(This file was downloaded from CompuServe. Most of the files mentioned at the end of this are available here on GEnie as well. If you can't find one leave a note for the sysop.) -scott INTRO.4TH 12-Oct-88 19328 51 Keywords: PD FREE OS REFERENCE FORTH 4TH Overview of the most powerful programming language there is. By Giles INTRO.4TH (ADVANTAGES OF FORTH) Preface: The purpose of this file is not just to tell u "Forth is Great", but rather to clarify just what advantages Forth has over other languages, and to communicate th "feel" of Forth in relation to programming tasks. I hope it does that job well enough to give u a sense of th possibilities, so that, when u pursue ur desire to see for urself what u can accomplish w/ it, u will be expecting to create elegance. And if u are intent, u will be gratified. Please read this w/o bias, and if u doubt any statements made, th author is prepared to provide proof or acceptable evidence, or upload a corrected version of this file. If, on th other hand, u are not willing to find out that there is a programming language considerably more capable & elegant than what u r familiar with, then better to not even give it a single quick scan! (grin) Giles Topic Headings Abreviation Definitions Commands That Fit Programming Environment Personal Experience What is Forth? Different Installations Examples Small Concept= Large Capability Grand Scale Programming Use My plans Your application Availability on CIS Learning Forth Social Aspects Problems Abreviation Definitions #, Number &, And cmd, Command hdw, Hardware r, Are sfw, software th, The u, You u're, You're ur, Your u've, You've w/, With w/o, Without 4th, Forth Commands That Fit Have u ever wished: 1. A particular command went about things just a little differently? 2. A particular command behaved consistantly, rather than doing th wrong thing at just th wrong time? 3. U had a particular command, that would make things SOOooooo simple? In Forth, th process of finding th code of a command & installing a rewritten version is trivial. Programming Environment Have u ever felt that programming would always be a pleasant experience, if only U never had to program around bad system sfw? Have u ever wished: 1. U could program twice as fast? ..Five times as fast? ..TEN times as fast?! And that u could debug th program as u write it, so that (generally) when u finished writing a module u wouldn't have to come back to it? 2. That all th clever little subroutines u've worked out were instantly available, w/o having to look for them, or take any special pains to integrate them into th present program. 3. That calling a subroutine required nothing more than naming it? 4. That someway ur programming environment would help u keep track of where u r, & how th routine u r working on now will affect other routines, or which ones will be affected? 5. That u could change th way ur compiler behaves? Or that u could add th ability to handle special cases w/o changing anything else? 6. That u could use hi-level commands, & a magic genie would come along & convert them to efficient machine code? Or maybe just th ones needing speed, & leaving th others in th most compact form to save memory? 7. That u never had to worry about linking library routines, or that ONE copy of routines would suffice for ALL processes? 8. That u could have a multitasking, multiuser operating system w/ all th features of, say for instance, OS9, but ALSO have th immediate utility of a powerful toolbox & programming language combined? 9. That u could bring th same, familiar environment & applications from obsolete hdw. to new hdw. w/ expanded capabilites, & easily add features to take advantage of th new hdw w/o having to change much if any of what u already have? Examples: Transfer ur system & applications to a Tandy Color Computer in order to have graphix that beat some MS-DOS & Macintosh machines at a fraction of th price. Or to an IBM styled machine, in order to take advantage of all th hdw options available, yet having an EFFECTIVE multasker, instead of being stuck w/ OS2. 