C# 解析“（true and true）或（true or false）”

发布于 2024-11-14 03:59:19 字数 419 浏览 2 评论 0原文

C#：我有一个字符串变量，如下所示：

 string a = "(true and true) or (true or false)";

这可以是任何内容，它可以变得更复杂，例如：

 string b = "((true and false) or (true or false) and not (true and false)) and false";

我所知道的是它是正确的。不可能发生这个表达式不能被“评估”的情况。

有什么方法可以让我对此进行评估吗？我只想知道该字符串的结果（结果）。这意味着我需要“true”或“false”而不是这个字符串。

我想我可以创建一个解析方法来执行此操作，逐步减少字符串，直到获得最终值，但我想知道是否有更好的方法。

原文

C#: I have a string variable that looks like this:

 string a = "(true and true) or (true or false)";

This can be anything, it can get more complex, like:

 string b = "((true and false) or (true or false) and not (true and false)) and false";

All i know is that it is correct. Cannot happen that this expression cannot be "evaluated".

Is there a way that I can somehow evaluate this? I would only like to know the outcome (result) of that string. This means I need "true" or "false" instead of this string.

I think I can make a parse method that does this, reducing the string step by step, until we got the final value, but I was wondering if there is a better approach.

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段念尘 2024-11-21 03:59:19

扩展 Rob 的评论，您可以将运行时编译与 C# 4.0 dynamic 支持结合使用，并执行如下操作：

var expression = "(true and false) or (true or false)";

var helper = "" + 
    "using System; " + 
    "public class Expression {{ public bool Eval() {{ return {0}; }} }}";

var replaced = expression.Replace("and", "&&").Replace("or", "||");

var references = new string[] { "System.dll" };
var parameters = new CompilerParameters(references, "Test.dll");
var compiler = new CSharpCodeProvider();


var results = compiler.CompileAssemblyFromSource(
    parameters, 
    String.Format(helper, replaced));

dynamic exp = Activator.CreateInstance(
    results.CompiledAssembly.GetType("Expression"));

Console.WriteLine(exp.Eval());

Expanding on Rob's comment, you can use runtime compilation in conjunction with C# 4.0 dynamic support and do something like this:

var expression = "(true and false) or (true or false)";

var helper = "" + 
    "using System; " + 
    "public class Expression {{ public bool Eval() {{ return {0}; }} }}";

var replaced = expression.Replace("and", "&&").Replace("or", "||");

var references = new string[] { "System.dll" };
var parameters = new CompilerParameters(references, "Test.dll");
var compiler = new CSharpCodeProvider();


var results = compiler.CompileAssemblyFromSource(
    parameters, 
    String.Format(helper, replaced));

dynamic exp = Activator.CreateInstance(
    results.CompiledAssembly.GetType("Expression"));

Console.WriteLine(exp.Eval());

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疯到世界奔溃 2024-11-21 03:59:19

也许是这样的？

string previous = string.Empty;
while (b != previous) 
{
     previous = b;
     b = b.Replace("true and false", "false");
     b = b.Replace("true and true", "true");
     b = b.Replace("false and true", "false");
     b = b.Replace("false and false", "false");
     b = b.Replace("false or false", "false");
     b = b.Replace("true or false", "true");
     b = b.Replace("true or true", "true");
     b = b.Replace("false or true", "true");
     b = b.Replace("(false)", "false");
     b = b.Replace("(true)", "true");
     b = b.Replace("not false", "true");
     b = b.Replace("not true", "false");
 }

请注意，规范允许不明确的表述，例如：

"false and false or true"
"false and true or true"

如果首先评估 and，则这两个表达式均为“true”，如果首先评估 or，则这两个表达式均为“false”第一的。因此，在每个级别都需要括号会更好。要求从左到右求值是另一种选择，但这会使代码变得更加复杂。

对于那些可能反对这种类型问题的解决方案的人，请记住，一些数学家认为所有数学都可以简化为这种符号操作。说是对罗素和怀特海数学原理<的主要批评之一/em> 是它给公式赋予了太多的含义。

Something like this maybe?

string previous = string.Empty;
while (b != previous) 
{
     previous = b;
     b = b.Replace("true and false", "false");
     b = b.Replace("true and true", "true");
     b = b.Replace("false and true", "false");
     b = b.Replace("false and false", "false");
     b = b.Replace("false or false", "false");
     b = b.Replace("true or false", "true");
     b = b.Replace("true or true", "true");
     b = b.Replace("false or true", "true");
     b = b.Replace("(false)", "false");
     b = b.Replace("(true)", "true");
     b = b.Replace("not false", "true");
     b = b.Replace("not true", "false");
 }

Note that the specification allows ambigious formulations, such as these:

"false and false or true"
"false and true or true"

Both of these expressions are "true" if the and is evaluted first, and "false" if the or is evaluated first. Therefore, requireing parenthesis at every level would be better. Requiring left-to-right evaluation is another option, but that makes the code a bit more complex.

For those of you who may object to this style of solution for this style of problem, remember that some mathematicians believe that all of mathematics may be reduced to this sort of symbol manipulation. It is said that one of the main criticisms of Russell and Whitehead’s Principia Mathematica is that it embues the formulas with too much meaning.

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