Function combine::char::hex_digit

pub fn hex_digit<I>() -> HexDigit<I> where
    I: Stream<Item = char>,
    I::Error: ParseError<I::Item, I::Range, I::Position>, 

Parses a hexdecimal digit with uppercase and lowercase.

use combine::Parser;
use combine::char::hex_digit;
assert_eq!(hex_digit().parse("F"), Ok(('F', "")));
assert!(hex_digit().parse("H").is_err());