In PostScript!
By Anders Piniesjö.
This is an attempt to solve the Advent of Code for 2025 in PostScript.
About 27 years or so ago I wrote PS-HTTPD, a web server in PostScript. Ten years after that I made PostScript based printer drivers for the Opera Web browser. During the years since then, I have forgotten most of that quite funky language. It was time to bring the memories back to life!
The goal is that each day's task should be executable on a PostScript printer. No non standard extensions will be used. It is possible that some tasks will be very demanding for a normal printer (e.g. day 8 step 2), but it should still be possible to print.
During development and for reasonable execution I use the fantastic Ghostscript. The Ghostscript developers have provided us a free PostScript intepreter since 1988!
The data input files (input.txt) are personal and not included
in this repository. To run a task, place your own input.txt in
respective directory and run make run.
PostScript (PS) is a Turing complete page description language invented by Adobe. It was introduced in 1982. The most recent version, PostScript 3, was released 1997.
PostScript has mainly been used as a page description language for sending documents to printers. It has historically also been used for monitor graphics, then called Display PostScript.
Compared to rasterized printer driver formats, such as PCL, PostScript allows more advanced possibilities. One major benefit is that PostScript in general is vector based and allows good print quality, regardless of printer resolution.
As a language it is largely different from modern normal languages.
It is stack based and is conceptually relatively close to the language
FORTH. Calculations are made by pushing values on the stack and
calling operaitons. Operations pops the operands from the stack and
pushes the result to the stack. PostScript has support for if and
if-else structures as well as normal loop structures, arrays and dicts.
Recursion is possible but limited. The main problem with PostScript
for something such as Advent of Code is that it lacks local scopes.
That also makes recursion problematic for tree searching.
The successor of PostScript is PDF.
I have currently managed to finish days 1 to 11.
I for long thought that day 10 part 2 exceeded what is practical or possible in PostScript. But after expressing my problems on Reddit, telling about the PostScript limitations i got good answers with new insights on day 10 part 2. That helped me develop a better solution. Even though it took some 10 minutes to calculate through all the "machines" for that task on a modern machine I got the correct answer! Many thanks to u/kupuguy for the specific solution idea that was possible in PostScript!