Just me working on Advent of Code.
Rather than treat this project as a discrete set of small, throwaway exercises, I'm working on this as if it's a full-fledged project that grows over time.
Each day's puzzle is written as if it needs to be maintained in the future; typespecs, tests, documentation, and use of modules over simpler data structures when it adds to readability or better models the domain.
As puzzles are added and commonalities become obvious, I'm adding utility mechanisms and refactoring the project as a whole to use them.
As a result, these puzzles will be more verbose that what you'd normally see in an Advent of Code project.
Use the Mix task:
$ mix advent YEAR DAY