gistfile1.rs

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

type FibInternalIter<T> = Map<
    (T, T), T,
    Unfold<
        (T, T), (fn((T, T)) -> (T, T), Option<(T, T)>, bool),
        fn(&mut (fn((T, T)) -> (T, T), Option<(T, T)>, bool)) -> Option<(T, T)>>,
    fn((T, T)) -> T>;

struct Fib<T> where T: Int {
    it : FibInternalIter<T>
}

impl <T> Iterator for Fib<T> where
    T: Int,
{
    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, _): (T, T)) -> T where T: Int {
    cur
}

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

fn main() {
    let mut it = fib::<i64>().take(10);
    for v in it {
        println!("{}", v);
    }
}