> My guess was only that when you try and get the agent to decide stuff like data types and type classes and how to structure the program it does a poor job and worse then if you did it in other languages.

It's about the same as for other languages, in my experience. LLMs are terrible at Haskell type design, but they're terrible at Rust type design too, terrible at deciding when and how to use Python classes, terrible at deciding when metaprogramming is appropriate, terrible at deciding what is well factored and what is not - great scripters, terrible lead engineers. The root causes seem to be things like bad domain modeling, judgement about which things matter and which things don't, prioritization, and so on, all of which produce bad designs in any language that will let you. The only really Haskell-specific defect I've noticed is an aversion to polymorphism and especially to HKTs.

Yes agree it's not a good architect (and thankful as it puts a ceiling of crappy vibe coded apps and what vibe coders can do). But in languages like go-lang and python it's easier for you to just hand off something you want made to an llm and come back and possibly maintain and fix it in the future or modify it.

I have found go-lang fantastic for this, and although I would not do this for an important thing, for writing little tools that are a little beyond what would usually be a script and you want to maintain, it's great. I did this for a tool to insert data from stripe into a db for my service and it was a one shot thing.

> LLMs are terrible at Haskell type design, but they're terrible at Rust type design too, terrible at deciding when and how to use Python classes, terrible at deciding when metaprogramming is appropriate, terrible at deciding what is well factored and what is not - great scripters, terrible lead engineers.

I find there are shibboleths you can say which get the LLM into a space where it can do better but generally I agree with you.

I also find that if the LLM is working in an existing code base with a really opinionated and consistently applied design that it will largely stay consistent with the codebase. Quality will drift as the ratio of human to LLM code changes so you periodically have to do a big cleanup to keep it from going too far.