type Flag = bool | f64 | int | string

fn parse_percent(value string) f64 {
    f_val := value.f64()
    if f_val >= 0 && f_val <= 100 {
        return f_val
    } else {
        return 0
    }
}

fn parse_option(str string, validator fn (string) ?Flag) ?Flag {
    return validator(str)
}

fn main() {
    t := parse_option('45', parse_percent)?
    println(t)
}