easy-file-0.2.1: Cross-platform File handling

Safe HaskellSafe
LanguageHaskell98

System.EasyFile

Contents

Description

This is a module of cross-platform file handling for Unix/Mac/Windows.

The standard module System.Directory and System.FilePath have following shortcomings:

  • getModificationTime exists in System.Directory. But getAccessTime, getChangeTime, getCreationTime do not exist.
  • getModificationTime returns obsoleted type, ClockTime. It should return modern type, UTCTime, I believe.
  • Some file functions are missing. A function to tell the link counter, for instance.
  • Path separator is not unified. Even though Windows accepts '/' as a file separator, getCurrentDirectory in System.Directory returns '\' as a file separator. So, we need to specify regular expression like this: "[/\\]foo[/\\]bar[/\\]baz".
  • getHomeDirectory returns HOMEDRIVE/HOMEPATH instead of the HOME environment variable on Windows.

This module aims to resolve these problems and provides:

Synopsis

Actions on directories

createDirectory :: FilePath -> IO ()

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]

createDirectoryIfMissing

Arguments

:: Bool

Create its parents too?

-> FilePath

The path to the directory you want to make

-> IO () 

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.

removeDirectory :: FilePath -> IO ()

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]

removeDirectoryRecursive :: FilePath -> IO ()

removeDirectoryRecursive dir removes an existing directory dir together with its contents and subdirectories. Symbolic links are removed without affecting their the targets.

renameDirectory :: FilePath -> FilePath -> IO ()

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]

getDirectoryContents :: FilePath -> IO [FilePath]

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]

getCurrentDirectory :: IO FilePath

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.

setCurrentDirectory :: FilePath -> IO ()

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 FilePaths.

Pre-defined directories

getHomeDirectory :: IO FilePath

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 Settingsuser.

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.

getHomeDirectory2 :: IO (Maybe FilePath)

Returns the current user's home directory from the HOME environment variable.

getAppUserDataDirectory :: String -> IO FilePath

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.

getUserDocumentsDirectory :: IO FilePath

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.

getTemporaryDirectory :: IO FilePath

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.

Actions on files

removeFile :: FilePath -> IO ()

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]

renameFile :: FilePath -> FilePath -> IO ()

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]

copyFile :: FilePath -> FilePath -> IO ()

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.

canonicalizePath :: FilePath -> IO FilePath

Canonicalize the path of an existing file or directory. The intent is that two paths referring to the same file/directory will map to the same canonicalized path.

Note: if you only require an absolute path, consider using makeAbsolute instead, which is more reliable and does not have unspecified behavior on nonexistent paths.

It is impossible to guarantee that the implication (same file/dir <=> same canonicalized path) holds in either direction: this function can make only a best-effort attempt.

The precise behaviour is that of the POSIX realpath function (or GetFullPathNameW on Windows). In particular, the behaviour on paths that don't exist can vary from platform to platform. Some platforms do not alter the input, some do, and some throw an exception.

An empty path is considered to be equivalent to the current directory.

Known bug(s): on Windows, this function does not resolve symbolic links.

Existence tests

doesFileExist :: FilePath -> IO Bool

The operation doesFileExist returns True if the argument file exists and is not a directory, and False otherwise.

doesDirectoryExist :: FilePath -> IO Bool

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.

Permissions

data Permissions :: *

Instances

getPermissions :: FilePath -> IO Permissions

The getPermissions operation returns the permissions for the file or directory.

The operation may fail with:

setPermissions :: FilePath -> Permissions -> IO ()

The setPermissions operation sets the permissions for the file or directory.

The operation may fail with:

copyPermissions :: FilePath -> FilePath -> IO ()

This function copy the permission of the first file to the second.

Timestamps

getCreationTime :: FilePath -> IO (Maybe UTCTime)

The getCreationTime operation returns the UTC time at which the file or directory was created. The time is only available on Windows.

getChangeTime :: FilePath -> IO (Maybe UTCTime)

The getChangeTime operation returns the UTC time at which the file or directory was changed. The time is only available on Unix and Mac. Note that Unix's rename() does not change ctime but MacOS's rename() does.

getModificationTime :: FilePath -> IO UTCTime

The getModificationTime operation returns the UTC 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.

getAccessTime :: FilePath -> IO UTCTime

The getModificationTime operation returns the UTC time at which the file or directory was last accessed.

