Parser Combinators 2

parser_combinators2.rs

#![feature(conservative_impl_trait)]

use std::cmp::PartialEq;

type ParseResult<T, I: Iterator<Item = T>> = Result<ParseStatus<T, I>, ParseError>;

#[derive(Debug)]
enum ParseStatus<T, I: Iterator<Item = T>> {
    Ok(Vec<T>, I),
    NeedMoreData(usize), // # of units needed
}

#[derive(Debug)]
enum ParseError {
    InvalidSlice,
}

trait Parser<T, I: Iterator<Item = T>> {
    fn parse(&mut self, input: I) -> ParseResult<T, I>;
}

impl<T, I, F> Parser<T, I> for F
where
    I: Iterator<Item = T>,
    F: Fn(I) -> ParseResult<T, I>,
{
    fn parse(&mut self, input: I) -> ParseResult<T, I> {
        (*self)(input)
    }
}

fn tag<'a, T, I>(tag: &'a [T]) -> impl Parser<T, I>
where
    T: PartialEq,
    I: Iterator<Item = T>,
{
    move |mut input: I| {
        let len = tag.len();
        let mut parsed = Vec::new();
        for i in 0..len {
            let v = match input.next() {
                Some(ref v) if *v != tag[i] => return Err(ParseError::InvalidSlice),
                Some(v) => v,
                None => return Ok(ParseStatus::NeedMoreData(len - i)),
            };
            parsed.push(v);
        }
        
        Ok(ParseStatus::Ok(parsed, input))
    }
}

fn main() {
    let mut tag_parser = tag(&['H', 'e', 'l', 'l', 'o']);
    println!("{:?}", tag_parser.parse("Hello world!".chars()));
}