From f94f5fc8d4f567ee8a72aa4ae457d3a6b3a9e22f Mon Sep 17 00:00:00 2001
From: Joey Hess <joey@kitenet.net>
Date: Thu, 7 Aug 2014 21:01:07 -0400
Subject: generalized using the extensions package

---
 Utility/Exception.hs | 49 +++++++++++++++++++++++++++++--------------------
 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/Utility/Exception.hs b/Utility/Exception.hs
index 1fecf65d5..13c9d508a 100644
--- a/Utility/Exception.hs
+++ b/Utility/Exception.hs
@@ -1,6 +1,6 @@
 {- Simple IO exception handling (and some more)
  -
- - Copyright 2011-2012 Joey Hess <joey@kitenet.net>
+ - Copyright 2011-2014 Joey Hess <joey@kitenet.net>
  -
  - License: BSD-2-clause
  -}
@@ -9,51 +9,60 @@
 
 module Utility.Exception where
 
-import Control.Exception
-import qualified Control.Exception as E
-import Control.Applicative
+import Control.Exception (IOException, AsyncException)
+import Control.Monad.Catch
 import Control.Monad
 import System.IO.Error (isDoesNotExistError)
 import Utility.Data
 
 {- Catches IO errors and returns a Bool -}
-catchBoolIO :: IO Bool -> IO Bool
+catchBoolIO :: MonadCatch m => m Bool -> m Bool
 catchBoolIO = catchDefaultIO False
 
 {- Catches IO errors and returns a Maybe -}
-catchMaybeIO :: IO a -> IO (Maybe a)
-catchMaybeIO a = catchDefaultIO Nothing $ Just <$> a
+catchMaybeIO :: MonadCatch m => m a -> m (Maybe a)
+catchMaybeIO a = do
+	catchDefaultIO Nothing $ do
+		v <- a
+		return (Just v)
 
 {- Catches IO errors and returns a default value. -}
-catchDefaultIO :: a -> IO a -> IO a
+catchDefaultIO :: MonadCatch m => a -> m a -> m a
 catchDefaultIO def a = catchIO a (const $ return def)
 
 {- Catches IO errors and returns the error message. -}
-catchMsgIO :: IO a -> IO (Either String a)
-catchMsgIO a = either (Left . show) Right <$> tryIO a
+catchMsgIO :: MonadCatch m => m a -> m (Either String a)
+catchMsgIO a = do
+	v <- tryIO a
+	return $ either (Left . show) Right v
 
 {- catch specialized for IO errors only -}
-catchIO :: IO a -> (IOException -> IO a) -> IO a
-catchIO = E.catch
+catchIO :: MonadCatch m => m a -> (IOException -> m a) -> m a
+catchIO = catch
 
 {- try specialized for IO errors only -}
-tryIO :: IO a -> IO (Either IOException a)
+tryIO :: MonadCatch m => m a -> m (Either IOException a)
 tryIO = try
 
 {- Catches all exceptions except for async exceptions.
  - This is often better to use than catching them all, so that
  - ThreadKilled and UserInterrupt get through.
  -}
-catchNonAsync :: IO a -> (SomeException -> IO a) -> IO a
+catchNonAsync :: MonadCatch m => m a -> (SomeException -> m a) -> m a
 catchNonAsync a onerr = a `catches`
-	[ Handler (\ (e :: AsyncException) -> throw e)
+	[ Handler (\ (e :: AsyncException) -> throwM e)
 	, Handler (\ (e :: SomeException) -> onerr e)
 	]
 
-tryNonAsync :: IO a -> IO (Either SomeException a)
-tryNonAsync a = (Right <$> a) `catchNonAsync` (return . Left)
+tryNonAsync :: MonadCatch m => m a -> m (Either SomeException a)
+tryNonAsync a = go `catchNonAsync` (return . Left)
+  where
+	go = do
+		v <- a
+		return (Right v)
 
 {- Catches only DoesNotExist exceptions, and lets all others through. -}
-tryWhenExists :: IO a -> IO (Maybe a)
-tryWhenExists a = eitherToMaybe <$>
-	tryJust (guard . isDoesNotExistError) a
+tryWhenExists :: MonadCatch m => m a -> m (Maybe a)
+tryWhenExists a = do
+	v <- tryJust (guard . isDoesNotExistError) a
+	return (eitherToMaybe v)
-- 
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