The base library does not provide strict variants for the basic concurrency primitives. Instead, the haddocks for Control.Concurrent.MVar recommend using Don Stewarts's strict-concurrency library: https://hackage.haskell.org/package/strict-concurrency But that library has not been buildable for years. The homepage seems no longer accessible, and there is no source repository link. I created a github repo from the tarball for version 0.2.4.1 (the latest, from 2010), and then made the minor tweaks needed to get it build with modern GHC. The library provides no tests, so I have no idea if what I did still provides the advertised guarantees or even actually works. My repo is here: https://github.com/ygale/strict-concurrency Is the library still as critical as it used to be? Perhaps not in this age of async and STM, but to me it still makes sense to offer strict versions of these primitives. If so, then perhaps this small and simple library should be taken under the wing of libraries as maintainer. In any case, could someone please at least apply my patch and upload to hackage, so that it will be buildable again? I became aware of this because I was hoping to use vacuum for a complex debugging task, but vacuum also hasn't been buildable for several years due to its dependence on strict-concurrency. Whether vacuum will actually work after several years of neglect is a separate question. Thanks, Yitz