struct Node {
pub mut:
    parent ?&Node
    id     int
}

fn set_trace(n &Node) int {
    if n.parent != none {
        set_trace(n.parent)
        assert n.id != 0
    } else {
        assert n.id == 1
    }
    return n.id
}

fn test_main() {
    mut initial_node := &Node{
        parent: none
        id:     1
    }
    mut child_node := &Node{
        parent: initial_node
        id:     2
    }
    assert set_trace(child_node) == 2
}