Function verify_fold_m_n

fn verify_fold_m_n<I, O, E, P, N, F, R>(
    min: usize,
    max: usize,
    parse: &mut P,
    init: &mut N,
    fold: &mut F,
    input: &mut I,
) -> Result<R, E>
where
    I: Stream,
    P: Parser<I, O, E>,
    N: FnMut() -> R,
    F: FnMut(R, O) -> Option<R>,
    E: ParserError<I>,