System/IO/Error.hs

{-# OPTIONS_GHC -XNoImplicitPrelude #-}

-----------------------------------------------------------------------------
-- |
-- Module : System.IO.Error
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
-- 
-- Maintainer : libraries@haskell.org
-- Stability : provisional
-- Portability : portable
--
-- Standard IO Errors.
--
-----------------------------------------------------------------------------

module System.IO.Error (

 -- * I\/O errors
 IOError, -- = IOException

 userError, -- :: String -> IOError

 mkIOError, -- :: IOErrorType -> String -> Maybe Handle
 -- -> Maybe FilePath -> IOError

 annotateIOError, -- :: IOError -> String -> Maybe Handle
 -- -> Maybe FilePath -> IOError

 -- ** Classifying I\/O errors
 isAlreadyExistsError, -- :: IOError -> Bool
 isDoesNotExistError,
 isAlreadyInUseError,
 isFullError, 
 isEOFError,
 isIllegalOperation, 
 isPermissionError,
 isUserError,

 -- ** Attributes of I\/O errors
 ioeGetErrorType, -- :: IOError -> IOErrorType
 ioeGetLocation, -- :: IOError -> String
 ioeGetErrorString, -- :: IOError -> String
 ioeGetHandle, -- :: IOError -> Maybe Handle
 ioeGetFileName, -- :: IOError -> Maybe FilePath

 ioeSetErrorType, -- :: IOError -> IOErrorType -> IOError
 ioeSetErrorString, -- :: IOError -> String -> IOError
 ioeSetLocation, -- :: IOError -> String -> IOError
 ioeSetHandle, -- :: IOError -> Handle -> IOError
 ioeSetFileName, -- :: IOError -> FilePath -> IOError

 -- * Types of I\/O error
 IOErrorType, -- abstract

 alreadyExistsErrorType, -- :: IOErrorType
 doesNotExistErrorType,
 alreadyInUseErrorType,
 fullErrorType,
 eofErrorType,
 illegalOperationErrorType, 
 permissionErrorType,
 userErrorType,

 -- ** 'IOErrorType' predicates
 isAlreadyExistsErrorType, -- :: IOErrorType -> Bool
 isDoesNotExistErrorType,
 isAlreadyInUseErrorType,
 isFullErrorType, 
 isEOFErrorType,
 isIllegalOperationErrorType, 
 isPermissionErrorType,
 isUserErrorType, 

 -- * Throwing and catching I\/O errors

 ioError, -- :: IOError -> IO a

 catch, -- :: IO a -> (IOError -> IO a) -> IO a
 try, -- :: IO a -> IO (Either IOError a)

 modifyIOError, -- :: (IOError -> IOError) -> IO a -> IO a
 ) where

#ifndef __HUGS__
import qualified Control.Exception.Base as New (catch)
#endif

#ifndef __HUGS__
import Data.Either
#endif
import Data.Maybe

#ifdef __GLASGOW_HASKELL__
import GHC.Base
import GHC.IO
import GHC.IO.Exception
import GHC.IO.Handle.Types
import Text.Show
#endif

#ifdef __HUGS__
import Hugs.Prelude(Handle, IOException(..), IOErrorType(..), IO)
#endif

#ifdef __NHC__
import IO
 ( IOError ()
 , Handle ()
 , try
 , ioError
 , userError
 , isAlreadyExistsError -- :: IOError -> Bool
 , isDoesNotExistError
 , isAlreadyInUseError
 , isFullError
 , isEOFError
 , isIllegalOperation
 , isPermissionError
 , isUserError
 , ioeGetErrorString -- :: IOError -> String
 , ioeGetHandle -- :: IOError -> Maybe Handle
 , ioeGetFileName -- :: IOError -> Maybe FilePath
 )
import qualified NHC.Internal as NHC (IOError(..))
import qualified NHC.DErrNo as NHC (ErrNo(..))
import Data.Maybe (fromJust)
import Control.Monad (MonadPlus(mplus))
#endif

-- | The construct 'try' @comp@ exposes IO errors which occur within a
-- computation, and which are not fully handled.
--
-- Non-I\/O exceptions are not caught by this variant; to catch all
-- exceptions, use 'Control.Exception.try' from "Control.Exception".

