[Araq]

(Disclaimer: I am the creator of Nimrod.)

What you say is entirely correct; however Nimrod's effect system is not tied to any runtime mechanisms like a GC and provides lots of other aspects of safety. For instance you can ensure at compile time that a particular piece of code performs no database operations.

Also the effect system will improve the safety for concurrent programming quite a lot; coming soon in some of the next versions. (Sorry, no papers about it yet.)