[antlr-interest] Lexer predicates...why don't they work for me?

[Diehl, Matthew J]

Hi,

The lexer is the part of ANTLR that I do not understand at all.  I think
I understand what it's doing, but obviously I don't.  It always feels
like it is a LL(1) lexer.  For instance if I have the following rules:

Apostrophe : '\''
CharacterLiteral : Apostrophe (.) Apostrophe ;

Given an input of:
foo = '0'; --works fine (token = CharacterLiteral)
Foo = signalA'RANGE --doesn't work.  It throws a lexer error saying that
'A' is not an apostrophe (''')
In this case I would like it to just return ''' as Apostrophe.

I tried using predicates:
CharacterLiteral : (Apostrophe (.) Apostrophe)=> Apostrophe (.)
Apostrophe ;

And also:
CharacterLiteral : Apostrophe (.) Apostrophe
                 | Apostrophe {$type=Apostrophe;} ;
   /*same error as above*/
CharacterLiteral : {input.LA(3)==Apostrophe}? Apostrophe (.) Apostrophe
;
   /*threw a 'did not pass predicate' error */

But none of it's working.  What am I doing wrong?  Thanks for your time
and consideration.

Matt