Doing a bit more digging has solved the problem - I don't think this
is necessarily a problem with merb.

Installing the ruby2ruby gem did not install the ParseTree gem as well
- although there seems to be a ParseTree class included with ruby2ruby
as well (Not sure as I haven't looked at ruby2ruby)?

The problem was that calling ParseTree.translate in
Merb::Server#load_action_arguments --> core_ext/get_args.rb just died
with no exceptions

Not sure how to fix this problem sort of problem for everyone: the
ParseTree constant _did_ exist, just presumably not the right one.

Thanks anyway - I would have jumped on IRC if I hadn't got any further
with this today...

Cheers,
Roland