Ruby interpreter in Eclipse?

I am interested in working in eclipse to use and extend to some of its
projects. However, I would really like to use Ruby (or jRuby) to poke around
interactively within eclipse (i.e. programatically browse around the java
objects, test out snippets of code, etc.) and to develop my extensions.

Is this doable? What's the best way? I am not an Eclipse expert.