Some kind of compare-and-set! operator which occurs at the transactor perhaps. Update: 1. you can do synchronous transactions. http://datomic.com/docs/javado

Some kind of compare-and-set! operator which occurs at the transactor perhaps. Update: 1. you can do synchronous transactions. http://datomic.com/docs/javadoc/datomic/Connection.html#transact(java.util.List) http://datomic.com/docs/javadoc/datomic/Connection.html#tran... 2. transactions can include data functions. "The database can be extended with data functions that expand into other data functions, or eventually bottom out as assertions and retractions. A set of assertions/ retractions/functions, represented as data structures, is sent to the transactor as a transaction, and either succeeds or fails all together, as one would expect."