CODEWITHSUNDEEP
antlrgrammarantlr4
user2085189
user2085189

Reputation: 101

Explanation for the following grammar written in ANTLR 4

I have a sample grammar written in ANTLR 4

query : select from ';' !? EOF!

I have understood 

query : select from ';'

how it works

What does !? EOF! means in the grammar and how it works?

Upvotes: 1

Views: 5806

Answers (1)

Bart Kiers
Bart Kiers

Reputation: 170278

The exclamation marks is used in ANTLR v3 grammars to denote that a certain node should be omitted from the generated AST. Since ANTLR v4 does not have AST's, this construct is no longer used.

In both v3 and v4, the ? denotes that a rule (lexer or parser) is optional and EOF means the end-of-file constant.

To summarize ';'!? means: optionally match a ';' and exclude it from the AST. And EOF! means: match the end-of-file and exclude this token from the AST.

So, the v3 parser rule:

query : select from ';'!? EOF!

should look like this in a v4 grammar:

query : select from ';'? EOF

Upvotes: 4

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