code: private function skip($kind)
      {
          $match = $this->lexer->token->kind === $kind;
  
          if ($match) {
              $this->lexer->advance();
          }
  
          return $match;
      }
docs: If the next token is of the given kind, return true after advancing
  the parser. Otherwise, do not change the parser state and return false.
  
  @param string $kind
  
  @return bool