Simon Willison’s Weblog

27th February 2025 - Link Blog

TypeScript types can run DOOM (via) This YouTube video (with excellent production values - "conservatively 200 hours dropped into that 7 minute video") describes an outlandishly absurd project: Dimitri Mitropoulos spent a full year getting DOOM to run entirely via the TypeScript compiler (TSC).

Along the way, he implemented a full WASM virtual machine within the type system, including implementing the 116 WebAssembly instructions needed by DOOM, starting with integer arithmetic and incorporating memory management, dynamic dispatch and more, all running on top of binary two's complement numbers stored as string literals.

The end result was 177TB of data representing 3.5 trillion lines of type definitions. Rendering the first frame of DOOM took 12 days running at 20 million type instantiations per second.

Here's the source code for the WASM runtime. The code for Add, Divide and ShiftLeft/ShiftRight provide a neat example of quite how much complexity is involved in this project.

The thing that delights me most about this project is the sheer variety of topics you would need to fully absorb in order to pull it off - not just TypeScript but WebAssembly, virtual machine implementations, TSC internals and the architecture of DOOM itself.