System/Directory.hs

    {-# LANGUAGE CPP, NondecreasingIndentation #-}
    #ifdef __GLASGOW_HASKELL__
    {-# LANGUAGE Trustworthy #-}
    #endif

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  System.Directory
    -- Copyright   :  (c) The University of Glasgow 2001
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  stable
    -- Portability :  portable
    --
    -- System-independent interface to directory manipulation.
    --
    -----------------------------------------------------------------------------

    module System.Directory
       (
        -- $intro

        -- * Actions on directories
          createDirectory
        , createDirectoryIfMissing
        , removeDirectory
        , removeDirectoryRecursive
        , renameDirectory

        , getDirectoryContents
        , getCurrentDirectory
        , setCurrentDirectory

        -- * Pre-defined directories
        , getHomeDirectory
        , getAppUserDataDirectory
        , getUserDocumentsDirectory
        , getTemporaryDirectory

        -- * Actions on files
        , removeFile
        , renameFile
        , copyFile

        , canonicalizePath
        , makeRelativeToCurrentDirectory
        , findExecutable
        , findFile
        , findFiles
        , findFilesWith

        -- * Existence tests
        , doesFileExist
        , doesDirectoryExist

        -- * Permissions

        -- $permissions

        , Permissions
        , emptyPermissions
        , readable
        , writable
        , executable
        , searchable
        , setOwnerReadable
        , setOwnerWritable
        , setOwnerExecutable
        , setOwnerSearchable

        , getPermissions
        , setPermissions
        , copyPermissions

        -- * Timestamps

        , getModificationTime
       ) where

    import System.FilePath
    import System.IO
    import System.IO.Error
    import Control.Monad           ( when, unless )
    import Control.Exception.Base as E

    #ifdef __HUGS__
    import Hugs.Directory
    #endif /* __HUGS__ */

    import Foreign
    import Foreign.C

    {-# CFILES cbits/directory.c #-}

    import Data.Maybe

    import Data.Time
    import Data.Time.Clock.POSIX

    #ifdef __GLASGOW_HASKELL__

    import GHC.IO.Exception ( IOErrorType(InappropriateType) )

    #ifdef mingw32_HOST_OS
    import System.Posix.Types
    import System.Posix.Internals
    import qualified System.Win32 as Win32
    #else
    import GHC.IO.Encoding
    import GHC.Foreign as GHC
    import System.Environment ( getEnv )
    import qualified System.Posix as Posix
    #endif

    #endif /* __GLASGOW_HASKELL__ */

    {- $intro
    A directory contains a series of entries, each of which is a named
    reference to a file system object (file, directory etc.).  Some
    entries may be hidden, inaccessible, or have some administrative
    function (e.g. `.' or `..' under POSIX
    <http://www.opengroup.org/onlinepubs/009695399/>), but in
    this standard all such entries are considered to form part of the
    directory contents. Entries in sub-directories are not, however,
    considered to form part of the directory contents.

    Each file system object is referenced by a /path/.  There is
    normally at least one absolute path to each file system object.  In
    some operating systems, it may also be possible to have paths which
    are relative to the current directory.
    -}

    -----------------------------------------------------------------------------
    -- Permissions

    {- $permissions

     The 'Permissions' type is used to record whether certain operations are
     permissible on a file\/directory. 'getPermissions' and 'setPermissions'
     get and set these permissions, respectively. Permissions apply both to
     files and directories. For directories, the executable field will be
     'False', and for files the searchable field will be 'False'. Note that
     directories may be searchable without being readable, if permission has
     been given to use them as part of a path, but not to examine the
     directory contents.

    Note that to change some, but not all permissions, a construct on the following lines must be used.

    >  makeReadable f = do
    >     p <- getPermissions f
    >     setPermissions f (p {readable = True})

    -}

    data Permissions
     = Permissions {
        readable,   writable,
        executable, searchable :: Bool
       } deriving (Eq, Ord, Read, Show)

    emptyPermissions :: Permissions
    emptyPermissions = Permissions {
                           readable   = False,
                           writable   = False,
                           executable = False,
                           searchable = False
                       }

    setOwnerReadable :: Bool -> Permissions -> Permissions
    setOwnerReadable b p = p { readable = b }

    setOwnerWritable :: Bool -> Permissions -> Permissions
    setOwnerWritable b p = p { writable = b }

    setOwnerExecutable :: Bool -> Permissions -> Permissions
    setOwnerExecutable b p = p { executable = b }

    setOwnerSearchable :: Bool -> Permissions -> Permissions
    setOwnerSearchable b p = p { searchable = b }

    {- |The 'getPermissions' operation returns the
    permissions for the file or directory.

    The operation may fail with:

    * 'isPermissionError' if the user is not permitted to access
      the permissions; or

    * 'isDoesNotExistError' if the file or directory does not exist.

