Following up on the Haskell benchmark, the OCaml benchmark, the Python benchmark, the ReScript benchmark, the Ruby benchmark, the Elixir benchmark, the Java benchmark, and the Elm benchmark, I ran the same AoC 2025 Days 1–5 setup in F#.
F# occupies an interesting middle ground. It's a functional-first language on .NET — strongly
typed with type inference, pattern matching, and pipelines, but with full access to the
imperative .NET ecosystem when needed. It sees real production use but isn't anywhere near as
common as C# or Python in training data. No scaffold was provided; each model had to figure
out dotnet fsi scripting or full project setup on its own.
The result: another clean sweep. Every model solved every part.