I've been working on creating a data structure in Perl to hold all legal chess moves, as a prerequisite for building a "Chess Problem Generator".  It's implemented as an HoHoAoA, with each key a different piece and each subhash key a single square on the board.  (I should point out that the data structure isn't complete (eg. castles, en-passant moves, and promotions aren't taken into account), but it contains everything else).

It occurred to me this morning that I could use the data structure to solve the "Eight Queens" problem of chess, whereby 8 queens must be placed on a chessboard in such a way that no queen is under attack by any other queen.  Using a brute force method where each valid position is tried (but as soon as a given queen attacks one of the already-placed queens, no further queens are attempted for that configuration), the entire set of solutions can quickly be generated.

I erroneously thought there were only 8 or so solutions, but to my surprise, there's a total of 92!  I was off by an order of magnitude!  Doing a 'google' of "8 queens problem" verifies that this is the correct answer; which makes me more sure that I haven't made a mistake with the original data structure.  (As a side note, once I had generated the bishop and rook moves, the queen moves were simply the combination of the two).

Here is the data structure (I've omitted all but the queen moves for brevity), which goes in a file called "Legal.pm": 

package Legal;

my $p_legal_moves = {
    'q' => {
        'a1' => [
            [ qw( b2 c3 d4 e5 f6 g7 h8 ) ],
            [ qw( a2 a3 a4 a5 a6 a7 a8 ) ],
            [ qw( b1 c1 d1 e1 f1 g1 h1 ) ],
        ],
        'a2' => [
            [ qw( b3 c4 d5 e6 f7 g8 ) ],
            [ qw( b1 ) ],
            [ qw( a3 a4 a5 a6 a7 a8 ) ],
            [ qw( a1 ) ],
            [ qw( b2 c2 d2 e2 f2 g2 h2 ) ],
        ],
        'a3' => [
            [ qw( b4 c5 d6 e7 f8 ) ],
            [ qw( b2 c1 ) ],
            [ qw( a4 a5 a6 a7 a8 ) ],
            [ qw( b3 c3 d3 e3 f3 g3 h3 ) ],
            [ qw( a2 a1 ) ],
        ],
        'a4' => [
            [ qw( b5 c6 d7 e8 ) ],
            [ qw( b3 c2 d1 ) ],
            [ qw( a5 a6 a7 a8 ) ],
            [ qw( b4 c4 d4 e4 f4 g4 h4 ) ],
            [ qw( a3 a2 a1 ) ],
        ],
        'a5' => [
            [ qw( b6 c7 d8 ) ],
            [ qw( b4 c3 d2 e1 ) ],
            [ qw( a6 a7 a8 ) ],
            [ qw( b5 c5 d5 e5 f5 g5 h5 ) ],
            [ qw( a4 a3 a2 a1 ) ],
        ],
        'a6' => [
            [ qw( b7 c8 ) ],
            [ qw( b5 c4 d3 e2 f1 ) ],
            [ qw( a7 a8 ) ],
            [ qw( b6 c6 d6 e6 f6 g6 h6 ) ],
            [ qw( a5 a4 a3 a2 a1 ) ],
        ],
        'a7' => [
            [ qw( b8 ) ],
            [ qw( b6 c5 d4 e3 f2 g1 ) ],
            [ qw( a8 ) ],
            [ qw( b7 c7 d7 e7 f7 g7 h7 ) ],
            [ qw( a6 a5 a4 a3 a2 a1 ) ],
