[antlr-interest] How can I decide at runtime if a rule contains an optional token

[Gavin Lambert]

At 06:23 26/04/2009, Gabriel Petrovay wrote:
 >This is my problem. I only know at runtime of a rule is alowed 
to
 >contain a token based on o flag in the parser. Moreover, this
 >token, if alowed, is optional.
 >
 >Example:
 >rule : T1 ({ isT2Alowed }?=> T2?) T3 ...

I haven't tested this, but in theory it should work:

rule : T1 ({ isT2Allowed }? => T2)? T3 ...

(When you use a predicate, lookahead is still checked -- so the T2 
will still be optional even when isT2Allowed.)