ANTLR4中的令牌否定

Question

I define LEGAL_ESCAPE token like this:

LEGAL_ESCAPE: '\\'('b'|'f'|'r'|'n'|'t'|'"')?;

Is there any way for me to use negative of this token to define another ILLEGAL_ESCAPE token?

Answer 1

Certainly:

LEGAL_ESCAPE    : ESC [bfrnt"] ;
ILLEGAL_ESCAPE  : ESC 
                   ( ~[bfrnt"]  // any char not in the set
                   | EOF        // it is a non char
                   )
                ;
fragment ESC    : '\\' ;

There are quite a few of these 'tricks' implicit in the various example grammars in the Antlr4 Grammar Repo . The abnf and less grammars are good starting points. The Java8, Antlr4 and Python3 grammars demonstrate many of the more involved capabilities.

Note, the negation operator ~ works on characters, sets and ranges of characters, on single tokens and sets of single tokens. But,

ILLEGAL_ESCAPE  : ~LEGAL_ESCAPE ;

is unlikely what you were asking for.