parser_combinators.rs

#![feature(conservative_impl_trait)]

fn take<'a>(take: &'a str) -> impl Fn(&'a str) -> (&'a str, &'a str) {
    move |input| {
        let len = input.chars().zip(take.chars()).take_while(|&(i, t)| i == t).count();
        (&input[0..len], &input[len..])
    }
}

fn chain<'a, F1, F2>(first: F1, second: F2) -> impl Fn(&'a str) -> ((&'a str, &'a str), &'a str)
where
    F1: Fn(&'a str) -> (&'a str, &'a str),
    F2: Fn(&'a str) -> (&'a str, &'a str)
{
    move |input| {
        let (res1, rem1) = first(input);
        let (res2, rem2) = second(rem1);
        ((res1, res2), rem2)
    }
}

fn map<'a, R, T, N, F>(parser: F, trans: T) -> impl Fn(&'a str) -> (N, &'a str)
where
    T: Fn(R) -> N,
    F: Fn(&'a str) -> (R, &'a str)
{
    move |input| {
        let (res, rem) = parser(input);
        (trans(res), rem)
    }
}

fn main() {
    let parse_hello = chain(take("hel"), take("lo"));
    let parse_hello_string = map(|i| parse_hello(i), |(lhs, rhs)| format!("{}{}", lhs, rhs));
    
    println!("{:?}", parse_hello("hello world"));
    println!("{:?}", parse_hello_string("hello world"));
}