use chumsky::prelude::*;

#[derive(Debug, PartialEq)]
enum Chain {
    End,
    Link(char, Box<Chain>),
}

fn parser() -> impl Parser<char, Chain, Error = Simple<char>> {
    let mut chain = Recursive::<_, _, Simple<char>>::declare();

    chain.define(just('+')
        .then(chain.clone())
        .map(|(c, chain)| Chain::Link(c, Box::new(chain)))
        .or_not()
        .map(|chain| chain.unwrap_or(Chain::End)));

    chain
}

fn main() {
    for _n in 1..100_000_000 {
        parser();
    }
}