Unfortunately it looks like the authors never completed the next book on the series about real time programming. How to design worlds. http://world.cs.brown.edu/1/
Thanks for pointing this out. I was interested to see they credit Paul Hudak's "Haskell School of Expression" for inspiration. I will have to take a fresh look at that given my newfound appreciation of HTDP (due to stumbling across Norman Ramsey's assessment of it). Also need to look deeper into Hudak's FRP now that I think about it.