[antlr-interest] Recursive rules and LL(*)

[Emond Papegaaij]

Hello,

I'm having a bit of a problem with a recursive rule combined with LL(*). The 
following (snapshot) of the grammar triggers the problem:

grammar TPL;
nodeDecl: (targetClass ':')? targetClass;
targetClass: '<' (targetClass)? '>';

This should match strings like '<<>>:<>' and '<<<>>>'. However the recursive 
rule does not work with the LL(*) algorithm. It tries to build the entire 
language in a single DFA and then bails out with:

tpl2.g:3:30: Alternative 1: after matching input such as '<' '<' '<' '<' '<' 
decision cannot predict what comes next due to recursion overflow to 
targetClass from targetClass
tpl2.g:3:30: Alternative 2: after matching input such as '<' '<' '<' '<' '<' 
decision cannot predict what comes next due to recursion overflow to 
targetClass from targetClass

Is there any way to make this work with LL(*)? The DFA should take all '<' 
and '>' tokens without trying to match the number of tokens and finally 
branch on ':' or EOF. A mismatch between the number of '<' and '>' tokens 
will be detected by the parser. Of course I could use the following rule:

nodeDecl options {k = 1;}
         : (targetClass ':')=> targetClass ':' targetClass
         | targetClass;

But I think the LL(*) version is more clear, and it should be faster.

Best regards
Emond Papegaaij