '-');
-
-                       if ($check eq 'white') {
-                               next if ($piece eq lc($piece));
-                       } else {
-                               next if ($piece eq uc($piece));
-                       }
-
-                       for my $dest_row (0..7) {
-                               for my $dest_col (0..7) {
-                                       next if ($row == $dest_row && $col == $dest_col);
-                                       next unless (can_reach($board, $piece, $row, $col, $dest_row, $dest_col));
-
-                                       my @nb = @$board;
-                                       substr($nb[$row], $col, 1, '-');
-                                       substr($nb[$dest_row], $dest_col, 1, $piece);
-
-                                       my $new_check = in_check(\@nb);
-                                       return 0 if ($new_check ne $check && $new_check ne 'both');
-                               }
-                       }
-               }
-       }
-
-       # nothing to do; mate
-       return 1;
-}
-
-sub in_check {
-       my $board = shift;
-       my ($black_check, $white_check) = (0, 0);
-
-       my ($wkr, $wkc, $bkr, $bkc) = find_kings($board);
-
-       # check all pieces for the possibility of threatening the two kings
-       for my $row (0..7) {
-               for my $col (0..7) {
-                       my $piece = substr($board->[$row], $col, 1);
-                       next if ($piece eq '-');
-               
-                       if (uc($piece) eq $piece) {
-                               # white piece
-                               $black_check = 1 if (can_reach($board, $piece, $row, $col, $bkr, $bkc));
-                       } else {
-                               # black piece
-                               $white_check = 1 if (can_reach($board, $piece, $row, $col, $wkr, $wkc));
-                       }
-               }
-       }
-
-       if ($black_check && $white_check) {
-               return 'both';
-       } elsif ($black_check) {
-               return 'black';
-       } elsif ($white_check) {
-               return 'white';
-       } else {
-               return 'none';
-       }
-}
-
-sub can_reach {
-       my ($board, $piece, $from_row, $from_col, $to_row, $to_col) = @_;
-       
-       # can't eat your own piece
-       my $dest_piece = substr($board->[$to_row], $to_col, 1);
-       if ($dest_piece ne '-') {
-               return 0 if (($piece eq lc($piece)) == ($dest_piece eq lc($dest_piece)));
-       }
-
-       if (lc($piece) eq 'k') {
-               return (abs($from_row - $to_row) <= 1 && abs($from_col - $to_col) <= 1);
-       }
-       if (lc($piece) eq 'r') {
-               return 0 unless ($from_row == $to_row || $from_col == $to_col);
-
-               # check that there's a clear passage
-               if ($from_row == $to_row) {
-                       if ($from_col > $to_col) {
-                               ($to_col, $from_col) = ($from_col, $to_col);
-                       }
-
-                       for my $c (($from_col+1)..($to_col-1)) {
-                               my $middle_piece = substr($board->[$to_row], $c, 1);
-                               return 0 if ($middle_piece ne '-');     
-                       }
-
-                       return 1;
-               } else {
-                       if ($from_row > $to_row) {
-                               ($to_row, $from_row) = ($from_row, $to_row);
-                       }
-
-                       for my $r (($from_row+1)..($to_row-1)) {
-                               my $middle_piece = substr($board->[$r], $to_col, 1);
-                               return 0 if ($middle_piece ne '-');     
-                       }
-
-                       return 1;
-               }
-       }
-       if (lc($piece) eq 'b') {
-               return 0 unless (abs($from_row - $to_row) == abs($from_col - $to_col));
-
-               my $dr = ($to_row - $from_row) / abs($to_row - $from_row);
-               my $dc = ($to_col - $from_col) / abs($to_col - $from_col);
-
-               my $r = $from_row + $dr;
-               my $c = $from_col + $dc;
-
-               while ($r != $to_row) {
-                       my $middle_piece = substr($board->[$r], $c, 1);
-                       return 0 if ($middle_piece ne '-');
-                       
-                       $r += $dr;
-                       $c += $dc;
-               }
-
-               return 1;
-       }
-       if (lc($piece) eq 'n') {
-               my $diff_r = abs($from_row - $to_row);
-               my $diff_c = abs($from_col - $to_col);
-               return 1 if ($diff_r == 2 && $diff_c == 1);
-               return 1 if ($diff_r == 1 && $diff_c == 2);
-               return 0;
-       }
-       if ($piece eq 'q') {
-               return (can_reach($board, 'r', $from_row, $from_col, $to_row, $to_col) ||
-                       can_reach($board, 'b', $from_row, $from_col, $to_row, $to_col));
-       }
-       if ($piece eq 'Q') {
-               return (can_reach($board, 'R', $from_row, $from_col, $to_row, $to_col) ||
-                       can_reach($board, 'B', $from_row, $from_col, $to_row, $to_col));
-       }
-
-       # TODO: en passant
-       if ($piece eq 'p') {
-               # black pawn
-               if ($to_col == $from_col && $to_row == $from_row + 1) {
-                       return ($dest_piece eq '-');
-               }
-               if ($to_col == $from_col && $from_row == 1 && $to_row == 3) {
-                       my $middle_piece = substr($board->[2], $to_col, 1);
-                       return ($dest_piece eq '-' && $middle_piece eq '-');
-               }
-               if (abs($to_col - $from_col) == 1 && $to_row == $from_row + 1) {
-                       return ($dest_piece ne '-');
-               }
-               return 0;
-       }
-       if ($piece eq 'P') {
-               # white pawn
-               if ($to_col == $from_col && $to_row == $from_row - 1) {
-                       return ($dest_piece eq '-');
-               }
-               if ($to_col == $from_col && $from_row == 6 && $to_row == 4) {
-                       my $middle_piece = substr($board->[5], $to_col, 1);
-                       return ($dest_piece eq '-' && $middle_piece eq '-');
-               }
-               if (abs($to_col - $from_col) == 1 && $to_row == $from_row - 1) {
-                       return ($dest_piece ne '-');
-               }
-               return 0;
-       }
-       
-       # unknown piece
-       return 0;
-}
-
 sub uciprint {
        my ($engine, $msg) = @_;
        print { $engine->{'write'} } "$msg\n";
@@ -1325,8 +942,3 @@ sub row_letter_to_num {
        return 7 - (ord(shift) - ord('1'));
 }
 
-sub move_to_uci_notation {
-       my ($from_row, $from_col, $to_row, $to_col, $promo) = @_;
-       $promo //= "";
-       return sprintf("%c%d%c%d%s", ord('a') + $from_col, 8 - $from_row, ord('a') + $to_col, 8 - $to_row, $promo);
-}