CFG 算术优先级/歧义
自从我与 CFG 合作以来已经有一段时间了。无论如何，我有一个特定的语法可以正确地完成所有操作，但最后（我排除了其他标准数学操作）。
S ::= S+T | ST | T
T ::= 非终结符 |身份证 | -S | (S)
根据我所拥有的一切..我知道-S 应该是-T。但另外......这对优先级有什么影响。是不是很暧昧？从数学上讲，我可以显然它是不正确的..但这不应该在歧义问题上产生影响。
如果它是 -T，那么它与 (S) 具有相同的优先级吗？
真正尝试理解这是如何发生的并循环回到开始状态。
Been a while since I've worked w/ CFG. Anyways, I have a particular grammar that goes through all the operations properly, but at the end (I excluded other standard mathematic operations).
S ::= S+T | S-T | T
T ::= nonterminal | ID | -S | (S)
per everything I have.. I know that -S should be -T. But additionally.. what does that do to the precedence. Is it ambiguous? Mathematically I can it obviously won't be correct.. but that shouldn't make a difference on the issue of ambiguity.
If it was a -T would that have equal precedence as the (S)?
really trying to comprehend how this occurs with it looping back to the Start state.
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如果将 -S 更改为 -T，歧义就解决了。
在更改之前，这里是一个歧义句的示例：-ab。是-(ab)，还是(-a)-b？
然而，随着变化，不再有任何歧义。
至于优先级，在您的具体示例中， -T 和 (S) 之间不必有规则，因为它始终是具有优先级的内部规则，这正是您所期望的行为。
If you change -S to -T, the ambiguity is solved.
Before the change, here is an example for an ambiguous sentence: -a-b. Is it -(a-b), or (-a)-b?
With the change, however, there is no more ambiguity.
As for precedence, in your specific example, there doesn't have to be a rule between -T and (S), since it is always the inner one that has precedence, which is exactly the behavior you would expect.