【Rust】スタックマシンでループ文を実装するための準備

ループで実行する処理文を記憶するために、”{ }”で囲まれている中身を取得してベクターで保存しておく。

fn main() {
    let mut stack = vec![];
    let mut instructions = vec![];

    let str = "1 2 + { 10 20 + }".to_string();
    let mut words: Vec<_> = str.split(" ").collect();

    while let Some((&word, mut rest)) = words.split_first() {
        if word.is_empty() {
            break;
        }
        if word == "{" {
            (instructions, rest) = parse_instruction(rest);
        } else if let Ok(parsed) = word.parse::<i32>() {
            stack.push(parsed.to_string());
        } else {
            match word {
              "+" => add(&mut stack),
              _ => panic!("{word:?} could not be parsed"),
            }
        }
        words = rest.to_vec();
    }
    println!("{:?}", stack);
    println!("{:?}", instructions);
}

fn parse_instruction<'src, 'a>(input: &'a [&'src str])-> (Vec<String>, &'a [&'src str]) {
    let mut tokens: Vec<String> = vec![];
    let mut words = input;

    while let Some((&word, mut rest)) = words.split_first() {
        if word.is_empty() {
            break;
        }
        if word == "}" {
            return (tokens, rest);
        } else {
            tokens.push(word.to_string())
        }
        words = rest;
    }
    (tokens, words)
}

fn add(stack: &mut Vec<String>) {
    let rhs: i32 = stack.pop().unwrap().parse::<i32>().unwrap();
    let lhs: i32 = stack.pop().unwrap().parse::<i32>().unwrap();
    stack.push((lhs + rhs).to_string());
}

Running `target/debug/sample`
[“3”]
[“10”, “20”, “+”]