# Strict Mutable Variables

The `io-classes:strict-mvar` package provides a strict interface to mutable
variables (`MVar`). It builds on top of `io-classes:io-classes`, and thus it
provides the interface for `MVar`s implementations from both
[base](https://hackage.haskell.org/package/base-4.17.0.0/docs/Control-Concurrent-MVar.html)
and [io-sim](https://github.com/input-output-hk/io-sim).