59 lines
1.8 KiB
Haskell
59 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 Control.Exception
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import qualified Control.Exception as E
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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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import Utility.Data
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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 = catchDefaultIO False
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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 <$> tryIO a
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{- catch specialized for IO errors only -}
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catchIO :: IO a -> (IOException -> IO a) -> IO a
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catchIO = E.catch
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{- try specialized for IO errors only -}
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tryIO :: IO a -> IO (Either IOException a)
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tryIO = try
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{- Catches all exceptions except for async exceptions.
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- This is often better to use than catching them all, so that
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- ThreadKilled and UserInterrupt get through.
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-}
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catchNonAsync :: IO a -> (SomeException -> IO a) -> IO a
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catchNonAsync a onerr = a `catches`
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[ Handler (\ (e :: AsyncException) -> throw e)
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, Handler (\ (e :: SomeException) -> onerr e)
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]
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tryNonAsync :: IO a -> IO (Either SomeException a)
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tryNonAsync a = (Right <$> 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 = eitherToMaybe <$>
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tryJust (guard . isDoesNotExistError) a
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