resourcet- Deterministic allocation and freeing of scarce resources.

Safe HaskellNone




newtype ExceptionT m a Source

The express purpose of this transformer is to allow non-IO-based monad stacks to catch exceptions via the MonadThrow typeclass.

Since 0.3.0



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, MonadUnsafeIO m, MonadIO m, Applicative 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

class Monad m => MonadThrow m where Source

A Monad which can throw exceptions. Note that this does not work in a vanilla ST or Identity monad. Instead, you should use the ExceptionT transformer in your stack if you are dealing with a non-IO base monad.

Since 0.3.0


monadThrow :: Exception e => e -> m a Source

class Monad m => MonadUnsafeIO m where Source

A Monad based on some monad which allows running of some IO actions, via unsafe calls. This applies to IO and ST, for instance.

Since 0.3.0


unsafeLiftIO :: IO a -> m a Source

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 (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

newtype Resource a Source

A method for allocating a scarce resource, providing the means of freeing it when no longer needed. This data type provides FunctorApplicativeMonad instances for composing different resources together. You can allocate these resources using either the bracket pattern (via with) or using ResourceT (via allocateResource).

This concept was originally introduced by Gabriel Gonzalez and described at: The implementation in this package is slightly different, due to taking a different approach to async exception safety.

Since 0.4.10


Resource ((forall b. IO b -> IO b) -> IO (Allocated a)) 

data Allocated a Source


Allocated !a !(IO ()) 

with :: MonadBaseControl IO m => Resource a -> (a -> m b) -> m b Source

Allocate the given resource and provide it to the provided function. The resource will be freed as soon as the inner block is exited, whether normally or via an exception. This function is similar in function to bracket.

Since 0.4.10

mkResource Source


:: IO a

allocate the resource

-> (a -> IO ())

free the resource

-> Resource a 

Create a Resource value using the given allocate and free functions.

Since 0.4.10