I just put together a new package, atomic-modify-general, for generalizations of the `atomicModifyIORef` operation. In particular: 1. Versions that allow a result of an arbitrary type (not necessarily a pair), where the caller passes in an extraction function. These work with `Array` and `SmallArray` from `primitive` as well as `IORef`. 2. A version that works with record types (not just pairs) whose first field is the new value to install in the `IORef`. This uses implementation details of the `atomicModifyMutVar#` primop as well as GHC's heap object layout to achieve better performance. Please try it out and let me know how it goes, and what extras you may want! Hackage: https://hackage.haskell.org/package/atomic-modify-general-0.1.0.0