Rule reference is not currently supported in a set in ANTLR4 Grammar

Question

I am trying to port Chris Lambro's ANTLR3 Javascript Grammar to ANTLR4

I am getting the following error,

Rule reference 'LT' is not currently supported in a set

in the following code ~(LT)*

LineComment
    : '//'  ~(LT)* -> skip
    ;

LT  : '\n'      // Line feed.
    | '\r'      // Carriage return.
    | '\u2028'  // Line separator.
    | '\u2029'  // Paragraph separator.
    ;

I need help understanding why I am getting this error, and how I can solve it .

I'm interested in an antlr4 grammar for JS too. Did you get very far? — kybernetikos, Jun 27 '13 at 20:21
I have a grammar that parses all JS expressions, functionCalls and if-else statements. I will try to opensource the grammar If possible — Gautam, Jun 29 '13 at 05:03

score 11 · Accepted Answer · answered May 28 '13 at 11:44

11

The ~ operator in ANTLR inverts a set of symbols (characters in the lexer, or tokens in the parser). Inside the set, you have a reference to the LT lexer rule, which is not currently supported in ANTLR 4. To resolve the problem, you need to inline the rule reference:

LineComment
    :   '//' ~([\n\r\u2028\u2029])* -> skip
    ;

answered May 28 '13 at 11:44

Sam Harwell

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But this is listed as fixed https://github.com/antlr/antlr4/issues/70, Why Can't I use it ? – Gautam May 29 '13 at 08:56
6

Previously if you had such a rule reference, it would still generate a lexer but the tokens it created would not be correct. The solution was to turn it into an error message instead of letting it fail silently. – Sam Harwell May 29 '13 at 13:14

Rule reference is not currently supported in a set in ANTLR4 Grammar

1 Answers1