Advent of Code is a fun challenge and this year I decided to attempt solving it in Purescript. Today I'm declaring this attempt a failure. This post will serve as a postmortem.

Choosing Purescript

Last year I solved my first Advent of Code using Go. It was fun and I knew immediately that I will come back for the next AoC. I also knew that I won't be solving it using the same language - learning on the go (pun intended) contributed significantly to my enjoyment of AoC 2022.

In November 2023 I listened to an old podcast where Richard Feldman evangelises Elm programming language. I got interested and initially decided to use Elm for the upcoming Advent of Code. While I was learning the basics of the language I also learned about the ongoing old controversy in Elm community related to how its BDFL handles communication and development. I decided that that's too much drama for my liking and that it has too little hope of resolving anytime soon - and that it's better to stay away from Elm.

That's how I ended up with Purescript. It was probably the only other frontend language that offered functional programming with a strong type system and a nice UI framework. I hoped that using an unconventional language would introduce me to frontend development without dealing with unpleasant Javascript ecosystem.

Learning Purescript

My only prior experience with functional programming was Microsoft's Power Query M language which is rather narrowly focused on data processing and is not a general purpose language.

So, with effectively zero prior knowledge I started learning from The Purescript Book but quickly switched to Functional Programming Made Easier by Charles Scalfani - the former was too fast paced for me. Scalfani's book was an enjoyable read even if a little too verbose. I did not follow author's advice to type out and run all code snippets from the book - that may have contributed to my eventual failure but I don't think that it was a major factor.

Failing Purescript

I enjoyed solving small textbook problems in Purescript. It's a very nice language. Here are the things I liked most about it:

I had no problems with understanding recursion, currying, pattern matching, etc. I had relatively little problems with understanding monads and related concepts.

My problem was that these nice abstract concepts just did not translate in my head to applicable programming techniques. Simple practical tasks tripped me up hard.

Parsing text was painful. For the first AoC puzzle I decided to tough it out with a bespoke char based parser even though I vaguely understood that there should be a monad based parser combinator library for that. That vague knowledge was not provided by any of these books, I've picked it up accidentally from some random blog post on the web.

For the second AoC day I used the proper library. It was better but still felt unnecessarily difficult. When third day's puzzle called for a parser not based on regular grammar my mind just blanked out. I was loaded up to the brim with pure theory and I lacked practical knowledge to apply it.

All this time while I was struggling with text parsing the actual tasks I picked up Purescript for (frontend experiments and puzzle solving) were deprioritized to background. I have to commend Purescript and Halogen on this because if it was anything less than straightforward none of UI and/or puzzle solutions would get done - I just barely devoted any time to that.

The project got stalled. I was reluctant to finish the last chapters of Scalfani's book because I was confident that they won't provide me with practical knowledge I was lacking. I was hesitant to go web diving for new, more practical learning materials because I wasn't sure they exist - Purescript community is rather small, and most learning resources are enumerated in multiple places. I evaluated those lists the first time I looked. I probably should've gone looking for more generic functional programming knowledge - and that would blow my free time budget.

So I'm just declaring bankruptcy on this project.


Even though I failed to cowboy my way into Purescript I still got the solutions to first two days of Advent of Code to show off - all logic executed client side, all UI generated on demand, all type safe and checked at compile time.

I could probably pour more effort, practise more, find new learning resources - and complete the remaining challenges. I'm stubborn enough to see this through. But my hobby time is not unlimited and there are other projects waiting - I'm certain I will enjoy some of those more.