another great thing is it's 'replayable'. If the event is stored in an atomic reference, you can get optimistic transactional semantics by running the state mon

another great thing is it's 'replayable'. If the event is stored in an atomic reference, you can get optimistic transactional semantics by running the state monad, comparing the results to the previous by using a CAS, etc. So you have free concurrent transactional semantics from using the state monad.