Size

getFileSize :: FilePath -> IO Word64

Getting the size of the file.

File/directory information

isSymlink :: FilePath -> IO Bool

This function tells whether or not a file/directory is symbolic link.

getLinkCount :: FilePath -> IO (Maybe Int)

This function returns the link counter of a file/directory.

hasSubDirectories :: FilePath -> IO (Maybe Bool)

This function returns whether or not a directory has sub-directories.

Separator predicates

type FilePath = String

File and directory names are values of type String, whose precise meaning is operating system dependent. Files can be opened, yielding a handle which can then be used to operate on the contents of that file.

pathSeparator :: Char

The character that separates directories.

pathSeparator ==  '/'
isPathSeparator pathSeparator

pathSeparators :: [Char]

The list of all possible separators.

Windows: pathSeparators == ['\\', '/']
Posix:   pathSeparators == ['/']
pathSeparator `elem` pathSeparators

isPathSeparator :: Char -> Bool

Rather than using (== pathSeparator), use this. Test if something is a path separator.

isPathSeparator a == (a `elem` pathSeparators)

extSeparator :: Char

File extension character

extSeparator == '.'

isExtSeparator :: Char -> Bool

Is the character an extension character?

isExtSeparator a == (a == extSeparator)

Extension methods

splitExtension :: FilePath -> (String, String)

Split on the extension. addExtension is the inverse.

uncurry (++) (splitExtension x) == x
uncurry addExtension (splitExtension x) == x
splitExtension "file.txt" == ("file",".txt")
splitExtension "file" == ("file","")
splitExtension "file/file.txt" == ("file/file",".txt")
splitExtension "file.txt/boris" == ("file.txt/boris","")
splitExtension "file.txt/boris.ext" == ("file.txt/boris",".ext")
splitExtension "file/path.txt.bob.fred" == ("file/path.txt.bob",".fred")
splitExtension "file/path.txt/" == ("file/path.txt/","")

takeExtension :: FilePath -> String

Get the extension of a file, returns "" for no extension, .ext otherwise.

takeExtension x == snd (splitExtension x)
Valid x => takeExtension (addExtension x "ext") == ".ext"
Valid x => takeExtension (replaceExtension x "ext") == ".ext"

replaceExtension :: FilePath -> String -> FilePath

Set the extension of a file, overwriting one if already present.

replaceExtension "file.txt" ".bob" == "file.bob"
replaceExtension "file.txt" "bob" == "file.bob"
replaceExtension "file" ".bob" == "file.bob"
replaceExtension "file.txt" "" == "file"
replaceExtension "file.fred.bob" "txt" == "file.fred.txt"

dropExtension :: FilePath -> FilePath

Remove last extension, and the "." preceding it.

dropExtension x == fst (splitExtension x)

addExtension :: FilePath -> String -> FilePath

Add an extension, even if there is already one there. E.g. addExtension "foo.txt" "bat" -> "foo.txt.bat".

addExtension "file.txt" "bib" == "file.txt.bib"
addExtension "file." ".bib" == "file..bib"
addExtension "file" ".bib" == "file.bib"
addExtension "/" "x" == "/.x"
Valid x => takeFileName (addExtension (addTrailingPathSeparator x) "ext") == ".ext"
Windows: addExtension "\\\\share" ".txt" == "\\\\share\\.txt"

hasExtension :: FilePath -> Bool

Does the given filename have an extension?

null (takeExtension x) == not (hasExtension x)

(<.>) :: FilePath -> String -> FilePath infixr 7

Alias to addExtension, for people who like that sort of thing.

splitExtensions :: FilePath -> (FilePath, String)

Split on all extensions

splitExtensions "file.tar.gz" == ("file",".tar.gz")

dropExtensions :: FilePath -> FilePath

Drop all extensions

not $ hasExtension (dropExtensions x)

takeExtensions :: FilePath -> String

Get all extensions

takeExtensions "file.tar.gz" == ".tar.gz"

Drive methods

splitDrive :: FilePath -> (FilePath, FilePath)

Split a path into a drive and a path. On Unix, / is a Drive.

