Re: Java Comment-Preserving Grammar

On 2004-05-24, Matthew Herrmann <matthew-google@faredge.com.au> wrote:
>
> Is there an available Java grammar which preserves comments in an output
> AST tree? I know there are plenty of java grammars out there, but all
> ignore comments. I'm happy to use any tool providing I can gain access to
> the comments in the tree.


The most straightforward way is to take a grammar and add the comment
annotation in the lexer as someone else suggested in this thread. We
are using such a technique on a language translator which is not only
attempting to preserve comments but also preprocessor constructs. Due
to time constraints we are using Parse::Yapp from the Perl CPAN site.
This is a pretty faithful re-implementation of yacc in Perl.


We use special fields in a token to flag whether or not a comment or
pre-processor construct is tied to this token, and the 'pre' tokens
should be handled first and 'post' operations should be handled
following. For comments, you don't really need 'post' field support
except when handling comments at the end of file condition:


....


a = b;


/* comment here */


In this example, 'comment here' would have to be a 'post' on the ';' token.
You could argue that EOF comments should be dropped in your case anyway.


If you have any more questions, please feel free to conact me.


-Clint

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