This module defines the "MRef" abstraction, which is a set of type-classes for things that behave like MVars. See the documentation there for more info.

This interface may be subject to future expansion. Presently, rather than providing something like tryTakeMVar, instances for "ReadRef sr m (Maybe a)" are provided, giving readReference the same type tryTakeMRef would have if it existed. There is currently nothing like tryPutMVar, though. Perhaps there should be. Or, perhaps this is the sort of thing the weird (to me) signature of atomicModifyIORef is for, and an argument for a similar signature for modifyStateRef or the addition of a new atomicModifyStateRef function.

I would like to resolve these questions in version 0.3 of this package.