The package swapper provides a wrapper for functors, which allows their data to be automatically and transparently swapped to disk and loaded back when necessary. The version 0.1 is the first public one. Hackage: http://hackage.haskell.org/package/swapper Github: http://github.com/roman-smrz/swapper/ The original motivation was the use with happstack-state, which is a system to maintain a global state whole kept in memory. If the data get too big, they can be swapped to disk by the operating system, yet sometimes a bit more control may be beneficial. That is provided by this package (a cache, with possible custom implementation, deciding which and how many items are kept in memory, is associated with the structure) and also the use of snapshots is optimized more than in the case of OS swap: only the data currently cached need to be added when creating snapshot and after loading one, the data are read only as needed. Regards, Roman Srmž