This library provides a Software Transactional Memory (STM) monad with commit and retry IO hooks. A retry-action is run (at least once) if the transaction retries, while comm it-actions are executed iff the transaction commits. The AdvSTM monad also gives some atomicity guarantees for commit-actions:

* When a TVar is modified in a transaction and this transaction commits,
the update remains invisible to other threads until the corresponding
onCommit action is run.

* If the onCommit action throws an exception, the original values of
the modified TVars are restored.

Note: The package can be used as a drop-in replacement for
'Control.Concurrent.STM'.