acid-state-0.12.4: Add ACID guarantees to any serializable Haskell data structure.

Portabilitynon-portable (uses GHC extensions)
Safe HaskellNone



AcidState container without a transaction log. Mostly used for testing.



class SafeCopy st => IsAcidic st where Source


acidEvents Source


:: [Event st]

List of events capable of updating or querying the state.

data AcidState st Source

State container offering full ACID (Atomicity, Consistency, Isolation and Durability) guarantees.

State changes are all-or-nothing. This is what you'd expect of any state variable in Haskell and AcidState doesn't change that.
No event or set of events will break your data invariants.
Transactions cannot interfere with each other even when issued in parallel.
Successful transaction are guaranteed to survive system failure (both hardware and software).

data Event st where Source

We distinguish between events that modify the state and those that do not.

UpdateEvents are executed in a MonadState context and have to be serialized to disk before they are considered durable.

QueryEvents are executed in a MonadReader context and obviously do not have to be serialized to disk.


UpdateEvent :: UpdateEvent ev => (ev -> Update (EventState ev) (EventResult ev)) -> Event (EventState ev) 
QueryEvent :: QueryEvent ev => (ev -> Query (EventState ev) (EventResult ev)) -> Event (EventState ev) 

type EventResult ev = MethodResult ev Source

Events return the same thing as Methods. The exact type of EventResult depends on the event.

class Method ev => UpdateEvent ev Source

All UpdateEvents are also Methods.

class Method ev => QueryEvent ev Source

All QueryEvents are also Methods.

data Update st a Source

Context monad for Update events.


data Query st a Source

Context monad for Query events.


openAcidState Source


:: IsAcidic st 
=> st

Initial state value.

-> AcidState st 

Create an AcidState given an initial value.

update :: UpdateEvent event => AcidState (EventState event) -> event -> (AcidState (EventState event), EventResult event) Source

Issue an Update event and wait for its result. Once this call returns, you are guaranteed that the changes to the state are durable. Events may be issued in parallel.

It's a run-time error to issue events that aren't supported by the AcidState.

update_ :: UpdateEvent event => AcidState (EventState event) -> event -> AcidState (EventState event) Source

Same as update but ignoring the event result.

query :: QueryEvent event => AcidState (EventState event) -> event -> EventResult event Source

Issue a Query event and wait for its result.

liftQuery :: Query st a -> Update st a Source

Run a query in the Update Monad.

runUpdate :: Update s r -> s -> (r, s) Source

Execute the Update monad in a pure environment.

runQuery :: Query s r -> s -> r Source

Execute the Query monad in a pure environment.