[antlr-interest] ANTLR Optional statements

[jg z]

The generated code is like this,

		switch ( LA(1)) {
		case ID:
		{
			match(ID);
			{
			switch ( LA(1)) {
			case COLON:
			{
				base_clause();
				break;
			}
			case ANTLR_USE_NAMESPACE(antlr)Token::EOF_TYPE:
			{
				break;
			}
			default:
			{
				throw
ANTLR_USE_NAMESPACE(antlr)NoViableAltException(LT(1),
getFilename());
			}
			}
			}
			break;
		}
		case ANTLR_USE_NAMESPACE(antlr)Token::EOF_TYPE:
		{
			break;
		}
		default:
		{
			throw
ANTLR_USE_NAMESPACE(antlr)NoViableAltException(LT(1),
getFilename());
		}
		}

The problem is, if there is no "ID", it would go into
default and throw an Exception.  It shouldn't do like
this as an optional statement, should it?   
--- mzukowski at bco.com wrote:
> What does it produce that's not right?
> 
> > -----Original Message-----
> > From: jg z [mailto:zjg1964 at yahoo.com]
> > Sent: Friday, April 05, 2002 6:44 AM
> > To: antlr-interest at yahoogroups.com
> > Subject: [antlr-interest] ANTLR Optional
> statements
> > 
> > 
> > We are trying to convert a C++ Parser from PCCTS
> to
> > ANTLR, and becoming increasingly frustrated by the
> > differences between the two systems.
> > 
> > For instance;
> > 
> > In cplusplus.g we have,
> > 
> > class_head
> >    :  (  STRUCT  
> >       |  UNION 
> >       |  CLASS 
> >       )
> >       {ID { base_clause } }
> >    ;
> > 
> > which works fine in PCCTS.
> > 
> > For ANTLR we have converted this to,
> > 
> > class_head
> >    :	
> >     (  STRUCT  
> >     |  UNION 
> >     |  CLASS 
> >     )
> >     (ID ( base_clause)? )?
> >    ;
> > 
> > However, the optional statements shown at the end
> of
> > this production no longer produces a properly
> optional
> > construction in the generated .cpp file.
> > 
> > What are we supposed to do?
> > 
> > David.
> > 
> > 
> > __________________________________________________
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