@hackage regions0.3

Provides the region monad for safely opening and working with scarce resources.

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. See:

http://okmij.org/ftp/Haskell/regions.html#light-weight

This package provides two modules:

  • Control.Monad.Trans.Region.Unsafe should only be used by library authors wishing to allow their users to open their type of resources in a region. It should not be used by end-users directly!

  • Control.Monad.Trans.Region provides the public and safe interface to regions which can be used by end-users.

Also see the regions-monadsfd and regions-monadstf packages which provide instances for the classes in the respected monads packages.

For an example of how to use this library see the safer-file-handles or usb-safe packages.