    -}

    #ifdef __GLASGOW_HASKELL__

    getPermissions :: FilePath -> IO Permissions
    getPermissions name = do
    #ifdef mingw32_HOST_OS
      withFilePath name $ \s -> do
      -- stat() does a better job of guessing the permissions on Windows
      -- than access() does.  e.g. for execute permission, it looks at the
      -- filename extension :-)
      --
      -- I tried for a while to do this properly, using the Windows security API,
      -- and eventually gave up.  getPermissions is a flawed API anyway. -- SimonM
      allocaBytes sizeof_stat $ \ p_stat -> do
      throwErrnoIfMinus1_ "getPermissions" $ c_stat s p_stat
      mode <- st_mode p_stat
      let usr_read   = mode .&. s_IRUSR
      let usr_write  = mode .&. s_IWUSR
      let usr_exec   = mode .&. s_IXUSR
      let is_dir = mode .&. s_IFDIR
      return (
        Permissions {
          readable   = usr_read  /= 0,
          writable   = usr_write /= 0,
          executable = is_dir == 0 && usr_exec /= 0,
          searchable = is_dir /= 0 && usr_exec /= 0
        }
       )
    #else
      read_ok  <- Posix.fileAccess name True  False False
      write_ok <- Posix.fileAccess name False True  False
      exec_ok  <- Posix.fileAccess name False False True
      stat <- Posix.getFileStatus name
      let is_dir = Posix.isDirectory stat
      return (
        Permissions {
          readable   = read_ok,
          writable   = write_ok,
          executable = not is_dir && exec_ok,
          searchable = is_dir && exec_ok
        }
       )
    #endif

    {- |The 'setPermissions' operation sets the
    permissions for the file or directory.

    The operation may fail with:

    * 'isPermissionError' if the user is not permitted to set
      the permissions; or

    * 'isDoesNotExistError' if the file or directory does not exist.

    -}

    setPermissions :: FilePath -> Permissions -> IO ()
    setPermissions name (Permissions r w e s) = do
    #ifdef mingw32_HOST_OS
      allocaBytes sizeof_stat $ \ p_stat -> do
      withFilePath name $ \p_name -> do
        throwErrnoIfMinus1_ "setPermissions" $
          c_stat p_name p_stat

        throwErrnoIfMinus1_ "setPermissions" $ do
          mode <- st_mode p_stat
          let mode1 = modifyBit r mode s_IRUSR
          let mode2 = modifyBit w mode1 s_IWUSR
          let mode3 = modifyBit (e || s) mode2 s_IXUSR
          c_wchmod p_name mode3
     where
       modifyBit :: Bool -> CMode -> CMode -> CMode
       modifyBit False m b = m .&. (complement b)
       modifyBit True  m b = m .|. b
    #else
          stat <- Posix.getFileStatus name
          let mode = Posix.fileMode stat
          let mode1 = modifyBit r mode  Posix.ownerReadMode
          let mode2 = modifyBit w mode1 Posix.ownerWriteMode
          let mode3 = modifyBit (e || s) mode2 Posix.ownerExecuteMode
          Posix.setFileMode name mode3
     where
       modifyBit :: Bool -> Posix.FileMode -> Posix.FileMode -> Posix.FileMode
       modifyBit False m b = m .&. (complement b)
       modifyBit True  m b = m .|. b
    #endif

    #ifdef mingw32_HOST_OS
    foreign import ccall unsafe "_wchmod"
       c_wchmod :: CWString -> CMode -> IO CInt
    #endif

    copyPermissions :: FilePath -> FilePath -> IO ()
    copyPermissions source dest = do
    #ifdef mingw32_HOST_OS
      allocaBytes sizeof_stat $ \ p_stat -> do
      withFilePath source $ \p_source -> do
      withFilePath dest $ \p_dest -> do
        throwErrnoIfMinus1_ "copyPermissions" $ c_stat p_source p_stat
        mode <- st_mode p_stat
        throwErrnoIfMinus1_ "copyPermissions" $ c_wchmod p_dest mode
    #else
      stat <- Posix.getFileStatus source
      let mode = Posix.fileMode stat
      Posix.setFileMode dest mode
    #endif

    -----------------------------------------------------------------------------
    -- Implementation

    {- |@'createDirectory' dir@ creates a new directory @dir@ which is
    initially empty, or as near to empty as the operating system
    allows.

    The operation may fail with:

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EROFS, EACCES]@

    * 'isAlreadyExistsError' \/ 'AlreadyExists'
    The operand refers to a directory that already exists.
    @ [EEXIST]@

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'InvalidArgument'
    The operand is not a valid directory name.
    @[ENAMETOOLONG, ELOOP]@

    * 'NoSuchThing'
    There is no path to the directory.
    @[ENOENT, ENOTDIR]@

    * 'ResourceExhausted'
    Insufficient resources (virtual memory, process file descriptors,
    physical disk space, etc.) are available to perform the operation.
    @[EDQUOT, ENOSPC, ENOMEM, EMLINK]@

    * 'InappropriateType'
    The path refers to an existing non-directory object.
    @[EEXIST]@

