Function find_comments_impl 

pub fn find_comments_impl<P, A, C, FT, FA>(
    input: &str,
    state_transition: FT,
    do_action: FA,
) -> Result<Vec<CommentMatch>, &'static str>
where
    P: Start + End + Copy + Eq,
    A: Copy + Eq,
    C: Start + Copy + Eq,
    FT: Fn(P, Option<char>) -> (P, A),
    FA: Fn(A, C, usize, Vec<CommentMatch>) -> Result<(C, Vec<CommentMatch>), &'static str>,