fn next_token(&mut self) -> Option<Token> {
        let token = self
            .tokens
            .get(self.index)
            .map(|(token, _range)| token.clone());
        self.index += 1;
        token
    }
/// Return the next token that has not yet been processed, or None if
/// reached end-of-file, and mark it as processed. OK to call repeatedly
/// after reaching EOF.
Return the next token that has not yet been processed, or None if
reached end-of-file, and mark it as processed. OK to call repeatedly
after reaching EOF.
Return the next token that has not yet been processed or None if reached end - of - file and mark it as processed . OK to call repeatedly after reaching EOF .
fn next_token(&mut self) -> Option<Token> {
        let token = self
            .tokens
            .get(self.index)
            .map(|(token, _range)| token.clone());
        self.index += 1;
        token
    }
fn next_token ( & mut self ) -> Option < Token > { let token = self . tokens . get ( self . index ) . map ( | ( token , _range ) | token . clone ( ) ) ; self . index += 1 ; token }
Return the next token that has not yet been processed, or None if
reached end-of-file, and mark it as processed.
Return the next token that has not yet been processed or None if reached end - of - file and mark it as processed .
&mut self
&mut self