def parameters(self):
        """
        parameters: '(' logical_or_expr (',' logical_or_expr)* ')'
        """
        nodes = []
        self._process(Nature.LPAREN)

        while self.token.nature != Nature.RPAREN:

            nodes.append(Parameters(variable=self.logical_or_expr()))

            if self.token.nature == Nature.COMMA:
                self._process(Nature.COMMA)

        self._process(Nature.RPAREN)
        return nodes