This is the final release version . It is free from the above link. Otherwise the tools may not appear properly. I don't have a solution to problem 6.14. If you do, I'd like to see it.
Recursion is limited of course.
At this time the depth of recursion is limited to 2k calls to avoid overrunning the system stack. We might be able to increase this a bit. If it is a problem, let me know. Tail recursion is now mapped to looping so there should be no limit on the amount of tail recursion you can do. There is now a window showing all robots in the world.