A Forth Apologia (1988)

http://holonforth.com/duncan.html

by nyc111 • 4 years ago

79 54 4 years ago

holonforth.com

mikewarot• 4 years ago

I believe there are two big problems with Forth

1) losing track of the parameters in the stack (unlike Lisp, there are no parens to match and serve as containers)

2) everything is a number/pointer. STOIC provides strings, hash tables and more, along with parameter type checking.

Those are, in my opinion, the two main factors that keep Forth from being the "dual" to Lisp.

kragen24• 4 years ago

these are real annoyances but most people get stuck in the stack manipulation tarpit first before those become the main problems

2over should be safe, legal, and rare

vanderZwan• 4 years ago

Well, there is Kitten, although it hasn't seen an update in two years and was moving quite slowly before that too.

https://kittenlang.org/

flembat• 4 years ago

Forth is extensible, it is not complete out of the box like a C compiler. Just extend it with named local variables and use them. There is no shame and unless you are on some rare and exotic stack machine, no performance penalty using local variables. I also need to add safe strings with their own memory pool, rather than block copying bytes around in the same dictionary where my code lives. I am just not a good enough programmer to use Forth strings without crashing a lot.

Gordonjcp2• 4 years ago

1) losing track of the parameters in the stack (unlike Lisp, there are no parens to match and serve as containers)

If you're losing parameters in the stack, you need to refactor. The whole idea of wrapping things in brackets is what makes Lisp such an unreadable mess.

2) everything is a number/pointer.

If you don't understand why everything is a number or pointer, you don't understand anything about programming languages.

ArtixFox• 4 years ago

It is all number or pointer all the way down but that's not the best interface to interact the computer with.

dottedmag3• 4 years ago

I have tried Forth and failed many times.

The biggest problem for me was the amount of effort needed to keep track of "local" variables.

Was I missing something? Is there a way to let Forth keep track of where on the stack "foo" lives if it is needed several times in a subroutine instead of always shuffling the stack or counting the elements on it?

JadeNB• 4 years ago

Was I missing something? Is there a way to let Forth keep track of where on the stack "foo" lives if it is needed several times in a subroutine instead of always shuffling the stack or counting the elements on it?

I'm not a Forth novice, much less an expert, but my impression is that the answer is that if you spend much time thinking about the location of variables, then you're "doing it wrong"—to steal the phrase, trying to write C in Forth, rather than to write Forth. My understanding is that the emphasis is on building highly domain-specific languages out of many small words, each of which is re-factored so much that it never needs to keep much track of any, or much, shuffling of variables on the stack.

dottedmag3• 4 years ago

So basically "use it as a language for combinators", right?

But combinator languages are pretty hard to read no matter what one does, don't they?

kragen24• 4 years ago

Was I missing something?

yes

use variable or value for variables, not the stack

the stack is for expression evaluation

roughly everyone has this problem at first

if you'd put it in a local variable in c or js, 85% of the time you should put it in a variable in forth. start with 100% or 110% and scale back from there

yes this means your words aren't reentrant by default

this is ok, most subroutines aren't recursive

never shuffle the stack or count the elements in it. if you find yourself doing that, put the elements you wanted to access in a variable or value

then you can access them by name. this is much easier

the possibility of shuffling the stack is an attractive nuisance, like a tar pit. an occasional dup or swap or r@ is okay, but start by not using them

literally write square as

    variable x
    : square x ! x @ x @ * ;

    value x
    : square to x  x x * ;

if that's what it takes to stop tying your code in knots

it is ok to name a variable x, its scope only extends to the next definition of an x. it's not like in c where every x needs to either be local to a subroutine or a single global unique x used by the entire program (or at least source file)

later you can graduate to sometimes replacing one local variable with the return stack and another one or occasionally two with the operand stack, but it is better for your code to be kind of boring and verbose than an incomprehensible soup of 2dup -rot tuck

forth is maybe not better than c but there is no reason to make it worse

dottedmag3• 4 years ago

This is roughly equivalent to C using "static globals" instead of named local variables, right?

carapace3• 4 years ago

Did you ever read "Thinking Forth"?

bowsamic• 4 years ago

I tried to write a simple program in Forth that needed to keep track of a list of pairs of numbers and after coming up against many issues I asked online in a Forth group and was told that Forth simply isn't suited for such programs (programs that need to work with dynamically sized amounts of arbitrary data). Maybe this is also true for your case

kragen24• 4 years ago

that is maybe an exaggeration but forth is certainly more designed for reactive systems than transformational ones

video games and motor controllers rather than computer algebra systems

the difficulties are the same as in c: you have to do your reallocation and deallocation and probably hashing manually

a surprising number of such problems turn out to work well enough if 'dynamically sized' becomes '1 billion or less' which simplifies the memory management dramatically

and you can write theorem provers and optimizing compilers and stuff in forth; it just isn't its strong point

