Fast Parse VS adventofcode

Perhaps use Li Haoyi's fastparse instead? https://github.com/com-lihaoyi/fastparse

You might want to adapt Li Haoyi’s XML parser for fastparse.

Mostly a mess of pattern matching. I really need to make some generic tree utilities. Haven't been able to find a decent parser combinator that works in Scala 3 (I usually use fastparse which depends heavily on Scala 2 macros, and scala-parser-combinators works in Scala 3, but I've had a lot of trouble getting it to not be too greedy), so I used the state monad from cats to parse at the bottom of the file, which I think turned out fairly nice.

Agreed! I would say that parser combinators are the sweet spot and the right choice in most cases.

Scala has them as well, e.g.: https://com-lihaoyi.github.io/fastparse/

And the good thing is, you don't have to learn a completely new language/syntax, you can use the host language's syntax and you have full IDE support as well.

Part one went fairly fast, but spent quite some time on getting part two right. I settled on the approach of just iterating over the grid and using a boolean to see if I had to count elements or not. However, I had some issues figuring out when to swap, this post by /u/rogual helped me figure it out. After that I lost quite some time on an error that only occurred with my input, not with the example input. It turned out that my loop (which I take form my p1 solution) didn't include the start node, which caused all sorts of counting issues.

[Language: Elixir] https://github.com/mathsaey/adventofcode/blob/master/lib/2023/4.ex