reflection (hackage): 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.  There are a handful of tutorials on how to use this library:  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.  Arnaud Spiwack's tutorial All about reflection explains how to use this library.
Keywords: bsd3|data|dependent-types|library|reflection