Back in the day computer mags had 20-liner competitions. The objective was to cram as much functionality into 20 lines of BASIC and people did amazing stuff with that.
To use the space as best as possible lines were filled to brim and BASIC commands abbreviated. PRINT was ? and other command abbreviations contained PETASCII characters that don't even have a Unicode equivalent[1].
The Commodore 64 particularly had square[2] 8x8 pixel characters and a line on the screen was 40 of them in a row. A logical line from the BASIC interpreter's perspective was still 80 characters long though, which made the program effectively 40 screen lines high.
You see, where this is going. The perfect 20-liner was close to a 40 by 40 square of character salad.
[1] They were one letter and a shifted letter, which could be displayed as symbol depending which mode you were in. They were printed expanded when listing the program. Everything was a bit complicated.
[2] Almost. Pixels were not perfectly square, with the aspect ratio depending on PAL or NTSC.
> Back in the day computer mags had 20-liner competitions.
In the magazines I remember from my days cutting my programming teeth on an Acorn Electron, there were 10-liners and 1-liners. What some people could squeeze out of 252 bytes was very impressive, even without using extra features (extra graphics primatives for instance) found in other models like the Master series.
My first summer job was a $2/hour "Night Operator" at Transdata, a Phoenix timesharing company. They shut down their timesharing service at night, so after running a few batch jobs, I had the SDS Sigma 5 all to myself.
We had a few one-card programs, some fun, some useful. A single card held 80 bytes of machine code.
The Sigma 5 had a small speaker on the front panel that you could toggle between two states to move the cone in or out. How often you toggled it determined the pitch of the sound.
One card was called BIRDS. It toggled the speaker to make it sound like several birds chirping at each other.
A more useful one was PRINT. You put it in front of a deck of cards, ran the deck through the card reader, and it would print the deck.
It was a bit slow, because it used a single memory buffer:
In other words, at any moment either the card reader or the printer would be operating, not both.
I studied the code and found there were just enough bytes left out of the 80 to implement double buffering by flipping a buffer pointer at each step:
1. Read card 1 into buffer A
2. Print card 1 while reading card 2 into buffer B
3. Print card 2 while reading card 3 into buffer A
4. Print card 3 while reading card 4 into buffer B
etc.
Current submission title “Print, a one-line BASIC program” is not great. Title from the page:
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
Could also be something like “10 PRINT: a book about a one-line Commodore 64 BASIC program” (taken from the first sentence with “is” changed to a colon).
Hey what happened to my submission title? I swear it started with “10 PRINT”. Perhaps a mod/admin changed it, but I don’t have an option to edit it now.
TLDR: the program prints a pseudorandom sequence of characters 205 and 206, which on Commodore 64 are graphics characters similar to / and \.
When repeated across multiple lines, it looks like an intricate random maze. But it is actually just a visual representation of whatever PRNG is used on the platform, with the default seed as set by the BASIC interpreter.
For those that don’t know ascii off the top of the head, it prints either a forward or backward slash repeatedly, which in the c64 font creates a pretty art piece like the graphic at the bottom of the screen.
The referenced book was so good until the “considered harmful” sections. As it indicates, GOTO is basically JMP, and I’m sorry if someone is offended by BASIC, but it’s not only the subject of the book but was the promoted language to the masses for early microcomputers, such that people would buy the related BASIC book at the store, along with the computer.
Try `10 PRINT CHR$(205.5+RND(0)1); : GOTO 10` in yabasic or `10 PRINT CHR$(47+INT(RND(1)2)*45); : GOTO 10` in most modern BASIC dialects, which explicitly chooses between '/' (47) and '\' (92) characters.
Back in the day computer mags had 20-liner competitions. The objective was to cram as much functionality into 20 lines of BASIC and people did amazing stuff with that.
To use the space as best as possible lines were filled to brim and BASIC commands abbreviated. PRINT was ? and other command abbreviations contained PETASCII characters that don't even have a Unicode equivalent[1].
The Commodore 64 particularly had square[2] 8x8 pixel characters and a line on the screen was 40 of them in a row. A logical line from the BASIC interpreter's perspective was still 80 characters long though, which made the program effectively 40 screen lines high.
