Forth has been something I've wanted to learn for years now. It seems weird to me that for most stuff in old computers, you have the option of "assembly" if you want your program to be fast, and "BASIC" if you want your program to be slow, but Forth lingers along as the "medium speed" language, despite at least looking pretty high-level.
Old 8 bits "family/home computers" were designed with teens and kids in mind - perhaps an influence of Alan Kay? BASIC means "Beginner's All-purpose Symbolic Instruction Code", so it was a good fit. The Amstrad CPC 6128 also came with a Logo implementation [1], which was an educational dialect of Lisp (I still remember how its associative lists blew my mind as a kid), on a separate disc.
Also, at that time "open source" wasn't really a thing, compilers/interpreters for various languages were professional, commercial tools [2].
The reason I used FORTH to code ChipWits in 84 was twofold. First, it allowed me to develop natively on the 128k Mac rather than buying an outrageously expensive Lisa. Second, I knew I was going to port it to other micros and FORTH was usually one of the first languages implemented on new computers. I eventually ported it to Apple II and C64 and about 70% of the Mac code was easily portable.
Forth really is one of easiest languages to build up from bare metal, piece by piece. And when you get it working, sure, it's arguably weird, but it's far better than where you started.
My personal inclination is to make the longer jump, and go straight for a deeply rudimentary Lisp. There's a trick where you start off with Lisp macros that expand to assembly, and I once knew someone who got it working for new hardware during a 10-hour plane flight. It's a slightly longer climb than Forth, but even a primitive Lisp is nice.
However, the deciding factor here really is the 6502 and 65C02 microprocessers. You really want at least 4 general-purpose registers for a primitive Lisp dialect, and that's pushing it. And the 65C02 basically has 1, or 3 if you clap your hands and believe. Even C is a serious challenge on a 65C02.
But Forth thrives in that enviroment. You only need a stack pointer and enough registers to do exactly 1 canned operation. So: victory to Forth.
And wow, I wish I had seen Chipwits back in the day. I was a massive fan of the Rocky's Boots logic game, but Chipwits never showed up in our neck of the woods. Thank you for open sourcing it!
It may look more high-level than something like C, but it is actually no more high level than a macro assembler with registers eliminated. As there's no syntax tree, essentially every word that is parsed from the input stream is replaced with a subroutine call. So the resulting FORTH code is nothing but a series of subroutine calls.
In my experience quite often writing in assembler is easier than FORTH unless you have a strategy and self discipline, which when acquired makes one a whole lot more productive than using assembler, and arguably more so than a high level language. There're no pointer arithmetics, no rudimentary type checking, not even an array type (you have cells and addresses). There is nothing that throws an error except things like stack over/under-flow checks, and if you are lucky your code will crash. If not debugging can be tricky. Stack imbalances won't be reported/checked for you, there is no bounds checking for anything (not even structs). But there are conventions/strategies to prevent these kinds of bugs from happening that one needs to either discover for themselves, or find out in books (the book Thinking Forth helps, but is not enough I would say).
Working with the stack can be more difficult than with registers, although the latter can be easily simulated with variables, which is often frowned upon. But words like CREATE ... DOES> enables meta-programming that helps with generating code with code, and makes it quite powerful, but can make your code complicated to reason about (see the concepts of compilation vs. execution vs. interpretation semantics described in ANS Forth).
In the end the appeal of FORTH for me is in its "simplicity" (but nowhere any ease of use as it requires mastery of laying out code in memory as you would do in an assembler without any help from the language itself), its overall philosophy (see Chuck Moore's A Problem Oriented Language) on focusing on the nature of the problem rather than thinking in terms of the tools/language given to you (build a "language" for the problem), and providing solutions with as minimal "cruft" as possible.
> Working with the stack can be more difficult than with registers, although the latter can be easily simulated with variables, which is often frowned upon
Yet every time I hear experienced Forth developers recommending to use more variables, and that newbies tend to eschew them, making the code much harder to read and understand than it is necessary.
You become a true Forth programmer once you go past the code golf and stack juggle phase.