    -}

    createDirectory :: FilePath -> IO ()
    createDirectory path = do
    #ifdef mingw32_HOST_OS
      Win32.createDirectory path Nothing
    #else
      Posix.createDirectory path 0o777
    #endif

    #else /* !__GLASGOW_HASKELL__ */

    copyPermissions :: FilePath -> FilePath -> IO ()
    copyPermissions fromFPath toFPath
      = getPermissions fromFPath >>= setPermissions toFPath

    #endif

    -- | @'createDirectoryIfMissing' parents dir@ creates a new directory
    -- @dir@ if it doesn\'t exist. If the first argument is 'True'
    -- the function will also create all parent directories if they are missing.
    createDirectoryIfMissing :: Bool     -- ^ Create its parents too?
                             -> FilePath -- ^ The path to the directory you want to make
                             -> IO ()
    createDirectoryIfMissing create_parents path0
      | create_parents = createDirs (parents path0)
      | otherwise      = createDirs (take 1 (parents path0))
      where
        parents = reverse . scanl1 (</>) . splitDirectories . normalise

        createDirs []         = return ()
        createDirs (dir:[])   = createDir dir throw
        createDirs (dir:dirs) =
          createDir dir $ \_ -> do
            createDirs dirs
            createDir dir throw

        createDir :: FilePath -> (IOException -> IO ()) -> IO ()
        createDir dir notExistHandler = do
          r <- E.try $ createDirectory dir
          case (r :: Either IOException ()) of
            Right ()                   -> return ()
            Left  e
              | isDoesNotExistError  e -> notExistHandler e
              -- createDirectory (and indeed POSIX mkdir) does not distinguish
              -- between a dir already existing and a file already existing. So we
              -- check for it here. Unfortunately there is a slight race condition
              -- here, but we think it is benign. It could report an exeption in
              -- the case that the dir did exist but another process deletes the
              -- directory and creates a file in its place before we can check
              -- that the directory did indeed exist.
              -- We also follow this path when we get a permissions error, as
              -- trying to create "." when in the root directory on Windows
              -- fails with
              --     CreateDirectory ".": permission denied (Access is denied.)
              -- This caused GHCi to crash when loading a module in the root
              -- directory.
              | isAlreadyExistsError e
             || isPermissionError e -> (do
    #ifdef mingw32_HOST_OS
                  withFileStatus "createDirectoryIfMissing" dir $ \st -> do
                     isDir <- isDirectory st
                     if isDir then return ()
                              else throw e
    #else
                  stat <- Posix.getFileStatus dir
                  if Posix.isDirectory stat
                     then return ()
                     else throw e
    #endif
                  ) `E.catch` ((\_ -> return ()) :: IOException -> IO ())
              | otherwise              -> throw e

    #if __GLASGOW_HASKELL__
    {- | @'removeDirectory' dir@ removes an existing directory /dir/.  The
    implementation may specify additional constraints which must be
    satisfied before a directory can be removed (e.g. the directory has to
    be empty, or may not be in use by other processes).  It is not legal
    for an implementation to partially remove a directory unless the
    entire directory is removed. A conformant implementation need not
    support directory removal in all situations (e.g. removal of the root
    directory).

    The operation may fail with:

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'InvalidArgument'
    The operand is not a valid directory name.
    @[ENAMETOOLONG, ELOOP]@

    * 'isDoesNotExistError' \/ 'NoSuchThing'
    The directory does not exist.
    @[ENOENT, ENOTDIR]@

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EROFS, EACCES, EPERM]@

    * 'UnsatisfiedConstraints'
    Implementation-dependent constraints are not satisfied.
    @[EBUSY, ENOTEMPTY, EEXIST]@

    * 'UnsupportedOperation'
    The implementation does not support removal in this situation.
    @[EINVAL]@

    * 'InappropriateType'
    The operand refers to an existing non-directory object.
    @[ENOTDIR]@

    -}

    removeDirectory :: FilePath -> IO ()
    removeDirectory path =
    #ifdef mingw32_HOST_OS
      Win32.removeDirectory path
    #else
      Posix.removeDirectory path
    #endif

    #endif

    -- | @'removeDirectoryRecursive' dir@  removes an existing directory /dir/
    -- together with its content and all subdirectories. Be careful,
    -- if the directory contains symlinks, the function will follow them.
    removeDirectoryRecursive :: FilePath -> IO ()
    removeDirectoryRecursive startLoc = do
      cont <- getDirectoryContents startLoc
      sequence_ [rm (startLoc </> x) | x <- cont, x /= "." && x /= ".."]
      removeDirectory startLoc
      where
        rm :: FilePath -> IO ()
        rm f = do temp <- E.try (removeFile f)
                  case temp of
                    Left e  -> do isDir <- doesDirectoryExist f
                                  -- If f is not a directory, re-throw the error
                                  unless isDir $ throw (e :: SomeException)
                                  removeDirectoryRecursive f
                    Right _ -> return ()

    #if __GLASGOW_HASKELL__
    {- |'removeFile' /file/ removes the directory entry for an existing file
    /file/, where /file/ is not itself a directory. The
    implementation may specify additional constraints which must be
    satisfied before a file can be removed (e.g. the file may not be in
    use by other processes).

