summaryrefslogtreecommitdiff
path: root/Utility/Exception.hs
blob: 8b110ae6ded9686c56e1ce3534041b140e58e2d0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
{- Simple IO exception handling (and some more)
 -
 - Copyright 2011-2015 Joey Hess <id@joeyh.name>
 -
 - License: BSD-2-clause
 -}

{-# LANGUAGE ScopedTypeVariables #-}
{-# OPTIONS_GHC -fno-warn-tabs #-}

module Utility.Exception (
	module X,
	catchBoolIO,
	catchMaybeIO,
	catchDefaultIO,
	catchMsgIO,
	catchIO,
	tryIO,
	bracketIO,
	catchNonAsync,
	tryNonAsync,
	tryWhenExists,
	catchIOErrorType,
	IOErrorType(..)
) 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, ioeGetErrorType)
import GHC.IO.Exception (IOErrorType(..))

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 = 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)
	, 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