        ],
        'a8' => [
            [ qw( b7 c6 d5 e4 f3 g2 h1 ) ],
            [ qw( b8 c8 d8 e8 f8 g8 h8 ) ],
            [ qw( a7 a6 a5 a4 a3 a2 a1 ) ],
        ],
        'b1' => [
            [ qw( a2 ) ],
            [ qw( c2 d3 e4 f5 g6 h7 ) ],
            [ qw( a1 ) ],
            [ qw( b2 b3 b4 b5 b6 b7 b8 ) ],
            [ qw( c1 d1 e1 f1 g1 h1 ) ],
        ],
        'b2' => [
            [ qw( a3 ) ],
            [ qw( c3 d4 e5 f6 g7 h8 ) ],
            [ qw( c1 ) ],
            [ qw( a1 ) ],
            [ qw( a2 ) ],
            [ qw( b3 b4 b5 b6 b7 b8 ) ],
            [ qw( c2 d2 e2 f2 g2 h2 ) ],
            [ qw( b1 ) ],
        ],
        'b3' => [
            [ qw( a4 ) ],
            [ qw( c4 d5 e6 f7 g8 ) ],
            [ qw( c2 d1 ) ],
            [ qw( a2 ) ],
            [ qw( a3 ) ],
            [ qw( b4 b5 b6 b7 b8 ) ],
            [ qw( c3 d3 e3 f3 g3 h3 ) ],
            [ qw( b2 b1 ) ],
        ],
        'b4' => [
            [ qw( a5 ) ],
            [ qw( c5 d6 e7 f8 ) ],
            [ qw( c3 d2 e1 ) ],
            [ qw( a3 ) ],
            [ qw( a4 ) ],
            [ qw( b5 b6 b7 b8 ) ],
            [ qw( c4 d4 e4 f4 g4 h4 ) ],
            [ qw( b3 b2 b1 ) ],
        ],
        'b5' => [
            [ qw( a6 ) ],
            [ qw( c6 d7 e8 ) ],
            [ qw( c4 d3 e2 f1 ) ],
            [ qw( a4 ) ],
            [ qw( a5 ) ],
            [ qw( b6 b7 b8 ) ],
            [ qw( c5 d5 e5 f5 g5 h5 ) ],
            [ qw( b4 b3 b2 b1 ) ],
        ],
        'b6' => [
            [ qw( a7 ) ],
            [ qw( c7 d8 ) ],
            [ qw( c5 d4 e3 f2 g1 ) ],
            [ qw( a5 ) ],
            [ qw( a6 ) ],
            [ qw( b7 b8 ) ],
            [ qw( c6 d6 e6 f6 g6 h6 ) ],
            [ qw( b5 b4 b3 b2 b1 ) ],
        ],
        'b7' => [
            [ qw( a8 ) ],
            [ qw( c8 ) ],
            [ qw( c6 d5 e4 f3 h1 ) ],
            [ qw( a6 ) ],
            [ qw( a7 ) ],
            [ qw( b8 ) ],
            [ qw( c7 d7 e7 f7 g7 h7 ) ],
            [ qw( b6 b5 b4 b3 b2 b1 ) ],
        ],
        'b8' => [
            [ qw( c7 d6 e5 f4 g3 h2 ) ],
            [ qw( a7 ) ],
            [ qw( a8 ) ],
            [ qw( c8 d8 e8 f8 g8 h8 ) ],
            [ qw( b7 b6 b5 b4 b3 b2 b1 ) ],
        ],
        'c1' => [
            [ qw( b2 a3 ) ],
            [ qw( d2 e3 f4 g5 h6 ) ],
            [ qw( b1 a1 ) ],
            [ qw( c2 c3 c4 c5 c6 c7 c8 ) ],
            [ qw( d1 e1 f1 g1 h1 ) ],
        ],
        'c2' => [
            [ qw( b3 a4 ) ],
            [ qw( d3 e4 f5 g6 h7 ) ],
            [ qw( d1 ) ],
            [ qw( b1 ) ],
            [ qw( b2 a2 ) ],
            [ qw( c3 c4 c5 c6 c7 c8 ) ],
            [ qw( d2 e2 f2 g2 h2 ) ],
            [ qw( c1 ) ],
        ],
        'c3' => [
            [ qw( b4 a5 ) ],
            [ qw( d4 e5 f6 g7 h8 ) ],
            [ qw( d2 e1 ) ],
            [ qw( b2 a1 ) ],
