https://ratfactor.com/forth/forth_talk_2023.html drawing of chuck moore with his real head Forth: The programming language that writes itself Charles H. Moore and the pursuit of simplicity. A talk by Dave Gauer, 2023. Made with minslides, which I made for this talk. Use the J and K keys to go forward and backward. You can also just scroll down like a regular web page. Toggle notes/annotations with the N key. Hello! These are my talk notes. The slides start out with fairly complete text and stand on their own, but they get more terse and cryptic later. I also use these notes to store the reference links and additional quotes for individual slides. I might also flesh the notes out to include a sort-of transcript of the spoken part of the talk. Stay tuned. Something that I will have in the actual talk: Raise your hand (and keep it raised) if you've: * heard of Forth * written any Forth * implemented a Forth or Forth-like * you are Chuck Moore The Legend When I was a wee programmer, I would sit around the virtual Usenet campfires listening to the tall tales and legends of the elders. usenet campfires on a desert scene: comp.lang.forth comp.lang.lisp and alt.religion.kibology The Legend I learned about magical languages with lots of (((((parenthesis))))). third eye open to the y combinator The Legend I listened, wide-eyed, to true tech tales like The Story of Mel. Royal McBee RPC-4000 computer drawing The Legend And I heard tell of a programming language so flexible that you could change the values of integers. The Legend chuck moore as an adorable wizard They said that language was called Forth and it was created by a mad wizard called Chuck Moore who could write any program in a couple screens of code. The Legend Years went by and I wrote a lot of PHP. I lost friends to the Internet Explorer 6 wars. But I never forgot about the legend of Forth. The blog series programming in the twenty-first century by game developer James Hague gave me the final push. Forth was a recurring theme and it just sounded so darned interesting. So I went on an adventure and I came back and I think I have some answers. a tired warrior returns from forth mountain (Oh, and I confirmed the legend. I can make any integer equal anything I want. Stick around 'til the end to see that Forth magic trick.) Postfix (RPN) notation hp-35 calculator with rpn syntax I thought this was what Forth was all about: 3 4 + 7 Noob: $ bc bc 1.07.1 Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc. This is free software with ABSOLUTELY NO WARRANTY. For details type `warranty'. (3 * 4) + (5 * 6) 42 Pro: $ dc 3 4 * 5 6 * + p 42 Forth pro: 3 4 * 5 6 * + . 42 That's true, but then I learned some more... Stack-based drawing of three stacks illustrating push swap and dup operations Op The Stack -- --------- 3 3 4 3 4 * 12 5 12 5 6 12 5 6 * 12 30 + 42 . REMOVED SLIDE: Using "the stack" in i386 assembly: mov eax, 3 mov ebx, 4 mul eax, ebx push eax mov eax, 5 mov ebx, 6 mul eax, ebx pop ebx add eax, ebx eax=42 Forth: CAKE DUP HAVE EAT Lack of explicit names for intermediate values. If I ask you to add these numbers: 2 6 1 3 7 Do you feel a need to give a name to each sum pair...or even the running total? That's true, but then I learned some more... Concatenative programming a confused cat working on an old pc Ah, this must be it because it sounds fancy. Contrast with applicative language: eat(bake(prove(mix(ingredients)))) Concatenative language: ingredients mix prove bake eat The canonical example of a concatenative language is Joy Joy Manfred von Thun inspired by Backus's 1977 ACM Turing Award lecture: top of the john backus paper Can Programming Be Liberated from the von Neumann Style? A Functional Style and Its Algebra of Programs Joy Joy is kind of like starting with a Lisp Minus function parameters Minus variables Minus traditional control structures Joy All functions are unary (an arity of 1) Stack in, stack out A program is a list of data and functions Joy's superpower: combinators Wikipedia: Combinatory logic Combinators Higher-order functions like map: inc = function(n){ return n + 1; }; bigger = list.map(inc); Concatenatively: list [inc] map Note the lack of a variable "bigger" here. This is a halmark of concatenative programming - we don't need to name every intermediate value which can be a blessing...or curse To Mock a Mockingbird cover of the book Identity (I x) = x K and S (K x y) = x (S x y z) = (x z (y z)) Combinators: A Centennial View cover of the book REMOVED SLIDE (I don't think I was explaining this right and at any rate, when I did my first read-through, it took me 2 hours!) A function using a combinator to reverse lists in Joy: reverselist == [] swap infra infra takes a list as one param and a program as a second and uses the list as temp stack and executes the