Since GHC 7.8 will now absorb the functionality that was previously only in the atomic-primops packagehttp://hackage.haskell.org/package/atomic-primops, it would be great to start exposing this for the data structures people actually want to use: i.e. unboxed vectors rather than raw MutableByteArrayshttp://hackage.haskell.org/package/atomic-primops-0.4/docs/Data-Atomics.html... . I've been reading through the code of vector, thinking that I would release some kind of "vector-atomics" package. Alas, I don't see how that is possible. There's no way to get at the MutableByteArray associated with an unboxed vector. (1) I think the minimum that would be necessary would be to modify "Data/Vector/Unboxed/Base.hs", where the instances for the type family actually exist, to provide an additional instance for each "MVector s Foo" that records the fact that the vector has and can expose a MutableByteArray. (2) Alternatively, an "exposeMutableByteArray" function could be added to the existing Unbox class. But this would affect other third party Unbox instances out there in the world... Is there any interest insupporting Unbox instances that are NOT implemented as a MutableByteArray? (3) The most invasive (but best for the user) change would be to extend the basic MVector interface to include notions of concurrency-related operations right inside the vector package (CAS, etc). But they should still probably go in a separate class (not class MVector), just because they will be specific to Unboxed and Storable vectors rather than boxed ones.... -Ryan