fn the_fun(elems: &[i64]) -> Option<i64> {
    use std::cmp::max;
    let mut largest: Option<i64> = None;
    for e in elems {
        match largest {
            Some(n) => largest = Some(max(n, *e)),
            None    => largest = Some(*e),
        }
    }
    largest
}

fn main() {
    let xs = vec![254, 89, 45, 3, 87, 32];
    let result = the_fun(&xs[..]);
    println!("{:?}", result)
}