[antlr-interest] Can I target C and Java from one grammar file?

[Jim Idle]

Andy Grove wrote:
> Hi,
>
> I need to generate C and Java from an ANTLR grammar containing  
> actions. Is there a preprocessor approach I can use rather than  
> maintaining two versions of the grammar?
>   
I use perforce and maintain a base grammar that has no actions, then 
change only the grammar base. When ready to test I integrate the changes 
via a prestored branch spec. Other SCCS can do the same sort of thing, 
though perforce is streets ahead of anything else at the merge process.

However, occasionally it is a pain to debug remotely when I want to just 
use the ANTLR works debugger before integrating a change, so I have 
written a pre-processor as an experiment (it is in ANTLR3 of course), 
and am trying to decide between the C# lexer base approach and the VB/C 
approach (albeit not having the stupidity of the VB pre-processor.)

I was then going to propose it to Ter as an addon for the next release 
(as it is non invasive if you don't use any pre-processing instructions.

Then you can have:

options
{
   #if TARGET="C"
       language = C;
   #else
       language = Java;
   #endif
}

Or perhaps

  language  =  TARGET_LANG;

and, referencing a prior thread:

#ifdef ANTLR_VER_MAJOR > 3 || ANTLR_VER_MINOR < 2
#abort "This grammar requires ANTLR 3.1.2 and above"
#endif

If I am willing to do the C macro thing. In general though, if you add 
macros, people start embedding code in them and the whole thing is 
macros, so I prefer the minimalist approach of C#.

As far as code generation goes, and maybe this would solve 
preprocessing, I think it would be good to be able to supply a string 
template for action code generation (rather than for the parser to use 
at runtime). So you would have:

language = template;

r1 : %r1predicate(x)%?=>   a=INT bINT c=INT 

For now though, m4 is your best bet (it is in the Java compiler even), 
or perhaps something simple with gawk.

Jim
> I'm thinking that the grammar would look something like this:
>
> selectStatement[int initRule]
> //IFDEF JAVA
> @init 	{if(initRule) sse.pushCall(sse.SELECTSTAT);}
> //ELIFDEF CPP
> @init 	{if(initRule) sse->pushCall(sse.SELECTSTAT);}
> //END
> 	:
> 	q = queryExpression[true]
> 	;
>
> Are there tools out there already or do I need to roll my own?
>
> Thanks,
>
> Andy Grove
> Chief Architect
> CodeFutures Corporation
>
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