File: Exception.hs

package info (click to toggle)
git-repair 1.20140914
  • links: PTS
  • area: main
  • in suites: jessie, jessie-kfreebsd
  • size: 416 kB
  • ctags: 4
  • sloc: haskell: 4,146; makefile: 29; sh: 10
file content (59 lines) | stat: -rw-r--r-- 1,801 bytes parent folder | download | duplicates (2)
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
{- Simple IO exception handling (and some more)
 -
 - Copyright 2011-2012 Joey Hess <joey@kitenet.net>
 -
 - License: BSD-2-clause
 -}

{-# LANGUAGE ScopedTypeVariables #-}

module Utility.Exception where

import Control.Exception
import qualified Control.Exception as E
import Control.Applicative
import Control.Monad
import System.IO.Error (isDoesNotExistError)
import Utility.Data

{- Catches IO errors and returns a Bool -}
catchBoolIO :: IO Bool -> IO Bool
catchBoolIO = catchDefaultIO False

{- Catches IO errors and returns a Maybe -}
catchMaybeIO :: IO a -> IO (Maybe a)
catchMaybeIO a = catchDefaultIO Nothing $ Just <$> a

{- Catches IO errors and returns a default value. -}
catchDefaultIO :: a -> IO a -> IO a
catchDefaultIO def a = catchIO a (const $ return def)

{- Catches IO errors and returns the error message. -}
catchMsgIO :: IO a -> IO (Either String a)
catchMsgIO a = either (Left . show) Right <$> tryIO a

{- catch specialized for IO errors only -}
catchIO :: IO a -> (IOException -> IO a) -> IO a
catchIO = E.catch

{- try specialized for IO errors only -}
tryIO :: IO a -> IO (Either IOException a)
tryIO = try

{- 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 :: IO a -> (SomeException -> IO a) -> IO a
catchNonAsync a onerr = a `catches`
	[ Handler (\ (e :: AsyncException) -> throw e)
	, Handler (\ (e :: SomeException) -> onerr e)
	]

tryNonAsync :: IO a -> IO (Either SomeException a)
tryNonAsync a = (Right <$> a) `catchNonAsync` (return . Left)

{- Catches only DoesNotExist exceptions, and lets all others through. -}
tryWhenExists :: IO a -> IO (Maybe a)
tryWhenExists a = eitherToMaybe <$>
	tryJust (guard . isDoesNotExistError) a