[antlr-interest] Serious Bug when using BitSetgeneration-Forgot
Terence Parr
parrt at cs.usfca.edu
Sat Nov 5 17:02:04 PST 2005
> Hopefully we can find a solution to this "Empty Pruction & BitSet
> wrong
> code generation".
>
> It has kept my puzzling about errors in my grammar for a long long
> time,
> but I have put off investigating it because there had been other more
> important things to look at. However, I know had to solve it, and it
> turned out to be a Bug !
Hi. Here is my test case:
class T extends Parser;
x : A|C|D|E|F|G|H;
s : a b ;
// here is the rule of interest
a : B
| {p1}? ( )
| {p2}? ( )
;
b : A|D|F|G|H;
All is well. It generates the following for rule a:
if ((LA(1)==B)) {
match(B);
}
else if (((_tokenSet_1.member(LA(1))))&&(p1)) {
{
}
}
else if (((_tokenSet_1.member(LA(1))))&&(p2)) {
{
}
}
clearly the bitsets are there. Can you nail your bug down to a
simple grammar like this that fails?
I realized that ANTLR will not (as I said in last email) delete the
lookahead; it's smart enough to know that the predicates are only
valid in the right context and so it keeps the lookahead the same.
Thanks,
Ter
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