pub fn string_cmp<'a, C, Input>(
    s: &'static str,
    cmp: C,
) -> impl Parser<Input, Output = &'a str>Expand description
Parses the string s, using cmp to compare each character.
let result = string_cmp("rust", |l, r| l.eq_ignore_ascii_case(&r))
    .parse("RusT")
    .map(|x| x.0);
assert_eq!(result, Ok("rust"));