[antlr-interest] Re: Antlr grammar to parse Java classfile?

Andreas Rueckert a_rueckert at gmx.net
Wed Dec 5 00:11:55 PST 2001


On Mit, 05 Dez 2001 J. Stephen Riley Silber wrote:

> > I know that predicates are one of the features ANTLR has. I think 
> this could
> > be the only salvation...
> Symantic predicates would indeed handle the "match n-times" problem.

Antlr turns every rule into a method, right? And you could call such a method
in a production? Why not do something like

// Parse the method block in the classfile
{ int mCount = 0; }
	:  mCount = methodCount
	     { for( int i=0; i < mCount; i++) { method(); } }

// Parse one method in the classfile
            : ....
, where methodCount returns the number of methods in the classfile and
the method rule parses a method in the classfile. Then construct a nice AST, so
the tree grammar could be really clean.

> The thing is, and sorry Terry--nothing personal, I just don't think 
> ANTLR is really the right tool for this kind of thing.

I agree, that the 'call the method rule n times' option is missing somehow. It
would make the creation of binary parsers somewhat easier.
> Building the .class file parser in any language with decent byte and 
> bit analysis constructs is gonna be easy--tedious, definitely, but 
> pretty easy.
> The real advantage of building a parser in ANTLR is when you have to 
> *change* the parser.  And in this case, for something so binary, I 
> think changing the ANTLR parser vs. changing a C parser (for example) 
> would end up being a wash.

Well, data abstraction also has the advantage of being more readable, than a
coded parser. And if you have all basic types, like u2, u4 etc. defined, you
could basically retype the classfile definition from the JVM specs to write the

	: magic_number
> Of course, I might be way off base here.  :-)
> In any event, I still think ANTLR is the best thing going in the 
> parser-generator world, by far!

I agree. And I've used lex,yacc,JavaCC etc.



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