Rust的语法语法是无上下文还是上下文敏感？(Is Rust's syntactical grammar context

Rust的语法语法是无上下文还是上下文敏感？(Is Rust's syntactical grammar context-free or context-sensitive?)

几乎没有任何编程语言的语法语法是规则的，因为它们允许任意深度嵌套的括号。 Rust也是这样做的：

let x = ((((()))));

但Rust的语法语法至少是无上下文的吗？ 如果没有，哪个元素使语法上下文敏感？ 或者语法甚至是递归可枚举的，就像C ++的语法语法一样 ？

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相关 ： Rust的词汇语法是常规的，无上下文的还是上下文敏感的？

The syntactical grammar of hardly any programming language is regular, as they allow arbitrarily deeply nested parenthesis. Rust does, too:

let x = ((((()))));

But is Rust's syntactical grammar at least context-free? If not, what element makes the grammar context-sensitive? Or is the grammar even recursively enumerable, like C++'s syntactical grammar?

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Related: Is Rust's lexical grammar regular, context-free or context-sensitive?

最满意答案

Rust包含一个宏处理器，其操作具有高度上下文相关性。

您可以尝试通过语法分析来解决这个问题，但不包括宏扩展 - 可能，但不是特别有用 - 或者假设宏扩展是由一些中间工具完成的，该工具被赋予一个免费的传递给让它成为图灵完整的。

但我倾向于说它只是意味着Rust语言是递归可枚举的。

宏定义的有效性存在许多限制，这可能会使语言（至少）对上下文敏感，即使您决定不执行宏扩展作为语法分析的一部分。

这并不意味着无上下文语法不能用作Rust语法分析的一部分。 它可能是必不可少的，使用诸如bison或Antlr之类的解析器生成器（以及两者的示例）甚至可能是有用的。 像大多数编程语言一样，有一个简单的Rust超集，它是无上下文的，可以使用无上下文语法工具进行有用的分析; 但是，最终有些文本需要在编译时被拒绝为无效，即使它们是CF超集的一部分。

Rust includes a macro processor, whose operation is highly context-sensitive.

You could attempt to skate around this issue by only doing syntactic analysis up to but not including macro expansion -- possible, but not particularly useful -- or by assuming that the macro expansion is done by some intermediate tool which is given a free pass to allow it to be Turing complete.

But I'm inclined to say that it simply means that the Rust language is recursively enumerable.

There are a number of restrictions on the validity of macro definitions which probably make the language (at least) context-sensitive, even if you settle for not performing the macro expansions as part of syntactic analysis.

This doesn't mean that a context-free grammar cannot be useful as part of the syntactic analysis of Rust. It's probably essential, and it could even be useful to use a parser generator such as bison or Antlr (and examples of both exist). Like most programming languages, there is a simple superset of Rust which is context-free, and which can be usefully analysed with context-free grammar tools; however, in the end there are texts which will need to be rejected at compile-time as invalid even though they are part of the CF superset.