            [ qw( b3 a3 ) ],
            [ qw( c4 c5 c6 c7 c8 ) ],
            [ qw( d3 e3 f3 g3 h3 ) ],
            [ qw( c2 c1 ) ],
        ],
        'c4' => [
            [ qw( b5 a6 ) ],
            [ qw( d5 e6 f7 g8 ) ],
            [ qw( d3 e2 f1 ) ],
            [ qw( b3 a2 ) ],
            [ qw( b4 a4 ) ],
            [ qw( c5 c6 c7 c8 ) ],
            [ qw( d4 e4 f4 g4 h4 ) ],
            [ qw( c3 c2 c1 ) ],
        ],
        'c5' => [
            [ qw( b6 a7 ) ],
            [ qw( d6 e7 f8 ) ],
            [ qw( d4 e3 f2 g1 ) ],
            [ qw( b4 a3 ) ],
            [ qw( b5 a5 ) ],
            [ qw( c6 c7 c8 ) ],
            [ qw( d5 e5 f5 g5 h5 ) ],
            [ qw( c4 c3 c2 c1 ) ],
        ],
        'c6' => [
            [ qw( b7 a8 ) ],
            [ qw( d7 e8 ) ],
            [ qw( d5 e4 f3 g2 h1 ) ],
            [ qw( b5 a4 ) ],
            [ qw( b6 a6 ) ],
            [ qw( c7 c8 ) ],
            [ qw( d6 e6 f6 g6 h6 ) ],
            [ qw( c5 c4 c3 c2 c1 ) ],
        ],
        'c7' => [
            [ qw( b8 ) ],
            [ qw( d8 ) ],
            [ qw( d6 e5 f4 g3 h2 ) ],
            [ qw( b6 a5 ) ],
            [ qw( b7 a7 ) ],
            [ qw( c8 ) ],
            [ qw( d7 e7 f7 g7 h7 ) ],
            [ qw( c6 c5 c4 c3 c2 c1 ) ],
        ],
        'c8' => [
            [ qw( d7 e6 f5 g4 h3 ) ],
            [ qw( b7 a6 ) ],
            [ qw( b8 a8 ) ],
            [ qw( d8 e8 f8 g8 h8 ) ],
            [ qw( c7 c6 c5 c4 c3 c2 c1 ) ],
        ],
        'd1' => [
            [ qw( c2 b3 a4 ) ],
            [ qw( e2 f3 g4 h5 ) ],
            [ qw( c1 b1 a1 ) ],
            [ qw( d2 d3 d4 d5 d6 d7 d8 ) ],
            [ qw( e1 f1 g1 h1 ) ],
        ],
        'd2' => [
            [ qw( c3 b4 a5 ) ],
            [ qw( e3 f4 g5 h6 ) ],
            [ qw( e1 ) ],
            [ qw( c1 ) ],
            [ qw( c2 b2 a2 ) ],
            [ qw( d3 d4 d5 d6 d7 d8 ) ],
            [ qw( e2 f2 g2 h2 ) ],
            [ qw( d1 ) ],
        ],
        'd3' => [
            [ qw( c4 b5 a6 ) ],
            [ qw( e4 f5 g6 h7 ) ],
            [ qw( e2 f1 ) ],
            [ qw( c2 b1 ) ],
            [ qw( c3 b3 a3 ) ],
            [ qw( d4 d5 d6 d7 d8 ) ],
            [ qw( e3 f3 g3 h3 ) ],
            [ qw( d2 d1 ) ],
        ],
        'd4' => [
            [ qw( c5 b6 a7 ) ],
            [ qw( e5 f6 g7 h8 ) ],
            [ qw( e3 f2 g1 ) ],
            [ qw( c3 b2 a1 ) ],
            [ qw( c4 b4 a4 ) ],
            [ qw( d5 d6 d7 d8 ) ],
            [ qw( e4 f4 g4 h4 ) ],
            [ qw( d3 d2 d1 ) ],
        ],
        'd5' => [
            [ qw( c6 b7 a8 ) ],
            [ qw( e6 f7 g8 ) ],
            [ qw( e4 f3 g2 h1 ) ],
            [ qw( c4 b3 a2 ) ],
            [ qw( c5 b5 a5 ) ],
            [ qw( d6 d7 d8 ) ],
            [ qw( e5 f5 g5 h5 ) ],
            [ qw( d4 d3 d2 d1 ) ],
        ],
        'd6' => [
