I've spent the past few weeks coming up with my own simple programming language, which compiles to linux/amd64 assembly.

I could have gone all out writing standard library routines for opening files, running shell commands, coding strstr, strcpy, and similar. And to be honest I did implement some things I didn't need as part of the learning process (for example print(getenv("HOME")) works). But I soon realized I needed some example programs to test things and show off.

So of course the first real program I implemented was a brainfuck interpreter. Which means my language is now, indirectly, turing complete!

My early versions took 9 minutes to output the famous mandelbrot program, so I had to make a bunch of optimizations, and later implemented support for switch/case statements to speed things up. Now I can generate the same output in two minutes - so room for improvement, but also a good bit of progress!

Cheating by implementing another language in my own was very very satisfying. Though of course this is all for fun/learning and not intended to be used seriously by anybody, not even myself!

https://github.com/skx/s-lang

Wow! And it also implements a very interesting variant of SUBLEQ that is turing complete.

>This VM implements an OISC - a One Instruction Set Computer. That instruction takes three signed 32-bit operands, a, b and c, and runs a program from memory m[] as follows:

1 PC (program counter) starts at 0

2 Fetch the next instruction (32-bit signed operands a, b and c)

3 If the low bit on any operand is set, remove it, and replace that operand with m[operand] i.e., a dereference of that address

4 Set m[b] = m[b] - m[a]

5 If m[b] is 0 or negative, set the PC to c, otherwise increment PC by 3 words

6 Go to step 2

I think I like this idea, but the linked-to Eternal Software Initiative [1] is a bit confusing. There are several different versions of the instructions to decode this, all conflicting.

There's the one here: Set m[b] = m[b] - m[a]

Then it links to the reference implementation on github [2] which says you just need the napkin notes [3], which is dividing everything read by 4, which is corroborated by the reference implmentation [4], but it's not clear why 4 is chosen here rather than 2, as it seems to waste a bit. Was this bit needed, or is it reserved for future expansion?

I presume the original implementation didn't do the divide by 4 and it was added later, but I don't see why it was needed, other than perhaps just making LLVM code gen a little easier. I'd need to work through lots of examples to work out if the system as described is impossible without dividing by 4 (although you'd presumably only be able to access even addresses, and the PC increases by 3 each time, so it would definitely be annoying to refer to code locations).

Then the reference implementation starts doing magic when location 64 is accessed, overwriting locations 64-67 with the current time, which is mentioned in the napkin description, but not the description on the main page.

Both descriptions mention the magic -1 address, so it seems strange that the very implementation-dependent UTC clock isn't also implemented with -ve addresses rather than trashing memory that is otherwise free for the implementation to use as desired.

Both descriptions also mention the regular timer interrupt process, which also seems disappointing, reusing address 0 as the interrupt handler location and 1 as the saved PC, which means that you have to overwrite the initial entry point at location 0 as soon as the program starts.

[1] https://eternal-software.org/

[2] https://github.com/adriancable/eternal

[3] https://github.com/adriancable/eternal/blob/main/docs/napkin...

[4] https://github.com/adriancable/eternal/blob/main/vm/vm.c

I downloaded and built this, and I feel confident in stating that this is the most impressive thing I have ever seen.

Here is the video:

https://www.youtube.com/live/MoWCwZx1Swc?si=eIOlRsKWNKRVRZeB...

What I find fascinating is the fact that you can implement those few lines in an esoteric language such as FRACTRAN or Game of Life and even boot Linux on them. Seems doable now. In theory.