I am increasingly wondering if we are in a post-language world in terms of development. Why would I ask an agent to write a server in anything other than the most efficient language, although efficiency can take several forms: runtime, token usage during development, and wall clock dev time (affected by slow compile times for example).

My intuition is that type-safe languages with fast compilers are the best option. Maybe Go? I personally prefer Java just due to my experience running it in production, but am not sure there's many arguments for it over Go in a greenfield application. The other candidate would be Rust, but I worry about token efficiency and tool performance, I suspect it's not worth it for the runtime improvements.

All that being said, in this article switching to Python seems like a wild choice. Relatively poor performance, no compile time checking at all. Python's big selling point was developer ergonomics, which seems largely irrelevant now.

These are all just thoughts at the moment, I should try to find some evidence one way or another.

My thought reading this article was: Why write the system in any one language at all? And I don't just mean having some parts in one language and others in another language, I mean redundant implementations of the same parts. You can use an AI to rewrite parts of the system, and then throw away the old part... or you could just keep the old part.

That is: Have a Haskell base system. Have a Python "development" version on which you iterate at lightning speed. But also, in the background, moving at whatever pace it takes, have an agent running that imports all the Python development changes into the Haskell version. Have nightly builds of the Haskell version to reap its benefits (issues caught by the type system, more efficient native code). They must have continuous or nightly processes to fix bugs in the Python code anyway, there is no way that all the things they ship "while still on the call with the customer" are always tested on the full test suite and always 100% correct.

And it doesn't have to be Python/Haskell of course. The "development" version could be a (hypothetical?) interpreted Haskell. I have no idea if ghci would be useful for this. Neither do I know if the 15-minute Haskell build time is spent in the frontend (so an interpreter would have to pay that cost too) or in code generation or linking (which the interpreter wouldn't need to care about). Anyway, these are things I would think about before I did what the OP did.

Language choice had less impact than people first assume even before LLMs in most software. A good engineering team produces good code in whatever language they happen to be using. In my own career I've worked in serious Java, Scala, Haskell, Javascript, PHP, and Python application stacks and I've seen plenty of good and bad examples.

I reckon language choice matters more at the edges of economic activity where a specific language feature really does make the difference in the end product, but most activity that is leveraging LLMs now is more generic enterprise SaaS software.

You are ignoring LLM-ergonomics, some time ago I saw benchmarks showing that popularity the language (and so more data available in training date) was strongly linked with LLM's performances, with top results with javascript and python. I don't know if a year later this is still true, but is absolutely possible

There is one simple thing you have to realize why Python is the optimal choice. You have so much training data. Python is the second most popular language on GitHub and is easy to read.