Hello, I'm happy to announce another member in the 'monadic regions' family: safer-file-handles: http://hackage.haskell.org/package/safer-file-handles-0.1 The package uses my 'regions' and 'explicit-iomodes' packages to add two safety features on top of the regular System.IO file handles and operations: * Regional file handles. Files must be opened in a region. When the region terminates all opened files are automatically closed. The main advantage of regions is that the handles to the opened files can not be returned from the region which ensures no I/O with closed files is possible. * Explicit IOModes. The regional file handles are parameterized by the IOMode in which they were opened. All operations on handles explicitly specify the needed IOMode. This way it is impossible to read from a write-only handle or write to a read-only handle for example. 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 technique is implemented in the 'regions' package which is re-exported from 'safer-file-handles'. See the 'safer-file-handles-examples' package for examples how to use this package: darcs get http://code.haskell.org/~basvandijk/code/safer-file-handles-examples regards, Bas P.S. While I wrote this message I realized a serious lack of expressive power of my regions package. Namely that I can't write a program that opens two different types of resources in the _same_ region. If for example I want to combine my usb-safe package and this package the following won't type-check: openBoth ∷ Device → FilePath → IO () openBoth usbDevice filePath = runTopRegion $ do h1 ← open usbDevice ∷ RegionT Device s IO (RegionalHandle Device (RegionT Device s IO)) h2 ← openFile filePath ReadMode ∷ RegionT File s IO (RegionalHandle File (RegionT File s IO)) return () The reason, as can be seen from the types of the monadic actions, is that the monad types differ between the two actions and bind ((>>=) :: Monad m => m a -> (a -> m b) -> m b) obviously requires them to be the same. The main problem thus, is that I parameterized the region with the type of resources. Note that I'm working on a solution where I remove the resource type from RegionT. So instead of: newtype RegionT resource s (pr ∷ * → *) α = RegionT { unRegionT ∷ ReaderT (IORef [Opened resource]) pr α } I will have: newtype RegionT s (pr ∷ * → *) α = RegionT { unRegionT ∷ ReaderT (IORef [SomeOpenedResource]) pr α } data SomeOpenedResource = ∀ resource. Resource resource ⇒ Some (Opened resource) Hopefully I will be able to release this fix before FP-NL tomorrow.