Thanks everyone for some great talks this evening.
The draft book that I referred to is "Programming a Problem-Oriented Language" by Charles "Chuck" Moore (
http://www.colorforth.com/POL.htm ) - some of it is a bit dated, or very specific to his particular language design, but all in all a very interesting document.
As I mentioned, anyone interested in Raspberry Pi might want to come along to a "Raspberry Jam" in Norwich on Sat 9 March ( see
http://norwichrpi.org/ ) I have never been to this meetup, so I don't really know what sort of things go on, but I'm planning to give it a try anyway.
I found out about it in the latest issue of "The Mag Pi" - a free PDF magazine for Raspberry Pi enthusuasts (
http://www.themagpi.com/ )
Frank.