I have done a lot of work on performance, and refined the design. The
big news is that you can now directly implement a protocol inside a
deftype, and you can also reify protocols. This cements protocols as
the superior way to model the things for which they are suitable,
since they can match the performance of interfaces without their
limitations.

In addition, defprotocol automatically generates a corresponding
interface, which can be used to reach the protocol from Java with the
highest performance. This same interface is used internally by the
deftype and reify support described above.

Small changes include:

 - No more use of . in reify/deftype method names
 - No more implicit this in reify/deftype
 - Protocols are supported directly, where interfaces are, in reify
and deftype (and my be intermingled).

I've striven to make these features consistent, flexible, and high
performance, with good support for dynamic interactive development. If
you have the time and inclination, please try them out.

Feedback is particularly welcome as they are being finalized.

Thanks,
Rich

[1] http://www.assembla.com/wiki/show/clojure/Datatypes
[2] http://www.assembla.com/wiki/show/clojure/Protocols
[3] http://github.com/richhickey/clojure/tree/new
[4] http://build.clojure.org/