program. The swap here is just to get the param order correct for infra, it has nothing to do with reversing the input list. Combinators let us factor out explicit loops. foo.map(bar) equals temp = []; for(i=0; i ; NEXT ; * code word ; ; NEXT ; EXIT ; NEXT ; EXIT ; NEXT ; QUIT (BRANCH -8 back to INTERPRET for more) Absolutely nothing else drives the flow of an indirect threaded Forth application. It's addresses stored in registers and one or two line assembly instructions at the end of the word that manipulate the return stack as needed and jump to the next instruction. Don't you see how simple it is? drawing of chuck as crazy charlie explaining a theory with wild eyes and a wall covered in paper and strings I hope this is recognizable... In case this meme is otherwise unknown or lost to the ages, it's a screencap of the character Charlie Kelly from the show It's Always Sunny in Philadelphia. the original meme screencap of crazy charlie with wild eyes and a wall covered in paper and strings https://en.wikipedia.org/wiki/Charlie_Kelly_(It%27s_Always_Sunny_in_Philadelphia) Forth is complex when taken as a whole. But it is made of tiny pieces, each of which is very simple. The concept was created over a period of years on very constrained systems. Each part created only as needed. an abstract drawing of boxes and arrows representing threaded code in memory Code words Simple: DEFCODE "SWAP",SWAP,0 pop eax pop ebx push eax push ebx NEXT Code words Simpler: DEFCODE "DUP",DUP,0 mov eax, [esp] push eax NEXT From JonesForth: "In this FORTH, we are using the normal stack pointer (%esp) for the parameter stack. We will use the i386's "other" stack pointer (%ebp, usually called the "frame pointer") for our return stack." Code words Simplest: DEFCODE "DROP",DROP,0 pop eax NEXT Code words in action 8 7 8 7 SWAP 7 8 DROP 7 DUP 7 7 Code words nasmjf has 130 code words. Mostly for efficiency. Code words sectorforth has 10. Regular ("colon") words : SDD SWAP DROP DUP ; 8 7 8 7 SDD 7 7 How "colon" works : SDD SWAP DROP DUP ; Colon (:) fetches the word name and sets "compile mode". Semicolon (;) completes the word's entry in the dictionary and unsets "compile mode". "Compiling" in Forth means: * Putting the address of a word in memory * Putting the code to push a literal onto the stack Compiling is very similar to interpreting, but we're storing addresses instead of executing them. Almost no syntax = simple interpreter * WORD (Overloaded term, sorry. Blame Chuck!) * Is it in the dictionary? (Compiling?) * Is it a literal? (Compiling?) * Otherwise, error! 8 7 SWAP DUP DROP : SDD SWAP DROP DUP ; 8 7 SDD Almost no syntax = extreme extensibility. The definition of IF...THEN from jonesforth.f: : IF IMMEDIATE ' 0BRANCH , HERE @ 0 , ; : THEN IMMEDIATE DUP HERE @ SWAP - SWAP ! ; Almost no syntax = extreme extensibility!!!!! The definition of ( ) nested comments from jonesforth.f: : ( IMMEDIATE 1 BEGIN KEY DUP '(' = IF DROP 1+ ELSE ')' = IF 1- THEN THEN DUP 0= UNTIL DROP ; ( From now on we can use ( ... ) for comments. ... The dictionary uses a linked list and word matching is done from the most recently defined word, so: * You can redefine any word, even ones originally defined in assembly. * Uses of previous definitions don't break because the links to the previous words still point to the original. * You are in complete control. * Forth = freedom grayscale apple It's not just the language itself that is unusually flexible, the usage of Forth allows for really surprising flexibility. Example paraphrased from Thinking Forth. Say we create a variable to hold a number of apples: VARIABLE APPLES 20 APPLES ! APPLES ? 20 Forth variables put addresses on the stack. I loved this example when I read the book. I have a physical copy of Thinking Forth, but Forth, Inc. has made it available for free online: https://www.forth.com/wp-content/uploads/ 2018/11/thinking-forth-color.pdf We pepper our program with this APPLES variable. Then we are told that we must now keep track of two different kinds of apples: red and green. What to do? red apple green apple A new variable will store the current type of apples. VARIABLE COLOR red apple A new variable and word will deal with red apples. The word sets the type of apple by storing the address of REDS in COLOR. VARIABLE REDS : RED REDS COLOR ! ; green apple Same for green. VARIABLE GREENS : GREEN GREENS COLOR ! ; And change APPLES from a variable to a word that gets the current count by color: : APPLES COLOR @ ; grayscale apple red apple green apple Now we have to re-write any use of APPLES, right? Wrong! The use of APPLES is identical. The syntax hasn't changed one bit for any existing code. We just need to make sure we've set the right color. 20 RED APPLES ! 30 GREEN APPLES ! GREEN APPLES ? 30 APPLES ? 30 RED APPLES ? 