[antlr-interest] Semantically guided parsing

[Juancarlo Añez]

I have to parse hierarchy of descriptions in which each level of the
hierarchy is indicated by an integer.

1 FIRST LEVEL
2 SECOND LEVEL
2 AGAIN SECOND
1 BACK TO FIRST

I've tried to have the parser pick up the hierarchy with semantic
predicates, but I get failures from the predicates instead of simple rule
rejection (the target is Python):

description[d]
    :
    level[d] text
   (description[$d+1])*


level[d]
    :
    { self.input.LA(1) == INTEGER and int(self.input.LT(1).getText()) ==
$d}?
    INTEGER
    ;

"rule level failed predicate: { self.input.LA(1) == INTEGER and int(
self.input.LT(1).getText()) == $d}?"

Any ideas?

-- 
Juancarlo *Añez*