INTRODUCTION
There are many ways to provide an introduction to any subject and FORTH is no exception. Skinner and Holland developed a system based on operand behavior. Their techniques have been successfully applied to many subjects.
Another scheme is to develop a careful step by step approach. Take one step at a time and build slowly. Always provide review of material and connection from one step to the next.
Alas, that is not the way we learned to do most things. That is not the way we learned to talk or think. Rather, we were exposed to many different areas of knowledge through experience from our early pre-school days. Bit by bit we took a little here and a little there and added it to our organization of what we already knew.
Learning in this manner is dependent upon the individual, not upon any course design. As we learned our native language we gradually expanded our understanding of the words we knew and added to our vocabulary. It is an active process for the student. There is substitute for that active process.
In this GUIDE, it is assumed that the user has a computer. That he knows how to turn it on. That he knows how to load his operating system. That he knows how to format his disks. That he has some sort of feeling for what the object code is that makes any program run. (It is a file of some sort which can be brought into the memory of his system to make it do certain things.) It is assumed that the user has used his computer for simple word processing.
It is assumed that he has learned, hopefully not from bitter experience, to make backups. He will learn how to use MVP-FORTH to make back up copies of his FORTH SCREENS disks later in this GUIDE.
Further, it is assumed that the user knows the meaning of bits, bytes, and words. It is assumed that user knows what mnemonics means. It is assumed that he has at least a vague understanding of what an assembler and compiler are. In essence, it is assumed that he has at least a beginning level of computer literacy!
It would be a big help if he also knew how to type.
MVP-FORTH includes a working vocabulary of about 140 words, labels for computer functions, with another 100 words which will be rarely if ever used by the programmer. In learning a foreign language, you can make flash cards and learn 10 or 20 new words a day. There should be no problem learning the 140 words. The problem in learning FORTH is that the functions of the FORTH words, labels, are not always what you might expect. The syntax of the FORTH language is completely foreign to many westerners. There is no way to relate FORTH syntax to that of western Indo-European languages.
The only way to learn FORTH is to let the concepts associated with the FORTH become a working part of your programming life.
This leads to a problem with any printed discussion of FORTH. How should you distinguish between the words which could be called ideograms, of the FORTH language and common English words. For example, a "," is a FORTH word. Also spaces are significant in FORTH. Proportional spacing with variable space widths makes recognition difficult. The FORTH words are not always easy to recognize when set in proportional type. Occasionally formatting instructions to the typesetter may include FORTH ideograms. Hopefully, all such occasions have been found and the formatting instructions overridden.
With this as an explanation, you are cautioned to remember that the text is a mixture of two different languages. There is no simple style which solves the problem completely. In some cases the pronounced name of a FORTH word is used within single quotes. The pronounced name is different from the symbols used to make up FORTH ideograms as noted in ALL ABOUT FORTH.
The FORTH GUIDE should ease the way for you to become aquainted with Forth. You are encouraged to use the GUIDE interactively on a system running MVP-FORTH. You would do well to have ALL ABOUT FORTH and to use it as a companion to the FORTH GUIDE. You should also have available the MVP-FORTH SOURCE LISTINGS, which is included on this disk and as Volume 2 of the MVP Forth Series. The information in those two volumes will not be repeated.
ALL ABOUT FORTH includes the 80x86 implementation of all of the words used in MVP-FORTH except the EDITOR and ASSEMBLER vocabularies. With each entry is an example. For ease of reference, all entries are in ASCII order. That does not make for easy reading.
The FORTH GUIDE is just a guide. If you have need of reference to a particular function, you should not be using this GUIDE. Rather, you should refer to ALL ABOUT FORTH. This GUIDE is divided up into sections. A collection of words which function together is discussed in each section. The interactive play among the words and their use is gradually developed.
The use of arithmetic operations is minimized. Most of you will have had an elementary school introduction to numbers. Little more than that limited expertise is needed here. Many FORTH functions require that you tell the system the necessary values before you execute the function. How this is done is really not that important. After you are at home with MVP-FORTH and your system, you can explore the additional arithmetic functions available.
Do not try too much at one time. Reread as necessary. You will probably not understand everything the first time through. You do not need to understand all parts referred to in this GUIDE to become moderately proficient with FORTH.
An elementary principle of all programming is: KEEP IT SIMPLE, STUPID. ( KISS )
Finally, this GUIDE will not tell you what applications you want to program. If you have nothing to program, you have no business learning any programming language. If you have nothing to say you have no business saying anything.