Implementing a Forth
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Implementing a Forth
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Re: Implementing a Forth
#2I went down the "make your own Forth" rabbit hole about 45 years ago.
In January 1979, Byte Magazine's Language Forum contained the article, "IPS, An Unorthodox High Level Language."[1] The article described IPS, a language based on Forth, but with the word names translated to German. Thus, Forth's SWAP became VERT, short for vertauschen. The intriguing article concluded with a reference to Charles Moore's 1974 paper, "FORTH, a New Way to Program a Minicomputer,"[2] which was discussed on HN in 2022.[3]
I had recently assembled a Quest Electronics Super Elf computer[4] with an expanded memory size of 4 KB. The IPS article mentioned implementations under 6 KB for 8080, 6502, and RCA COSMAC microprocessors, so I thought Forth might fit. The Super Elf included an 1861 video display controller chip, with a resolution of 64 x 128 pixels (big pixels!). I designed a font of 3 x 5 pixel characters to provide 21 lines of 16 characters. Good luck distinguishing M, N, H, U, and W without some context. I bought a (possibly surplus) keyboard from Radio Shack and screwed it onto a wedge of wood to achieve a usable typing angle.
Moore's paper described about 75 Forth words. I wrote them on index cards and jotted down Forth definitions or RCA 1802 assembly code. I wrote an 1802 assembler in Fortran to ease the conversion into 1802 machine code. I still have the printouts and punch cards in storage.
Development proceeded slowly. During a break at work, I would punch my assembly code for a few Forth words, run the assembler, and bring home the printout. That night I would load previous work into the Super Elf from cassette tape, key in the new words (and changes) via the Super Elf's hex keypad, and save back to another cassette tape. Then I would test the new Forth words and note any changes needed on the printout. Lather, rinse, and repeat until, at last, it all worked.
The finished Forth system consumed a little more than 3 KB of the 4 KB of memory. User programs, data, and Forth stacks occupied the remaining memory. The R key stuck. The @ symbol was a 3 x 5 pixel blob (this is the very important Forth memory fetch operator). But it worked!
I demonstrated the system at the local personal computer club--spun off from the local ham radio club. Based on their enthusiasm, I advanced to developing tinyForth[5] for the TRS-80, a story for another day.
[1] https://archive.org/details/BYTE-MAGAZINE-COMPLETE/197901_By...
[2] https://articles.adsabs.harvard.edu/pdf/1974A%2526AS...15..4...
[3] https://news.ycombinator.com/item?id=33134663
[4] https://www.oldcomputermuseum.com/super_elf.html
[5] https://archive.org/details/80-microcomputing-magazine-1980-...
Re: Implementing a Forth
#3Not sure if this counts as an implementation, but this is my Forth compiler, written in the high-level language Go [0]. This is also a challenge, as Forth usually requires machine language, call stack access, and is naturally written in assembler. Took several tries until I found working data structures.
The funniest thing is, you can easily write and invent your own control structures in Forth, as well as change the behavior existing ones such as the do/while loop.
\ alter the behavior of do by printing the current index in each loop.
: do immediate
[COMPILE] do \ first compile previous do impl.
' i , \ then print current index
' . ,
;
Re: Implementing a Forth
#4I went down the "make your own Forth" rabbit hole about 45 years ago. In January 1979, Byte Magazine's Language Forum contained the article, "IPS, An Unorthodox High Level Language."[1] The article described IPS, a language based on Forth, but with the word names translated to German. Thus, Forth's SWAP became VERT, short for vertauschen. The intriguing article concluded with a reference to Charles Moore's 1974 paper…
Wow! What an amazing story!
I started writing forth few months ago, wrote few interpreters, with jit or with types etc, and its just amazing, I think anyone should do it. TBH I don't think any other exercise has thought me as much about programming as this.
I also notice the "return" of Forth, as it is probably the easiest high level language to make for computers with addressable memory and fetch execute cycle. The parser is just few lines of assembly and of course you can write the parser in the inner interpreter's bytecode, you don't even need assembly :) So hobbyists can just "make it" and make their own tiny operating systems with it. Of course everyone makes their own dialect, but I think thats OK. Things like https://github.com/howerj/lfsr LFSR CPU/VM running Forth, or UXN or duskos/collapseos.
Now you can also use language models to help you onboard into the language, it do some practice programs and rewrite one program in many ways.
So if you are young or old and never tried to Forth, don't miss out, its super fun.
Re: Implementing a Forth
#5I went down the "make your own Forth" rabbit hole about 45 years ago. In January 1979, Byte Magazine's Language Forum contained the article, "IPS, An Unorthodox High Level Language."[1] The article described IPS, a language based on Forth, but with the word names translated to German. Thus, Forth's SWAP became VERT, short for vertauschen. The intriguing article concluded with a reference to Charles Moore's 1974 paper…
What kind of programs would one naturally reach for Forth as the optimal solution? It has always struck me as a very low level language but I rarely hear this caveat from its advocates.
Re: Implementing a Forth
#6I went down the "make your own Forth" rabbit hole about 45 years ago. In January 1979, Byte Magazine's Language Forum contained the article, "IPS, An Unorthodox High Level Language."[1] The article described IPS, a language based on Forth, but with the word names translated to German. Thus, Forth's SWAP became VERT, short for vertauschen. The intriguing article concluded with a reference to Charles Moore's 1974 paper…
What kind of programs would one naturally reach for Forth as the optimal solution? It has always struck me as a very low level language but I rarely hear this caveat from its advocates.
I highly doubt it's useful these days on general purpose computers, where even the very smallest ones can easily implement C (or better) or even run a whole operating system like Zephyr or Yocto.
However if you're creating your own computer from scratch or have other artificial constraints (like it needs to fit into a boot sector[1]), and if you want to really understand precisely how your language works down to the lowest level detail while still having high-ish level constructs, then Forth is the ideal small language for that.
Re: Implementing a Forth
#7I am under impression that more people implement Forth than use it for programming...
Re: Implementing a Forth
#8I am under impression that more people implement Forth than use it for programming...
That's okay, it's a fun thing to do!
Re: Implementing a Forth
#9I am currently implementing a stack based language as an intermediate language for a C compiler that I am developing. I have developed a relatively straight forward compiler for the stack language to the M1 assembler from live-bootstrap. This stack language has local variables. It actually makes use of two stacks: One in the traditional sense and one for the local variables (and the return address for calls). It reads as a kind of very primitive post-fix C kind of language. See: https://github.com/FransFaase/MES-replacement and https://www.iwriteiam.nl/D2506.html#2b
Re: Implementing a Forth
#10I went down the "make your own Forth" rabbit hole about 45 years ago. In January 1979, Byte Magazine's Language Forum contained the article, "IPS, An Unorthodox High Level Language."[1] The article described IPS, a language based on Forth, but with the word names translated to German. Thus, Forth's SWAP became VERT, short for vertauschen. The intriguing article concluded with a reference to Charles Moore's 1974 paper…
What kind of programs would one naturally reach for Forth as the optimal solution? It has always struck me as a very low level language but I rarely hear this caveat from its advocates.
It made more sense in the 8 bit home computer era, where you could do a more high level coding with more performance than a BASIC interpreter, without having to mess with hexdumps for DATA segments, or Assembly opcodes.