20 grayscale apple red apple green apple "I didn't create Forth, I discovered it." -- Chuck, apocryphally Making nasmjf gave me so many ideas, I had to try some experiments. my lenovo 11e thinkpad with assembly code waiting romantically on the bed with a candle. text reads 'Assembly Nights II' Meow5 meow5 cat logo An exercise in extreme concatenative programming where all code is concatenated (inlined). Meow5 : meow "Meow. " print ; meow Meow. : meow5 meow meow meow meow meow ; meow5 Meow. Meow. Meow. Meow. Meow. Meow5 Despite attempting to make something radically different, it's remarkable how many times Forth's solution was the path of least resistance. "Aha! That's why." Example: string quoting " Hello World." Meow5 has this quoting: "Hello World." But the effects are cascading...and limit flexibility "Aha! That's why." This is why I titled this "The programming language that writes itself" * In the boostrapping sense * In the metaprogramming sense * In the "mathematical truth" sense Also in this sense... PlanckForth Hand-written 1Kb binary binary layout of planckforth as taken from the repo I took this image straight from the repo. I just LOVE this so much. https://github.com/nineties/planckforth Forth is an idea that has taken form in countless applications, many of them custom and home-grown. * Power plants, robotics, missile tracking systems, industrial automation. * Embedded language in video games. * Microcontrollers. * Legacy: databases, accounting, word processors, graphics, and computation systems. * On the modern OpenFirmware boot loader. https://www.forth.com/resources/forth-apps/ https://en.wikipedia.org/wiki/Forth_(programming_language) http://www.forth.org/successes.html Jupiter Ace, 1982 drawing of the jupiter ace home computer Operating system: Forth. OS and library of routines in 8 KB of ROM. "Ten times faster than [interpreted] BASIC" and less than half the memory requirements. https://en.wikipedia.org/wiki/Jupiter_Ace https://vintagecomputer.ca/jupiter-ace-4000/ "The most distinguishing feature among many computers of the era was that it offered Forth as a base language and not the usual BASIC that was the popular flavor of the day." Canon Cat, 1987 drawing of the canon cat word processor home computer Operating system: Forth. OS and office suite in 256 KB of ROM. Innovative interface by Jef Raskin. https://en.wikipedia.org/wiki/Canon_Cat https://vintagecomputer.ca/canon-cat/ "While the Canon Cat is a more powerful word processor than most, it's most exciting characteristic is the utilization of a new (for the time) user interface known as the Humane Interface." Also, you have to check out the picture of Jef with a little model of the Cat on his Wikipedia page: https://en.wikipedia.org/wiki/ Jef_Raskin title says Forth in Space and chuck is an astronaut on EVA who says May the Forth be with you. "May the Forth be with you." is courtesy my daughter. :-) NASA unreadable list of a ton of nasa projects using forth The 2003 list by NASA's James Rash is too long to easily list. https://www.forth.com/resources/space-applications/ Space Shuttle Scientific Instrumentation Interface nasa mission patch for ssbuv "There is always great concern about software reliability, especially with flight software." https://www.forth.com/space-shuttle-instrumentation-interface/ NASA Robot Arm Simulator robot arm in space shuttle Control of 50-foot long, six-joint arm for Space Shuttle simulator. Extensive math routines convert two three-axis joystick commands into required joint velocities in six different co-ordinate systems. Entire system developed by one programmer in five weeks. https://www.forth.com/space-shuttle-robot-arm/ Shuttle Essential Services Node drawing of the shuttle launching Multitasking operating system, Forth language compiler, and libraries for UT69R000 radiation-hardened microprocessor used in Space Shuttle instrumentation. https://www.forth.com/resources/forth-apps/ Harris RTX2010 used in a ton of space applications. block diagram of harris chip * Direct execution of Forth * Radiation hardened * 8MHz clock, extremely low latency * Two stacks, 256 words deep https://en.wikipedia.org/wiki/RTX2010 Rosetta and Philae drawing of rosetta approaching comet First mission to send a lander to a comet! Forth used for the Rosetta Ion and Electron Sensor instrument, using Harris RTX2010 Forth microprocessor. The Philae lander is powered by two 8MHz Harris RTX2010 16-bit stack processors...used by the Philae CDMS to control all aspects of the lander. https://www.nasa.gov/rosetta https://www.cpushack.com/2014/11/12/ here-comes-philae-powered-by-an-rtx2010/ "Why was the RTX2010 chosen? Simply put the RTX2010 is the lowest power budget processor available that is radiation hardened, and powerful enough to handle the complex landing