This turned out to be my fault, not a discrepancy between the CSharp2 and Java
targets. And it's probably a funny story (from the outside, at least :-) ), so
I'll record it here.
While getting started with antlr a few weeks back, I tried a few approaches to
setting up my input stream, lexer and parser.
I remember having trouble ensuring that the parser correctly ignored whitespace
tokens, and experimenting with a few calls before getting the desired result. I
guess it was about then that I inserted this line:
var cts = new CommonTokenStream(); // fine...
cts.DiscardTokenType(Token.HIDDEN_CHANNEL); // not fine.
While I guessed that DiscardTokenType would discard a class of tokens based on
the assigned channel, it was actually just discarding all occurrences of
whatever token happened be arbitrarily assigned internal reference number 99
(the value of Token.HIDDEN_CHANNEL) in this particular revision of my lexer
definition.
Sigh.
That explains about two weeks' worth of weird behaviour where seemingly trivial
modifications to the grammar introduced or resolved parse errors that I just
could not reconcile with my grammar definition.
It also explains why things worked just fine when running in AntlrWorks under
the Java target - unlike _my_ setup code, the AntlrWorks test harness probably
doesn't randomly throw away tokens from the input stream :-).
Regards,
Andrew
---- original message below -----
Hi,
Are there any differences or known issues with the CSharp2 target that cause
it to behave differently to the "equivalent" Java target generated lexer and
parser?
I'm asking because my grammar, which works on 105 of 105 test cases when I
use the Java target, fails on 6 of 105 test cases when I use the CSharp2 target.
I'm not using actions or anything target language-specific.
Using AntlrWorks' integrated and remote debuggers and my limited knowledge,
I've got one lead right now: I've noticed that the Java version logs LT(1)
events for each token, so that as the parser pulls tokens from an input stream:
A B C
I see LT(1) 'A' then LT(1) 'B' then LT(1) 'C'. That seems right to me.
But when the problematic test cases are parsed in the CSharp2 target, I see
LT(1) 'A' and then for some reason the next LT(1) sees 'C', not 'B'. This seems
wrong.
I'm new to Antlr - does this point to an issue with the generated lexer or
the parser? What's next troubleshooting step would you suggest?
Happy to respond with specifics of the grammar and the error messages if you
think they'd be useful.
Thanks in advance,
Andrew
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