Is the string sorted?

fp_sort.rs

fn is_sorted(input: &str) -> bool {
    let input_iter: Vec<_> = input.chars().collect();
    let initial = input_iter[0];
    input
        .chars()
        .fold(Some(initial), |acc, current| {
            if acc != None {
                if Some(current) >= acc {
                    return Some(current)
                } else {
                    return None
                }
            }
            acc
        })
        .is_some()
}

fn is_sorted_ignore_case(input: &str) -> bool {
    let input = input.to_lowercase();
    is_sorted(&input)
}

fn main() {
    dbg!(is_sorted("abc"));
    dbg!(is_sorted("bac"));
    dbg!(is_sorted("023BCDabc"));
    dbg!(is_sorted_ignore_case("abBcCD"));
}