List.rs

use std::fmt;
use List::{Cons, Nil};

enum List<T> {
  Cons(T, Box<List<T>>),
  Nil
}

impl<T> fmt::Display for List<T> where T : fmt::Display {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    match *self {
      Cons(ref head, ref tail) => 
        {
          write!(f, "{head} ::", head = head);
          write!(f, "{tail}", tail = tail)
        }
      Nil => write!(f, "Nil")
    }
  }
}

fn main() {
  let list = Cons("A", Box::new(Cons("B", Box::new(Cons("C", Box::new(Nil))))));
  println!("Hello, {rust}", rust=list);
}

result.txt

>rustc list.rs
<std macros>:2:1: 2:54 warning: unused result which must be used, #[warn(unused_
<std macros>:2 $ dst . write_fmt ( format_args ! ( $ ( $ arg ) * ) ) )
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<std macros>:1:1: 2:56 note: in expansion of write!
list.rs:15:11: 15:47 note: expansion site

>list
Hello, A ::B ::C ::Nil