In the yesod book on persistence, the following paragraph talks about "... store strongly typed Haskell data":
Some Haskellers have attempted a more revolutionary route: creating Haskell specific data stores that allow one to easily store any strongly typed Haskell data. These options are great for certain use cases, but they constrain one to the storage techniques provided by the library and do not interface well with other languages.
I did a quick google search but it turned up sql related libraries on hackage. Also there is no hackage category "data base", only "data" which I don't want to search manually. Who are "those haskellers" and what are the currently developed haskell projects in this regard?
Bartek's comment pretty much answers the question (if you come up with a better one please write your answer):
According to hackage Web/Databases and Persistence page, there is ACID-state and happstack-state.