def advance_tok(self):
        """Advances self.pos by one, if it is not already at the end."""
        if self.pos != self.end_pos:
            self.pos = self.pos + 1
            try:
                # If self.pos has not been backtracked,
                # we need to request a new token from the lexer
                if len(self.tokens) >= self.pos:
                    self.tokens.append(next(self.lex))
            except StopIteration:
                # Create an EOF token, whose span starts at the
                # end of the last token to use for error messages
                if len(self.tokens) > 0:
                    span = (self.tokens[self.pos-1].span[1],)*2
                else:
                    span = (0, 0)
                self.tokens.append(lexer.Token(None, None, span, None))
                self.end_pos = self.pos
dataset/ETHPy150Open blaze/datashape/datashape/parser.py/DataShapeParser.advance_tok/swapped operands of `>=`