[plt-scheme] tree regular expression matcher availability?

Howdy, all.

I'm trying to use match for processing some data structures with 
optional elements, nested sublists (some of which have additional nested 
sublists in turn), and am finding it somewhat unwieldy -- handling cases 
where zero-or-one matches are allowed, for instance, seems surprisingly 
complex.

The trx module described at 
http://repository.readscheme.org/ftp/papers/sw2004/bagrak.pdf looks like 
just the thing (and the examples given therein have more than a little 
in common with my actual, real-world use case) -- but unless my 
google-fu is weak, it appears not to be actually available.

Does an equivalent module exist for PLT scheme?