#ifndef __NHC__
try :: IO a -> IO (Either IOError a)
try f = catch (do r <- f
 return (Right r))
 (return . Left)
#endif

#if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
-- -----------------------------------------------------------------------------
-- Constructing an IOError

-- | Construct an 'IOError' of the given type where the second argument
-- describes the error location and the third and fourth argument
-- contain the file handle and file path of the file involved in the
-- error if applicable.
mkIOError :: IOErrorType -> String -> Maybe Handle -> Maybe FilePath -> IOError
mkIOError t location maybe_hdl maybe_filename =
 IOError{ ioe_type = t, 
 ioe_location = location,
 ioe_description = "",
#if defined(__GLASGOW_HASKELL__)
 ioe_errno = Nothing,
#endif
 ioe_handle = maybe_hdl, 
 ioe_filename = maybe_filename
 }
#endif /* __GLASGOW_HASKELL__ || __HUGS__ */
#ifdef __NHC__
mkIOError EOF location maybe_hdl maybe_filename =
 NHC.EOFError location (fromJust maybe_hdl)
mkIOError UserError location maybe_hdl maybe_filename =
 NHC.UserError location ""
mkIOError t location maybe_hdl maybe_filename =
 NHC.IOError location maybe_filename maybe_hdl (ioeTypeToErrNo t)
 where
 ioeTypeToErrNo AlreadyExists = NHC.EEXIST
 ioeTypeToErrNo NoSuchThing = NHC.ENOENT
 ioeTypeToErrNo ResourceBusy = NHC.EBUSY
 ioeTypeToErrNo ResourceExhausted = NHC.ENOSPC
 ioeTypeToErrNo IllegalOperation = NHC.EPERM
 ioeTypeToErrNo PermissionDenied = NHC.EACCES
#endif /* __NHC__ */

#ifndef __NHC__
-- -----------------------------------------------------------------------------
-- IOErrorType

-- | An error indicating that an 'IO' operation failed because
-- one of its arguments already exists.
isAlreadyExistsError :: IOError -> Bool
isAlreadyExistsError = isAlreadyExistsErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- one of its arguments does not exist.
isDoesNotExistError :: IOError -> Bool
isDoesNotExistError = isDoesNotExistErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- one of its arguments is a single-use resource, which is already
-- being used (for example, opening the same file twice for writing
-- might give this error).
isAlreadyInUseError :: IOError -> Bool
isAlreadyInUseError = isAlreadyInUseErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the device is full.
isFullError :: IOError -> Bool
isFullError = isFullErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the end of file has been reached.
isEOFError :: IOError -> Bool
isEOFError = isEOFErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the operation was not possible.
-- Any computation which returns an 'IO' result may fail with
-- 'isIllegalOperation'. In some cases, an implementation will not be
-- able to distinguish between the possible error causes. In this case
-- it should fail with 'isIllegalOperation'.
isIllegalOperation :: IOError -> Bool
isIllegalOperation = isIllegalOperationErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the user does not have sufficient operating system privilege
-- to perform that operation.
isPermissionError :: IOError -> Bool
isPermissionError = isPermissionErrorType . ioeGetErrorType

-- | A programmer-defined error value constructed using 'userError'.
isUserError :: IOError -> Bool
isUserError = isUserErrorType . ioeGetErrorType
#endif /* __NHC__ */

-- -----------------------------------------------------------------------------
-- IOErrorTypes

#ifdef __NHC__
data IOErrorType = AlreadyExists | NoSuchThing | ResourceBusy
 | ResourceExhausted | EOF | IllegalOperation
 | PermissionDenied | UserError
#endif

-- | I\/O error where the operation failed because one of its arguments
-- already exists.
alreadyExistsErrorType :: IOErrorType
alreadyExistsErrorType = AlreadyExists

-- | I\/O error where the operation failed because one of its arguments
-- does not exist.
doesNotExistErrorType :: IOErrorType
doesNotExistErrorType = NoSuchThing

-- | I\/O error where the operation failed because one of its arguments
-- is a single-use resource, which is already being used.
alreadyInUseErrorType :: IOErrorType
alreadyInUseErrorType = ResourceBusy

-- | I\/O error where the operation failed because the device is full.
fullErrorType :: IOErrorType
fullErrorType = ResourceExhausted

-- | I\/O error where the operation failed because the end of file has
-- been reached.
eofErrorType :: IOErrorType
eofErrorType = EOF

