Es100.rs

use std::default::Default;
use std::ops::{Add, Div, Mul, Sub};
use std::rc::Rc;

enum Value<
    T: Add<Output = T> + Mul<Output = T> + Div<Output = T> + Sub<Output = T> + Copy + Default,
> {
    Times,
    Plus,
    Minus,
    Divide,
    Number(T),
}
struct Node<
    T: Add<Output = T> + Mul<Output = T> + Div<Output = T> + Sub<Output = T> + Copy + Default,
> {
    left: Option<Rc<Node<T>>>,
    right: Option<Rc<Node<T>>>,
    value: Value<T>,
}
fn calc<
    T: Add<Output = T> + Mul<Output = T> + Div<Output = T> + Sub<Output = T> + Copy + Default,
>(
    node: &Node<T>,
) -> T {
    if node.left.is_none() && node.right.is_none() {
        match node.value {
            Value::Number(n) => n,
            _ => T::default(),
        }
    } else {
        match node.value {
            Value::Number(n) => n,
            Value::Times => calc(node.left.as_ref().unwrap()) * calc(node.right.as_ref().unwrap()),
            Value::Plus => calc(node.left.as_ref().unwrap()) + calc(node.right.as_ref().unwrap()),
            Value::Divide => calc(node.left.as_ref().unwrap()) / calc(node.right.as_ref().unwrap()),
            Value::Minus => calc(node.left.as_ref().unwrap()) - calc(node.right.as_ref().unwrap()),
        }
    }
}

fn main() {
    let tree_root: Node<i8> = Node {
        value: Value::Times,
        left: Some(Rc::new(Node {
            value: Value::Plus,
            left: Some(Rc::new(Node {
                value: Value::Number(1),
                left: None,
                right: None,
            })),
            right: Some(Rc::new(Node {
                value: Value::Minus,
                left: Some(Rc::new(Node {
                    value: Value::Number(8),
                    left: None,
                    right: None,
                })),
                right: Some(Rc::new(Node {
                    value: Value::Number(4),
                    left: None,
                    right: None,
                })),
            })),
        })),
        right: Some(Rc::new(Node {
            value: Value::Number(18),
            left: None,
            right: None,
        })),
    };
    println!("Output = {}", calc(&tree_root));
}