nom 5.0.0-alpha2

#[macro_use]
extern crate nom;

#[derive(Debug, PartialEq)]
pub struct Color {
  pub red: u8,
  pub green: u8,
  pub blue: u8,
}

fn from_hex(input: &str) -> Result<u8, std::num::ParseIntError> {
  u8::from_str_radix(input, 16)
}

fn is_hex_digit(c: char) -> bool {
  c.is_digit(16)
}

named!(hex_primary<&str, u8>,
  map_res!(take_while_m_n!(2, 2, is_hex_digit), from_hex)
);

named!(hex_color<&str, Color>,
  do_parse!(
           tag!("#")   >>
    red:   hex_primary >>
    green: hex_primary >>
    blue:  hex_primary >>
    (Color { red, green, blue })
  )
);

#[test]
fn parse_color() {
  assert_eq!(
    hex_color("#2F14DF"),
    Ok((
      "",
      Color {
        red: 47,
        green: 20,
        blue: 223,
      }
    ))
  );
}