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Editorial Team
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Asked: 2026-06-19T00:01:18+00:00

I need help with my ANTLR 4 grammar after deciding to switch to v4

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I need help with my ANTLR 4 grammar after deciding to switch to v4 from v3. I am not very experienced with ANTLR so I am really sorry if my question is dumb 😉

In v3 I used the following code to detect Java-style comments:

COMMENT
    :   '//' ~('\n'|'\r')* '\r'? '\n' {$channel=HIDDEN;}
    |   '/*' ( options {greedy=false;} : . )* '*/' {$channel=HIDDEN;}
    ;

In v4 there are no rule-specific options. The actions (move to hidden channel) are also invalid.

Could somebody please give me a hint how to do it in ANTLR v4?

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1 Answer

  1. Editorial Team

    The v4 equivalent would look like:

    COMMENT
    :   ( '//' ~[\r\n]* '\r'? '\n'
        | '/*' .*? '*/'
        ) -> channel(HIDDEN)
    ;

    which will put all single- and multi line comment on the HIDDEN channel. However, if you’re not doing anything with these HIDDEN-tokens, you could also skip these tokens, which would look like this:

    COMMENT
    :   ( '//' ~[\r\n]* '\r'? '\n'
        | '/*' .*? '*/'
        ) -> skip
    ;

    Note that to tell the lexer or parser to match ungreedy, you don’t use options {greedy=false;} anymore, but append a ?, similar to many regex implementations.

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