haskell A common problem is the desire to have an action run at a scheduled interval, but only if it is needed. For example, instead of having every web request result in a new @getCurrentTime@ call, we'd like to have a single worker thread run every second, updating an @IORef@. However, if the request frequency is less than once per second, this is a pessimization, and worse, kills idle GC. This library allows you to define actions which will either be performed by a dedicated thread or, in times of low volume, will be executed by the calling thread. yesodweb/wai