The short answer is, nobody was using it, so it's gone.
The code is still around, but nobody has tried to get it to run with
1.2. A while ago I expressed an interest in something of the sort, but
nobody jumped. IIRC, the code is primarily (entirely?) Scheme, so it
should be quite straightforward to convert. If you do so, please post
it in contrib, as I would definitely use it! I find Scheme is good for
scripting but awkward for interactive use, so something like CTAX
would be very nice. There are also, as you say, numerous applications
for it in parsing.
So let us know what you decide to do...
Andrew
aarchiba@undergrad.math.uwaterloo.ca