Solution to the Sierpinski mini-challenge

sierpinski.pl

sub MAIN($n) {
    whole($n, node());
}

my $counter = 0;
sub node(*@parents) {
    my $node = "node " ~ ++$counter;
    say "Creating $node", @parents && " with parents " ~ @parents.grep(&defined).join(', ');
    return $node;
}

sub whole($n, $top) {
    if $n == 0 {
        return $top, $top;
    }

    my ($BOTTOM_join_top, $BOTTOM_join_right, $right) = chipped($n, $top);
    my $bottom = node($BOTTOM_join_top, $BOTTOM_join_right);

    return $bottom, $right;
}

sub chipped($n, $top, $JOIN_top?, $JOIN_right?) {
    if $n == 1 {
        my $right = node($top, $JOIN_top, $JOIN_right);
        return $top, $right, $right;
    }

    my ($TOP_bottom, $TOP_right) = whole($n - 1, $top);
    my ($RIGHT_join_top, $RIGHT_join_right, $RIGHT_right) = chipped($n - 1, $TOP_right, $JOIN_top, $JOIN_right);
    my ($BOTTOM_join_top, $BOTTOM_join_right, $) = chipped($n - 1, $TOP_bottom, $RIGHT_join_top, $RIGHT_join_right);

    return $BOTTOM_join_top, $BOTTOM_join_right, $RIGHT_right;
}