语法分析器源程序代码

以下是一个简单的语法分析器的源代码，使用了递归下降分析的方法：

class SyntaxAnalyzer:
    def __init__(self, tokens):
        self.tokens = tokens
        self.current_token = None
        self.index = -1
        self.advance()

    def advance(self):
        self.index += 1
        if self.index < len(self.tokens):
            self.current_token = self.tokens[self.index]
        else:
            self.current_token = None

    def parse(self):
        if self.current_token is None:
            return None
        result = self.expr()
        if self.current_token is not None:
            raise Exception("Unexpected token: {}".format(self.current_token))
        return result

    def expr(self):
        result = self.term()

        while self.current_token is not None and self.current_token.type in ('+', '-'):
            op = self.current_token
            self.advance()
            right = self.term()
            if op.type == '+':
                result += right
            else:
                result -= right
        return result

    def term(self):
        result = self.factor()

        while self.current_token is not None and self.current_token.type in ('*', '/'):
            op = self.current_token
            self.advance()
            right = self.factor()
            if op.type == '*':
                result *= right
            else:
                result /= right
        return result

    def factor(self):
        token = self.current_token
        if token.type == 'number':
            self.advance()
            return token.value
        elif token.type == '(':
            self.advance()
            result = self.expr()
            if self.current_token is None or self.current_token.type != ')':
                raise Exception("Expected ')' after expression")
            self.advance()
            return result
        else:
            raise Exception("Unexpected token: {}".format(token))

这个语法分析器可以解析简单的四则运算表达式，支持加减乘除和括号。你可以根据需要对其进行修改和扩展。