Not too long ago, I went down a rabbit hole of specifying GHA yaml via dhall, and quickly hit some problems; the specific thing I was starting with was the part I was frustrated with, which was the "expresssions" evaluation stuff.
However, I quickly ran into the whole "no recursive data structures in dhall" (at least, not how you would normally think about it), and of course, a standard representation of expressions is a recursively defined data type.
I do get why dhall did this, but it did mean that I quickly ran into super advanced stuff, and realized that I couldn't in good conscience use this as my team of mixed engineers would need to read/maintain it in the future, without any knowledge of how to do recursive definitions in dhall, and without the inclination to care either.
basically, to do recursive definitions, you have to lambda encode your data types, work with them like that, and then finally "reify" them with, like, a concrete list type at the end, which means that all those lambdas evaluate away and you're just left with list data. This is neat and intresting and worthy of learning, but would be wildly overly-complicated for most eng teams I think.
However, I quickly ran into the whole "no recursive data structures in dhall" (at least, not how you would normally think about it), and of course, a standard representation of expressions is a recursively defined data type.
I do get why dhall did this, but it did mean that I quickly ran into super advanced stuff, and realized that I couldn't in good conscience use this as my team of mixed engineers would need to read/maintain it in the future, without any knowledge of how to do recursive definitions in dhall, and without the inclination to care either.
an intro to this: https://docs.dhall-lang.org/howtos/How-to-translate-recursiv...
An example in the standard lib is how it works with JSON itself: https://store.dhall-lang.org/Prelude-v23.1.0/JSON/Type.dhall...
basically, to do recursive definitions, you have to lambda encode your data types, work with them like that, and then finally "reify" them with, like, a concrete list type at the end, which means that all those lambdas evaluate away and you're just left with list data. This is neat and intresting and worthy of learning, but would be wildly overly-complicated for most eng teams I think.
After hitting this point in the search, I decided to go another route: https://github.com/rhysd/actionlint
and this project solved my needs such that I couldn't justify spending more time on it any longer.