简单计算器的LL1语法(+，-，*，/，pow，root)

class CalculatorParser:
    def __init__(self, expression):
        self.expression = expression
        self.index = 0

    def parse(self):
        return self.parse_expression()

    def parse_expression(self):
        term = self.parse_term()
        return self.parse_expression_prime(term)

    def parse_expression_prime(self, left):
        if self.index >= len(self.expression):
            return left

        operator = self.expression[self.index]
        if operator == '+':
            self.index += 1
            right = self.parse_term()
            return self.parse_expression_prime(left + right)
        elif operator == '-':
            self.index += 1
            right = self.parse_term()
            return self.parse_expression_prime(left - right)
        else:
            return left

    def parse_term(self):
        factor = self.parse_factor()
        return self.parse_term_prime(factor)

    def parse_term_prime(self, left):
        if self.index >= len(self.expression):
            return left

        operator = self.expression[self.index]
        if operator == '*':
            self.index += 1
            right = self.parse_factor()
            return self.parse_term_prime(left * right)
        elif operator == '/':
            self.index += 1
            right = self.parse_factor()
            return self.parse_term_prime(left / right)
        else:
            return left

    def parse_factor(self):
        if self.index >= len(self.expression):
            raise ValueError("Invalid expression")

        if self.expression[self.index] == '(':
            self.index += 1
            result = self.parse_expression()
            if self.expression[self.index] != ')':
                raise ValueError("Invalid expression")
            self.index += 1
            return result
        else:
            return self.parse_number()

    def parse_number(self):
        if self.index >= len(self.expression):
            raise ValueError("Invalid expression")

        start = self.index
        while self.index < len(self.expression) and self.expression[self.index].isdigit():
            self.index += 1
        return int(self.expression[start:self.index])


# 使用示例
expression = "2 + 3 * (4 - 1)"
parser = CalculatorParser(expression)
result = parser.parse()
print(result)  # 输出: 11