How to handle changing the implementation of Events when using Data.Acid

Question

The solution is to not use higher order functions like 'alter'. The benefits of acid-state (ACID guarantees, running code remotely, etc) comes at the cost of only using serialisable data. This restriction is unlikely to ever be lifted.

Usually this is a not a big problem; Just specialise your code. If this doesn't cut it, maybe you want to keep your state in an MVar.