本文介绍了现代编程语言的语法是上下文无关的还是上下文敏感的?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

C ++,C#或Java语言是上下文无关的还是上下文敏感的?

Are the C++, C# or Java languages context-free or context-sensitive?

推荐答案

由于模板系统是图灵完备的,要确定一段C ++代码是否合法C ++很难.例如,我可以定义一个模板类,该模板类在字符串上模拟TM,然后如果机器接受,则创建一个值为1的常量,否则为0.如果我这样做了,那么以下代码将是合法的,前提是TM在给定的输入上停止了:

C++ is neither context-free nor context-sensitive, since the template system is Turing-complete and determining whether a piece of C++ code is legal C++ is undecidably hard. For example, I could define a template class that simulates a TM on a string and then creates a constant with value 1 if the machine accepts and 0 if it does not. If I did that, then the following code would be legal iff the TM halted on the given input:

int myArray[TMTemplate</* ... args ... */>::value];

由于TM拒绝,因此会创建大小为0的数组,这是不允许的.

Since if the TM rejects, this creates an array of size 0, which is not allowed.

C#和Java都不是上下文无关的,因为众所周知,检查变量是否在特定范围内正确且一致地使用并不是上下文无关的(证明很复杂,并且依赖于奥格登的引理).但是,我不确定它们是否上下文相关.

Neither C# nor Java is context-free, because checking of whether a variable is used correctly and consistently throughout a particular scope is known not to be context-free (the proof is complex and relies on Ogden's lemma). However, I'm not sure whether or not they are context-sensitive.

希望这可以部分回答您的问题!

Hope this gives a partial answer to your questions!

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05-27 13:04
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