CODEWITHSUNDEEP
parsingantlrantlr4grammarlexer
Kronos
Kronos

Reputation: 184

How to choose lexer/parser rule on instanciation

I have a grammar for parsing diverse SQL code.

Problem :

- sometimes, I want it to handle nested comments (ex: Microsoft SQL):

COMMENT: '/*' (COMMENT|.)*? ('*/' | EOF) -> channel(HIDDEN);

- sometimes, I want it to not handle them (ex: Oracle):

COMMENT: '/*' .*? '*/' -> channel(HIDDEN);

I don't want to :

Best solution would be to have an argument, passed to the lexer/parser, to choose which "COMMENT implementation" to use.

Can I do this ? If yes, how, if not, is there a satisfying solution to my problem ?

Thanks !

Upvotes: 0

Views: 60

Answers (1)

kaby76
kaby76

Reputation: 1408

You can achieve this using a semantic predicate in your lexer. You will need to (1) split the lexer and parser from each other. (2) Create a base class for the lexer with a boolean field, property, or method that you can set true if you want the lexer to allow nested comments, or false to disallow. For sake of below code, assume you add "bool nested = false;" to the lexer base class. (3) Within your lexer grammar, create one COMMENT rule as shown below. (4) After creating you lexer, assign the "nested" field to true if you want nested comments to be recognized.

COMMENT
   : (
      {nested}? '/*' (COMMENT|.)*? ('*/' | EOF)
      | '/*' .*? '*/') -> channel(HIDDEN)
   ;

Upvotes: 2

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