monad-var

The aim of this library is to provide a unified set of operations (new, read, write, swap, various strict mutate* functions and their derivatives (like mutate-and-return-the-old-value) and a certain interface for MVar-like things) over all common variable types: IORef, STRef s, MVar, TVar, TMVar. When possible type classes are generalized to be over abstract containers rather than variables: e.g. it'd make sense to implement MonadRead TChan and MonadMutate_ Vector instances, but no such instances are provided right now. There are also some lenses to be described in an upcoming blog post.