def get_trees(self, data, showerrors = False): # -> list:
        """ returns a list of trees with valid guesses """
        if showerrors:
            raise NotImplementedError("This parser doesn't implement errors")
        self.data = data
        self.index = 0
        try:
            return [self.__aux_parser(self._productionset.initialsymbol)]
        except (IndexError, ParseError):
            return []
returns a list of trees with valid guesses