[antlr-interest] Rewrite action causing error in parser?

[Jim Idle]

x
@init {Boolean isPresent = false;}
:
  (A { isPresent = true; })? B

	-> {isPresent}? ^(A B)
     -> ^(IMAGINE B)
;

Jim

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Ross Bamford
> Sent: Sunday, October 16, 2011 4:41 PM
> To: Maximilien Colange
> Cc: antlr-interest at antlr.org
> Subject: Re: [antlr-interest] Rewrite action causing error in parser?
>
> Further investigation confirms that this does seem to crop up quite a
> bit, which suggests I'm definitely doing something wrong. I'm just
> hoping that someone might be able to suggest a different way to do what
> I need to do (i.e. insert an imaginary token in place of the optional
> one if it's not specified)?
>
> Thanks,
> Ross
>
>
> On Sun, Oct 16, 2011 at 11:53 PM, Maximilien Colange
> <macolange at gmail.com>wrote:
>
> > It appears that this "bug" is frequently reported.
> > It would be nice if ANTLR raised an error (or a warning) when a token
> > is given a reference in a syntactic predicate.
> >
> > However, I do not know whether it is easy to detect. I already
> > encountered this problem, and it occured in a "hidden" ANTLR-
> generated
> > syntactic predicate. I am afraid the error is difficult to detect in
> > such cases.
> >
> > And just for curiosity, why is not it possible to reference local
> > variables or to assign from token in a syntactic predicate ?
> >
> > --
> > Maximilien
> >
> > Le 10/15/11 11:34 PM, Jim Idle a écrit :
> > > Your problem does not look to be the rewrite rule, but the fact
> that
> > > you are referencing a local variable in a predicate, or have tried
> > > to assign from a token in a predicate.
> > >
> > > Look for something like this
> > >
> > > ((id=IDENTIFIER)=>  id=IDENTIFIER)? ....
> > >
> > >
> > > But regardless, this is the rewrite rule that is the problem as far
> > > as I can see. Try commenting it out for instance.
> > >
> > > Jim
> > >
> > >> -----Original Message-----
> > >> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> > >> bounces at antlr.org] On Behalf Of Ross Bamford
> > >> Sent: Saturday, October 15, 2011 5:40 AM
> > >> To: antlr-interest at antlr.org
> > >> Subject: [antlr-interest] Rewrite action causing error in parser?
> > >>
> > >> Hi all,
> > >>
> > >> I have a grammar I'm currently working on (posted in another
> thread
> > >> the other day), which has the following rule:
> > >>
> > >> meth_call_expr
> > >>    :   (id = IDENTIFIER DOT)? func_call_expr ->  ^(METHOD_CALL {
> > >> ($id==null) ?
> > >> adaptor.create(SELF, "SELF") : adaptor.create(IDENTIFIER,
> > >> $id.getText()) }
> > >> func_call_expr)
> > >>    ;
> > >>
> > >> As you can see, I'm using an action in the rewrite rule to insert
> > >> either the
> > >> (optional) IDENTIFIER, or an imaginary SELF node if IDENTIFIER is
> > >> not specified. The problem I'm having is that this generates a
> > >> parser that won't compile. Specifically, it generates the
> following
> > >> bit of code (edited by hand for brevity and to highlight the
> error):
> > >>
> > >> /* **** [ CODE ] **** */
> > >>      // $ANTLR start synpred6_BasicLang
> > >>      public final void synpred6_BasicLang_fragment() throws
> > >> RecognitionException {
> > >>
> > >>          Token =null; //<-- ERROR HERE
> > >>
> > >>          /* ... later on ... */
> > >>
> > >>          switch (alt23) {
> > >>              case 1 :
> > >>                  //
> > >>
> C:\\Users\\chantelle\\workspace\\basiclang\\src\\com\\roscopeco\\ba
> > >> sicl
> > >> ang\\parser\\BasicLang.g:99:8:
> > >> id= IDENTIFIER DOT
> > >>                  {
> > >>
> > >>
> id=(Token)match(input,IDENTIFIER,FOLLOW_IDENTIFIER_in_synpred6_Basi
> > >> cLan
> > >> g232);
> > >> if (state.failed) return ; //<-- AND HERE
> > >>
> > >>
> > >> match(input,DOT,FOLLOW_DOT_in_synpred6_BasicLang234);
> > >> if
> > >> (state.failed) return ;
> > >>
> > >>                  }
> > >>                  break;
> > >>
> > >>          }
> > >> /* **** [ END ] **** */
> > >>
> > >> Obviously the problem is the "Token =null" line, which should be
> > >> "Token id = null". Changing it by hand fixes the errors and makes
> > >> the parser work as expected.
> > >>
> > >> So I have two questions - is this the right way to go about
> > >> inserting an imaginary token if an optional token isn't in the
> > >> input, and if so, what am I doing wrong to cause the error above?
> > >>
> > >> Thanks in advance,
> > >> Ross
> > >>
> > >> List: http://www.antlr.org/mailman/listinfo/antlr-interest
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