            [ qw( c7 b8 ) ],
            [ qw( e7 f8 ) ],
            [ qw( e5 f4 g3 h2 ) ],
            [ qw( c5 b4 a3 ) ],
            [ qw( c6 b6 a6 ) ],
            [ qw( d7 d8 ) ],
            [ qw( e6 f6 g6 h6 ) ],
            [ qw( d5 d4 d3 d2 d1 ) ],
        ],
        'd7' => [
            [ qw( c8 ) ],
            [ qw( e8 ) ],
            [ qw( e6 f5 g4 h3 ) ],
            [ qw( c6 b5 a4 ) ],
            [ qw( c7 b7 a7 ) ],
            [ qw( d8 ) ],
            [ qw( e7 f7 g7 h7 ) ],
            [ qw( d6 d5 d4 d3 d2 d1 ) ],
        ],
        'd8' => [
            [ qw( e7 f6 g5 h4 ) ],
            [ qw( c7 b6 a5 ) ],
            [ qw( c8 b8 a8 ) ],
            [ qw( e8 f8 g8 h8 ) ],
            [ qw( d7 d6 d5 d4 d3 d2 d1 ) ],
        ],
        'e1' => [
            [ qw( d2 c3 b4 a5 ) ],
            [ qw( f2 g3 h4 ) ],
            [ qw( d1 c1 b1 a1 ) ],
            [ qw( e2 e3 e4 e5 e6 e7 e8 ) ],
            [ qw( f1 g1 h1 ) ],
        ],
        'e2' => [
            [ qw( d3 c4 b5 a6 ) ],
            [ qw( f3 g4 h5 ) ],
            [ qw( f1 ) ],
            [ qw( d1 ) ],
            [ qw( d2 c2 b2 a2 ) ],
            [ qw( e3 e4 e5 e6 e7 e8 ) ],
            [ qw( f2 g2 h2 ) ],
            [ qw( e1 ) ],
        ],
        'e3' => [
            [ qw( d4 c5 b6 a7 ) ],
            [ qw( f4 g5 h6 ) ],
            [ qw( f2 g1 ) ],
            [ qw( d2 c1 ) ],
            [ qw( d3 c3 b3 a3 ) ],
            [ qw( e4 e5 e6 e7 e8 ) ],
            [ qw( f3 g3 h3 ) ],
            [ qw( e2 e1 ) ],
        ],
        'e4' => [
            [ qw( d5 c6 b7 a8 ) ],
            [ qw( f5 g6 h7 ) ],
            [ qw( f3 g2 h1 ) ],
            [ qw( d3 c2 b1 ) ],
            [ qw( d4 c4 b4 a4 ) ],
            [ qw( e5 e6 e7 e8 ) ],
            [ qw( f4 g4 h4 ) ],
            [ qw( e3 e2 e1 ) ],
        ],
        'e5' => [
            [ qw( d6 c7 b8 ) ],
            [ qw( f6 g7 h8 ) ],
            [ qw( f4 g3 h2 ) ],
            [ qw( d4 c3 b2 a1 ) ],
            [ qw( d5 c5 b5 a5 ) ],
            [ qw( e6 e7 e8 ) ],
            [ qw( f5 g5 h5 ) ],
            [ qw( e4 e3 e2 e1 ) ],
        ],
        'e6' => [
            [ qw( d7 c8 ) ],
            [ qw( f7 g8 ) ],
            [ qw( f5 g4 h3 ) ],
            [ qw( d5 c4 b3 a2 ) ],
            [ qw( d6 c6 b6 a6 ) ],
            [ qw( e7 e8 ) ],
            [ qw( f6 g6 h6 ) ],
            [ qw( e5 e4 e3 e2 e1 ) ],
        ],
        'e7' => [
            [ qw( d8 ) ],
            [ qw( f8 ) ],
            [ qw( f6 g5 h4 ) ],
            [ qw( d6 c5 b4 a3 ) ],
            [ qw( d7 c7 b7 a7 ) ],
            [ qw( e8 ) ],
            [ qw( f7 g7 h7 ) ],
            [ qw( e6 e5 e4 e3 e2 e1 ) ],
        ],
        'e8' => [
            [ qw( f7 g6 h5 ) ],
            [ qw( d7 c6 b5 a4 ) ],
            [ qw( d8 c8 b8 a8 ) ],
            [ qw( f8 g8 h8 ) ],
            [ qw( e7 e6 e5 e4 e3 e2 e1 ) ],
        ],
        'f1' => [
