如何返回一行代码并恢复调用堆栈? [英] How to return to a line of code and restore the call-stack?

问题描述

我早些时候提出了一个问题，但我认为我对自己的答案类型不够清楚希望，所以让我提供一个更具体的示例:

I asked a question earlier, but I don't think I was clear enough about the sort of answers I was hoping for, so let me provide a more concrete example:

class Program
{
    private static bool State;

    static void Main(string[] args)
    {
        State = false;
        Console.WriteLine(And());
        Console.ReadLine();
    }

    static bool And()
    {
        return Or() && C();
    }

    static bool Or()
    {
        return A() || AB();
    }

    static bool C()
    {
        return State;
    }

    static bool A()
    {
        return true;
    }

    static bool AB()
    {
        State = true;
        return true;
    }
}

该程序的流程如下:

1. And()被调用
2. And()调用Or()
3. Or()调用A()
4. A()返回true
5. 流程返回Or()，后者返回true(延迟评估)
6. 流返回到And()，And()调用C()
7. C()返回false
8. 流返回到And()，后者返回false

现在，如果Or()没有执行延迟评估(我将||更改为|)，则程序将返回true.但是，除非整个解析结果失败(And()返回false)，否则我不希望AB()执行.

Now if Or() did not perform lazy evaluation (I change || to |), the program will return true. However, I don't want AB() to executed unless the result of the entire parse fails (And() returns false).

所以我想做的是，在Or()函数中的某个位置，将当前状态保存在堆栈中(静态变量)，这样，如果And()返回false，我就可以从堆栈中弹出一个项目，然后尝试替代方法.

So what I'd like to do, is somewhere in the Or() function, save the current state on a stack (static variable) so that if And() returns false, I can pop an item off the stack and try the alternative.

我将如何在C#中完成此任务?

How would I accomplish this in C#?

推荐答案

它让我觉得很琐碎-只需重新安排电话:

It strikes me as being fairly trivial- just rearrange the calls:

static void Main(string[] args)
{
    State = false;
    Console.WriteLine(Or());
    Console.ReadLine();
}

static bool Or()
{
    return A() && C() || AB() && C();
}

还是我错过了什么?也许C()有副作用，所以它不应被调用两次?

Or am I missing something? Maybe C() has side effects such that it should not be called twice?

现在，我了解您要执行的操作.帮个忙.听取您的建议，获取GPPG副本，或者(可能更简单) ANTLR ， ANTLRWorks . 所以，比尝试手动滚动解析器容易得多，并且出错率低，并且最终仍会得到C#.

Now I understand what you are trying to do. Do yourself a favor. Listen to the suggestions you've gotten, get a copy of GPPG, or (probably much simpler) ANTLR, with ANTLRWorks. It is so, so much easier and less error prone than attempting to roll a parser by hand, and you still get C# at the end.

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