fn main() {

    let preloaded = RefCell::new(Cache::new(|x| {
        println!(" -> preload({})", x);

        format!("{} - preloaded", x)
        }));

    let parsed = RefCell::new(Cache::new( |x| {
        let mut preloaded = preloaded.borrow_mut();
        let xp = preloaded.get(x);

        println!("  -> parsed({})", x);

        format!("{} - parsed", xp)
    }));

    let processed = RefCell::new(Cache::new(|x| {
        let mut parsed = parsed.borrow_mut();
        let xp = parsed.get(x);

        println!("    -> process({})", x);

        format!("{} - processed", xp)
    }));

    println!("{}", preloaded.borrow_mut().get("A"));
    println!("{}", processed.borrow_mut().get("B"));
    println!("{}", preloaded.borrow_mut().get("A"));
    println!("{}", parsed.borrow_mut().get("B"));

}

/* Run results:
 -> preload(A)
A - preloaded
 -> preload(B)
  -> parsed(B)
    -> process(B)
B - preloaded - parsed - processed
A - preloaded
B - preloaded - parsed
*/