[kccqzy]

The author didn't write a good objection to option 2. Both the ST monad (real mutations) and the variety of State monads (simulated mutations) work fine in practice. What's even better is the STM monad, the software transactional memory monad that is not only about mutations but also solves synchronization between threads in a way that's intuitive and easy to use. But let's stick to the ST monad. Has the author looked at how hash maps and hash sets are implemented in Haskell? It's arrays and mutation!

> And if you only need mutation locally inside a function, using ST makes your code fundamentally more imperative in a way that really forces you to change your programming style. This isn't great either and doesn't exactly help with readability, so the mental overhead is rarely worth it.

What?? You are explicitly opting into writing mutation code. Of course that's going to change your programming code. It is expected to be different. Readability is increased because it clearly delineates a different coding style. And it's not even that different from other monadic code, even when you compare to non-mutating monadic code.

Terrible article.

[kqr]

Also optics like lenses, traversals and prisms make State-based mutation very syntactically convenient.

[revskill]

Author wants to avoid ST Monad to do mutation i think.