range in rust, without the need to think about range direction

rng.rs

#![feature(core)]
extern crate core;
use self::core::num::Int;

fn rng<T:PartialEq+Int, F:FnMut(T)> (d:T,dt:T,mut f:F) {
 if d>dt { for n in (dt..d).rev() { f(n); } }
 else { for n in (d..dt) { f(n); } }
}

fn main () {
 rng (5,0, |n| println!("{:?}",n));
}

/*
4
3
2
1
0
*/