            [ qw( e2 d3 c4 b5 a6 ) ],
            [ qw( g2 h3 ) ],
            [ qw( e1 d1 c1 b1 a1 ) ],
            [ qw( f2 f3 f4 f5 f6 f7 f8 ) ],
            [ qw( g1 h1 ) ],
        ],
        'f2' => [
            [ qw( e3 d4 c5 b6 a7 ) ],
            [ qw( g3 h4 ) ],
            [ qw( g1 ) ],
            [ qw( e1 ) ],
            [ qw( e2 d2 c2 b2 a2 ) ],
            [ qw( f3 f4 f5 f6 f7 f8 ) ],
            [ qw( g2 h2 ) ],
            [ qw( f1 ) ],
        ],
        'f3' => [
            [ qw( e4 d5 c6 b7 a8 ) ],
            [ qw( g4 h5 ) ],
            [ qw( g2 h1 ) ],
            [ qw( e2 d1 ) ],
            [ qw( e3 d3 c3 b3 a3 ) ],
            [ qw( f4 f5 f6 f7 f8 ) ],
            [ qw( g3 h3 ) ],
            [ qw( f2 f1 ) ],
        ],
        'f4' => [
            [ qw( e5 d6 c7 b8 ) ],
            [ qw( g5 h6 ) ],
            [ qw( g3 h2 ) ],
            [ qw( e3 d2 c1 ) ],
            [ qw( e4 d4 c4 b4 a4 ) ],
            [ qw( f5 f6 f7 f8 ) ],
            [ qw( g4 h4 ) ],
            [ qw( f3 f2 f1 ) ],
        ],
        'f5' => [
            [ qw( e6 d7 c8 ) ],
            [ qw( g6 h7 ) ],
            [ qw( g4 h3 ) ],
            [ qw( e4 d3 c2 b1 ) ],
            [ qw( e5 d5 c5 b5 a5 ) ],
            [ qw( f6 f7 f8 ) ],
            [ qw( g5 h5 ) ],
            [ qw( f4 f3 f2 f1 ) ],
        ],
        'f6' => [
            [ qw( e7 d8 ) ],
            [ qw( g7 h8 ) ],
            [ qw( g5 h4 ) ],
            [ qw( e5 d4 c3 b2 a1 ) ],
            [ qw( e6 d6 c6 b6 a6 ) ],
            [ qw( f7 f8 ) ],
            [ qw( g6 h6 ) ],
            [ qw( f5 f4 f3 f2 f1 ) ],
        ],
        'f7' => [
            [ qw( e8 ) ],
            [ qw( g8 ) ],
            [ qw( g6 h5 ) ],
            [ qw( e6 d5 c4 b3 a2 ) ],
            [ qw( e7 d7 c7 b7 a7 ) ],
            [ qw( f8 ) ],
            [ qw( g7 h7 ) ],
            [ qw( f6 f5 f4 f3 f2 f1 ) ],
        ],
        'f8' => [
            [ qw( g7 h6 ) ],
            [ qw( e7 d6 c5 b4 a3 ) ],
            [ qw( e8 d8 c8 b8 a8 ) ],
            [ qw( g8 h8 ) ],
            [ qw( f7 f6 f5 f4 f3 f2 f1 ) ],
        ],
        'g1' => [
            [ qw( f2 e3 d4 c5 b6 a7 ) ],
            [ qw( h2 ) ],
            [ qw( f1 e1 d1 c1 b1 a1 ) ],
            [ qw( g2 g3 g4 g5 g6 g7 g8 ) ],
            [ qw( h1 ) ],
        ],
        'g2' => [
            [ qw( f3 e4 d5 c6 b7 a8 ) ],
            [ qw( h3 ) ],
            [ qw( h1 ) ],
            [ qw( f1 ) ],
            [ qw( f2 e2 d2 c2 b2 a2 ) ],
            [ qw( g3 g4 g5 g6 g7 g8 ) ],
            [ qw( h2 ) ],
            [ qw( g1 ) ],
        ],
        'g3' => [
            [ qw( f4 e5 d6 c7 b8 ) ],
            [ qw( h4 ) ],
            [ qw( h2 ) ],
            [ qw( f2 e1 ) ],
            [ qw( f3 e3 d3 c3 b3 a3 ) ],
            [ qw( g4 g5 g6 g7 g8 ) ],
            [ qw( h3 ) ],
            [ qw( g2 g1 ) ],
        ],
        'g4' => [
