{- Simple IO exception handling (and some more) - - Copyright 2011-2016 Joey Hess - - License: BSD-2-clause -} {-# LANGUAGE CPP, ScopedTypeVariables #-} {-# OPTIONS_GHC -fno-warn-tabs #-} module Utility.Exception ( module X, giveup, catchBoolIO, catchMaybeIO, catchDefaultIO, catchMsgIO, catchIO, tryIO, bracketIO, catchNonAsync, tryNonAsync, tryWhenExists, catchIOErrorType, IOErrorType(..), catchPermissionDenied, ) where import Control.Monad.Catch as X hiding (Handler) import qualified Control.Monad.Catch as M import Control.Exception (IOException, AsyncException) #ifdef MIN_VERSION_GLASGOW_HASKELL #if MIN_VERSION_GLASGOW_HASKELL(7,10,0,0) import Control.Exception (SomeAsyncException) #endif #endif import Control.Monad import Control.Monad.IO.Class (liftIO, MonadIO) import System.IO.Error (isDoesNotExistError, ioeGetErrorType) import GHC.IO.Exception (IOErrorType(..)) import Utility.Data {- Like error, this throws an exception. Unlike error, if this exception - is not caught, it won't generate a backtrace. So use this for situations - where there's a problem that the user is excpected to see in some - circumstances. -} giveup :: [Char] -> a #ifdef MIN_VERSION_base #if MIN_VERSION_base(4,9,0) giveup = errorWithoutStackTrace #else giveup = error #endif #else giveup = error #endif {- 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 = catchDefaultIO Nothing $ a >>= (return . Just) {- 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) #ifdef MIN_VERSION_GLASGOW_HASKELL #if MIN_VERSION_GLASGOW_HASKELL(7,10,0,0) , M.Handler (\ (e :: SomeAsyncException) -> throwM e) #endif #endif , 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) {- Catches only IO exceptions of a particular type. - Ie, use HardwareFault to catch disk IO errors. -} catchIOErrorType :: MonadCatch m => IOErrorType -> (IOException -> m a) -> m a -> m a catchIOErrorType errtype onmatchingerr a = catchIO a onlymatching where onlymatching e | ioeGetErrorType e == errtype = onmatchingerr e | otherwise = throwM e catchPermissionDenied :: MonadCatch m => (IOException -> m a) -> m a -> m a catchPermissionDenied = catchIOErrorType PermissionDenied