💾 Archived View for biomimetic.me › subleq.gmi captured on 2021-03-30 at 09:09:46. Gemini links have been rewritten to link to archived content
⬅️ Previous capture (2021-03-30)
-=-=-=-=-=-=-
One big reason for the success of Gemini is that it has a deliberately simple specification, which means that programmers can actually implement it. As opposed to implementing basically an entire operating system as required for a "browser" these days.
I wondered, what if there was a way to do something similar for sharing simple programs? So I did some googling for things like "simplest possible VM". I found SUBLEQ: a One Instruction Set Computer (OISC).
SUBLEQ stands for SUBtract and Branch if Less than or EQ to zero. The core of it sums up very simply:
# For the code SUBLEQ a,b,c: mem[b] = mem[b] - mem[a] if mem[b] <= 0 goto c
So its a series of instructions (all of the same type -- SUBLEQ) where each instruction is composed of three numbers.
That's it for the actual computation. Literally. The rest of it is related to waiting for a character from STDIN and writing out a character to STDOUT. To write a character out, the second operand is -1, and that means to print what is in the first operand. To read a character, the first operand is -1, and the character is read into the second operand. The third operand indicates a code location for branching.
A program to print "Hi" looks like this:
9 -1 3 10 -1 6 0 0 -1 72 105 0
This is probably not the best explanation. If you want more explanations, see:
SUBLEQ - A One Instruction Set Computer (OISC)
There are implementations for this for almost all popular programming languages on Rosetta code. They are all less than a page of code:
Mine is around 27 lines.
#!/usr/bin/python3
import sys
from readchar import readchar
def run(mem):
codePos = 0
mem = mem + [0] * 65536
printing = False
while codePos >= 0:
a, b, c = mem[codePos:codePos+3]
if a == -1:
sys.stdout.buffer.flush()
mem[b] = ord(readchar())
if mem[b] == 3:
sys.exit(0)
codePos += 3
elif b == -1:
sys.stdout.buffer.write(bytes([mem[a]]))
printing = True
codePos += 3
else:
mem[b] = mem[b] - mem[a]
if mem[b] <= 0:
codePos = c
else:
codePos += 3
if printing and mem[b] != -1:
sys.stdout.buffer.flush()
printing = False
There is another file that reads the numbers in that make up the "machine code", but that's the entire virtual machine. With a short program like that, one can run basically any type of console program. Which, I was initially thinking the fact that the limitations of only character input/output and pausing for input were going to be problematic.
But after thinking about it, I think the limitations make sense for this concept. The idea was to have something really simple to implement that would allow people (theoretically) to share simple programs. Simple enough to implement that it would be easy for people to create their own clients/hosts (the way there are lots of Gemini clients). And also, we want to get away from the type of BS that shows up in browsers, such as browser tabs freezing up from out-of-control scripts secretly mining cryptocurrency etc.
The fact that it pauses for input is probably good for this concept, because it makes it less likely for people to start creating laggy programs. Most programs will pretty quickly need input from the user and then whatever loop there is will get a rest.
There are multiple macro assemblers and even a high-level C(ish) compiler (called hsq)! At the bottom of the Lawrence Woodman's page linked above (techtinkering.com) is a link to his excellent subleq assembler "sblasm".
Oleq Mazonka's Higher Subleq C compiler
Anything you can imagine, up to and including Nethack (assuming your terminal supports ANSI escape codes) (and beyond). I did not code anything as cool as that, but did play with it some. I used hsq, wrote some code for ANSI escape codes for colors and moving the cursor, and made this Dice Roller thing:
Here is a simple way you can try this concept out. First, paste the code above into /usr/bin/subleqvm, and then add this code to the bottom (which actually reads in the "machine code" file):
with open(sys.argv[1],'r') as f:
text = f.read()
lines = text.split('\n')
list = []
for line in lines:
list_ = line.split(' ')
for item in list_:
if item != '':
list.append(int(item))
run(list)
Make it executable and run 'pip install readchar' if necessary. Now, assuming you have the av98 Gemini client, run it and type:
handler application/subleq subleqvm %s go biomimetic.me/roller.sq
It should launch the Python script in another process/window and run the dice roller.
One note about the hsq compiler. It can also run subleq programs. But on my computer, it requires you to press enter before recognizing any character input. I hope if anyone else actually builds a subleq VM, they don't do it that way, because that means programs like mine that expect people to just press certain keys and then immediately react won't work.
One other thing about hsq is that it assumes your subleq VM will auto-expand memory at will. Mine doesn't do that. Instead it just adds an extra 64KB to the end. I think that's a better idea than letting it expand indefinitely. And it will still work with hsq-compiled programs.