            [ qw( f5 e6 d7 c8 ) ],
            [ qw( h5 ) ],
            [ qw( h3 ) ],
            [ qw( f3 e2 d1 ) ],
            [ qw( f4 e4 d4 c4 b4 a4 ) ],
            [ qw( g5 g6 g7 g8 ) ],
            [ qw( h4 ) ],
            [ qw( g3 g2 g1 ) ],
        ],
        'g5' => [
            [ qw( f6 e7 d8 ) ],
            [ qw( h6 ) ],
            [ qw( h4 ) ],
            [ qw( f4 e3 d2 c1 ) ],
            [ qw( f5 e5 d5 c5 b5 a5 ) ],
            [ qw( g6 g7 g8 ) ],
            [ qw( h5 ) ],
            [ qw( g4 g3 g2 g1 ) ],
        ],
        'g6' => [
            [ qw( f7 e8 ) ],
            [ qw( h7 ) ],
            [ qw( h5 ) ],
            [ qw( f5 e4 d3 c2 b1 ) ],
            [ qw( f6 e6 d6 c6 b6 a6 ) ],
            [ qw( g7 g8 ) ],
            [ qw( h6 ) ],
            [ qw( g5 g4 g3 g2 g1 ) ],
        ],
        'g7' => [
            [ qw( f8 ) ],
            [ qw( h8 ) ],
            [ qw( h6 ) ],
            [ qw( f6 e5 d4 c3 b2 a1 ) ],
            [ qw( f7 e7 d7 c7 b7 a7 ) ],
            [ qw( g8 ) ],
            [ qw( h7 ) ],
            [ qw( g6 g5 g4 g3 g2 g1 ) ],
        ],
        'g8' => [
            [ qw( h7 ) ],
            [ qw( f7 e6 d5 c4 b3 a2 ) ],
            [ qw( f8 e8 d8 c8 b8 a8 ) ],
            [ qw( h8 ) ],
            [ qw( g7 g6 g5 g4 g3 g2 g1 ) ],
        ],
        'h1' => [
            [ qw( g2 f3 e4 d5 c6 b7 a8 ) ],
            [ qw( g1 f1 e1 d1 c1 b1 a1 ) ],
            [ qw( h2 h3 h4 h5 h6 h7 h8 ) ],
        ],
        'h2' => [
            [ qw( g3 f4 e5 d6 c7 b8 ) ],
            [ qw( g1 ) ],
            [ qw( g2 f2 e2 d2 c2 b2 a2 ) ],
            [ qw( h3 h4 h5 h6 h7 h8 ) ],
            [ qw( h1 ) ],
        ],
        'h3' => [
            [ qw( g4 f5 e6 d7 c8 ) ],
            [ qw( g2 f1 ) ],
            [ qw( g3 f3 e3 d3 c3 b3 a3 ) ],
            [ qw( h4 h5 h6 h7 h8 ) ],
            [ qw( h2 h1 ) ],
        ],
        'h4' => [
            [ qw( g5 f6 e7 d8 ) ],
            [ qw( g3 f2 e1 ) ],
            [ qw( g4 f4 e4 d4 c4 b4 a4 ) ],
            [ qw( h5 h6 h7 h8 ) ],
            [ qw( h3 h2 h1 ) ],
        ],
        'h5' => [
            [ qw( g6 f7 e8 ) ],
            [ qw( g4 f3 e2 d1 ) ],
            [ qw( g5 f5 e5 d5 c5 b5 a5 ) ],
            [ qw( h6 h7 h8 ) ],
            [ qw( h4 h3 h2 h1 ) ],
        ],
        'h6' => [
            [ qw( g7 f8 ) ],
            [ qw( g5 f4 e3 d2 c1 ) ],
            [ qw( g6 f6 e6 d6 c6 b6 a6 ) ],
            [ qw( h7 h8 ) ],
            [ qw( h5 h4 h3 h2 h1 ) ],
        ],
        'h7' => [
            [ qw( g8 ) ],
            [ qw( g6 f5 e4 d3 c2 b1 ) ],
            [ qw( g7 f7 e7 d7 c7 b7 a7 ) ],
            [ qw( h8 ) ],
            [ qw( h6 h5 h4 h3 h2 h1 ) ],
        ],
        'h8' => [
            [ qw( g7 f6 e5 d4 c3 b2 a1 ) ],
            [ qw( g8 f8 e8 d8 c8 b8 a8 ) ],
            [ qw( h7 h6 h5 h4 h3 h2 h1 ) ],
        ],
    },
}

