You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lexer.rs
    path of file: ./repos/eww/crates/simplexpr/src/parser
    
    the code of the file until where you have to start completion: use eww_shared_util::{Span, Spanned};
use once_cell::sync::Lazy;
use regex::{Regex, RegexSet}
    
    pub fn next_token(&mut self) -> Option<Result<Sp<Token>, LexicalError>> {
        loop {
            if self.failed || self.pos >= self.source.len() {
                return None;
            }
            let remaining = self.remaining();

            if remaining.starts_with(&['"', '\'', '`'][..]) {
                return self.string_lit().map(|x| x.map(|(lo, segs, hi)| (lo, Token::StringLit(segs), hi)));
            } else {
                let match_set = LEXER_REGEX_SET.matches(remaining);
                let matched_token = match_set
                    .into_iter()
                    .map(|i: usize| {
                        let m = LEXER_REGEXES[i].find(remaining).unwrap();
                        (m.end(), i)
                    })
                    .min_by_key(|(_, x)| *x);

                let (len, i) = match matched_token {
                    Some(x) => x,
                    None => {
                        self.failed = true;
                        return Some(Err(LexicalError(Span(self.pos + self.offset, self.pos + self.offset, self.file_id))));
                    }
                };

                let tok_str = &self.source[self.pos..self.pos + len];
                let old_pos = self.pos;
                self.advance_by(len)?;
                match LEXER_FNS[i](tok_str.to_string()) {
                    Token::Skip | Token::Comment => {}
                    token => {
                        return Some(Ok((old_pos + self.offset, token, self.pos + self.offset)));
                    }
                }
            }
        }
    }