Antlr4中语义谓词的语法 [英] Syntax of semantic predicates in Antlr4

问题描述

在 什么是ANTLR3中的语义谓词"?/em> 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.

很遗憾，Antlr4中的语法/语义似乎已更改，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
    : '}'
    ;

有人可以告诉我如何处理 end_of_statement 的第三种情况:接受下一个令牌是否为'}'，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

现在只有一种类型的语义谓词，如下所示:

There is now just a single type of semantic predicates, which looks like this:

{ <<boolean-epxression>> }?

抽象类Parser的input属性(生成的解析器从中扩展)现在在其前面带有下划线.

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，请使用以下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}?

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