Within Unicode is defined a DSL used internally by the library implementers to define some business logic, like most DSLs it is turing complete. Anyone with the ability to make you run their rules file already has the ability to make you run arbitrary code (it's a software vendor for software you use).

It's still always fun to find Weird Machines, but as they go, this one is not very weird (it's one of the known families of programming languages, the Mathematica language being the most well known example. The person who specified this most likely was aware that this is turing complete and it's the rules author's responsibility not to write infinite loops).

https://www.youtube.com/watch?v=uNjxe8ShM-8

Llama.ttf: A font which is also an LLM

https://fuglede.github.io/llama.ttf/

https://news.ycombinator.com/item?id=40766791 (June 23, 2024)

And so it is (https://en.wikipedia.org/wiki/Semi-Thue_system#Undecidabilit...).

It's a scary and wonderful part of our world that you can bootstrap so much complexity out of a little iterated self-reference.

My only quibble with the article is in this line...

> The surprise is that it lives in a data format for locale files, shipped in every OS, whose specification doesn't mention the possibility.

... I'm not surprised. After all, the processor that interprets the data format is Turing-complete not only in its instructions, but in the page table! See https://github.com/jbangert/trapcc

If anything, when you build a system and it starts to get complex, you have to go out of your way to ensure it's decidable and can't accidentally bootstrap the universe.