Function nom::character::complete::digit0

pub fn digit0<T, E: ParseError<T>>(input: T) -> IResult<T, T, E> where
    T: InputTakeAtPosition,
    <T as InputTakeAtPosition>::Item: AsChar, 

Recognizes zero or more ASCII numerical characters: 0-9 fn parser(input: &str) -> IResult<&str, &str> { digit0(input) }

assert_eq!(parser("21c"), Ok(("c", "21"))); assert_eq!(parser("a21c"), Ok(("a21c", ""))); assert_eq!(parser(""), Ok(("", "")));

}