vm.rust

#[derive(Debug)]
enum Value {
    Nil,
    Integer(i64),
    String(usize),
    Pair(usize)
}

#[derive(Debug)]
struct State {
    strings: Vec<Option<String>>,
    pairs: Vec<Option<(Value, Value)>>
}

impl State {
    fn new_string(&mut self, val: String) -> Value {
        let entry = Some(val);
        for i in 0..self.strings.len() {
            if self.strings[i].is_none() {
                self.strings[i] = entry;
                return Value::String(i);
            }
        }
        self.strings.push(entry);
        Value::String(self.strings.len() - 1)
    }
    fn new_pair(&mut self, left: Value, right: Value) -> Value {
        let entry = Some((left, right));
        for i in 0..self.pairs.len() {
            if self.pairs[i].is_none() {
                self.pairs[i] = entry;
                return Value::Pair(i);
            }
        }
        self.pairs.push(entry);
        Value::String(self.pairs.len() - 1)
    }
}

fn main() {
    let mut state = State {
        strings: Vec::new(),
        pairs: Vec::new()
    };
    println!("A new string: {:?}", state.new_string(String::from("Hello World")));
    let mut next = Value::Nil;
    for i in 0..10 {
        next = state.new_pair(Value::Integer(10 - i), next);
        println!("A new pair: {:?}", next);
    }
    println!("{:?} {:?}", Value::String(0), state);
}