struct Number {
    natural ?string
    integer string
}

fn number(n int) Number {
    return if n >= 0 { // a single return here
        Number{
            natural: '${n}'
            integer: '${n}'
        }
    } else {
        Number{
            integer: '${n}'
        }
    }
}

fn test_main() {
    mut ret := []Number{}
    for n in [1, 0, -1] {
        ret << number(n)
    }
    assert ret[0] == Number{
        natural: ?string('1')
        integer: '1'
    }
    assert ret[1] == Number{
        natural: ?string('0')
        integer: '0'
    }
    assert ret[2] == Number{
        natural: ?string(none)
        integer: '-1'
    }
}