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@jordanorelli
Last active September 4, 2022 23:33
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use std::rc::Rc;
pub enum List<T> {
Node { value: T, next: Rc<List<T>> },
Empty,
}
impl <T> List<T> {
pub fn empty() -> Self {
List::Empty
}
pub fn new(v: T) -> Rc<Self> {
Rc::new(List::Node{
value: v,
next: Rc::new(List::Empty),
})
}
pub fn is_empty(&self) -> bool {
match self {
List::Node{value: _, next: _} => false,
List::Empty => true,
}
}
/// head gives a reference to the value at the front of this list
pub fn head(&self) -> Option<&T> {
match self {
List::Node{value, next} => Some(value),
List::Empty => None,
}
}
/// len computs the number of elements visible from this list node
pub fn len(&self) -> u32 {
let mut node = self;
let mut count: u32 = 0;
loop {
match node {
List::Node{value, next} => {
count += 1;
node = next;
},
List::Empty => return count,
}
}
}
/// pre prepends a value onto a list node. That is, it takes a list node and creates a new list
/// node that points to it, returning the new list node.
pub fn pre(self: &Rc<Self>, v: T) -> Rc<Self> {
Rc::new(List::Node{
value: v,
next: Rc::clone(self),
})
}
}
mod list;
use list::*;
fn dump<T: std::fmt::Display>(l: &List<T>) {
match l {
List::Node{value, next} => {
println!("{}", value);
dump(next);
},
List::Empty => return,
}
}
fn main() {
let root = List::pre(&List::new(100), 77);
let mut a = root.pre(12);
let mut b = root.pre(18);
b = List::pre(&b, 7);
println!("count from root: {}", root.len());
println!("count from a: {}", a.len());
println!("count from b: {}", b.len());
println!("a head: {:?}", a.head());
println!("dumping a");
dump(&a);
println!("dumping b");
dump(&b);
println!("dumping root");
dump(&root);
}
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