822a8c0ff8
Fixed handling of case when file does not exist to work like it did before, and avoid an excess stat call.
58 lines
1.8 KiB
Haskell
58 lines
1.8 KiB
Haskell
{- Simple IO exception handling (and some more)
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-
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- Copyright 2011-2012 Joey Hess <joey@kitenet.net>
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-
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- Licensed under the GNU GPL version 3 or higher.
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-}
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{-# LANGUAGE ScopedTypeVariables #-}
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module Utility.Exception where
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import Prelude hiding (catch)
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import Control.Exception
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import Control.Applicative
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import Control.Monad
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import System.IO.Error (isDoesNotExistError)
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{- Catches IO errors and returns a Bool -}
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catchBoolIO :: IO Bool -> IO Bool
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catchBoolIO a = catchDefaultIO False a
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{- Catches IO errors and returns a Maybe -}
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catchMaybeIO :: IO a -> IO (Maybe a)
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catchMaybeIO a = catchDefaultIO Nothing $ Just <$> a
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{- Catches IO errors and returns a default value. -}
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catchDefaultIO :: a -> IO a -> IO 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 :: IO a -> IO (Either String a)
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catchMsgIO a = either (Left . show) Right <$> tryIO a
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{- catch specialized for IO errors only -}
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catchIO :: IO a -> (IOException -> IO a) -> IO a
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catchIO = catch
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{- try specialized for IO errors only -}
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tryIO :: IO a -> IO (Either IOException a)
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tryIO = try
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{- Catches all exceptions except for async exceptions.
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- This is often better to use than catching them all, so that
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- ThreadKilled and UserInterrupt get through.
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-}
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catchNonAsync :: IO a -> (SomeException -> IO a) -> IO a
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catchNonAsync a onerr = a `catches`
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[ Handler (\ (e :: AsyncException) -> throw e)
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, Handler (\ (e :: SomeException) -> onerr e)
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]
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tryNonAsync :: IO a -> IO (Either SomeException a)
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tryNonAsync a = (Right <$> a) `catchNonAsync` (return . Left)
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{- Catches only DoesNotExist exceptions, and lets all others through. -}
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tryWhenExists :: IO a -> IO (Maybe a)
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tryWhenExists a = either (const Nothing) Just <$>
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tryJust (guard . isDoesNotExistError) a
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