There are many practical examples already in Haskell. Pure functional programming is not necessarily about avoiding effects, but about controlling, tracking and

There are many practical examples already in Haskell. Pure functional programming is not necessarily about avoiding effects, but about controlling, tracking and managing them. This enables better reasoning and more safety guarantees. For example, software transactional memory, the STM monad, allows optimistic updates to shared mutable state by safely supporting rollbacks.