#[derive(Debug)]
enum List {
    Cons(Rc<RefCell<i32>>, Rc<List>),
    Nil,
}

use List::{Cons, Nil};
use std::rc::Rc;
use std::cell::RefCell;

fn main() {
    let value = Rc::new(RefCell::new(5));

    let a = Rc::new(Cons(Rc::clone(&value), Rc::new(Nil)));
    println!("a before = {:?}", a);

    let b = Cons(Rc::new(RefCell::new(6)), Rc::clone(&a));
    println!("b before = {:?}", b);

    let c = Cons(Rc::new(RefCell::new(10)), Rc::clone(&a));
    println!("c before = {:?}", a);

    *value.borrow_mut() += 10;

    println!("a after = {:?}", a);
    println!("b after = {:?}", b);
    println!("c after = {:?}", c);
}