[antlr-interest] non-determinism warning

[Monty Zukowski]

Tarun Khanna wrote:
> Hi All,
> 
> I stumbled across this problem once more, so here I am looking for some
> standard solution to such a problem.
> 
> Consider the following production ->
> 
> F: LP exp RP |  (DOT IDENT)* (DOT TAB)?
> 
> There is non-determinism because the parser doesn't know, when to stop
> matching the first DOT and start looking for the second DOT.
> 
> Syntactic or semantic predicates can not be used as, there are no
> alternates. I don't want to use a look ahead of more than 1.
> 

Why not?  ANTLR only uses the extra lookahead when it is necessary.  k=2
is the perfect solution for this.

Otherwise you could keep your own state and do something like

 (DOT
   {!tabMatched}?(IDENT|TAB{tabMatched=true;})
   | (SOME_IMAGINARY_TOKEN_THAT_YOUR_LEXER_NEVER_PRODUCES)
 )*

Monty