my @list = (qw(
    a b c d e f
));
sub by_score {
    my( $score ) = @_;
    return sub($$) {
        my( $a,$b ) = @_;
        warn "$a / $b";
        $score->{$a} <=> $score->{$b}
    }
}

my $by = by_score({ a => 5, b => 4, c => 3, d => 6, e => -1 });
print join ",", sort( {$by->($a,$b)} @list );

$by = by_score({ a => -5, b => 4, c => -3, d => 6, e => -1 });
print join ",", sort( {$by->($a,$b)} @list );