rust-parser-combinator/src/choice.rs

use crate::Parser;

pub fn choice<'a, I, O, E>(parsers: &'a [&'a dyn Parser<I, O, E>]) -> impl Parser<I, O, E> + 'a {
    move |mut input: I| {
        //TODO need a more principled way to return an error when no choices work
        let mut err = None;

        for parser in parsers.iter() {
            match parser.parse(input) {
                Ok(res) => return Ok(res),
                Err((e, rest)) => {
                    err = Some(e);
                    input = rest;
                }
            }
        }
        Err((err.unwrap(), input))
    }
}