Function combine::parser::byte::letter

pub fn letter<Input>() -> impl Parser<Input, Output = u8, PartialState = ()> where
    Input: Stream<Token = u8>,
    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>, 

Parses an ASCII alphabet letter (a–z, A–Z).

use combine::Parser;
use combine::parser::byte::letter;
assert_eq!(letter().parse(&b"a"[..]), Ok((b'a', &b""[..])));
assert_eq!(letter().parse(&b"A"[..]), Ok((b'A', &b""[..])));
assert!(letter().parse(&b"9"[..]).is_err());