[antlr-interest] RewriteEmptyStreamException upon mismatch

[Jim Idle]

The error message is correct of course, but if you still want to try and
produce a tree then what you need to do is detect that the subrule failed.
The easiest way to do this is to use:

c: X ;
b: myc=c 
	-> {$myc==null}? ^( ERROR )   // Or something sensible etc
	-> ^( X c)
;

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Alan Rooks
> Sent: Friday, October 05, 2007 1:02 PM
> To: antlr-interest at antlr.org
> Subject: [antlr-interest] RewriteEmptyStreamException upon mismatch
> 
> I'm getting a RewriteEmptyStreamException from ANTLR (3.0.1) at
> runtime,
> which appears to be due to a combination of using rewrite rules to
> build the
> AST, and exception handling due to mismatched input.
> 
> I think this must be a bug; does anyone have any ideas for a workaround
> that
> will still allow me to use rewrite rules and handle syntax errors?
> 
> Here's a very simple grammar that demonstrates the problem:
> 
> ===============================
> grammar Test;
> 
> options {
>     output = AST;
> }
> 
> WS: (' '|'\t'|'\r'|'\n')+ { skip(); } ;
> 
> X: 'x' ;
> PLUS: '+' ;
> 
> c: X ;
> b: c -> ^( X c ) ;
> a: b ( PLUS^ b )? ;
> ===============================
> 
> This should accept "x" or "x + x".  If I run TestParser.a() and give it
> just
> "x +", then I get:
> 
>    BR.recoverFromMismatchedToken
>    line 0:-1 mismatched input '<EOF>' expecting X
>    Exception in thread "main" \
>            org.antlr.runtime.tree.RewriteEmptyStreamException: rule c
>         at org.antlr.runtime.tree.RewriteRuleElementStream._next( \
>                                     RewriteRuleElementStream.java:158)
>         at org.antlr.runtime.tree.RewriteRuleElementStream.next( \
>                                     RewriteRuleElementStream.java:145)
>         at TestParser.b(TestParser.java:128)
>         at TestParser.a(TestParser.java:204)
>         at RunTest.main(RunTest.java:10)
> 
> If I change the rewrite rule to other forms, such as "b: c -> ^( c ) ;"
> or
> "b: c -> c ;", I still get the same error.  However, if I remove the
> rewrite
> rule and just leave "b: c ;" - which I think is supposed to actually
> have
> the same effect as the simpler rewrite rules above - then I don't get
> the
> exception... ANTLR just prints the first two lines above, about the
> mismatched input.
> 
> Can anyone confirm that getting the RewriteEmptyStreamException
> indicates a
> bug?  Or tell me what I'm doing wrong?  I really need the generality of
> the
> rewrite rules in my actual grammar, so ideas for workarounds would be
> greatly appreciated.
> 
> Thanks in advance,
> 
> Alan
> 
> -------------------------
> Alan Rooks
> AMI Semiconductor Canada
> http://www.amis.com/
> -------------------------
> AMI Semiconductor - "Silicon Solutions for the Real World"
> NOTICE:
> This electronic message contains information that may be confidential
> or privileged. The information is intended for the use of the
> individual or entity named above. If you are not the intended
> recipient, please be aware that any disclosure, copying, distribution
> or use of the contents of this information is prohibited. If you
> received this electronic message in error, please notify the sender and
> delete the copy you received.
> 
> 
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.488 / Virus Database: 269.14.1/1050 - Release Date:
> 10/4/2007 5:03 PM
> 

No virus found in this outgoing message.
Checked by AVG Free Edition. 
Version: 7.5.488 / Virus Database: 269.14.1/1050 - Release Date: 10/4/2007
5:03 PM
 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.antlr.org/pipermail/antlr-interest/attachments/20071005/263f3b59/attachment.html