sub legal_moves() {
    return $p_legal_moves;
}

1;

[download]

and here is the code for solving the eight-queens problem ... enjoy! 

#!/usr/bin/perl -w
#
#  Solves the "Eight Queens" problems on a standard chess board.
#
#  051226 by liverpole
#

##############
### Strict ###
##############
use strict;
use warnings;


####################
### User-defined ###
####################
my $border = " +---+---+---+---+---+---+---+---+";
my @rows   = qw( 1 2 3 4 5 6 7 8 );
my @cols   = qw( a b c d e f g h );


#################
### Libraries ###
#################
use Legal;


##################
### Prototypes ###
##################
sub legal($$);
sub show_board($$);


####################
### Main program ###
####################
my $plegal = Legal::legal_moves();
my $psquares = $plegal->{'q'};
my $count = 0;
map {
    my $p = { "a$_" => 1 };
    map {
        legal($p, "b$_") and map {
            legal($p, "c$_") and map {
                legal($p, "d$_") and map {
                    legal($p, "e$_") and map {
                        legal($p, "f$_") and map {
                            legal($p, "g$_") and map {
                                legal($p, "h$_") and show_board($p, ++
+$count);
                                delete $p->{"h$_"};
                            } @rows;
                            delete $p->{"g$_"};
                        } @rows;
                        delete $p->{"f$_"};
                    } @rows;
                    delete $p->{"e$_"};
                } @rows;
                delete $p->{"d$_"};
            } @rows;
            delete $p->{"c$_"};
        } @rows;
        delete $p->{"b$_"};
    } @rows;
} @rows;


###################
### Subroutines ###
###################
sub legal($$) {
    my ($pboard, $move) = @_;
    my $psquare = $psquares->{$move};
    foreach my $plist (@$psquare) {
        # Return 0 if placing the queen at $move attacks any other que
+en
        map { ($pboard->{$_} || 0) and return 0 } @$plist;
    }
    $pboard->{$move} = 1;    # Put the queen on the board
    return 1;
}


sub show_board($$) {
    my ($pboard, $count) = @_;
    printf "Board #${count} [%s]\n$border\n", join(' ', sort keys %$pb
+oard);
    foreach my $row (reverse @rows) {
        print " | ";
        map { printf "%s | ", ($pboard->{"$_$row"} || 0)? "Q": " " } @
+cols;
        print "$row\n$border\n";
    }
    printf "   %s\n\n\n", join('   ', @cols);
}

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In reply to Solving the Eight Queens problem by liverpole

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