Heiko Wundram wrote:
Am Freitag, 22. September 2006 15:26 schrieb Tim Van Holder:
I would expect this to accept any input starting with A(B|C?D?E)+,
but in practice, it only accepts input starting with A(B|CDE)+,
because for the xyzzy nterm, it always tries to reduce the opt_C.
From the
On 25 Sep 2006, at 09:01, Heiko Wundram wrote:
Bison reduces everything as far as possible before erroring out
(that's a
general properly of LALR(1)-parsers), but here, there's absolutely
no rule
for it to do what you want, so the error occurs on the shift on the
expected
E.
Actually,
Heiko Wundram wrote:
Am Montag, 25. September 2006 08:49 schrieben Sie:
snip grammar info
Except that it actually takes the entire opt_C opt_D E path - if an A
is seen, it will reduce opt_C and opt_D then error out on the E rule,
while it should have reduced up to the bar nterm, and only try
Am Montag, 25. September 2006 10:34 schrieb Tim Van Holder:
I don't expect it to reduce foo, I expect it to reduce bar - it's the
foo rule I expect to error out on an unexpected token (and that error
would be avoided by the YYACCEPT).
Err, how do you expect it to reduce to bar? There's no rule
On 25 Sep 2006, at 10:45, Heiko Wundram wrote:
[I now see Hans Aberg's reply - so ok, it's an artifact of LALR(1), I
can live with that - and I hereby second any motion to introduce
that
LR(1) option]
It's not only an artifact of LALR(1). AFAIK, bison table generation
uses
$default
Am Montag, 25. September 2006 11:02 schrieben Sie:
I am not sure what additional compressions that Bison uses besides
LALR(1), but the phenomenon is due to these compressions, where one
deliberately merges states, accepting certain additional extra
reductions. The technique is described in the
Heiko Wundram wrote:
Am Montag, 25. September 2006 10:34 schrieb Tim Van Holder:
If seeing a portion of the actual grammar where I encountered the
behaviour would be clearer, let me know and I'll post it.
Sure, please post that.
I consider the topic more or less closed now, but here goes
Am Freitag, 22. September 2006 15:26 schrieb Tim Van Holder:
I would expect this to accept any input starting with A(B|C?D?E)+,
but in practice, it only accepts input starting with A(B|CDE)+,
because for the xyzzy nterm, it always tries to reduce the opt_C.
From the .output:
state 1
2
