[wishlist] Extensible grammars

[Keunwoo Lee <klee@cs.washington.edu>]

I'd like to have extensible grammars, in the style of Polyglot's PPG
extension to CUP:

http://www.cs.cornell.edu/Projects/polyglot/ppg.html

The relevant features are "include", "drop", "override", "extend", and
"transfer".

I'm currently evaluating several tools for use in a Java extension, and
the ability to extend a large existing grammar by writing a delta rather
than editing the original grammar file would be handy.  I like SableCC
much better than CUP, but SableCC doesn't have this feature.  It seems
that it would be a simple addition.

Thanks,

~k.lee