I don’t know how I missed the @headius tweet about jruby on the Raspberry-Pi, but it seems it should soon be possible to run jruby apps on the Raspberry-Pi. If that is is the case it might worth creating a custom version of propane to run on the Raspberry-Pi (with OPENGL/JOGL binaries for arm). Or alternatively a stripped down version, without OPENGL. In the tweet @headius was using the jirb console, if that is what floats your boat the advantage of propane over other ruby-processing implementations it is easy to load and run propane sketches from irb/pry, or if you have the patience from irb input. I expect you you want in install the raspbian image on the PI and create symbolic links to jruby, java using update-alternatives.
So @headius thinks it should work worth a fork, wait for progress (PS: I haven’t got a PI yet, but that should not matter I’ve never had a Mac either and that seems to work). Here is direct link to download the experimental propane gem might require the soon to be released jruby-18.104.22.168.
For regular coding on raspberry-pi I guess you might use geany? Unfortunately atom is not yet available, I would probably stick to vim given a choice.