    The operation may fail with:

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'InvalidArgument'
    The operand is not a valid file name.
    @[ENAMETOOLONG, ELOOP]@

    * 'isDoesNotExistError' \/ 'NoSuchThing'
    The file does not exist.
    @[ENOENT, ENOTDIR]@

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EROFS, EACCES, EPERM]@

    * 'UnsatisfiedConstraints'
    Implementation-dependent constraints are not satisfied.
    @[EBUSY]@

    * 'InappropriateType'
    The operand refers to an existing directory.
    @[EPERM, EINVAL]@

    -}

    removeFile :: FilePath -> IO ()
    removeFile path =
    #if mingw32_HOST_OS
      Win32.deleteFile path
    #else
      Posix.removeLink path
    #endif

    {- |@'renameDirectory' old new@ changes the name of an existing
    directory from /old/ to /new/.  If the /new/ directory
    already exists, it is atomically replaced by the /old/ directory.
    If the /new/ directory is neither the /old/ directory nor an
    alias of the /old/ directory, it is removed as if by
    'removeDirectory'.  A conformant implementation need not support
    renaming directories in all situations (e.g. renaming to an existing
    directory, or across different physical devices), but the constraints
    must be documented.

    On Win32 platforms, @renameDirectory@ fails if the /new/ directory already
    exists.

    The operation may fail with:

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'InvalidArgument'
    Either operand is not a valid directory name.
    @[ENAMETOOLONG, ELOOP]@

    * 'isDoesNotExistError' \/ 'NoSuchThing'
    The original directory does not exist, or there is no path to the target.
    @[ENOENT, ENOTDIR]@

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EROFS, EACCES, EPERM]@

    * 'ResourceExhausted'
    Insufficient resources are available to perform the operation.
    @[EDQUOT, ENOSPC, ENOMEM, EMLINK]@

    * 'UnsatisfiedConstraints'
    Implementation-dependent constraints are not satisfied.
    @[EBUSY, ENOTEMPTY, EEXIST]@

    * 'UnsupportedOperation'
    The implementation does not support renaming in this situation.
    @[EINVAL, EXDEV]@

    * 'InappropriateType'
    Either path refers to an existing non-directory object.
    @[ENOTDIR, EISDIR]@

    -}

    renameDirectory :: FilePath -> FilePath -> IO ()
    renameDirectory opath npath = do
       -- XXX this test isn't performed atomically with the following rename
    #ifdef mingw32_HOST_OS
       -- ToDo: use Win32 API
       withFileStatus "renameDirectory" opath $ \st -> do
       is_dir <- isDirectory st
    #else
       stat <- Posix.getFileStatus opath
       let is_dir = Posix.fileMode stat .&. Posix.directoryMode /= 0
    #endif
       if (not is_dir)
            then ioError (ioeSetErrorString
                              (mkIOError InappropriateType "renameDirectory" Nothing (Just opath))
                              "not a directory")
            else do
    #ifdef mingw32_HOST_OS
       Win32.moveFileEx opath npath Win32.mOVEFILE_REPLACE_EXISTING
    #else
       Posix.rename opath npath
    #endif

    {- |@'renameFile' old new@ changes the name of an existing file system
    object from /old/ to /new/.  If the /new/ object already
    exists, it is atomically replaced by the /old/ object.  Neither
    path may refer to an existing directory.  A conformant implementation
    need not support renaming files in all situations (e.g. renaming
    across different physical devices), but the constraints must be
    documented.

    The operation may fail with:

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'InvalidArgument'
    Either operand is not a valid file name.
    @[ENAMETOOLONG, ELOOP]@

    * 'isDoesNotExistError' \/ 'NoSuchThing'
    The original file does not exist, or there is no path to the target.
    @[ENOENT, ENOTDIR]@

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EROFS, EACCES, EPERM]@

    * 'ResourceExhausted'
    Insufficient resources are available to perform the operation.
    @[EDQUOT, ENOSPC, ENOMEM, EMLINK]@

    * 'UnsatisfiedConstraints'
    Implementation-dependent constraints are not satisfied.
    @[EBUSY]@

    * 'UnsupportedOperation'
    The implementation does not support renaming in this situation.
    @[EXDEV]@

    * 'InappropriateType'
    Either path refers to an existing directory.
    @[ENOTDIR, EISDIR, EINVAL, EEXIST, ENOTEMPTY]@

    -}

    renameFile :: FilePath -> FilePath -> IO ()
    renameFile opath npath = do
       -- XXX this test isn't performed atomically with the following rename
    #ifdef mingw32_HOST_OS
       -- ToDo: use Win32 API
       withFileOrSymlinkStatus "renameFile" opath $ \st -> do
       is_dir <- isDirectory st
    #else
       stat <- Posix.getSymbolicLinkStatus opath
       let is_dir = Posix.isDirectory stat
    #endif
       if is_dir
            then ioError (ioeSetErrorString
                              (mkIOError InappropriateType "renameFile" Nothing (Just opath))
                              "is a directory")
            else do
    #ifdef mingw32_HOST_OS
       Win32.moveFileEx opath npath Win32.mOVEFILE_REPLACE_EXISTING
    #else
       Posix.rename opath npath
    #endif