JustLurking2022• 4 years ago

It's been around for decades and has virtually zero traction, which is to say, Stop trying to make Forth happen.

kragen24• 4 years ago

i mean, you're not wrong, walter, you're just

it's unlikely to displace c or rust or python or unix or freertos or openocd

but it does have something special, like a delorean or something; unlikely to be forgotten either

rvense• 4 years ago

Not all programming is about making maximal products in minimal time. I also use hand tools all the time, a lot more than if I was a carpenter billing by the hour. How artless one must be to worry about 'traction' off the clock!

eschneider2• 4 years ago

Back in the day, Forth wasn't so much software, as an amazing idea for how to make software for platforms where you had no tools/or terrible tools, which was most personal computers or embedded environments. Once you groked how Forth worked, it was quite practical to put together a language kernel in ASM or machine code and you were off to the races.

kragen24• 4 years ago

i think maybe a lot of the difficulty i had understanding forth was that i mistakenly thought of it as a programming language, and considered as a programming language it's not that great, much like bash

eschneider2• 4 years ago

Forth is definitely a language, and depending on what you have available, it can be a great option. These days, when you can download gcc cross compilers for almost anything, there's less need to roll-your-own Forth, but it's still pretty interesting to study.

Animats• 4 years ago

I once wrote a robot controller in Forth, because that was the only thing available on a dinky microcontroller in the mid-1980s.

Would not have done it if the C compiler for that target had been cheaper. We have better tools now. Back then, it was one of the few ways to do interactive development on really tiny machines. In that niche, it was useful.

diffxx2• 4 years ago

Forth is a mindset as much as a programming language. It is a language for minimalists. If you can solve your problem efficiently in Forth, you can be confident that your solution will work in essentially any computing environment. Unlike C, the core of Forth is small enough that a single individual can implement it in a few days at most. This is incredibly liberating because you will realize that you will never be seriously hindered by the tools provided to you because the Forth way is to just write your own tools. Of course this goes against the modern programming culture which has become extremely maximalist and makes you dependent on complex tools like VSCode + LSP in order to be productive. There is another way.

The language itself leaves a lot to be desired, in my opinion, but the core idea of having a small extensible compiler around which one can build efficient problem specific DSLs is brilliant. Unfortunately I think it is too easy to get bogged down in the bad parts (or at least parts that appear bad to our modern programming sensibilities). For a good overview of what makes Forth special, I recommend Thinking in Forth https://thinking-forth.sourceforge.net even if you never expect to program in Forth. It was written in the 80s but it still holds up. Read the first 80 pages or so carefully and I can almost promise that it will change the way you think about programming in a good way.

Once you have internalized the Forth mindset, you don't need to actually write Forth code. But you may be grateful that Forth taught you how to find your optimal programming language that exists somewhere inside of yourself.

haolez• 4 years ago

Forth is an important skill for a zombie apocalypse. You can create a simple computer, with a simple instruction set, and get a high level programming language in a short time :)

kragen24• 4 years ago

interestingly enough, while this seems like an obviously good application for forth, i have never actually seen someone get to a working c compiler this way

DuncanMak• 4 years ago

Kragen, how much of what you said here about Forth also applies to PostScript, do you think?

I have been tinkering with PostScript but not Forth, I grok that PostScript is a lot closer to LISP. A lot of people (without actually learning these languages/systems) say Forth and PS are similar, but I know that's not really the case - their resemblance is fairly superficial.

kragen24• 4 years ago

i agree, and though it is certainly possible to get ensnared in dup exch baling wire in ps, it isn't nearly as common, maybe because you can just 6 dict begin for some tasty recursion-safe local variables when you have the appetite

or maybe because you can't >r r@ r@ rdrop, or because garbage-collected [arrays] remove the temptation to write subroutines with 6 parameters

ps is fairly big compared to forth, not the 16 megs of libgs.so.9.50 but definitely a lot more than 8k

what they have in common is interactive repl orientation, user-defined control structures, great flexibility, lack of static types, and of course rpn

i was going to say 'closures' but of course ps's scoping is dynamic so it lacks them

A Forth Apologia (1988)

Related Stories