Antlr4 中语义谓词的语法 [英] Syntax of semantic predicates in Antlr4
问题描述
在 ANTLR3 中的语义谓词"是什么? Bart Kiers 很好地概述了 Antlr3 中的不同语义谓词.
In What is a 'semantic predicate' in ANTLR3? Bart Kiers gives a very well overview about the different semantic predicates in Antlr3.
太糟糕了,Antlr4 中的语法/语义似乎发生了变化,因此无法编译:
Too bad the syntax/semantics were seemingly changed in Antlr4, so this does not compile:
end_of_statement
: ';'
| EOF
| {input.LT(1).getType() == RBRACE}? =>
;
RBRACE
: '}'
;
有人能告诉我如何做 end_of_statement 的第三种情况:如果下一个令牌是 '}' 则接受但不要使用它.
Could someone please tell me how to do the third case of end_of_statement: Accept if the next token is a '}' but do not consume it.
推荐答案
现在只有一种语义谓词,看起来像这样:
There is now just a single type of semantic predicates, which looks like this:
{ <<boolean-epxression>> }?
抽象类 Parser
的 input
属性(您生成的解析器从中扩展)现在在它前面有一个下划线.
And the input
attribute from the abstract class Parser
(which your generated parser extends from) now has an underscore in front of it.
因此,在您的情况下,使用以下 ANTLR v3 语法:
So, in your case, the following ANTLR v3 syntax:
{input.LT(1).getType() == RBRACE}? =>
在 ANTLR v4 中看起来像这样:
would look like this in ANTLR v4:
{_input.LT(1).getType() == RBRACE}?
这篇关于Antlr4 中语义谓词的语法的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!