    #endif /* __GLASGOW_HASKELL__ */

    {- |@'copyFile' old new@ copies the existing file from /old/ to /new/.
    If the /new/ file already exists, it is atomically replaced by the /old/ file.
    Neither path may refer to an existing directory.  The permissions of /old/ are
    copied to /new/, if possible.
    -}

    copyFile :: FilePath -> FilePath -> IO ()
    copyFile fromFPath toFPath =
        copy `catchIOError` (\exc -> throw $ ioeSetLocation exc "copyFile")
        where copy = bracket (openBinaryFile fromFPath ReadMode) hClose $ \hFrom ->
                     bracketOnError openTmp cleanTmp $ \(tmpFPath, hTmp) ->
                     do allocaBytes bufferSize $ copyContents hFrom hTmp
                        hClose hTmp
                        ignoreIOExceptions $ copyPermissions fromFPath tmpFPath
                        renameFile tmpFPath toFPath
              openTmp = openBinaryTempFile (takeDirectory toFPath) ".copyFile.tmp"
              cleanTmp (tmpFPath, hTmp)
                  = do ignoreIOExceptions $ hClose hTmp
                       ignoreIOExceptions $ removeFile tmpFPath
              bufferSize = 1024

              copyContents hFrom hTo buffer = do
                      count <- hGetBuf hFrom buffer bufferSize
                      when (count > 0) $ do
                              hPutBuf hTo buffer count
                              copyContents hFrom hTo buffer

              ignoreIOExceptions io = io `catchIOError` (\_ -> return ())

    -- | Given a path referring to a file or directory, returns a
    -- canonicalized path. The intent is that two paths referring
    -- to the same file\/directory will map to the same canonicalized
    -- path.
    --
    -- Note that it is impossible to guarantee that the
    -- implication (same file\/dir \<=\> same canonicalizedPath) holds
    -- in either direction: this function can make only a best-effort
    -- attempt.
    --
    -- The precise behaviour is that of the C realpath function
    -- GetFullPathNameW on Windows). In particular, the behaviour
    -- on paths that do not exist is known to vary from platform
    -- to platform. Some platforms do not alter the input, some
    -- do, and on some an exception will be thrown.
    canonicalizePath :: FilePath -> IO FilePath
    canonicalizePath fpath =
    #if defined(mingw32_HOST_OS)
             do path <- Win32.getFullPathName fpath
    #else
      do enc <- getFileSystemEncoding
         GHC.withCString enc fpath $ \pInPath ->
           allocaBytes long_path_size $ \pOutPath ->
             do _ <- throwErrnoPathIfNull "canonicalizePath" fpath $ c_realpath pInPath pOutPath
                -- NB: pOutPath will be passed thru as result pointer by c_realpath
                path <- GHC.peekCString enc pOutPath
    #endif
                return (normalise path)
            -- normalise does more stuff, like upper-casing the drive letter

    #if !defined(mingw32_HOST_OS)
    foreign import ccall unsafe "realpath"
                       c_realpath :: CString
                                  -> CString
                                  -> IO CString
    #endif

    -- | 'makeRelative' the current directory.
    makeRelativeToCurrentDirectory :: FilePath -> IO FilePath
    makeRelativeToCurrentDirectory x = do
        cur <- getCurrentDirectory
        return $ makeRelative cur x

    -- | Given an executable file name, searches for such file in the
    -- directories listed in system PATH. The returned value is the path
    -- to the found executable or Nothing if an executable with the given
    -- name was not found. For example (findExecutable \"ghc\") gives you
    -- the path to GHC.
    --
    -- The path returned by 'findExecutable' corresponds to the
    -- program that would be executed by 'System.Process.createProcess'
    -- when passed the same string (as a RawCommand, not a ShellCommand).
    --
    -- On Windows, 'findExecutable' calls the Win32 function 'SearchPath',
    -- which may search other places before checking the directories in
    -- @PATH@.  Where it actually searches depends on registry settings,
    -- but notably includes the directory containing the current
    -- executable. See
    -- <http://msdn.microsoft.com/en-us/library/aa365527.aspx> for more
    -- details.
    --
    findExecutable :: String -> IO (Maybe FilePath)
    findExecutable fileName = do
       files <- findExecutables fileName
       return $ listToMaybe files

    -- | Given a file name, searches for the file and returns a list of all
    -- occurences that are executable.
    --
    -- /Since: 1.2.1.0/
    findExecutables :: String -> IO [FilePath]
    findExecutables binary = do
    #if defined(mingw32_HOST_OS)
        file <- Win32.searchPath Nothing binary ('.':exeExtension)
        return $ maybeToList file
    #else
        path <- getEnv "PATH"
        findFilesWith isExecutable (splitSearchPath path) (binary <.> exeExtension)
      where isExecutable file = do
                perms <- getPermissions file
                return $ executable perms
    #endif

