my $first;
my $prev_node;
for (1..5) {
        my $node = { value => $_, prev => $prev_node };
        $first //= $node;
        $prev_node->{next} = $node;
        $prev_node = $node;
}

my $node = $first;
while ($node) {
        say $node->{value};
        $node = $node->{next};
}