factored out some useful error catching methods

Utility/Misc.hs

@@ -8,7 +8,9 @@
 module Utility.Misc where
 
 import System.IO
+import System.IO.Error (try)
 import Control.Monad
+import Control.Applicative
 
 {- A version of hgetContents that is not lazy. Ensures file is 
  - all read before it gets closed. -}
@@ -26,5 +28,20 @@ readMaybe s = case reads s of
 	_ -> Nothing
 
 {- Catches IO errors and returns a Bool -}
-catchBool :: IO Bool -> IO Bool
-catchBool = flip catch (const $ return False)
+catchBoolIO :: IO Bool -> IO Bool
+catchBoolIO a = catchDefaultIO a False
+
+{- Catches IO errors and returns a Maybe -}
+catchMaybeIO :: IO a -> IO (Maybe a)
+catchMaybeIO a = catchDefaultIO (Just <$> a) Nothing
+
+{- Catches IO errors and returns a default value. -}
+catchDefaultIO :: IO a -> a -> IO a
+catchDefaultIO a def = catch a (const $ return def)
+
+{- Catches IO errors and returns the error message. -}
+catchMsgIO :: IO a -> IO (Either String a)
+catchMsgIO a = dispatch <$> try a
+	where
+		dispatch (Left e) = Left $ show e
+		dispatch (Right v) = Right v

Utility/TempFile.hs

@@ -31,9 +31,9 @@ withTempFile :: String -> (FilePath -> Handle -> IO a) -> IO a
 withTempFile template a = bracket create remove use
 	where
 		create = do
-			tmpdir <- catch getTemporaryDirectory (const $ return ".")
+			tmpdir <- catchDefaultIO getTemporaryDirectory "."
 			openTempFile tmpdir template
 		remove (name, handle) = do
 			hClose handle
-			catchBool (removeFile name >> return True)
+			catchBoolIO (removeFile name >> return True)
 		use (name, handle) = a name handle