'Require that the next symbol matches symbol_string, or emit an error.
Args:
symbol_string: next symbol expected by the caller
Raises:
BadQueryError if the next symbol doesn\'t match the parameter passed in.'

def __Expect(self, symbol_string):

    if (not self.__Accept(symbol_string)):
        self.__Error(('Unexpected    Symbol:    %s' % symbol_string))
