    {-# OPTIONS_GHC -fno-implicit-prelude #-}

    -----------------------------------------------------------------------------
    -- |
    -- 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

    #ifndef __NHC__
        mkIOError,			-- :: IOErrorType -> String -> Maybe Handle
    				--    -> Maybe FilePath -> IOError

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

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

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

    #ifndef __NHC__
        ioeSetErrorType,		-- :: IOError -> IOErrorType -> IOError
        ioeSetErrorString,		-- :: IOError -> String -> IOError
        ioeSetLocation,		-- :: IOError -> String -> IOError
        ioeSetHandle,		-- :: IOError -> Handle -> IOError
        ioeSetFileName,		-- :: IOError -> FilePath -> IOError
    #endif

        -- * 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)

    #ifndef __NHC__
        modifyIOError,		-- :: (IOError -> IOError) -> IO a -> IO a
    #endif
      ) where

    import Data.Either
    import Data.Maybe

    #ifdef __GLASGOW_HASKELL__
    import GHC.Base
    import GHC.IOBase
    import GHC.Exception
    import Text.Show
    #endif

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

    #ifdef __NHC__
    import IO
      ( IOError ()
      , 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 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 = "",
    			ioe_handle = maybe_hdl,
    			ioe_filename = maybe_filename
     			}
    #ifdef __NHC__
    mkIOError EOF       location maybe_hdl maybe_filename =
        EOFError location (fromJust maybe_hdl)
    mkIOError UserError location maybe_hdl maybe_filename =
        UserError location ""
    mkIOError t         location maybe_hdl maybe_filename =
        NHC.FFI.mkIOError location maybe_filename maybe_handle (ioeTypeToInt t)
      where
        ioeTypeToInt AlreadyExists     = fromEnum EEXIST
        ioeTypeToInt NoSuchThing       = fromEnum ENOENT
        ioeTypeToInt ResourceBusy      = fromEnum EBUSY
        ioeTypeToInt ResourceExhausted = fromEnum ENOSPC
        ioeTypeToInt IllegalOperation  = fromEnum EPERM
        ioeTypeToInt PermissionDenied  = fromEnum EACCES
    #endif
    #endif /* __GLASGOW_HASKELL__ || __HUGS__ */

    #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 }

    -- | 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
    annotateIOError (IOError ohdl errTy _ str opath) loc hdl path =
      IOError (hdl `mplus` ohdl) errTy loc str (path `mplus` opath)
      where
        Nothing `mplus` ys = ys
        xs      `mplus` _  = xs
    #endif /* __GLASGOW_HASKELL__ || __HUGS__ */

    #if 0 /*__NHC__*/
    annotateIOError (IOError msg file hdl code) msg' file' hdl' =
        IOError (msg++'\n':msg') (file`mplus`file') (hdl`mplus`hdl') code
    annotateIOError (EOFError msg hdl) msg' file' hdl' =
        EOFError (msg++'\n':msg') (hdl`mplus`hdl')
    annotateIOError (UserError loc msg) msg' file' hdl' =
        UserError loc (msg++'\n':msg')
    annotateIOError (PatternError loc) msg' file' hdl' =
        PatternError (loc++'\n':msg')
    #endif