use std::mem;

#[derive(Debug)]
struct CharList {
    c: char,
    next: Option<Box<CharList>>,
}

fn make(s:&str) -> CharList {
    let mut result = CharList{
        c: 'a',
        next: None
    };
    {
        let mut tail = &mut result.next;
        for c in s.chars() {
            let cl = CharList {
                c: c,
                next: None
            };
            mem::replace(tail, Some(Box::new(cl)));
            let next = &mut tail.as_mut().unwrap().next;
            tail = next
        }
    }
    result
}

fn main() {
    println!("Value: {:?}", make("bcdef"));
}