Geere Ron. Forth: The Next Step

Addison-Wesley, 1986. — 100 p. — ISBN: 0-201-18050-2.Most computer languages appear to have a field of use for which they are most appropriate. Forth is no exception and has become the standard
language of the International Astronomical Union and is used for the control of radio telescopes. Forth naturally finds its way into other control applications such as process control, machine tool control and robotics. In addition it has been used in diverse applications such as video games, spreadsheets and the space shuttle aft flight deck simulator. A major advantage of Forth is that it can be tailored to the application, rather than the converse. In essence, Forth provides us with the tools to do the job.
Like the English language, Forth is extensible. What is meant by that?
Suppose by way of example we invent a completely new item, we will therefore need to call it something, say a 'whatsit'. We can now define what we mean by a 'whatsit' in terms of other words that we already know. To find the meaning of these other existing words we can look them up in a dictionary, although this presupposes that we already know a minimal number of words.
In principle this is what we do in Forth. There are many books on Forth which go to great pains to explain the minimum required word set and give a few examples of their use. However when it comes to progressing beyond this stage it depends very much on one's own ability. At this point if the programmer does not take to Forth naturally, as can happen when weaned on a more conventional procedural language, it is tempting to say, ' H m m , very interesting' and then go back to one's familiar language. After all, compared with a level-2 BASIC, Forth lacks the comfortable line numbers, floating point arithmetic, trigonometric functions, strings and arrays. But Forth is extensible. If the user finds it necessary the required
features may be added in a form most suited to the application. In this book some c o m m o n extensions are presented, together with some
programs that have been f o u n d either useful or entertaining. It is hoped that in so doing the methods will stimulate readers to see solutions to their own programming problems. T h e extensions are commonplace and may be standard in some Forths but lacking in others. Inevitably when seeking a missing definition in a hurry, one never seems able to find it readily when it is most needed. Hopefully the collection in this book will fulfil that need. One of Forth's many virtues is that it is far more portable than languages such as BASIC, the latter having over 100 differing dialects. This portability is achieved by first defining a virtual Forth computer for a given machine.