alt Hacker NewsAn attempt to articulate Forth's practical strengths and eternal usefulness
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I'm familiar enough with Forth, picked it up in the 80's with Blazin' Forth on a C64 with Leo Brodie's book at my side. Played a little with the boot environment on some Sun boxes, made some simple contributions to another Forth project on x86 that I can't remember the name of. I never got the wide-eyed wonder some people seem to have about it though, let alone saw it as a silver bullet. The tax bracket code at the bottom of the article is a pretty good illustration of why: it's a really elegant sort of macro assembler, but I'm not really interested in writing whole apps in macro assembly.
Oh, cool! SmithForth[0] is how I originally learned about x86-64 microarchitecture. It's a Forth that bootstraps off hand-coded x86-64 opcodes. I decided to go the other direction and decompile the binary by hand. It really is a beautiful piece of code. Highly recommended reading.
Also, you're excited by Forth and Lisp, you might like Forsp[1]. It uses a call-by-push-value evaluation strategy in a way that really makes the language feel like a true hybrid of the two. The implementation is also brilliantly simple.
Anyway, thank you for the article. I lurk on the DuskOS mailing list and wish I could find out where the Forthers gather IRL so I could osmote more of their world into my own.
There is an aspect of the history of Forth and C I have been trying to wrap my head around.
The early B compiler was reported to generate threaded code (like Forth). The threaded code was abandoned fairly early in the port to the PDP11 from the PDP7 as it was deemed to slow to write an operating system in.
At which point unix and C lost a very interesting size optimization. With the net result that Forth was more portable and portable between machines circa 1970 and Unix had to wait until circa 1975 with UnixV6.
I have been trying to go back through the history to see if I could understand why threaded code was deemed too slow. Today the most part of executables is code that is not run often and would probably benefit from a smaller representation (less memory and cache space making the system faster overall). So this is a practical question even today.
I found a copy of unix for the PDP7. Reproduced from old printouts typed in. If I have read the assembly correctly the B compiler was not using an efficient form of threaded code at all.
The PDP7 is an interesting machine. It's cells were 18 bits wide. The adress bus was 12bits wide. Which meant there was room for an opcode and a full address in every cell.
As I read the B compiler it was using a form of token threading with everything packed into a single 18 bit cell. The basic operations of B were tokens and an if token encoded with a full address in the cell. Every token had to be decoded via a jump table, the address of the target code was then plugged into a jump instruction which was immediately run.
Given the width of the cells, I wonder what the conclusions about performance of B would have been if subroutine threading or a similar technique using jmp instructions would have been.
Does anyone know if Forth suffers measurably in inner loops from have to call words that perform basic operations?
Is this where a Forth programmer would be accustomed to write the inner loop in assembly to avoid the performance penalty?
>The project's README then proceeds into lengthy detail about how to implement >Forth in C.
Seems people have/are more fun/interested implementing Forth interpreters/compilers than actually using Forth. Same with CHIP-8. It's all about making emulators.
The bootstrapping part ignores all the other stuff Forth leaves out, like all the analysis and optimization a C compiler does.
Article is lame in multiple ways, and also eForth was written by Bill Muench. Dr Ting adopted Muench's version to use assembly language bootstrapping instead of metacompilation. Bootstrapping is possibly easier for beginners to understand, but metacompilation is part of Forth's fiendish cleverness and it's a shame for an aficionado to miss out on it.
What I like about Forth is that it can be expressed at the lowest level of computation, and that it can be used to bridge that to the highest level of computation. For example, Forth only requires about 12 opcodes to run, which can be implemented in a few dozen chips. But now that you have that, since it's Turing-complete, you can now pull across a lisp or C compiler, and build a working operating system from there. Granted, that would be a lot of work, but it's relatively straightforward work, and that's always impressed me.
Lovely article, which I took the liberty to share on the Forthish discord [1]
It's hard to see practical strengths, especially with provided code examples. Most of tax code is stack tossing hiding core logic.
Code as structure could be more conveniently expressed as language data structures as structure nowdays.
Shouldn't Forth (when directly translated to either ARM or x86_64 assembly) be faster than compiled C?
This is a pretty good explanation. I think it maybe undersells the importance of the REPL a bit. (I'm not a Forth expert, but I did write StoneKnifeForth, a self-compiling compiler in a Forth subset, and I've frequently complained about the quality of Forth explainers.)
What... what are those "development effort estimates"? They seem to assume an average rate of approximately 11 lines of code written per day which seems a bit too low if you ask me.
Besides, once a C compiler is written for one platform, porting it to another one takes significantly less time than writing from scratch (especially if the compiler is written with portability in mind).
I often use a heavily forth inspired script language in my bigger c# projects. I have a hidden repl and can input scripts. I like how easy it is to produce results with such low vocabulary. Also there is no expression parsing
I always recommend the book Starting Forth [0].
It has the most charming illustrations I've ever seen in a text book.
I like the spirit of this article, but I find it strange that they open their article by quoting me, but then don't include Dusk OS's C compiler in the list.
Fairly counting SLOC is a tricky problem, but my count is 1119 lines of code for the C compiler (written in Forth of course), that's less than 8x the count of chibicc, described as the smallest.
EForth running under Subleq:
https://howerj.github.io/subleq.htm
https://howerj.github.io/subleq.htm
The same, but multiplexing instructions (it runs much faster):
Considerably better than most such articles that I have read on this but I think if the Forth community wants to get people into Forth it really needs to stop talking about how it can fit in a boot sector and the REPL; the former is not of interest or use to most programmers and the latter is probably a major cause of the misconception of Forth code being impossible to read.
What I see as the real strength of Forth is that if you write your program in source files, there is no abstraction. You stick your word definitions in those source files and let the application you are writing dictate the words you define instead of relying on the dictionary you built up on REPL and things quickly start becoming easy and the code remains readable. It might seem like a lot of work and endlessly reinventing the wheel but if you start with a featureful Forth like gforth it does not take that much time or effort once you have the basics down; you can build complex applications with gforth as easily as you can build up a full Forth with that minimal Forth that fits in your boot sector.
The main thing is learning that application development with Forth is top down design and bottom up writing. You break the application up into its major functions, break those into smaller functions, break those into words and then break those words into those simple sort words that everyone in the Forth community says you should write. Then you start writing code. I am just starting to get the hang of Forth and it is surprisingly quick and powerful once you start getting the sense of it.