90 lines
2.5 KiB
Haskell
90 lines
2.5 KiB
Haskell
{- Simple IO exception handling (and some more)
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-
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- Copyright 2011-2014 Joey Hess <id@joeyh.name>
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-
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- License: BSD-2-clause
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-}
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{-# LANGUAGE ScopedTypeVariables #-}
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{-# OPTIONS_GHC -fno-warn-tabs #-}
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module Utility.Exception (
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module X,
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catchBoolIO,
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catchMaybeIO,
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catchDefaultIO,
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catchMsgIO,
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catchIO,
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tryIO,
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bracketIO,
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catchNonAsync,
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tryNonAsync,
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tryWhenExists,
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) where
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import Control.Monad.Catch as X hiding (Handler)
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import qualified Control.Monad.Catch as M
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import Control.Exception (IOException, AsyncException)
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import Control.Monad
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import Control.Monad.IO.Class (liftIO, MonadIO)
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import System.IO.Error (isDoesNotExistError)
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import Utility.Data
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{- Catches IO errors and returns a Bool -}
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catchBoolIO :: MonadCatch m => m Bool -> m Bool
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catchBoolIO = catchDefaultIO False
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{- Catches IO errors and returns a Maybe -}
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catchMaybeIO :: MonadCatch m => m a -> m (Maybe a)
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catchMaybeIO a = do
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catchDefaultIO Nothing $ do
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v <- a
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return (Just v)
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{- Catches IO errors and returns a default value. -}
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catchDefaultIO :: MonadCatch m => a -> m a -> m a
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catchDefaultIO def a = catchIO a (const $ return def)
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{- Catches IO errors and returns the error message. -}
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catchMsgIO :: MonadCatch m => m a -> m (Either String a)
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catchMsgIO a = do
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v <- tryIO a
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return $ either (Left . show) Right v
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{- catch specialized for IO errors only -}
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catchIO :: MonadCatch m => m a -> (IOException -> m a) -> m a
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catchIO = M.catch
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{- try specialized for IO errors only -}
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tryIO :: MonadCatch m => m a -> m (Either IOException a)
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tryIO = M.try
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{- bracket with setup and cleanup actions lifted to IO.
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-
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- Note that unlike catchIO and tryIO, this catches all exceptions. -}
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bracketIO :: (MonadMask m, MonadIO m) => IO v -> (v -> IO b) -> (v -> m a) -> m a
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bracketIO setup cleanup = bracket (liftIO setup) (liftIO . cleanup)
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{- Catches all exceptions except for async exceptions.
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- This is often better to use than catching them all, so that
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- ThreadKilled and UserInterrupt get through.
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-}
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catchNonAsync :: MonadCatch m => m a -> (SomeException -> m a) -> m a
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catchNonAsync a onerr = a `catches`
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[ M.Handler (\ (e :: AsyncException) -> throwM e)
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, M.Handler (\ (e :: SomeException) -> onerr e)
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]
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tryNonAsync :: MonadCatch m => m a -> m (Either SomeException a)
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tryNonAsync a = go `catchNonAsync` (return . Left)
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where
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go = do
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v <- a
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return (Right v)
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{- Catches only DoesNotExist exceptions, and lets all others through. -}
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tryWhenExists :: MonadCatch m => m a -> m (Maybe a)
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tryWhenExists a = do
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v <- tryJust (guard . isDoesNotExistError) a
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return (eitherToMaybe v)
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