Here is the (C-like) code for the dice roller program above which can be compiled with High-level subleq (hsq):
int printf(char * s);
int getchar();
int RED = 1;
int GREEN = 2;
int WHITE = 15;
int BLACK = 0;
int BLUE = 4;
int YELLOW = 11;
void clearScreen() {
printf("\x1B[2J");
}
void fgColor(int clr) {
printf("\x1B[38;5;%dm", clr);
}
int bgColor(int clr) {
printf("\x1B[48;5;%dm", clr);
}
int setPos(int x, int y) {
printf("\x1B[%d;%dH",y,x);
}
int repeatChar(int ch, int times) {
for (int i=0; i<times; i++) {
printf("%c",ch);
}
}
int fillbox(int color, int x, int y, int w, int h) {
bgColor(color);
int s = y;
for (int j=0; j<h; j++) {
setPos(x,y+j);
repeatChar(32, w);
}
}
int seed = 1234567;
int rand() {
seed = (8121 * seed + 28411) % 134456;
return seed;
}
int d6() {
return rand() % 6 + 1;
}
void diceline(int y, char* descr) {
setPos(3, y);
fgColor(WHITE);
char* yellow = "\x1B[38;5;11m";
char* whites = "\x1B[38;5;15m";
printf("╔═══════════════╦════════════════════════════╗");
setPos(3, y+1);
printf("║ ");
printf(descr,yellow,whites);
printf(" ║ ║");
setPos(3, y+2);
printf("╚═══════════════╩════════════════════════════╝");
}
int rolls[101];
int lines[101];
int totals[101];
void initrolls() {
for (int i=0; i<101; i++) {
rolls[i] = 0;
lines[i] = 0;
totals[i] = 0;
}
lines[4] = 4;
lines[6] = 7;
lines[8] = 10;
lines[10] = 13;
lines[12] = 16;
lines[20] = 19;
lines[100] = 22;
}
void ui() {
clearScreen();
fillbox(BLUE, 1, 2, 51, 25);
setPos(20,2);
fgColor(YELLOW);
printf("Dice Roller");
initrolls();
diceline(lines[4],"(%s4%s)-sided ");
diceline(lines[6],"(%s6%s)-sided " );
diceline(lines[8], "(%s8%s)-sided ");
diceline(lines[10], "1(%s0%s)-sided ");
diceline(lines[12], "(%s1%s)2-sided ");
diceline(lines[20], "(%s2%s)0-sided ");
diceline(lines[100], "(%sh%s)100-sided");
setPos(15,25);
fgColor(YELLOW);
char* yellows = "\x1B[38;5;11m";
char* whites = "\x1B[38;5;15m";
printf("(%sc%s)lear rolls (%sq%s)uit",yellows, whites);
}
void clearrolls() {
initrolls();
for (int i=0; i<101; i++) {
if (lines[i] > 0) {
setPos(22, lines[i]+1);
bgColor(BLUE);
repeatChar(' ',26);
}
}
}
int lastroll = 0;
int roll(int sides) {
if (sides<0||sides>56) return 0;
if (sides != lastroll) clearrolls();
lastroll = sides;
if (sides == 0) { sides = 10;}
else if (sides == 1) { sides = 12; }
else if (sides == 2) { sides = 20; }
else if (sides == 56) { sides = 100; }
if (lines[sides]==0) return 0;
int r = rand() % sides + 1;
int max = 7;
if (sides == 100) max = 5;
if (rolls[sides] == max) {
clearrolls();
}
totals[sides] += r;
rolls[sides] += 1;
int n = 3;
if (sides == 100) { n = 4; }
setPos(20 + (rolls[sides] * n)+1, lines[sides]+1);
fgColor(BLACK);
bgColor(WHITE);
printf("%d", r);
fgColor(GREEN);
bgColor(WHITE);
setPos(45, lines[sides]+1);
printf("%d", totals[sides]);
}
int getseed() {
clearScreen();
setPos(1,1);
fgColor(WHITE);
printf("Enter a random number seed (6 arbitrary characters): ");
for (int i=0; i<6; i++) {
int d = getchar();
printf("%c", d);
seed -= d * i;
}
printf("\n");
}
int main() {
getseed();
ui();
setPos(10,10);
fgColor(YELLOW);
while (1) {
int d = getchar();
if (d == 'c') clearrolls();
if (d == 'q') break;
else roll(d-48);
}
fgColor(BLACK);
bgColor(BLACK);
clearScreen();
fgColor(WHITE);
}