10. That u had a powerful environment on which u could write a similar environment, (but with all ur own improvements, of course), and compile th new environment & have a system of ur very own, w/ no royalties owed to anyone? (Perhaps for ur own system to be manufactured & sold.) 11. To have th ability to implement other languages, such as BASIC, LISP, Pascal, Prolog simply & efficiently? In Forth, u can move about freely. There is no "black box" compiler to shackle u w/ unnecessary restraints. No restriction to predefined data structures. U cannot get lost in GOTOs or jumps because 4th neither has nor needs them. Forth assumes u know what u r doing, & often how u do it is implicit. Personal Experience Before I knew of the existance of Forth I knew I would have to have a language that was infinitely extensible, and selfcompiling to do the things I wanted to do. When I learned what Forth was, it was like manna from heaven. With systems such as OS9 having some of th advantages of Forth, & excellent file handling, and w/ the availability of a powerful text editor such as TSEdit, a person has a very effective system for gathering textual data piecemeal & editing it. But in using such a system, I have had to program around deficiencies of other languages, been so hampered in reaching the hdw. functions of the machine, that some applications that should have been done were not practical to tackle, (because of time restraints) and as a result been forced to use sfw for which we haven't the source. And so have been unable to adapt it exactly to our needs, or add enhancements and upgrades that we should have had. So, I am FORCED to incorporate the advantages of OS9 into Forth, as I can no longer do without 4th's other, inherent advantages. What is Forth? Forth is an infinitely extensible metacompilable language/op system in which subroutining is inherent. (Metacompilable is a Forth term meaning it can compile new versions of itself from source) The stack's use is direct and largely automatic, and you can directly manipulate it. Tho most implementations are sparse from an applications viewpoint, (tho I know of none that do not include an editor & assembler), it is so trivial to extend it, that you can relatively easily write a LISP or BASIC interpreter, C compiler, or a Prolog extension. (I have seen most of these in sigs or elsewhere.) Since Forth is so compact, (it compiles to only subroutine addresses), and so fast, (tho slower than Machine Lang. to do exactly the same operations, practically it's often faster, because of the better organization of the functional blocks), and it can duplicate the power of any existing language, as well as any you dream up that are MORE powerful, it's hard to deny that Forth can be the MOST powerful language there is. As a practical matter, complete control is in the programmer's hands, so the extensions will be just as bad as the programmer forces them to be! (grin) On the other hand, you don't have to say "stupid compiler writer! Why didn't he do it THIS way?!". You can just recompile the whole system to suit yourself! Good idea to, because that way, it is your own system. to sell as an application, developmment system, arcade game, or whatever, with no royalties owed to anyone, and as a complete standalone system. Different Installations It is also easily transportable. You can redefine the primitives for the new cpu, and recompile it, with all the resources of the present system at hand. And because of th small # of necessary primitives, & of th extreme modularity & interactive method of programming this allows, u will not believe how easy such a port is until u see it! Examples You may know that the RSdos BASIC PALETTE cmd (for th Coco) takes a slot number (0-15) and puts a color value (0-63) into it. The zero slot's hdw address is 65456. So I defined a PALETTE cmd in Forth thusly: : PAL -80 + C! ; : is a word called Colon, and is the most commonly used compiler. It enters the following word, (a word is a group of non-space characters bounded by spaces, in this case PAL), into the dictionary, and compiles the addresses of the following words, (which normally must have already been defined), into the dictionary as it's definition. -80 is the signed 16 bit integer equivalent of 65456. Mention of a number puts it on the stack. + takes the 2 top stack entries and adds them, leaving the result on top of the stack. ! is pronounced "store". It takes the second stack item and stores it in the address on top of the stack. But it stores SIXTEEN bit values. In this case we only want to store 1 byte, so we use Cstore, C being for "character". Of course C! is a different word from !. ; terminates all definitions started with :. So now instead of PALETTE8,38 as I would use in basic, I can do 38 8 PAL. 38 pushes 38 on the stack. 8 pushes on the 8. PAL first takes the top item and adds it and 65456 to give the address of slot 8, then stores 38 (second stack item) into one byte at that address. And all of a sudden, your text is orange.