parser_combinators.rs

use std::ops::{Mul, Add};

struct Parser {
    parser: Box<Fn(&[u8], usize) -> Vec<usize>>,
}

fn empty() -> Parser {
    Parser{parser: Box::new(|_s: &[u8], idx| vec![idx])}
}

fn byte(c: u8) -> Parser {
    Parser{parser: Box::new(move |s : &[u8], idx| {
        if idx < s.len() && s[idx] == c {
            return vec![idx + 1];
        } else {
            return vec![];
        }
    })}
}

fn token(s: String) -> Parser {
    let bytes = s.as_bytes();
    let mut res = empty();
    for b in bytes {
        res = res * byte(*b);
    }
    res
}

impl Mul for Parser {
    type Output = Parser;
    fn mul(self, other: Self) -> Parser {
        Parser{parser: Box::new(move |s: &[u8], idx| {
            let mid = (self.parser)(s, idx);
            let mut res = vec![];
            for m in mid {
                res.append(&mut (other.parser)(s, m));
            }
            res
        })}
    }
}

impl Add for Parser {
    type Output = Parser;
    fn add(self, other: Self) -> Parser {
        Parser{parser: Box::new(move |s: &[u8], idx| {
            let mut res = (self.parser)(s, idx);
            res.append(&mut (other.parser)(s, idx));
            res
        })}
    }
}

fn main() {
    let s = String::from("aabbc");
    let p = empty() + token(String::from("a")) * p * token(String::from("b"));
    for v in (p.parser)(s.as_bytes(), 0) {
        println!("{}", v);
    }
}