Functional Data Structures ex 2.1

Example2_1.rs

use std::rc::Rc;

#[derive(Debug)]
pub struct List<T> {
    head: Link<T>,
}

type Link<T> = Option<Rc<Node<T>>>;
// Option because sometimes there is no Node.
// Nodes need to be wrapped in an RC because we need to
// allow multiple Links to own a single node.

#[derive(Debug)]
struct Node<T> {
    elem: T,
    next: Link<T>,
}

impl<T> List<T> {
    pub fn new() -> Self {
        List { head: None }
    }
    pub fn append(&self, elem: T) -> List<T> {
        List { head: Some(Rc::new(Node {
            elem: elem,
            next: self.head.clone(),
        }))}
    }
}

fn create_range_list(n : i32) -> List<i32> {
    let mut l : List<i32> = List::new();
    for i in 0..n {
       l = l.append(i);
    }
    l
}

fn main() {
    let a = create_range_list(4);
    let b = List { head: Some(Rc::clone(&a.head.unwrap())) };
    let c = List { head: Some(Rc::clone(&b.head.unwrap())) };
    let d = List { head: Some(Rc::clone(&c.head.unwrap())) };

}