fn check_sum(v: Vec<i32>) -> Result<i32, String> {
    if v.is_empty() {
        return Err("Empty vec!".into());
    }

    let mut sum = 0;
    for i in v {
        sum += i;
    }
    return Ok(sum);
}

fn main() {
    let v = Vec::new();
    check_sum(v).expect("Got an error");
}