nomで日付のパーステスト

date_parse.rs

#[macro_use]
extern crate nom;
use nom::*;

fn take_digits_n(input: &[u8], n: u8) -> IResult<&[u8],&[u8]> { 
    verify!(input, take!(n), |chars: &[u8]| chars.iter().all(|c: &u8| is_digit(*c)) )
}

named!(take_4_digits, apply!(take_digits_n, 4));
named!(take_1_or_2_digits, alt_complete!( apply!(take_digits_n, 2) | apply!(take_digits_n, 1)) );
named!(date<(&str, &str, &str)>, do_parse!(
      year: map_res!(take_4_digits, std::str::from_utf8) >>
      tag!("-") >>
      month: map_res!(take_1_or_2_digits, std::str::from_utf8) >>
      tag!("-") >>
      day: map_res!(take_1_or_2_digits, std::str::from_utf8) >>
      (year, month, day)
   )
);

fn main() {
    println!("{:?}", date(b"2017-1-30"));
    println!("{:?}", date(b"2017-1-1"));
    println!("{:?}", date(b"2017-10-30"));
    println!("{:?}", date(b"2017-100-300")); // parse error
}