This package provides the region monad transformer. Scarce resources like files, memory pointers or USB devices for example can be opened in a region. When the region terminates, all opened resources will be automatically closed. The main advantage of regions is that the opened resources can not be returned from the region which ensures no I/O with closed resources is possible.

The primary technique used in this package is called "Lightweight monadic regions" which was invented by Oleg Kiselyov and Chung-chieh Shan.

Also see the regions-mtl and regions-monadstf packages which provide instances for the classes in the respected monad transformers packages.

For an example on how to use this library see the safer-file-handles, usb-safe or regional-pointers packages.