Remember that your tree parser rule for the body should be:
method_body
: ^(METHOD_BODY statement_list)
| METHOD_BODY // Empty body
;
Jim
> -----Original Message-----
> From: [email protected] [mailto:antlr-interest-
> [email protected]] On Behalf Of Christian
> Sent: Thursday, November 03, 2011 2:37 PM
> To: [email protected]
> Subject: Re: [antlr-interest] Check if rule returns empty result
>
> Thank you for your explanation. And your solution works great, too.
>
> Christian
>
> Am 03.11.2011 21:31, schrieb Jim Idle:
> > You don't want that anyway as your nodes will not have token start
> and
> > stop information and you might need that.
> >
> > method_declaration
> > : method_header method_body
> > ;
> >
> > method_body
> > : (
> > ';'!
> > | '{'! statement_list? '}'!
> > )
> > -> ^(METHOD_BODY statement_list?)
> > ;
> >
> > method_header
> > : attributes ID etc
> >
> > ->^(METHOD_HEADER attributes ID )
> > ;
> >
> >
> > Jim
> >
> >> -----Original Message-----
> >> From: [email protected] [mailto:antlr-interest-
> >> [email protected]] On Behalf Of Christian
> >> Sent: Thursday, November 03, 2011 1:01 PM
> >> To: [email protected]
> >> Subject: [antlr-interest] Check if rule returns empty result
> >>
> >> Hi at all,
> >>
> >> I have the following rules:
> >>
> >> method_declaration
> >> : method_header method_body -> ^(METHOD_HEADER method_header)
> >> ^(METHOD_BODY method_body)
> >> ;
> >>
> >> method_body:
> >> ';'!
> >> | '{'! statement_list? '}'!;
> >> ;
> >>
> >> Of course, method_body is executed because it has no question mark.
> >> However, introducing rewrite rules and operators cause a problem. By
> >> using ^(METHOD_BODY method_body), method_body must return a non-
> empty
> >> value. However, statement_list? is optional and thus may not match
> at
> >> all. In this case, method_body returns nothing anymore and I get an
> >> RewriteEmpty exception.
> >>
> >> How can I solve this problem by only changing rewrite rules?
> >>
> >> Regards,
> >> Christian
> >>
> >> List: http://www.antlr.org/mailman/listinfo/antlr-interest
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