HN commenters link it as a delightful example of how far TypeScript types can be pushed, since they are Turing complete.
The Michigan TypeScript group shows the Doom engine running entirely inside the TypeScript type system. It is open source, and two follow-up videos cover why and how they did it.
“I must link this wonderful video about TypeScript types running... DOOM.” (HN, 2025)
Typescript types (and Idris) are Turing complete. You can actually get typescript types to run doom. [this video] Idris on the other hand is SPECIFICALLY designed so types and the program live in the same language. See the documentation intro: [link] THe powerful thing about these languages is that they can prove your program correct. For testing you can never verify your program to be correct. Testing is a statistical sampling technique. To verify a program as correct via tests you have to test every possible input and output combination of your program, which is impractical. So instead people write tests for a subset of the possibilities which ONLY verifies the program as correct for that subset. Think about it. If you have a function: def add(x: int, y: int) -> int How would you verify this program is 100% correct? You have to test every possible combination of x, y and add(x, y). But instead you test like 3 or 4 possibilities in your unit tests and this helps with the overall safety of the program because of statistical sampling. If a small sample of the logic is correct, it says something about the entire population of the logic.. Types on the other hand prove your program correct. def add(x: int, y: int) -> int: return x + y If the above is type checked, your program is proven correct for ALL possible types. If those types are made more advanced via being programmable, then it becomes possible for type checking to prove your ENTIRE program correct. Imagine: def add<A: addabl
Example of TypeScript types being Turing complete.
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