[antlr-interest] Java API for checking ambiguity in grammars using ANLTR

[sathya moorthy]

Thanks Stephen
Let me try with your suggestion and let you know.

--Sathya

On Tue, Jun 12, 2012 at 12:45 PM, Stephen Gaito
<stephen at perceptisys.co.uk>wrote:

> Sathay,
>
> An interesting puzzle ;-)
>
> So AntlrWorks detects ambiguous grammars in the analyze method in the
> > org/antlr/works/grammar/antlr/ANTLRGrammarEngineImpl.java
> class. (see:
> >
> https://github.com/antlr/antlrworks/blob/master/src/org/antlr/works/grammar/antlr/ANTLRGrammarEngineImpl.java
>  and search for "analyze" ).
>
> It does this by setting an error listener to catch all errors coming
> from the ANTLR tool's compilation of the grammar. Essentially across the
> following code:
> > Grammar g = getDefaultGrammar();
> > ...
> > List rules = g.checkAllRulesForLeftRecursion();
> > ...
> > if ( g.nfa==null ) {
> >   g.composite.createNFAs();
> > }
> > g.createLookaheadDFAs();
> > if(engine.isCombinedGrammar()) {
> >   // If the grammar is combined, analyze also the lexer
> >   if(lexerGrammar != null) {
> >     lexerGrammar.composite.createNFAs();
> >     lexerGrammar.createLookaheadDFAs();
> >   }
> > }
> AntlrWorks reports the ambiguous grammar messages by looking for the
> following messages/exceptions which have been caught and stored in a
> list by the ErrorListener:
> > private void buildError(Object o) {
> >   if(o instanceof *GrammarUnreachableAltsMessage*)
> >
> > errors.add(buildUnreachableAltsError((GrammarUnreachableAltsMessage)o));
> >   else if(o instanceof *GrammarNonDeterminismMessage*)
> >
> > errors.add(buildNonDeterministicError((GrammarNonDeterminismMessage)o));
> >   else if(o instanceof *NonRegularDecisionMessage*)
> >
> > errors.add(buildNonRegularDecisionError((NonRegularDecisionMessage)o));
> > }
> *SO....*
>
> If you wanted to programatically check for ambiguous grammars, you could
> simulate the code in this ANTLRGrammarEngineImpl class in a try { }
> "block" and catch the above messages.
>
> You could also infer this on the command line by looking at the output
> of the antlr -Xdfa command.... but this is rather harder as there is no
> /*explicit*/ statement that the grammar is ambiguous....
>
> I hope this helps!
>
> Regards,
> Stephen Gaito
>
> On 12/06/12 04:13, sathya moorthy wrote:
> > I want to know whether the grammar is ambiguous by calling some ANTLR API
> > but I want to know is there such API?
> > The purpose is not to generate files from the grammar if it is ambiguous.
> >
> > Antlr generates files even if it is ambiguous(in some cases)
> >
> > On Mon, Jun 11, 2012 at 2:53 PM, Loring Craymer <lgcraymer at yahoo.com>
> wrote:
> >
> >> You want code generated even if the grammar is reported to be ambiguous.
> >>  ANTLR tells you how it handles ambiguity (some alternatives are
> disabled);
> >> if this is not what you want, fix your grammar.
> >>
> >> --Loring
> >>
> >>
> >>   ------------------------------
> >> *From:* sathya moorthy <brsmoorthy at gmail.com>
> >> *To:* antlr-interest at antlr.org
> >> *Sent:* Monday, June 11, 2012 1:54 AM
> >> *Subject:* Re: [antlr-interest] Java API for checking ambiguity in
> >> grammars using ANLTR
> >>
> >> Guys any help would be great
> >> thanks
> >> Sathya
> >>
> >> On Sat, Jun 9, 2012 at 1:40 PM, sathya moorthy <brsmoorthy at gmail.com>
> >> wrote:
> >>
> >>> Hi,
> >>>
> >>> When i use ANTLR IDE, it suggests that the grammar is ambiguous but
> still
> >>> i am able to generate code using that grammar.
> >>> Is there a specific API in ANTLR which will tell whether the grammar is
> >>> ambiguous?
> >>> If the grammar is ambiguous i dont want to generate the code for that
> >>> specific file.
> >>>
> >>> Regards,
> >>> Sathya
> >>>
> >>>
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