# compiles an expression
    def compile_expression(self):
        self.off += "  "
        self.write(self.off, 'expression', False)
        self.compile_term()
        data = self.get_data()
        used = False
        while data[1] in self.op:
            self.write_value(self.off + "  ", data)
            used = True
            self.compile_term()
        if not used:
            self.next_data = data
        self.write(self.off, 'expression', True)
        print(data)
        self.off = self.off[0:-2]