enum Result<T, E>
    Ok(T),
    Err(E)
end

int Error
    message: String
end

class BadArgumentError(argument: String) : Error
    pub message = "Invalid argument: ${argument}"
end

fn main(args: Array<String>) -> Result<Int, Error>
    let left = args.get(0).flatMap(Int::parse)
    if left is None then
        return Err(BadArgumentError(args.get(0)))
    end

    let right = args.get(1).flatMap(Int::parse)
    if right is None then
        return Err(BadArgumentError(args.get(1)))
    end

    Ok(left.unwrap() + right.unwrap())
end