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|
{- Simple IO exception handling (and some more)
-
- Copyright 2011-2014 Joey Hess <joey@kitenet.net>
-
- License: BSD-2-clause
-}
{-# LANGUAGE ScopedTypeVariables #-}
module Utility.Exception (
module X,
catchBoolIO,
catchMaybeIO,
catchDefaultIO,
catchMsgIO,
catchIO,
tryIO,
bracketIO,
catchNonAsync,
tryNonAsync,
tryWhenExists,
) where
import Control.Monad.Catch as X hiding (Handler)
import qualified Control.Monad.Catch as M
import Control.Exception (IOException, AsyncException)
import Control.Monad
import Control.Monad.IO.Class (liftIO, MonadIO)
import System.IO.Error (isDoesNotExistError)
import Utility.Data
{- Catches IO errors and returns a Bool -}
catchBoolIO :: MonadCatch m => m Bool -> m Bool
catchBoolIO = catchDefaultIO False
{- Catches IO errors and returns a Maybe -}
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 :: MonadCatch m => a -> m a -> m a
catchDefaultIO def a = catchIO a (const $ return def)
{- Catches IO errors and returns the error message. -}
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 :: MonadCatch m => m a -> (IOException -> m a) -> m a
catchIO = M.catch
{- try specialized for IO errors only -}
tryIO :: MonadCatch m => m a -> m (Either IOException a)
tryIO = M.try
{- bracket with setup and cleanup actions lifted to IO.
-
- Note that unlike catchIO and tryIO, this catches all exceptions. -}
bracketIO :: (MonadMask m, MonadIO m) => IO v -> (v -> IO b) -> (v -> m a) -> m a
bracketIO setup cleanup = bracket (liftIO setup) (liftIO . cleanup)
{- 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 :: MonadCatch m => m a -> (SomeException -> m a) -> m a
catchNonAsync a onerr = a `catches`
[ M.Handler (\ (e :: AsyncException) -> throwM e)
, M.Handler (\ (e :: SomeException) -> onerr e)
]
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 :: MonadCatch m => m a -> m (Maybe a)
tryWhenExists a = do
v <- tryJust (guard . isDoesNotExistError) a
return (eitherToMaybe v)
|
