In ANTLR v4, there are no longer gated semantic predicates, { … }?=>, and there are also no longer syntactic predicates, ( … )=>, because the parsing algorithm used in v4 can resolve the ambiguities (the need for such predicates are no longer needed). So, this should just work for you: expr : refIdentifier | … Read more
Negating can occur inside lexer and parser rules. Inside lexer rules you can negate characters, and inside parser rules you can negate tokens (lexer rules). But both lexer- and parser rules can only negate either single characters, or single tokens, respectively. A couple of examples: lexer rules To match one or more characters except lowercase … 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
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
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