(grin) To make this cmd "system independent", you could first define a constant, SL0T, thusly: 65456 CONSTANT SL0T (Constant is a compiling word that compiles...You got it, Constants! (grin) Then define PAL thusly: : PAL SL0T + C! ; That way, only SL0T would have to be changed for another system. All system dependent values could be stored in a single place, and so be easy to set up for a different system. Here's an edited example of th procedure for installing a rewritten primitive, as explained by my friend Bob McIsaac: -------------- ' <EMIT> DUMP ..display code being used. You can figure a new version then install the hex code using: CREATE EMIT NNNN , NNNN , NNNN , NEXT SMUDGE If it works then install it:- ' EMIT ' <EMIT> CFA ! FREEZE This works because the code field addrs of a word always points to executable code and this can be anywhere in memory. --------------- In this example: A dictionary header is made up like this: Up to th 1st 31 bytes are th name field. Next 2 bytes are th LINK FIELD, which points to th previously defined word. Next 2 bytes r th CODE FIELD, & point to executable code. (Th following parameter field, if th word is a primitive.) The remaining bytes r th PARAMETER FIELD, which may contain executable code, addresses for other words, variable storage, constant storage, tables, or what have u. ' (pronounced "tick") puts th PFA (Parameter Field Address) of th word following it, on th stack. DUMP gives a hex dump starting at th address on th stack. CREATE creates a dictionary header for th word following it, in which th 1st character is altered (smudged, by flipping a bit) so that it can't be found, (while it is being defined). , (Comma) Inserts th 16 bit value on top th stack at th current end of th dictionary, & bumps th dictionary pointer 16 bits, (to th NEW end of dictionary). NEXT puts code in place for a "return" for th virtual Forth machine. SMUDGE flips th flipped bit in th altered letter of th keyword, so that actually, in this case, it's working more like an "unsmudge". (grin) CFA takes a PFA & converts it to a CFA (Code Field Address). In this case, th PFA of <EMIT> is converted to its CFA ! Takes th second stack item (in this case, th PFA of EMIT) & stores it in 16 bits at th address on top of th stack, (in this case, th CFA of <EMIT>). FREEZE sets th system so that it permanently recognizes this installation. Small Concept= Large Capability Just a few additional concepts give u a great deal of added power. Understanding "Compile time" & "Run time" behaviors of words, and "Compiling" words, allows u to do things in th most direct way possible. And th "Reverse Polish Notation" use of th stack allows elimination of all other local variables. I find Forth the easiest language in which to conceptualize a task. Many procedures that would not be trivial in any OTHER design of language, can b programed in Forth out of hand. Each part of the problem can always be programmed seperately, as a preliminary word to the final word that does the whole job. Also you can start out with a word that just handles limited conditions, and keep adding new functions to it as you elaborate on the problem. If you choose word names carefully, Forth is self documenting, also you can add comments inside (or outside, of course), the definition. Grand Scale Programming I have talked about designing or redesigning whole systems, for customization, or porting to new hdw, & I expect it sounds like something that someone might spend months, or maybe even years doing, but it more likely would take u only a matter of days, because: 1. Forth systems tend to be very small 2. U usually have th tools to do things in th most direct way possible. When u don't, u can MAKE them. 3. Th combination of interactive programing w/ very small modules which are all subroutines usable individually, allows u to very efficiently "snowball" th power of ur code. In other words, tho in any language a good programmer tries to write code whose power increases geometrically w/ th amount of code he writes, Forth was designed to allow u to do this very efficiently. 4. Th modularity, interactivity, use of subroutines by naming them, as well as automatic stack use, makes debugging a breeze! Use You can code interactively, at the term, to test things, but then for real work, you enter the editor, and edit scripts or source onto disk. Then you can take input from disk with a LOAD cmd, and do execution and compiling directly from disk (until your file gives the cmd to take input from term). Forth can accomplish everything OS9 can, simpler. My plans I've always wanted to write my own OS because I eventually wanted to put out my own hdw, and wanted complete control of maintenance and no royalties. There are many PD Forths, and Forth workalikes out there to build upon. The system I want to develop now, would include "Universal Random Block