A version of nix supporting flakes. The flake.lock file locks versions for all dependencies. … well, except those required for testing with cabal test. The Haskell package doctest-parallel was broken in nixpkgs at the time, so flake.nix just ignores tests.

nix run . -- --help

Step into shell with dependencies, like ghc, cabal and the Haskell packages from adventofcode2021.cabal

nix develop

Hack away at lib/Day01.hs until it passes tests for that day.

# Stays up, reloading when files change.
ghcid -T Day01.test

Alternatively, run full test suite with cabal.

cabal test

Run the first task of the first day.

cabal run exe:adventofcode2021 -- -d 1 -t run1 -i data/day01/example_input.txt