I highly recommend correcting all instances of this warning in code of any importance. This warning was created (by me actually) to alert you to situations like the following: shiftExpr : ID ((‘<<‘ | ‘>>’) ID)?; Since ANTLR 4 encourages action code be written in separate files in the target language instead of embedding them … Read more
This seems to be a common misunderstanding of ANTLR: Language Processing in ANTLR: The Language Processing is done in two strictly separated phases: Lexing, i.e. partitioning the text into tokens Parsing, i.e. building a parse tree from the tokens Since lexing must preceed parsing there is a consequence: The lexer is independent of the parser, … Read more
There are a couple of alternatives you shouldn’t rule out: JParsec is a parser combinator framework that allows you to construct your parser entirely from code. Scala’s parser combinator framework addresses a similar concern; however, Scala’s syntax makes all of this much more readable. Then there’s also the parser combinator framework done by John Metsker, … Read more
ANTLR 4 For predicates in ANTLR 4, checkout these stackoverflow Q&A’s: Syntax of semantic predicates in Antlr4 Semantic predicates in ANTLR4? ANTLR 3 A semantic predicate is a way to enforce extra (semantic) rules upon grammar actions using plain code. There are 3 types of semantic predicates: validating semantic predicates; gated semantic predicates; disambiguating semantic … Read more
A fragment is somewhat akin to an inline function: It makes the grammar more readable and easier to maintain. A fragment will never be counted as a token, it only serves to simplify a grammar. Consider: NUMBER: DIGITS | OCTAL_DIGITS | HEX_DIGITS; fragment DIGITS: ‘1’..’9′ ‘0’..’9’*; fragment OCTAL_DIGITS: ‘0’ ‘0’..’7’+; fragment HEX_DIGITS: ‘0x’ (‘0’..’9′ | … Read more