[cosmic_quanta]

Someone truly new to Haskell shouldn't use it professionally.

Once you've learned what is necessary to, say, modify already-existing applications, you should be familiar with monads and some basic monad transformers like ReaderT.

Once you're there, I don't think 'choosing an effect system' is a perilous question. The monad transformer library, mtl, is an effect system, the second simplest one after IO.

[solomonb]

The original poster said they want to use Haskell professionally but that they are struggling to understand how to structure programs.

> Once you're there, I don't think 'choosing an effect system' is a perilous question. The monad transformer library, mtl, is an effect system, the second simplest one after IO.

I'm aware of that, generally when people say "choose effect system" they mean choose some algebraic effect system, all of which (in Haskell) have huge pitfalls. The default should be monad transformers unless you have some exceptional situation.

[tome]

> generally when people say "choose effect system" they mean choose some algebraic effect system

This isn't really true. Bluefin and effectful are effect systems, but not algebraic effect systems.

[HelloNurse]

On a software engineering level choosing such unusually deep-reaching libraries unusually soon in the development of a program is a major but uninformed commitment, a dangerous bet that more practical programming languages try to avoid imposing on the user.

[cosmic_quanta]

I realize I didn't mention monad transformers at all in my original post, I only linked to them!

I should have mentioned that, as you say, monad transformers should be the default effect system choice for 99% of people