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

[Ross Bamford]

Works like a charm! Thanks Jim :)


On Tue, Oct 18, 2011 at 12:27 AM, Jim Idle <jimi at temporal-wave.com> wrote:

> 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
> > > >>
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