fn merged[K, V](a map[K]V, b map[K]V) map[K]V {
    mut o := a.clone()
    for k, v in b {
        $if V is $map {
            o[k] = merged(o[k], v)
        } $else {
            o[k] = v
        }
    }
    return o
}

fn test_main() {
    a := {
        'aa': {
            '11': 1
        }
    }
    b := {
        'bb': {
            '22': 2
        }
    }
    c := merged(a, b)
    assert c == {
        'aa': {
            '11': 1
        }
        'bb': {
            '22': 2
        }
    }
}