gistfile1.rs

use std::num::Int;
use std::iter::{Iterator, iterate};

struct FibIter<'a, T:Int> {
    iterator : Box<Iterator<Item=T> + 'a>
}

impl <'a, T:Int> Iterator for FibIter<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<T> {
        self.iterator.next()
    }
}

fn fib<'a, T : Int + 'a>() -> FibIter<'a, T> {
    let start = (<T as Int>::zero(), <T as Int>::one());
    FibIter {
        iterator: Box::new(
                      iterate(start,
                              |&: (cur, nxt) : (T, T)| (nxt, cur+nxt))
                        .map(|&: (fst, _) : (T, T)| fst))
                    as Box<Iterator<Item=T>>
    }
}

fn main() {
    let mut it = fib::<i32>().take(20);
    for v in it {
        println!("{}", v);
    }
}