Currently, atomicWriteIORef is implemented using atomicModifyIORef. That seems pretty heavy for the job, allocating closures and forcing thunks. Is there a reason not to do it with casMutVar#? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20180622/9929866d/attachment.html>