// `?` expands to an early return on the error branch.
#[derive(Debug)]
enum Error {
    Odd,
}

fn halve(n: i32) -> Result<i32, Error> {
    if n % 2 != 0 {
        return Err(Error::Odd);
    }
    Ok(n / 2)
}

fn quarter(n: i32) -> Result<i32, Error> {
    let half = halve(n)?;
    let q = halve(half)?;
    Ok(q)
}

fn main() {
    println!("{:?}", quarter(8));
    println!("{:?}", quarter(6));
    println!("{:?}", quarter(5));
}