    -- | Search through the given set of directories for the given file.
    -- Used by 'findExecutable' on non-windows platforms.
    findFile :: [FilePath] -> String -> IO (Maybe FilePath)
    findFile path fileName = do
        files <- findFiles path fileName
        return $ listToMaybe files

    -- | Search through the given set of directories for the given file and
    -- returns a list of paths where the given file exists.
    --
    -- /Since: 1.2.1.0/
    findFiles :: [FilePath] -> String -> IO [FilePath]
    findFiles = findFilesWith (\_ -> return True)

    -- | Search through the given set of directories for the given file and
    -- with the given property (usually permissions) and returns a list of
    -- paths where the given file exists and has the property.
    --
    -- /Since: 1.2.1.0/
    findFilesWith :: (FilePath -> IO Bool) -> [FilePath] -> String -> IO [FilePath]
    findFilesWith _ [] _ = return []
    findFilesWith f (d:ds) fileName = do
        let file = d </> fileName
        exist <- doesFileExist file
        b <- if exist then f file else return False
        if b then do
                   files <- findFilesWith f ds fileName
                   return $ file : files
            else findFilesWith f ds fileName

    #ifdef __GLASGOW_HASKELL__
    {- |@'getDirectoryContents' dir@ returns a list of /all/ entries
    in /dir/.

    The operation may fail with:

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'InvalidArgument'
    The operand is not a valid directory name.
    @[ENAMETOOLONG, ELOOP]@

    * 'isDoesNotExistError' \/ 'NoSuchThing'
    The directory does not exist.
    @[ENOENT, ENOTDIR]@

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EACCES]@

    * 'ResourceExhausted'
    Insufficient resources are available to perform the operation.
    @[EMFILE, ENFILE]@

    * 'InappropriateType'
    The path refers to an existing non-directory object.
    @[ENOTDIR]@

    -}

    getDirectoryContents :: FilePath -> IO [FilePath]
    getDirectoryContents path =
      modifyIOError ((`ioeSetFileName` path) .
                     (`ioeSetLocation` "getDirectoryContents")) $ do
    #ifndef mingw32_HOST_OS
        bracket
          (Posix.openDirStream path)
          Posix.closeDirStream
          loop
     where
      loop dirp = do
         e <- Posix.readDirStream dirp
         if null e then return [] else do
           es <- loop dirp
           return (e:es)
    #else
      bracket
         (Win32.findFirstFile (path </> "*"))
         (\(h,_) -> Win32.findClose h)
         (\(h,fdat) -> loop h fdat [])
      where
            -- we needn't worry about empty directories: adirectory always
            -- has at least "." and ".." entries
        loop :: Win32.HANDLE -> Win32.FindData -> [FilePath] -> IO [FilePath]
        loop h fdat acc = do
           filename <- Win32.getFindDataFileName fdat
           more <- Win32.findNextFile h fdat
           if more
              then loop h fdat (filename:acc)
              else return (filename:acc)
                     -- no need to reverse, ordering is undefined
    #endif /* mingw32 */

    #endif /* __GLASGOW_HASKELL__ */

    {- |If the operating system has a notion of current directories,
    'getCurrentDirectory' returns an absolute path to the
    current directory of the calling process.

    The operation may fail with:

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'isDoesNotExistError' \/ 'NoSuchThing'
    There is no path referring to the current directory.
    @[EPERM, ENOENT, ESTALE...]@

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EACCES]@

    * 'ResourceExhausted'
    Insufficient resources are available to perform the operation.

    * 'UnsupportedOperation'
    The operating system has no notion of current directory.

    Note that in a concurrent program, the current directory is global
    state shared between all threads of the process.  When using
    filesystem operations from multiple threads, it is therefore highly
    recommended to use absolute rather than relative `FilePath`s.

    -}
    #ifdef __GLASGOW_HASKELL__
    getCurrentDirectory :: IO FilePath
    getCurrentDirectory = do
    #ifdef mingw32_HOST_OS
      Win32.getCurrentDirectory
    #else
      Posix.getWorkingDirectory
    #endif

    {- |If the operating system has a notion of current directories,
    @'setCurrentDirectory' dir@ changes the current
    directory of the calling process to /dir/.

    The operation may fail with:

    * 'HardwareFault'
    A physical I\/O error has occurred.
    @[EIO]@

    * 'InvalidArgument'
    The operand is not a valid directory name.
    @[ENAMETOOLONG, ELOOP]@

    * 'isDoesNotExistError' \/ 'NoSuchThing'
    The directory does not exist.
    @[ENOENT, ENOTDIR]@

    * 'isPermissionError' \/ 'PermissionDenied'
    The process has insufficient privileges to perform the operation.
    @[EACCES]@

    * 'UnsupportedOperation'
    The operating system has no notion of current directory, or the
    current directory cannot be dynamically changed.