Anything that you say is missing can be added. I'm no expert but when I had some confusion about the stack I would create a word that did something in a balanced way, test it quickly, and use that word instead to build on. Forth makes it easy to climb the levels abstraction quickly.
The method that it uses to interpret/compile a word varies by implementation. Subroutine call is just one of them.
For sure, it can be extended indefinitely. It's good that you made that clear. You can add a C compiler if you like (see Dusk OS) even, or a generic BNF parser generator (see Bradford Rodriguez) into "the language". Anything that you devise for code correctness, and static analysis can be added. My points about the lack of these language features were towards the previous comment about FORTH looking "more high-level than C". These are definitely major shortcoming for an inexperienced programmer to be able to do anything reasonably complex in FORTH (similar to using assembly).
> ... I would create a word that did something in a balanced way, test it quickly, and use that word instead to build on. Forth makes it easy to climb the levels abstraction quickly.
I would say any programming language with functions provide the same ease by that definition. That is, in each you can write a set of functions, than use them to compose higher level functions ad infinitum until you create a DSL as essentially a collection of functions for your problem space. Although doing so in C-like languages syntactically it may look more like Lisp than FORTH. In FORTH it looks more concise, and reads left-to-right thanks to it being accidentally a "concatenative language" with point-free notation and combinatory calculus roots. A great example of this being formalized is Joy by Manfred von Thun.
So I think what makes FORTH unique is more of the philosophy around it (again, see POL book by Chuck), which is a kind of zealous struggle for simplicity, but not easy, and keeping the problem in focus and not ignoring what's inside the boxes you build upon. You could say it's a panacea for yak-shaving if done right. Concrete examples for what FORTH does away in its search for simplicity and avoidance of yak-shaving, here are a few:
- no in-fix notation or ASTs: computers understand post/reverse-Polish by default by virtue of them being a stack(/register) machine, the programmer can do this work without major difficulty,
- no filesystem: blocks and table of block indices are enough most of the time,
- no floating point: fixed point is good enough for most problems,
- no classes, arrays, structs: you can build your own constructs suited for your problem as they are needed, there is no one size fits all solution,
Etc. The list goes on. Some of these are added into the so-called standards, but some argue trying to standardize FORTH defeats itself.
> The method that it uses to interpret/compile a word varies by implementation. Subroutine call is just one of them.
I used a vague terminology there, and should have clarified by saying "regardless of the threading model". What I meant was that effectively the FORTH source compilation is a one step pass that converts string tokens into series of "subroutine" (conceptually) calls that map 1:1 with the source code (homoiconicity); direct/indirected threaded, token threaded, or subroutine threaded all effectively is laying out/interpreting a series of subroutine calls, including those in FORTH CPUs like Harris RTX or GA144.
Very fast (faster than naive assembler) but not at all high-level; having to look after the stack is a bit of a pain. Writing your own FORTH is fun - it doesn't need to be in assembler - I once wrote a FORTH-like scripting language in C++.
Depends on how naive the assembler programmer is, and, I would think rarely, if ever, on modern hardware because the many subroutine calls kill branch prediction benefits. Also, on lots of old 8-bit hardware, defaulting to 16-bit integers will kill performance relative to native assembly in cases where 8-bit integers suffice.
(Of course, you can fairly easily replace hot loops by assembly or (more difficult) change the forth compiler to compile parts to native code, fuse words, etc)
but it's also very extendable. It's ability to slap on new control structures and DSL's is on par with Lisp. I'd say it's very low level and much higher level than the most languages simultaneously.
Yeah, that's what I was kind of getting at. It looks like it starts low level, but it seems like it allows effectively an infinite amount of abstraction.
I think writing a toy Forth interpreter is a good way to learn about the language. It's easy and I had a lot of fun with it. But it is so ridiculously easy, at least up to a certain point, some may find it too elementary, or too tempting to go beyond a toy implementation.
One of the great things about it was, it came with an assembler vocabulary to code your inner loops or other lowest-level stuff in. I gather BBC Basic had something like that, but I never saw and and I did get to use Forth in this way back in the day. Most of those systems made it harder to flexibly mix the higher and lower-level coding.
