is very dated, but still a great book. It does, as I remember, address FIG Forth, Forth 79, and Forth 83. Of course most of it is the same for the three.
There are indeed many Forths. The old joke says that if you've seen one Forth, well, you've seen one Forth. That's not to say there are loads of scarcely related dialects. Once you're in the door, it should take very little effort to move to a new one you haven't worked with yet. For the most part though, you'll probably settle down with one that runs on your hardware, mold it to your liking, keep extending it a lot, and use it a lot.
I wish I could tell you my '02 Forth is ready for distribution. It's a Forth '83 implementation that came with a DOS-based metacompiler we bought 15 years ago. Although the Forth source mostly came from the public-domain FIG-Forth and I augmented and modified it extensively, there are still a few parts that could get me in trouble with copyrights if I distributed it without re-writing those parts. That metacompiler is no longer available, and it had some very serious bugs too. I use Forth regularly on my workbench computer, but any new re-compiles of the kernel itself in EPROM are going to have to come from converting the source code to an assembly source so I can break free of this PC metacompiler whose limits I have exceeded. If I could put the time into it, I would like to get a complete 6502 Forth going that would be a turnkey solution, so the beginner would not be faced with the backwards situation of having to learn the innards before he can make anything at all work.
Since the book does cover FIG-Forth and the source code is on this website, that might be a good place to start. It may not be ideal, but you can go a long, long way with it. Don't be afraid to keep coming back and asking questions.
Oh, and one other thing: Replace the FIG-Forth U* code which has a bug in it with the code at http://www.6502.org/forum/viewtopic.php?t=689
, and replace the FIG-Forth U/ which also has a bug in it with the code at http://www.6502.org/source/integers/umm ... modfix.htm
. I think there was a bug in FIG-Forth's > also. I'll have to look.