procedure. Philae runs on batteries for the first phase of its mission (later it will switch to solar/back up batteries) so the power budget is critical. The RTX2010 is a Forth based stack processor which allows for very efficient coding, again useful for a low power budget." photo of comet 67p taken by rosetta ( This is one of the final images taken by Philae as it made the soft descent to the surface of comet 67p. https://www.nasa.gov/feature/jpl/ final-descent-image-from-rosetta-spacecraft Stop Writing Dead Programs Awesome talk by Jack Rusher screenshot of jack's talk at the quoted position Stop Writing Dead Programs crop of jack rusher from the previous screenshot "...Space probes written in Lisp and Forth have been debugged while off world... If they had proven their programs correct by construction, shipped them into space, and then found out their spec was wrong, they would have just had some dead junk on Mars. But what these guys had was the ability to fix things while they are running on space probes... In addition, the spec is always wrong!" -- Jack Rusher, Stop Writing Dead Programs, 2022 Check out Jack's awesome transcript here, which was super helpful when I wanted to re-find this quote. https://jackrusher.com/ strange-loop-2022/ "Had I had more time, I would have done an entire series of slides on FORTH. It's a tiny language that combines interactive development, expressive metaprogramming, and tremendous machine sympathy. I've shipped embedded systems, bootloaders, and other close-to-the-metal software in FORTH." I finally found a story about Forth being updated in space, if not the story: "Also in 1993 I used MCL to help generate a code patch for the Gallileo magnetometer. The magnetometer had an RCA1802 processor, 2k each of RAM and ROM, and was programmed in Forth using a development system that ran on a long-since-decommissioned Apple II. The instrument had developed a bad memory byte right in the middle of the code. The code needed to be patched to not use this bad byte. The magnetometer team had originally estimated that resurrecting the development environment and generating the code patch would take so long that they were not even going to attempt it. Using Lisp I wrote from scratch a Forth development environment for the instrument (including a simulator for the hardware) and used it to generate the patch. The whole project took just under 3 months of part-time work." https://mecrisp-stellaris-folkdoc.sourceforge.io/lisp.html When we defeat the alien kill-bots and reprogram them, it will surely be with a Forth of some sort. alien kill-bots being controlled by forth Forth is an idea unreadably tiny diagram of lineage of various Forth implementations Obviously the graphic is unreadably tiny. For the full-size original and the gForth program used to create it, check out: http://www.complang.tuwien.ac.at/forth/family-tree/ What about Chuck? Charles H. Moore founded Forth, Inc in 1973. Has been porting Forth to various systems since. drawing of chuck at a desk programming on a pc with a crt. equipment looks 1990s era Image from the great quote collection (are you tired of seeing this link?) http://www.ultratechnology.com/moore4th.htm photo used as reference for above drawing colorForth screenshot of colorforth Screenshot from this Quora answer by Tikhon Jelvis: https:// www.quora.com/What-is-your-undergraduate-research-experience-like "An idiosyncratic programming environment, the colors simplify Forth's semantics, speed compiling, and are said to aid Moore's own poor eyesight: colorForth uses different colors in its source code (replacing some of the punctuation in standard Forth) to determine how different words are treated." "The language comes with its own tiny (63K) operating system. Practically everything is stored as source code and compiled when needed. The current colorForth environment is limited to running on Pentium grade PCs with limited support for lowest-common-denominator motherboards, AGP video, disk, and network hardware." https:// en.wikipedia.org/wiki/ColorForth Neat interview mentioning colorForth (amongst other things!) here: https://www.red-gate.com/simple-talk/opinion/geek-of-the-week/ chuck-moore-geek-of-the-week/ Fighting the good fight against software complexity since the 1950s. "I am utterly frustrated with the software I have to deal with. Windows is beyond comprehension! UNIX is no better. DOS is no better. There is no reason for an OS. It is a non-thing. Maybe it was needed at one time. -- Chuck Moore, 1997 Once again, from the compiled quotes at ultratechnology.com "If they are starting from the OS they have made the first mistake. The OS isn't going to fit on a floppy disk and boot in ten seconds." -- Chuck Moore, 1999 Once again, from the compiled quotes at ultratechnology.com Instead