^ 和 !在 ANTLR 语法中代表 [英] What does ^ and ! stand for in ANTLR grammar

问题描述

我很难弄清楚 ^ 和 !代表 ANTLR 语法术语.

I was having difficulty figuring out what does ^ and ! stand for in ANTLR grammar terminology.

推荐答案

查看 ANTLR 备忘单:

! 不包含在 AST 中
^ 制作AST根节点

! don't include in AST
^ make AST root node

而且^也可以用于重写规则:... ->^( ... ).例如，以下两个解析器规则是等价的:

And ^ can also be used in rewrite rules: ... -> ^( ... ). For example, the following two parser rules are equivalent:

expression
  :  A '+'^ A ';'!
  ;

和:

expression
  :  A '+' A ';' -> ^('+' A A)
  ;

两者都创建了以下 AST:

Both create the following AST:

  +
 / \
A   A

换句话说:+ 是根，两个 A 的子元素，; 从树.

In other words: the + is made as root, the two A's its children, and the ; is omitted from the tree.

这篇关于^ 和 !在 ANTLR 语法中代表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！