    * 'InappropriateType'
    The path refers to an existing non-directory object.
    @[ENOTDIR]@

    Note that in a concurrent program, the current directory is global
    state shared between all threads of the process.  When using
    filesystem operations from multiple threads, it is therefore highly
    recommended to use absolute rather than relative `FilePath`s.

    -}

    setCurrentDirectory :: FilePath -> IO ()
    setCurrentDirectory path =
    #ifdef mingw32_HOST_OS
      Win32.setCurrentDirectory path
    #else
      Posix.changeWorkingDirectory path
    #endif

    #endif /* __GLASGOW_HASKELL__ */

    #ifdef __GLASGOW_HASKELL__
    {- |The operation 'doesDirectoryExist' returns 'True' if the argument file
    exists and is either a directory or a symbolic link to a directory,
    and 'False' otherwise.
    -}

    doesDirectoryExist :: FilePath -> IO Bool
    doesDirectoryExist name =
    #ifdef mingw32_HOST_OS
       (withFileStatus "doesDirectoryExist" name $ \st -> isDirectory st)
    #else
       (do stat <- Posix.getFileStatus name
           return (Posix.isDirectory stat))
    #endif
       `E.catch` ((\ _ -> return False) :: IOException -> IO Bool)

    {- |The operation 'doesFileExist' returns 'True'
    if the argument file exists and is not a directory, and 'False' otherwise.
    -}

    doesFileExist :: FilePath -> IO Bool
    doesFileExist name =
    #ifdef mingw32_HOST_OS
       (withFileStatus "doesFileExist" name $ \st -> do b <- isDirectory st; return (not b))
    #else
       (do stat <- Posix.getFileStatus name
           return (not (Posix.isDirectory stat)))
    #endif
       `E.catch` ((\ _ -> return False) :: IOException -> IO Bool)

    {- |The 'getModificationTime' operation returns the
    clock time at which the file or directory was last modified.

    The operation may fail with:

    * 'isPermissionError' if the user is not permitted to access
      the modification time; or

    * 'isDoesNotExistError' if the file or directory does not exist.

    Note: When linked against @unix-2.6.0.0@ or later the reported time
    supports sub-second precision if provided by the underlying system
    call.

    -}

    getModificationTime :: FilePath -> IO UTCTime
    getModificationTime name = do
    #ifdef mingw32_HOST_OS
     -- ToDo: use Win32 API so we can get sub-second resolution
     withFileStatus "getModificationTime" name $ \ st -> do
     modificationTime st
    #else
      stat <- Posix.getFileStatus name
      let mod_time :: POSIXTime
    #if MIN_VERSION_unix(2,6,0)
          mod_time = Posix.modificationTimeHiRes stat
    #else
          mod_time = realToFrac $ Posix.modificationTime stat
    #endif
      return $ posixSecondsToUTCTime mod_time
    #endif

    #endif /* __GLASGOW_HASKELL__ */

    #ifdef mingw32_HOST_OS
    withFileStatus :: String -> FilePath -> (Ptr CStat -> IO a) -> IO a
    withFileStatus loc name f = do
      modifyIOError (`ioeSetFileName` name) $
        allocaBytes sizeof_stat $ \p ->
          withFilePath (fileNameEndClean name) $ \s -> do
            throwErrnoIfMinus1Retry_ loc (c_stat s p)
            f p

    withFileOrSymlinkStatus :: String -> FilePath -> (Ptr CStat -> IO a) -> IO a
    withFileOrSymlinkStatus loc name f = do
      modifyIOError (`ioeSetFileName` name) $
        allocaBytes sizeof_stat $ \p ->
          withFilePath name $ \s -> do
            throwErrnoIfMinus1Retry_ loc (lstat s p)
            f p

    modificationTime :: Ptr CStat -> IO UTCTime
    modificationTime stat = do
        mtime <- st_mtime stat
        return $ posixSecondsToUTCTime $ realToFrac (mtime :: CTime)

    isDirectory :: Ptr CStat -> IO Bool
    isDirectory stat = do
      mode <- st_mode stat
      return (s_isdir mode)

    fileNameEndClean :: String -> String
    fileNameEndClean name = if isDrive name then addTrailingPathSeparator name
                                            else dropTrailingPathSeparator name

    foreign import ccall unsafe "HsDirectory.h __hscore_S_IRUSR" s_IRUSR :: CMode
    foreign import ccall unsafe "HsDirectory.h __hscore_S_IWUSR" s_IWUSR :: CMode
    foreign import ccall unsafe "HsDirectory.h __hscore_S_IXUSR" s_IXUSR :: CMode
    foreign import ccall unsafe "__hscore_S_IFDIR" s_IFDIR :: CMode
    #endif

    #ifndef mingw32_HOST_OS
    #ifdef __GLASGOW_HASKELL__
    foreign import ccall unsafe "__hscore_long_path_size"
      long_path_size :: Int
    #else
    long_path_size :: Int
    long_path_size = 2048   --  // guess?
    #endif /* __GLASGOW_HASKELL__ */
    #endif /* !mingw32_HOST_OS */

    {- | Returns the current user's home directory.

