EBNF 到流畅界面

EBNF（扩展巴科斯范式）是一种用于描述语法规则的元语言。它通过一系列的产生式规则来定义语法结构，并且可以用于生成自然语言。在本篇文章中，我们将介绍如何将EBNF转化为流畅界面，并通过一个案例代码来展示其应用。

 ::=  ( ("+" | "-")  )*
 ::=  ( ("*" | "/")  )*
 ::=  | "("  ")"
 ::= [0-9]+

python
class Calculator:
    def __init__(self):
        self.result = 0
    
    def calculate(self, expression):
        self.result = self._parse_expression(expression)
    
    def _parse_expression(self, expression):
        terms = expression.split("+")
        result = 0
        for term in terms:
            if "-" in term:
                numbers = term.split("-")
                result += int(numbers[0])
                for number in numbers[1:]:
                    result -= int(number)
            else:
                result += int(term)
        return result
calculator = Calculator()
expression = input("请输入表达式：")
calculator.calculate(expression)
print("计算结果为：", calculator.result)