Control.Eff.Resource

Allocate resources which are guaranteed to be released.

For more information, see the resourcet package.

Documentation

type Resource m = State (ResourceState m)

The Resource effect. This effect keeps track of all registered actions, and calls them upon exit (via runResource). 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.

data ResourceState m

A resource's state. Type parameter m is the Monad the resource deallocation will run in.

Instances

Typeable1 ResourceState

data ReleaseKey

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

Instances

Typeable ReleaseKey

runResource :: (Typeable1 m, Monad m, SetMember Lift (Lift m) r) => Eff (Resource (m ()) :> r) a -> Eff r a

Unwrap a Resource effect, and call all registered release actions.

allocate

Arguments

:: (Typeable1 m, Monad m, Member (Resource (m ())) r, SetMember Lift (Lift m) r)

=> m a

allocate

-> (a -> m ())

free resource

-> Eff r (ReleaseKey, a)

Perform some allocation, and automatically register a cleanup action.

register :: (Typeable1 m, Member (Resource (m ())) r) => m () -> Eff r ReleaseKey

Register some action that will be called precisely once, either when runResource is called or when the ReleaseKey is passed to release.

release :: (Typeable1 m, SetMember Lift (Lift m) r, Member (Resource (m ())) r) => ReleaseKey -> Eff r ()

Call a release action early, and deregister it from the list of cleanup actions to be performed.

unprotect :: (Typeable1 m, Member (Resource (m ())) r) => ReleaseKey -> Eff r (Maybe (m ()))

Unprotect resource from cleanup actions, this allowes you to send resource into another resourcet process and reregister it there.

It returns an release action that should be run in order to clean resource or Nothing in case if resource is already freed.