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ninefathom | 3 years ago
At the time, I had no idea that it was a discrete programming language; it only registered in my mind as part of the OpenBoot/OpenFirmware environments. Then I ran into the FreeBSD bootloader and things finally clicked. "Aha," I thought, "this is an actual programming language." But what made it so popular for the early boot process, and where else was it used?
The modularity was stunning. It was easy- almost absurdly so- to build complex code up from a series of tiny individual functions. That, coupled with the minuscule interpreters and simple stack-based approach, made perfect sense for situations where developers need to perform complex tasks with minimum of storage overhead, and with portability as a first class citizen.
Gordonjcp|3 years ago
Probably simplicity. You can get a very basic Forth system going in a few dozen assembly instructions. Then, you write some Forth "primitives", words written in assembly, to do things like basic arithmetic, branching, stack manipulation, and memory manipulation. There are endless debates about how many primitives you really need, but in general a couple of dozen primitives ought to get you started.
Then the rest of Forth is just written in Forth! You might not really have recognisable Forth source at this stage but more complex words can be written out as lists of the addresses of primitives. Think of it as like rolling your own macro assembler. The "inner interpreter" reads these lists of addresses and either jumps directly to the machine code in a primitive, or into a command that starts the inner interpreter chewing on a new word, pushing the one you've just come from onto the return stack.
It seems really really complex until at some point as you stare at it, it'll just snap into focus and you see it's actually a very simple thing that does a very clever trick.
masklinn|3 years ago
> if you have an interactive terminal, a dictionary, and the colon compiler, can you really build everything else based on just eight primitives?
> Turns out the answer is yes
The eight primitives come from an old usenet thread: https://groups.google.com/g/comp.lang.forth/c/NS2icrCj1jQ
DonHopkins|3 years ago
https://github.com/openbios
https://wiki.laptop.org/go/FORTH
https://news.ycombinator.com/item?id=29261810
Speaking of Forth experts -- there's Mitch Bradley, who created OpenFirmware:
https://news.ycombinator.com/item?id=21822840
Here's the interview with Mitch Bradley saved on archive.org:
https://web.archive.org/web/20120118132847/http://howsoftwar...
[...]
https://news.ycombinator.com/item?id=27484426
I wrote malloc.fth for Mitch Bradley's ForthMacs, which ended up in OpenFirmware:
https://github.com/openbios/openfirmware/blob/master/ofw/cor...
[...]
https://news.ycombinator.com/item?id=26892629
In a lot of FORTH implementations, constant numbers like 0, 1, -1 and others are hard coded, not just for speed but also for space: a call to a code word only takes one cell, instead of using two cells with a LIT [value].
Here's some Breshenham line code I first wrote in FORTH (Mitch Bradley's SunForth on a 68k Sun-2 with cg2 graphics board), then translated to 68k code (using the rpn FORTH assembler) -- the FORTH code is commented out before the corresponding assembly code:
https://donhopkins.com/home/archive/forth/cg/line.f
[...]
https://news.ycombinator.com/item?id=17480298
Cool! Does it include a FORTH 6502 assembler written in FORTH? I love writing assembly code in RPN with Forth macros!
You can write FORTH code with loops and conditionals and any kind of logic and parameters, that dynamically assembles machine code! Much better than your typical macro assembler.
Here's some 6502 assembler for an Apple ][ SUPDUP terminal emulator that does ram card bank switching:
http://www.donhopkins.com/home/archive/forth/supdup.f
[...]
https://news.ycombinator.com/item?id=22456471
In what way is PostScript worse than Forth? Please answer with specific details, and provide links to code if you can. I programmed a lot of Forth code before learning and moving on to programming a lot of PostScript code, so I've used each of them extensively, and much prefer PostScript, and I'm happy to show you why and explain by showing you code.
[...]
https://news.ycombinator.com/item?id=21968175
Kragen is right that PostScript is a lot more like Lisp or Smalltalk than Forth, especially when you use Owen Densmore's object oriented PostScript programming system (which NeWS was based on). PostScript is semantically very different and much higher level that Forth, and syntactically similar to Forth but uses totally different names (exch instead of swap, pop instead of drop, etc).
[...]
kragen|3 years ago