Semantic predicates in ANTLR4?

by

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
 | refIdentifier
 | lambdaExpression
 ;

Note that there is just one type of predicate in v4: semantic predicates, { ... }?. If you need to inspect the contents of a token, for example, you can do it like this:

id_capitals_only
 : {_input.LT(1).getText().matches("[A-Z]+")}? ID
 ;

ID
 : [a-zA-Z]+
 ;

EDIT

And as Sam Harwell mentions in the comments:

The semantic predicates {…}? in V4 work like the gated semantic predicates did in V3. The ungated predicates from V3 do not have a counterpart in ANTLR 4.

Leave a Comment