This package addresses the configuration problem which is propagating configurations that are available at run-time, allowing multiple configurations to coexist without resorting to mutable global variables or System.IO.Unsafe.unsafePerformIO .

That package is an implementation of the ideas presented in the paper "Functional Pearl: Implicit Configurations" by Oleg Kiselyov and Chung-chieh Shan (original paper). However, the API has been streamlined to improve performance.

Austin Seipp's tutorial Reflecting values to types and back provides a summary of the approach taken by this library, along with more motivating examples.