A factorial test in Rust

fact.rs

use std::cmp::Ordering;
use std::io;

const ONE: u64 = 1;

fn main() {
    loop {
        let mut guess = String::new();

        io::stdin()
            .read_line(&mut guess)
            .expect("Failed to read line");

        let guess: u64 = match guess.trim().parse() {
            Ok(num) => num,
            Err(_) => continue,
        };

        println!("{}", fib(guess));
    }
}

fn fib(x: u64) -> u64 {
    //    match x.cmp(&ONE) {
    //        Ordering::Less => x,
    //        Ordering::Equal => x,
    //        Ordering::Greater => x * fib(x - 1),
    //    }
    if let Ordering::Greater = x.cmp(&ONE) {
        x * fib(x - 1)
    } else {
        x
    }
}