Build env:
$ direnv allow .
Build app:
$ hpack && cabal build
Set session cookie for the fetcher:
$ echo 'export AOC_SESSION=<my-aoc-2020-session-cookie>' > .envrc.private
Fetch day 1 input file:
$ cabal run fetch -- --day 1
Solve day 1:
$ cabal run solve -- --day 1
Build and use with nix:
$ nix-build nix/release.nix
$ result/bin/solve --day 1