You see, where this is going. The perfect 20-liner was close to a 40 by 40 square of character salad.
[1] They were one letter and a shifted letter, which could be displayed as symbol depending which mode you were in. They were printed expanded when listing the program. Everything was a bit complicated.
[2] Almost. Pixels were not perfectly square, with the aspect ratio depending on PAL or NTSC.
> Back in the day computer mags had 20-liner competitions.
In the magazines I remember from my days cutting my programming teeth on an Acorn Electron, there were 10-liners and 1-liners. What some people could squeeze out of 252 bytes was very impressive, even without using extra features (extra graphics primatives for instance) found in other models like the Master series.
My first summer job was a $2/hour "Night Operator" at Transdata, a Phoenix timesharing company. They shut down their timesharing service at night, so after running a few batch jobs, I had the SDS Sigma 5 all to myself.
We had a few one-card programs, some fun, some useful. A single card held 80 bytes of machine code.
The Sigma 5 had a small speaker on the front panel that you could toggle between two states to move the cone in or out. How often you toggled it determined the pitch of the sound.
One card was called BIRDS. It toggled the speaker to make it sound like several birds chirping at each other.
A more useful one was PRINT. You put it in front of a deck of cards, ran the deck through the card reader, and it would print the deck.
It was a bit slow, because it used a single memory buffer:
In other words, at any moment either the card reader or the printer would be operating, not both.I studied the code and found there were just enough bytes left out of the 80 to implement double buffering by flipping a buffer pointer at each step:
Twice as fast!Current submission title “Print, a one-line BASIC program” is not great. Title from the page:
Could also be something like “10 PRINT: a book about a one-line Commodore 64 BASIC program” (taken from the first sentence with “is” changed to a colon).From the text: “10 PRINT is a book about a one-line Commodore 64 BASIC program, published in November 2012.”
10 PRINT is their official shortened version.
Hey what happened to my submission title? I swear it started with “10 PRINT”. Perhaps a mod/admin changed it, but I don’t have an option to edit it now.
It's automatically removed to reduce the prevalence of listicles on the front page.
I'd recommend always checking submission titles afterwards because the auto-filter often butchers them. You can edit them at least for a few minutes.
TLDR: the program prints a pseudorandom sequence of characters 205 and 206, which on Commodore 64 are graphics characters similar to / and \.
When repeated across multiple lines, it looks like an intricate random maze. But it is actually just a visual representation of whatever PRNG is used on the platform, with the default seed as set by the BASIC interpreter.
https://sta.c64.org/cbm64pet.html
There is a 10-byte assembler (Intel) port of the same program:
https://trixter.oldskool.org/2012/12/17/maze-generation-in-t...
For those that don’t know ascii off the top of the head, it prints either a forward or backward slash repeatedly, which in the c64 font creates a pretty art piece like the graphic at the bottom of the screen.
And for those who do know ASCII off the top of their head, it's actually PETSCII. 205 (0xcd) is a right diagonal and 206 (0xce) is a left diagonal.
ASCII / (0x2f) and \ (0x5c) has three problems:
1. They're not as conveniently located (chr$(47+(rnd(1)*45) isn't quite as pretty)
2. They don't fill up character cell so there are gaps in the "maze"
3. PETSCII doesn't have a \ (0x5c is £)
This is indescribably beautiful. Thanks for sharing it! It went straight to the top of my reading queue.
The referenced book was so good until the “considered harmful” sections. As it indicates, GOTO is basically JMP, and I’m sorry if someone is offended by BASIC, but it’s not only the subject of the book but was the promoted language to the masses for early microcomputers, such that people would buy the related BASIC book at the store, along with the computer.
I tried this on all the basic interpreters available on Ubuntu (yabasic, sdlbasic, basic256 and bwbasic), couldn't get it to work on any of them.
In a couple cases the only remaining issue was the lack of a RND() function definition
Try `10 PRINT CHR$(205.5+RND(0)1); : GOTO 10` in yabasic or `10 PRINT CHR$(47+INT(RND(1)2)*45); : GOTO 10` in most modern BASIC dialects, which explicitly chooses between '/' (47) and '\' (92) characters.
What about freebasic? I know it's a compiler, though.
See also https://youtu.be/34CXQr5OLas