[antlr-interest] OPEN, EOF ambiguity

[Cliff Hudson]

I think you might just have to pop up one level to think about how to
express this - no magic needed.  The way that grammar is written, your file
is composed of one or more cltexts, which themselves may be composed either
of a module or any number of phrases (including none at all).  It seems to
me this can be re-specified to say that your file may be composed of any
combination of modules and texts, but may also be empty.  The empty file
condition should *not* be specified by the closure on phrase but rather as a
top-level rule.  For example:

start_rule
  : clif_file
  |
  ;

clif_file:
  cltext+ ;

cltext
  : module
  | text
  ;

text:
  phrase+;

This ensures that each cltext will produce at least something, and no
production from that rule will lead to the EOF condition so there will be no
confusion by ANTLR.

NOTE: I don't have ANTLR handy to test this...

On Thu, Apr 8, 2010 at 1:11 PM, Cameron Ross <cross at kojeware.com> wrote:

> Yes, this is the way I have it implemented in my production version.
>  However, I have to conform to a language specification which allows text
> to
> have zero or more phrases.  Is there some ANLTR magic that I can use to
> support this?
>
>
> On Thu, Apr 8, 2010 at 4:07 PM, Jim Idle <jimi at temporal-wave.com> wrote:
>
> > Your text rule can be empty, you need to rejig your use of + and * or you
> > end up with the empty match in more than one place.
> >
> >
> >
> > Jim
> >
> >
> >
> > From: Cameron Ross [mailto:cross at kojeware.com]
> > Sent: Thursday, April 08, 2010 1:05 PM
> > To: Jim Idle
> > Subject: Re: [antlr-interest] OPEN, EOF ambiguity
> >
> >
> >
> > These rules give the gist of it...
> >
> >
> >
> > start_rule
> >
> >          : clif_file EOF
> >
> >          ;
> >
> >
> >
> > clif_file
> >
> >          : cltext+
> >
> >          ;
> >
> >
> >
> > cltext
> >
> >          : (OPEN CL_MODULE) => module -> ^(CLTEXT module)
> >
> >          | text -> ^(CLTEXT text)
> >
> >          ;
> >
> >
> >
> > module
> >
> >          : OPEN CL_MODULE interpretablename exclusion_set? cltext CLOSE
> ->
> > ^(MODULE ^(MODULE_IDENTIFIER interpretablename) exclusion_set? cltext)
> >
> >          ;
> >
> >
> >
> > text
> >
> >          : phrase* -> ^(TEXT phrase*)
> >
> >          ;
> >
> > ...
> >
> >
> >
> >
> >
> >
> >
> > On Thu, Apr 8, 2010 at 3:57 PM, Jim Idle <jimi at temporal-wave.com> wrote:
> >
> > You probably need to send the grammar rather than that graphic. It is
> > likely something more fundamental and we cannot see what you predicates
> are
> > doing from the graphic.
> >
> > Jim
> >
> >
> > > -----Original Message-----
> > > From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> > > bounces at antlr.org] On Behalf Of Cameron Ross
> > > Sent: Thursday, April 08, 2010 12:34 PM
> > > To: antlr-interest at antlr.org
> > > Subject: [antlr-interest] OPEN, EOF ambiguity
> > >
> > > Hi,
> > >
> > > I have a grammar with an ambiguity that I just can't resolve.  When I
> > > check the grammar using AntlrWorks I get the following: "Decision can
> > > match input such as "{EOF, OPEN}" using multiple alternatives: 1, 2".
> > > I've attached a screen grab of the syntax diagram generated by
> > > AntrlWorks.  I don't understand why ANLTR is thinking that EOF is
> > > ambiguous with OPEN.  I've checked the grammar and clif_file is the
> > > only rule that is not referenced from within the grammar, so I don't
> > > think that ANLTR should see module as a start rule.  Any help is much
> > > appreciated.
> > >
> > > Cameron
> >
> >
> >
> >
> >
> > List: http://www.antlr.org/mailman/listinfo/antlr-interest
> > Unsubscribe:
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> >
> >
> >
> >
> > --
> > Kojeware Corporation
> >
> >
> >
> >
> > List: http://www.antlr.org/mailman/listinfo/antlr-interest
> > Unsubscribe:
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> >
>
>
>
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