resourcet-1.1.6: Deterministic allocation and freeing of scarce resources.

Safe HaskellSafe




data InvalidAccess Source

Indicates either an error in the library, or misuse of it (e.g., a ResourceT's state is accessed after being released).

Since 0.3.0




functionName :: String

class (MonadThrow m, MonadIO m, Applicative m, MonadBase IO m) => MonadResource m where Source

A Monad which allows for safe resource allocation. In theory, any monad transformer stack included a ResourceT can be an instance of MonadResource.

Note: runResourceT has a requirement for a MonadBaseControl IO m monad, which allows control operations to be lifted. A MonadResource does not have this requirement. This means that transformers such as ContT can be an instance of MonadResource. However, the ContT wrapper will need to be unwrapped before calling runResourceT.

Since 0.3.0


liftResourceT :: ResourceT IO a -> m a Source

Lift a ResourceT IO action into the current Monad.

Since 0.4.0

data ReleaseKey Source

A lookup key for a specific release action. This value is returned by register and allocate, and is passed to release.

Since 0.3.0


ReleaseKey !(IORef ReleaseMap) !Int 


data ReleaseMap Source


ReleaseMap !NextKey !RefCount !(IntMap (ReleaseType -> IO ())) 

type ResIO a = ResourceT IO a Source

Convenient alias for ResourceT IO.

newtype ResourceT m a Source

The Resource transformer. This transformer keeps track of all registered actions, and calls them upon exit (via runResourceT). Actions may be registered via register, or resources may be allocated atomically via allocate. allocate corresponds closely to bracket.

Releasing may be performed before exit via the release function. This is a highly recommended optimization, as it will ensure that scarce resources are freed early. Note that calling release will deregister the action, so that a release action will only ever be called once.

Since 0.3.0




unResourceT :: IORef ReleaseMap -> m a

transResourceT :: (m a -> n b) -> ResourceT m a -> ResourceT n b Source

Transform the monad a ResourceT lives in. This is most often used to strip or add new transformers to a stack, e.g. to run a ReaderT.

Note that this function is a slight generalization of hoist.

Since 0.3.0