Tony Morris

Exactly, this is why unsafePerformIO is unsafe. Escaping IO isn't if you know what you doing but it's unpredictable.

In order to break RF, unsafePerformIO needs to be observe aka, the result must be needed.

Sure but the determined dev can force that, GHC providing escape hatches, etc. Point being we also rely on conventions & best practices.

I'm not disagreeing that Haskell is much better at this btw. I just think that IO/Task has value in Scala, I personally like it a lot

I don't try to compare both. I wrote almost Haskell and Scala for a decade. I prefer Scala to not do the same mistakes Haskell did.

What languages do you use now professionally? Would you prefer a codebase that didn't try to track effects in Scala (ala scalaz.c.Task)?

Professionally and on my side projects I use Haskell. I want effect tracking. It's just you have to use monad transformers to compose stuff

Things get ugly pretty quick. Plus, stacking monad transformers ain't cheap. You end up rolling your own most of the time