# score for the center, edges, and corners
#  positive for x, negative for o
# 012
# 345
# 678
# center = 5
# corner = 2
# edge = 1

sub eval {
    local($board) = @_;

    # print "blocker: >$board<\n";

    local($score) = 0;
    local($i);

    # center
    $score += docount($board, 4, 5);

    # corner
    $score += docount($board, 0, 2);
    $score += docount($board, 2, 2);
    $score += docount($board, 6, 2);
    $score += docount($board, 8, 2);

    # edge
    $score += docount($board, 1, 1);
    $score += docount($board, 3, 1);
    $score += docount($board, 5, 1);
    $score += docount($board, 7, 1);

    return($score);
}

sub docount {
    local($board, $i, $p) = @_;

    local($total) = 0;

    if (substr($board, $i, 1) eq "x") {
	$total += $p;
    }
    if (substr($board, $i, 1) eq "o") {
	$total -= $p;
    }

    return $total;
}