    The directory returned is expected to be writable by the current user,
    but note that it isn't generally considered good practice to store
    application-specific data here; use 'getAppUserDataDirectory'
    instead.

    On Unix, 'getHomeDirectory' returns the value of the @HOME@
    environment variable.  On Windows, the system is queried for a
    suitable path; a typical path might be
    @C:\/Documents And Settings\/user@.

    The operation may fail with:

    * 'UnsupportedOperation'
    The operating system has no notion of home directory.

    * 'isDoesNotExistError'
    The home directory for the current user does not exist, or
    cannot be found.
    -}
    getHomeDirectory :: IO FilePath
    getHomeDirectory =
      modifyIOError ((`ioeSetLocation` "getHomeDirectory")) $ do
    #if defined(mingw32_HOST_OS)
        r <- E.try $ Win32.sHGetFolderPath nullPtr Win32.cSIDL_PROFILE nullPtr 0
        case (r :: Either IOException String) of
          Right s -> return s
          Left  _ -> do
            r1 <- E.try $ Win32.sHGetFolderPath nullPtr Win32.cSIDL_WINDOWS nullPtr 0
            case r1 of
              Right s -> return s
              Left  e -> ioError (e :: IOException)
    #else
        getEnv "HOME"
    #endif

    {- | Returns the pathname of a directory in which application-specific
    data for the current user can be stored.  The result of
    'getAppUserDataDirectory' for a given application is specific to
    the current user.

    The argument should be the name of the application, which will be used
    to construct the pathname (so avoid using unusual characters that
    might result in an invalid pathname).

    Note: the directory may not actually exist, and may need to be created
    first.  It is expected that the parent directory exists and is
    writable.

    On Unix, this function returns @$HOME\/.appName@.  On Windows, a
    typical path might be

    > C:/Documents And Settings/user/Application Data/appName

    The operation may fail with:

    * 'UnsupportedOperation'
    The operating system has no notion of application-specific data directory.

    * 'isDoesNotExistError'
    The home directory for the current user does not exist, or
    cannot be found.
    -}
    getAppUserDataDirectory :: String -> IO FilePath
    getAppUserDataDirectory appName = do
      modifyIOError ((`ioeSetLocation` "getAppUserDataDirectory")) $ do
    #if defined(mingw32_HOST_OS)
        s <- Win32.sHGetFolderPath nullPtr Win32.cSIDL_APPDATA nullPtr 0
        return (s++'\\':appName)
    #else
        path <- getEnv "HOME"
        return (path++'/':'.':appName)
    #endif

    {- | Returns the current user's document directory.

    The directory returned is expected to be writable by the current user,
    but note that it isn't generally considered good practice to store
    application-specific data here; use 'getAppUserDataDirectory'
    instead.

    On Unix, 'getUserDocumentsDirectory' returns the value of the @HOME@
    environment variable.  On Windows, the system is queried for a
    suitable path; a typical path might be
    @C:\/Documents And Settings\/user\/My Documents@.

    The operation may fail with:

    * 'UnsupportedOperation'
    The operating system has no notion of document directory.

    * 'isDoesNotExistError'
    The document directory for the current user does not exist, or
    cannot be found.
    -}
    getUserDocumentsDirectory :: IO FilePath
    getUserDocumentsDirectory = do
      modifyIOError ((`ioeSetLocation` "getUserDocumentsDirectory")) $ do
    #if defined(mingw32_HOST_OS)
        Win32.sHGetFolderPath nullPtr Win32.cSIDL_PERSONAL nullPtr 0
    #else
        getEnv "HOME"
    #endif

    {- | Returns the current directory for temporary files.

    On Unix, 'getTemporaryDirectory' returns the value of the @TMPDIR@
    environment variable or \"\/tmp\" if the variable isn\'t defined.
    On Windows, the function checks for the existence of environment variables in
    the following order and uses the first path found:

    *
    TMP environment variable.

    *
    TEMP environment variable.

    *
    USERPROFILE environment variable.

    *
    The Windows directory

    The operation may fail with:

    * 'UnsupportedOperation'
    The operating system has no notion of temporary directory.

    The function doesn\'t verify whether the path exists.
    -}
    getTemporaryDirectory :: IO FilePath
    getTemporaryDirectory = do
    #if defined(mingw32_HOST_OS)
      Win32.getTemporaryDirectory
    #else
      getEnv "TMPDIR"
        `catchIOError` \e -> if isDoesNotExistError e then return "/tmp"
                              else throw e
    #endif

    -- ToDo: This should be determined via autoconf (AC_EXEEXT)
    -- | Extension for executable files
    -- (typically @\"\"@ on Unix and @\"exe\"@ on Windows or OS\/2)
    exeExtension :: String
    #ifdef mingw32_HOST_OS
    exeExtension = "exe"
    #else
    exeExtension = ""
    #endif