[antlr-interest] OPEN, EOF ambiguity

[Cameron Ross]

Hi Cliff,

What you've suggested is how I have the production version of the grammar
implemented now.  However, the language spec that I must conform to
specifically states that a text can have zero or more phrases (which is the
crux of the problem).  I can leave my implementation the way it is and try
to have the spec changed, but it would be a heck of a lot easier to just
implement to the current spec.

Thanks for the help,
Cameron.

On Thu, Apr 8, 2010 at 8:49 PM, Cliff Hudson <cliff.s.hudson at gmail.com>wrote:

> 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:
>> > http://www.antlr.org/mailman/options/antlr-interest/your-email-address
>> >
>> >
>> >
>> >
>> > --
>> > Kojeware Corporation
>> >
>> >
>> >
>> >
>> > List: http://www.antlr.org/mailman/listinfo/antlr-interest
>> > Unsubscribe:
>> > http://www.antlr.org/mailman/options/antlr-interest/your-email-address
>> >
>>
>>
>>
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>>
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>
>


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