[antlr-interest] Tree grammar conditionally run subrule

[fridi]

Hi all,


I tried to skip a rule in an if-then-else construct using gated symantic 
predicates.

ifElse
scope {
   boolean expResult;
} :
    ^(
       IFTHEN b = expression { $ifElse::expResult = b; }
       (
          {$ifElse::expResult == true}?=> actionSequence
          | . // if expResult == false, no action required but eat the token
       )
      )
    |
    ^(
       IFTHENELSE b = expression { $ifElse::expResult = b; }
       (
          {$ifElse::expResult == true}? actionSequence
          . // if expResult == true, call the 'then' action and 'eat' 
the else action
          | . actionSequence // if expResult == false, 'eat' the 'then' 
action and call the else action
       )
      );


leeds to
Eval.g: node from after line 1:21 no viable alternative at input 'DOWN

This works well until the subrule itself is a tree (i.e. nested 
if-then-else). So it seems, that the '.' does not match the whole subtree?

Thanks for any hint, fridi
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