This is much like C. The easiest way to use assembly in C or Forth is to know your 'ABI' and write separate assembly code functions where needed. In Forth at least you can write a CODE word.
Forth is very good for writing small software in tight memory constraints. Unfortunately it is pretty hard to read; for bigger software projects there are many better languages.
Relatedly, there's http://tumbleforth.hardcoded.net/, which I think looks lovely. Has anyone gone through that and would like to share their experience?
I got about halfway through it during a slow work week. It was a throwback to my hardware classes from college. It got me thinking differently about computing.
I am young and stupid, but from a rear-view perspective it looks like maybe certain abstractions were chosen in the old days when there were hardware limitations, and that our current "evolutionary branch" of programming languages has a lot of abstractions that have not aged well, leading to a lot of layers of load-bearing cruft --much like any engineering project.
Collapse OS might not be practical today, but it has a "liberating" appeal. Freeing yourself from all these layers of abstraction sounds really enticing. A way to enjoy computing as it existed in the 1960s, but without the terrible developer experience. (or so I imagine)
Currently my pie-in-the-sky project would be to work through these projects, get Dusk OS building on a virtual machine, then physical machine, then write a Scheme interpreter for Dusk OS in C --and go hog-wild from there.
I have a couple of rivers to cross before I get there. I implemented a Scheme interpreter in Python in a couple of hours, then improved the scanner/Tokenizer in a couple more hours. Now I'm reading through crafting interpreters to see how I would go about implementing a Scheme interpreter in C. After that's done and I implement an interpreter in C, I'll revisit this guide and try to jump headfirst into DuskOS.
I found this quite easy to follow: https://www.buildyourownlisp.com/ for building a not-quite-Scheme in C. I didn't get massively far but only because of the sheer amount of other shiny things.
>This little assembler crash course gives us a better understanding of what is compiled by the C compiler, but not how it compiles it. We don't know how it's ran either. To know that, we'd have to dig through software that weighs millions of lines of code. Maybe you'd have the patience to do it, I don't, so let's continue tumbling down the rabbit hole. We'll go bare metal and then build an operating system of our own, with a C compiler of our own. It's simpler this way.
>What’s a linker? Aw, forget about it, it’s another piece of overcomplicated software that has convinced the world that it’s essential. We won’t need one in what’s coming.
Virgil Dupras, the author of the Tumble Forth series there, also authors DuskOS, an OS written entirely in a custom Forth. His consistent and prodigious output really is quite impressive. I don't really hold to the collapse philosophy, but the DuskOS mailing list has just the right amount of volume that it's perfect for lurking.
Virgil's work inspired me to give Forth a bit of a go, and last year I spent some time hand decompiling SmithForth[1]. It really is remarkable how little assembler is required to bootstrap the language. I can totally see how Forth could give you a repl in embedded environments, which sounds way more fun than the typical dev cycle I hear about.
Just following up on this - this comment was my initial excitement at seeing some real Forth-based thing. I've had time since then to follow up and read the wikipedia page for ChipWits now and the blog post: the original game looks very cool. The logo from the manual on WP is so great.
I'd been making a list recently of games (old and new) that have puzzles and programming type stuff in them. It's going on the list! I could very well get on to it next after I'm finished the ketman assembly "game" (although it's not really a game, I suppose).
We kept the gameplay of the original pretty much intact in the new game.
I don't want to spam Hacker News, but since you played the original, I'd love to get your reaction to the reboot: https://chipwits.com
Forth seems to be one of those write once languages like perl. Easy to start writing and building, but come back to the code in a year or so, no clue what it does.
That's awesome. I will! I was probably around 12-14? when I spent many hours with that game. After that it was DOS and Doom. But I think when I eventually drifted towards the path to being a software engineer I did grasp a lot of the basic concepts faster because I played games like this as a kid. The other path was being a musician of course.
https://chipwits.com/2023/04/08/forth-programming-language-g...
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