gistfile1.rs

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

struct Fib<T, I> where T: Int, I: Iterator<Item=T> {
    it : I
}

impl <T, I> Iterator for Fib<T, I> where
    T: Int,
    I: Iterator<Item=T>,
{
    type Item = T;

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

fn step<T>((cur, next): (T, T)) -> (T, T) where T: Int {
    (next, cur + next)
}

fn fst<T>((cur, next): (T, T)) -> T where T: Int {
    cur
}

fn fib<T, I>() -> Fib<T, I> where T: Int, I: Iterator<Item=T> {
    let iterator : I = iterate((<T as Int>::zero(), <T as Int>::one()), step::<T>).map(fst::<T>);
    Fib { it : iterator }
}