factor out Annex exception handling module

Annex/Exception.hs

@@ -0,0 +1,27 @@
+{- exception handling in the git-annex monad
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.Exception (
+	bracketIO,
+	handle,
+	throw,
+) where
+
+import Control.Exception.Control (handle)
+import Control.Monad.IO.Control (liftIOOp)
+import Control.Exception hiding (handle, throw)
+
+import AnnexCommon
+
+{- Runs an Annex action, with setup and cleanup both in the IO monad. -}
+bracketIO :: IO c -> (c -> IO b) -> Annex a -> Annex a
+bracketIO setup cleanup go =
+	liftIOOp (Control.Exception.bracket setup cleanup) (const go)
+
+{- Throws an exception in the Annex monad. -}
+throw :: Control.Exception.Exception e => e -> Annex a
+throw = liftIO . throwIO