Access", or URBA which means the ability to access all common disk formats, (Mac, MSdos, Amiga, OS9, RSdos, CPM, ProDOS, CDOS, etc.) Each format description would be contained in a "DOS Descriptor Block" data structure, and if a new format became popular, you could just add another DDB. With additional device descriptors, and drivers, you could access WORMs, and VHS, etc. Naturally it will have multitasking, & I want to add all the most useful commands of OS9. Of course it will always have the advantage of being a programming lang. as well as an OS, over OS9. Your Application Altho there are versions that run on top of OS9, Flex, CPM, MSdos, etc., etc, to get the greatest advantages, you need Forth on the bottom! Availability on CIS Put your checkbook away! You can get versions of Forth for the popular CPUs for down-load time: 6809 The TIL09 system is on Cocosig (g coco), in "Languages & Op. Systems" Lib. It makes ROM calls on the Tandy Color Computer. Here is a list of necessary files: TIL09.DOC, & M4TH.DOC, Describe operation & capabilities of TIL09. TEDIT.DOC, Describes editor use, & other necessary commands imbedded in th editor. TILBUG.4TH, Bug fixes. TIL09.GLO, System glossary. TILASM.DOC, Overview of assembler. TIL09.BIN, Executable system. From BASIC, do LOADM"TIL09":EXEC. Uses logical sector/block disk access. TILDOS.ARC, TILDOS uses RSDOS disk files. Instructions are included. META1.BIN, & META2.BIN, are source for TIL09. TDCMP.BIN, is source for th metacompiler/decompiler. TEDIT.BIN, is th source for th editor. TILASM.4TH, source for th assembler. 68000 Do a g clm332 to get to Computer Languages Magazine's forum, & there, in th Forth library u can find: README.68K, installation instructions. F83-68.BIN, the executable Forth system. (Uses CPM disk access.) KER68K.SCR, source, necessary for adapting the system & helpful in understanding it. META68.SCR, source for the metacompiler, n case you want to alter the system, or make a completely new one. UTL68K.SCR, source for utilities. Atari16 forum has basically th same forth as F83-68K, but different disk access extensions for a non CP/M Forth. 8086 Also in CLM's Forth Libr.: README.PC, Dox for MS-DOS 4th. CMD4TH.BIN, IBM-PC dedicated Forth. (Does NOT go thru PC-DOS) F83-86.BIN, DOES go thru PC/MS-DOS. KER-86.SCR, System source. CPU-86.SCR, Assembler source. META86.SCR, Metacompiler source. 8080 Also in CLM's Forth Libr.: README.80, Dox. KERNAL.SCR, System source. (CPM80) F83-80.BIN, Executable system.(CPM80) Learning Forth For a first text, I'd recommend: "Starting Forth" by Leo Brodie. A glossary is in Cocosigs DL9... TIL09.GLO. Maybe not Forth '83 de rigueur, but it is helpful. Th entire text for th: Forth '83 Standard is available in th Forth forum, (g forth), as FORTH-.DOC. There is also a reference file in Forth lib in CLM (g clm332).... 4THRES.TX0 (Forth resorce). You will also find FIG's address in here. We r planning a 4th workshop in Cocosig. Anyone interested may contact me for th schedule. Also, if anyone knows of other live "Forth Introductions", I'll appreciate hearing of them. Social Aspects There are people, some of whom r pretty good programmers, that consider Forth a "Cult" language. I've tried to figure why this is so, (*I* don't feel like a cultist.(grin)), & so far I've come up w/ these possibilities: 1. Forth IS after all fundamentally "different" from any other language. (Despite its similarity to LISP.) 2. Once some people realize how much they can accomplish w/ Forth, they may get overexcited, & sound as tho they have gone overboard! (Hehe..couldn't happen to ME!) 3. I think it likely that Forth is better than what they (th people that call it a "cult" lang.) are used to, & maybe, for whatever reason, they would rather not find that out!(grin) 4. Tho Forth tends to attract good programmers, (Th best!), it also attracts a few poor ones. (I once saw a guy use a whole screen to define a single primitive. (grin)) Such a programmer is not likely to present Forth to a newcommer in its best light, also if th newcommer is himself a fairly good programmer, he's likely to figure that if his less capable friend thinks well of a language, it's probably a dud! hehe So, then, if he hears th enthusiasm of someone who really knows & uses th potential of Forth somewhere near its fullest, he's likely to attribute such enthusiasm to "cultism". (grin). Problems Plex or contact me as follows: Giles Spruill 73347,2651 Advanced Automation, Inc. 1217 N.E. Miami Ct., Suite 6 Miami, FL 33132 Ph# (305) 371-6408 I would also appreciate any advice that would help make this file better.
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