-- | I\/O error where the operation is not possible.
illegalOperationErrorType :: IOErrorType
illegalOperationErrorType = IllegalOperation

-- | I\/O error where the operation failed because the user does not
-- have sufficient operating system privilege to perform that operation.
permissionErrorType :: IOErrorType
permissionErrorType = PermissionDenied

-- | I\/O error that is programmer-defined.
userErrorType :: IOErrorType
userErrorType = UserError

-- -----------------------------------------------------------------------------
-- IOErrorType predicates

-- | I\/O error where the operation failed because one of its arguments
-- already exists.
isAlreadyExistsErrorType :: IOErrorType -> Bool
isAlreadyExistsErrorType AlreadyExists = True
isAlreadyExistsErrorType _ = False

-- | I\/O error where the operation failed because one of its arguments
-- does not exist.
isDoesNotExistErrorType :: IOErrorType -> Bool
isDoesNotExistErrorType NoSuchThing = True
isDoesNotExistErrorType _ = False

-- | I\/O error where the operation failed because one of its arguments
-- is a single-use resource, which is already being used.
isAlreadyInUseErrorType :: IOErrorType -> Bool
isAlreadyInUseErrorType ResourceBusy = True
isAlreadyInUseErrorType _ = False

-- | I\/O error where the operation failed because the device is full.
isFullErrorType :: IOErrorType -> Bool
isFullErrorType ResourceExhausted = True
isFullErrorType _ = False

-- | I\/O error where the operation failed because the end of file has
-- been reached.
isEOFErrorType :: IOErrorType -> Bool
isEOFErrorType EOF = True
isEOFErrorType _ = False

-- | I\/O error where the operation is not possible.
isIllegalOperationErrorType :: IOErrorType -> Bool
isIllegalOperationErrorType IllegalOperation = True
isIllegalOperationErrorType _ = False

-- | I\/O error where the operation failed because the user does not
-- have sufficient operating system privilege to perform that operation.
isPermissionErrorType :: IOErrorType -> Bool
isPermissionErrorType PermissionDenied = True
isPermissionErrorType _ = False

-- | I\/O error that is programmer-defined.
isUserErrorType :: IOErrorType -> Bool
isUserErrorType UserError = True
isUserErrorType _ = False

-- -----------------------------------------------------------------------------
-- Miscellaneous

#if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
ioeGetErrorType :: IOError -> IOErrorType
ioeGetErrorString :: IOError -> String
ioeGetLocation :: IOError -> String
ioeGetHandle :: IOError -> Maybe Handle
ioeGetFileName :: IOError -> Maybe FilePath

ioeGetErrorType ioe = ioe_type ioe

ioeGetErrorString ioe
 | isUserErrorType (ioe_type ioe) = ioe_description ioe
 | otherwise = show (ioe_type ioe)

ioeGetLocation ioe = ioe_location ioe

ioeGetHandle ioe = ioe_handle ioe

ioeGetFileName ioe = ioe_filename ioe

ioeSetErrorType :: IOError -> IOErrorType -> IOError
ioeSetErrorString :: IOError -> String -> IOError
ioeSetLocation :: IOError -> String -> IOError
ioeSetHandle :: IOError -> Handle -> IOError
ioeSetFileName :: IOError -> FilePath -> IOError

ioeSetErrorType ioe errtype = ioe{ ioe_type = errtype }
ioeSetErrorString ioe str = ioe{ ioe_description = str }
ioeSetLocation ioe str = ioe{ ioe_location = str }
ioeSetHandle ioe hdl = ioe{ ioe_handle = Just hdl }
ioeSetFileName ioe filename = ioe{ ioe_filename = Just filename }

