map_poly.rs

use std::rc::Rc;

enum List<T> {
    Null,
    Cons(Rc<T>, Rc<List<T>>),
}


fn map_noref<A, B, F>(f: &F, lst: Rc<List<A>>) -> Rc<List<B>>
    where F: Fn(Rc<A>) -> Rc<B>
{
    match (*lst) {
        List::Null => Rc::new(List::Null),
        List::Cons(ref h, ref t) => {
            let newHead = f(h.clone());
            let newTail = map_noref(f, t.clone());
            Rc::new(List::Cons(newHead, newTail))
        }
    }
}


fn map_ref<A, B, F>(f: &F, lst: Rc<List<A>>) -> Rc<List<B>>
    where F: Fn(&Rc<A>) -> Rc<B>
{
    match (*lst) {
        List::Null => Rc::new(List::Null),
        List::Cons(ref h, ref t) => {
            let newHead = f(h);
            let newTail = map_ref(f, t.clone());
            Rc::new(List::Cons(newHead, newTail))
        }
    }
}

fn main() {}