acid-state is a NoSQL, RAM-cloud, persistent data store. One of attractive feature is that it's designed to store arbitrary Haskell datatypes and queries are written using plain old Haskell code. This means you do not have to learn a special query language, or figure out how to turn your beautiful Haskell datastructures into some limited set of ints and strings.
acid-state and safecopy are the successors to the old happstack-state and happstack-data libraries. You can learn more at the acid-state homepage. acid-state is now completely independent from Happstack and can be used with any web framework. However, Happstack is still committed to the improvement and promotion of acid-state.
Apps written using happstack-state can be migrated to use acid-state relatively easily. Details on the process or documented here. #include "AcidStateCounter.lhs" #include "IxSet.lhs"