Dear Klaus,
Thank you for pointing me in the right direction. It proved fairly 
straight forward to open for programming with dynamic roles by hacking 
the Parser/Encoder. I also added some other extensions to make the roles 
visible in the debugger and to show them with the right value.

I used this extension as the foundation for a demo and talk at the ETH, 
Zürich, Switzerland. The complete program can be loaded from two packages:
       http://folk.uio.no/trygver/babymc/BabyPragmaroles-TRee.2.mcz
              that shows what I have done to the Parser etc.
       http://folk.uio.no/trygver/babymc/BabyETH-TRee.11.mcz
              that contains the demo itself and illustrates my first 
excursion into programming with roles.
If anybody should want to load these packages, BabyPragmaroles must be 
loaded first, otherwise the BabyETH methods will not be properly compiled.

But loading is not necessary because a fully loaded image is stored in 
the following zip file that contains image and changes files (note: 
Squeak 3.10.6 which is Squeak3.10.gamma.7159):
       http://folk.uio.no/trygver/2007/BabyETHImage.ZIP

I post this to the squeak-dev list in case anybody would like to see a 
snapshot of what I'm up to these days.
I've added a lot of comments that may explain more than they confuse.

My next steps: Larger examples and badly needed programming tools.

Enjoy
-- Trygve

-- 

Trygve Reenskaug      mailto: trygver at ifi.uio.no
Morgedalsvn. 5A       http://folk.uio.no/trygver
N-0378 Oslo           Tel: (+47) 22 49 57 27
Norway