fn expect_punct(&mut self, expect: Punct) -> Result<(), ParseErr> {
        match &self.get()?.kind {
            TokenKind::Punct(punct) if *punct == expect => Ok(()),
            t => Err(error_unexpected(
                self.prev_loc(),
                format!("Expect {:?} Got {:?}", expect, t),
            )),
        }
    }
Get the next token and examine whether it is an expected Punct.
If not, return RubyError.
ruruby-parse/src/parser.rs