Function flat_take

pub fn flat_take<I, C, O, E, F>(
    len: C,
    parser: F,
) -> impl FnMut(I) -> IResult<I, O, E>
where
    I: Input,
    C: ToUsize + Copy,
    E: ParseError<I>,
    F: Parser<I, Output = O, Error = E>,

Return a closure that takes len bytes from input, and applies parser.