advent

Haskell solutions to every Advent of Code puzzle from 2015 to 2025: 262 days, one file each, shown here next to a short critique of how each one works and where it is weak.

The years read differently. 2015 to 2020 aim for idiomatic, fairly clean Haskell with a few shared helpers. From 2021 the solutions use a replacement Prelude, Relude at first and then a custom one, and from 2022 they prioritise fun: by 2024 and 2025 every solution is written against quaalude, a dense Unicode prelude with no imports needed, and the median solution is less than a third of the length it was in 2018.

Pick a year and a day below, or use ← and → to step through them. In 2024 and 2025 code, dotted names are quaalude's: hover or focus one for its type.

Shorter every era. Lines of code per solution, blank lines and comments excluded.

About this page

Each critique was drafted by a language model (Claude Opus 5.5) from the solution's code and the types of any quaalude names it uses. A second model (GPT-5.4) then checked every claim against the code: 194 critiques were revised at least once, 170 passed the check, and for the other 92 the drafting model ruled on each remaining objection from the code (accepting 43, rejecting 162 as mistaken or pedantic). A sample was checked by hand. They describe the code, not the answers, and are deliberately short.

Puzzle text and inputs are not reproduced here: they belong to Advent of Code, whose author asks that they are not redistributed. Each day links to its puzzle. The page is generated from the repository by scripts/site.