of being rewritten, software has features added. And becomes more complex. So complex that no one dares change it, or improve it, for fear of unintended consequences. But adding to it seems relatively safe. We need dedicated programmers who commit their careers to single applications. Rewriting them over and over until they're perfect. -- Chuck Moore, 2009 Once again, from the compiled quotes at ultratechnology.com His real love seems to be hardware. Remember that Harris RTX2010? That's basically his design. chuck as a mad scientist chip creator Has been designing hardware since 1983 starting with the Novix N400 gate array and dev board. (An improved processor sold to Harris to become the RTX* chips.) Has been designing chips ever since. With his own VLSI software, "OKAD", written in 500 lines of Forth, of course. "Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) chips were developed and then widely adopted, enabling complex semiconductor and telecommunication technologies. The microprocessor and memory chips are VLSI devices." https://en.wikipedia.org/wiki/ Very_Large_Scale_Integration In 500 lines of colorForth these tools provide everything required to design a chip. They are derived from an earlier version called OKAD that successfully generated many versions of Forth microprocessor chips. https://colorforth.github.io/vlsi.html A whole book about the NC4000 chip: http://forth.org/OffeteStore/ 4001-footstepsFinal.pdf List of chips (and links to more): http://forth.org/cores.html This question and answer(s) are excellent for understanding what OKAD is: https://retrocomputing.stackexchange.com/questions/25506/ did-forths-inventor-charles-moore-really-write-a-cad-program-in-only-5-lines-of GreenArrays. "Programming a 144-computer chip to minimize power" (2013) 144 asynchronous computers on a chip. Idle cores use 100 nW. Active ones use 4 mW, run at 666 Mips, then return to idle. All computers running flat out: 550mW (half a Watt). screenshot from Chuck's 2013 strange loop talk about 144 computer chip youtube.com: "Programming a 144-computer chip to minimize power" - Chuck Moore (2013) https://www.greenarraychips.com/ "COMPLETE SYSTEMS: We refer to our chips as Multi-Computer Systems because they are, in fact, complete systems. Supply one of our chips with power and a reset signal, and it is up and running. All of our chips can load their software at high speed using a single wire that can be daisy chained for multiple chips; if desired, most can be bootstrapped by a simple SPI flash memory." "Contrast this with a Multi-Core CPU, which is not a computing system until other devices such as crystals, memory controllers, memories, and bus controllers have been added. All of these things consume energy, occupy space, cost money, add complexity, and create bottlenecks." "NO CLOCKS: Most computing devices have one or more clocks that synchronize all operations. When a conventional computer is powered up and waiting to respond quickly to stimuli, clock generation and distribution are consuming energy at a huge rate by our standards, yet accomplishing nothing." https://www.greenarraychips.com/home/ documents/greg/PB002-100822-GA-Arch.pdf "If you talk about molecular computers that are circulating in your bloodstream, they aren't going to have very much power and they aren't going to have very much memory and they aren't going to be able to use much energy. -- Chuck Moore, Programming a 144-computer chip to minimize power, 2013 Totally, like, my opinion: The complete domination of x86 PCs in practically all areas of computing until very recently is an accident of history. There is absolutely no reason to believe that this is how the majority of computing will continue to be done in the decades to come. Even relatively low-energy devices like our smart phones require massive computing power to do most tasks, especially anything having to do with a web browser. There are physical realities about how much computing power (and memory) you can have per unit of energy. There are plenty of applications where low energy computing is a hard requirement and I believe these applications will only increase. Also, virtualization changes things, too. We went from single applications taking over the whole computer to running a bunch of things on the same computer, to virtualized computers or containers where we're back to applications thinking they're the only thing on the computer again. VMs tend to be constrained by both power and memory. I think Forth-likes have a strong future as we look towards: * Tiny, ubiquitious computers * Solar power * Heavily constrained VMs The Legend Confirmed chuck moore as an adorable wizard Now, behold a new definition of the integer 4: : 4 12 ; Which results in: ." The value of 4 is " 4 . CR The value of 4 is 12 Tada!