code: def expect(self, f, *args):
          
          match = self.accept(f, *args)
          if match:
              return match
  
          try:
              func_name = f.func_name
          except AttributeError:
              func_name = "<unnamed grammar function>"
  
          start, end = self.current_position()
          raise errors.EfilterParseError(
              query=self.tokenizer.source, start=start, end=end,
              message="Was expecting %s here." % (func_name))
docs: Like 'accept' but throws a parse error if 'f' doesn't match.