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 with or withIO. The with functions correspond 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.

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

Unwrap a ResourceT transformer, and call all registered release actions.

Note that there is some reference counting involved due to resourceForkIO. If multiple threads are sharing the same collection of resources, only the last call to runResourceT will deallocate the resources.

Perform some allocation, and automatically register a cleanup action.

If you are performing an IO action, it will likely be easier to use the withIO function, which handles types more cleanly.

Same as with, but explicitly uses IO as a base.

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

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

Read a value from a reference.

Write a value to a reference.

Create a new reference.

Introduce a reference-counting scheme to allow a resource context to be shared by multiple threads. Once the last thread exits, all remaining resources will be released.

Note that abuse of this function will greatly delay the deallocation of registered resources. This function should be used with care. A general guideline:

If you are allocating a resource that should be shared by multiple threads, and will be held for a long time, you should allocate it at the beginning of a new ResourceT block and then call resourceForkIO from there.

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 the original and new monad must both have the same Base monad.

The express purpose of this transformer is to allow the ST monad to catch exceptions via the ResourceThrow typeclass.

Same as runExceptionT, but immediately throw any exception returned.

A Monad with a base that has mutable references, and allows some way to run base actions and clean up properly.

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

A Resource which can safely run IO calls.

A helper class for ResourceIO, stating that the base monad provides IO actions.

A Resource which can throw exceptions. Note that this does not work in a vanilla ST monad. Instead, you should use the ExceptionT transformer on top of ST.

A base monad which provides mutable references and some exception-safe way of interacting with them. For monads which cannot handle exceptions (e.g., ST), exceptions may be ignored. However, in such cases, scarce resources should not be allocated in those monads, as exceptions may cause the cleanup functions to not run.

The instance for IO, however, is fully exception-safe.

Minimal complete definition: Ref, newRef', readRef' and writeRef'.

Determine if the current ResourceT is still active. This is necessary for such cases as lazy I/O, where an unevaluated thunk may still refer to a closed ResourceT.