extensible grammars

Extensible grammars are really hot right now.  The "Right Way" to do
this is MacroML; it gives you "macros with types" so you can do
typechecking on your program and then be assured that you can change
the macro without breaking your program as long as the macro's type
doesn't change.

  http://www.cs.indiana.edu/hyplan/sabry/papers/macroml.ps

It looks like somebody's taken a stab at bringing this to Java.  It's
not as elegant as MacroML, but it might do.  It'd sure be better than
Preprocessor.java...

  http://www.ai.mit.edu/~jrb/jse/jse.pdf

-- 
"It's lucky," he added, after a pause, "that there are such a lot of
islands in the world.  I almost envy you, Mr. Watson."

                                                   -- Mustapha Mond