#elif defined(__NHC__)
ioeGetErrorType :: IOError -> IOErrorType
ioeGetLocation :: IOError -> String

ioeGetErrorType e | isAlreadyExistsError e = AlreadyExists
 | isDoesNotExistError e = NoSuchThing
 | isAlreadyInUseError e = ResourceBusy
 | isFullError e = ResourceExhausted
 | isEOFError e = EOF
 | isIllegalOperation e = IllegalOperation
 | isPermissionError e = PermissionDenied
 | isUserError e = UserError

ioeGetLocation (NHC.IOError _ _ _ _) = "unknown location"
ioeGetLocation (NHC.EOFError _ _ ) = "unknown location"
ioeGetLocation (NHC.PatternError loc) = loc
ioeGetLocation (NHC.UserError loc _) = loc

ioeSetErrorType :: IOError -> IOErrorType -> IOError
ioeSetErrorString :: IOError -> String -> IOError
ioeSetLocation :: IOError -> String -> IOError
ioeSetHandle :: IOError -> Handle -> IOError
ioeSetFileName :: IOError -> FilePath -> IOError

ioeSetErrorType e _ = e
ioeSetErrorString (NHC.IOError _ f h e) s = NHC.IOError s f h e
ioeSetErrorString (NHC.EOFError _ f) s = NHC.EOFError s f
ioeSetErrorString e@(NHC.PatternError _) _ = e
ioeSetErrorString (NHC.UserError l _) s = NHC.UserError l s
ioeSetLocation e@(NHC.IOError _ _ _ _) _ = e
ioeSetLocation e@(NHC.EOFError _ _) _ = e
ioeSetLocation (NHC.PatternError _) l = NHC.PatternError l
ioeSetLocation (NHC.UserError _ m) l = NHC.UserError l m
ioeSetHandle (NHC.IOError o f _ e) h = NHC.IOError o f (Just h) e
ioeSetHandle (NHC.EOFError o _) h = NHC.EOFError o h
ioeSetHandle e@(NHC.PatternError _) _ = e
ioeSetHandle e@(NHC.UserError _ _) _ = e
ioeSetFileName (NHC.IOError o _ h e) f = NHC.IOError o (Just f) h e
ioeSetFileName e _ = e
#endif

-- | Catch any 'IOError' that occurs in the computation and throw a
-- modified version.
modifyIOError :: (IOError -> IOError) -> IO a -> IO a
modifyIOError f io = catch io (\e -> ioError (f e))

-- -----------------------------------------------------------------------------
-- annotating an IOError

-- | Adds a location description and maybe a file path and file handle
-- to an 'IOError'. If any of the file handle or file path is not given
-- the corresponding value in the 'IOError' remains unaltered.
annotateIOError :: IOError 
 -> String 
 -> Maybe Handle 
 -> Maybe FilePath 
 -> IOError 

#if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
annotateIOError ioe loc hdl path = 
 ioe{ ioe_handle = hdl `mplus` ioe_handle ioe,
 ioe_location = loc, ioe_filename = path `mplus` ioe_filename ioe }
 where
 mplus :: Maybe a -> Maybe a -> Maybe a
 Nothing `mplus` ys = ys
 xs `mplus` _ = xs
#endif /* __GLASGOW_HASKELL__ || __HUGS__ */

#if defined(__NHC__)
annotateIOError (NHC.IOError msg file hdl code) msg' hdl' file' =
 NHC.IOError (msg++'\n':msg') (file`mplus`file') (hdl`mplus`hdl') code
annotateIOError (NHC.EOFError msg hdl) msg' _ _ =
 NHC.EOFError (msg++'\n':msg') hdl
annotateIOError (NHC.UserError loc msg) msg' _ _ =
 NHC.UserError loc (msg++'\n':msg')
annotateIOError (NHC.PatternError loc) msg' _ _ =
 NHC.PatternError (loc++'\n':msg')
#endif

#ifndef __HUGS__
-- | The 'catch' function establishes a handler that receives any 'IOError'
-- raised in the action protected by 'catch'. An 'IOError' is caught by
-- the most recent handler established by 'catch'. These handlers are
-- not selective: all 'IOError's are caught. Exception propagation
-- must be explicitly provided in a handler by re-raising any unwanted
-- exceptions. For example, in
--
-- > f = catch g (\e -> if IO.isEOFError e then return [] else ioError e)
--
-- the function @f@ returns @[]@ when an end-of-file exception
-- (cf. 'System.IO.Error.isEOFError') occurs in @g@; otherwise, the
-- exception is propagated to the next outer handler.
--
-- When an exception propagates outside the main program, the Haskell
-- system prints the associated 'IOError' value and exits the program.
--
-- Non-I\/O exceptions are not caught by this variant; to catch all
-- exceptions, use 'Control.Exception.catch' from "Control.Exception".
catch :: IO a -> (IOError -> IO a) -> IO a
catch = New.catch
#endif /* !__HUGS__ */