uncurry (++) (splitDrive x) == x
Windows: splitDrive "file" == ("","file")
Windows: splitDrive "c:/file" == ("c:/","file")
Windows: splitDrive "\\\\shared\\test" == ("\\\\shared\\","test")
Windows: splitDrive "\\\\shared" == ("\\\\shared","")
Windows: splitDrive "\\\\?\\UNC\\shared\\file" == ("\\\\?\\UNC\\shared\\","file")
Windows: splitDrive "\\\\?\\UNCshared\\file" == ("\\\\?\\","UNCshared\\file")
Windows: splitDrive "\\\\?\\d:\\file" == ("\\\\?\\d:\\","file")
Windows: splitDrive "/d" == ("","/d") -- xxx
Posix:   splitDrive "/test" == ("/","test") -- xxx
Posix:   splitDrive "//test" == ("//","test")
Posix:   splitDrive "test/file" == ("","test/file")
Posix:   splitDrive "file" == ("","file")

joinDrive :: FilePath -> FilePath -> FilePath

Join a drive and the rest of the path.

         uncurry joinDrive (splitDrive x) == x
Windows: joinDrive "C:" "foo" == "C:foo"
Windows: joinDrive "C:/" "bar" == "C:/bar"
Windows: joinDrive "\\\\share" "foo" == "\\\\share/foo" -- xxx
Windows: joinDrive "/:" "foo" == "/:/foo" -- xxx

takeDrive :: FilePath -> FilePath

Get the drive from a filepath.

takeDrive x == fst (splitDrive x)

hasDrive :: FilePath -> Bool

Does a path have a drive.

not (hasDrive x) == null (takeDrive x)

dropDrive :: FilePath -> FilePath

Delete the drive, if it exists.

dropDrive x == snd (splitDrive x)

isDrive :: FilePath -> Bool

Is an element a drive

Operations on a FilePath, as a list of directories

splitFileName :: FilePath -> (String, String)

Split a filename into directory and file. combine is the inverse.

uncurry (++) (splitFileName x) == x
Valid x => uncurry combine (splitFileName x) == x
splitFileName "file/bob.txt" == ("file/", "bob.txt")
splitFileName "file/" == ("file/", "")
splitFileName "bob" == ("", "bob")
Posix:   splitFileName "/" == ("/","")
Windows: splitFileName "c:" == ("c:","")

takeFileName :: FilePath -> FilePath

Get the file name.

takeFileName "test/" == ""
takeFileName x `isSuffixOf` x
takeFileName x == snd (splitFileName x)
Valid x => takeFileName (replaceFileName x "fred") == "fred"
Valid x => takeFileName (x </> "fred") == "fred"
Valid x => isRelative (takeFileName x)

replaceFileName :: FilePath -> String -> FilePath

Set the filename.

Valid x => replaceFileName x (takeFileName x) == x

dropFileName :: FilePath -> FilePath

Drop the filename.

dropFileName x == fst (splitFileName x)

takeBaseName :: FilePath -> String

Get the base name, without an extension or path.

takeBaseName "file/test.txt" == "test"
takeBaseName "dave.ext" == "dave"
takeBaseName "" == ""
takeBaseName "test" == "test"
takeBaseName (addTrailingPathSeparator x) == ""
takeBaseName "file/file.tar.gz" == "file.tar"

replaceBaseName :: FilePath -> String -> FilePath

Set the base name.

replaceBaseName "file/test.txt" "bob" == "file/bob.txt"
replaceBaseName "fred" "bill" == "bill"
replaceBaseName "/dave/fred/bob.gz.tar" "new" == "/dave/fred/new.tar"
replaceBaseName x (takeBaseName x) == x

takeDirectory :: FilePath -> FilePath

Get the directory name, move up one level.

          takeDirectory x `isPrefixOf` x
          takeDirectory "foo" == ""
          takeDirectory "/foo/bar/baz" == "/foo/bar"
          takeDirectory "/foo/bar/baz/" == "/foo/bar/baz"
          takeDirectory "foo/bar/baz" == "foo/bar"
Windows:  takeDirectory "foo\\bar\\\\" == "foo\\bar" -- xxx
Windows:  takeDirectory "C:/" == "C:/"

replaceDirectory :: FilePath -> String -> FilePath

Set the directory, keeping the filename the same.

replaceDirectory x (takeDirectory x) `equalFilePath` x

combine :: FilePath -> FilePath -> FilePath

Combine two paths, if the second path isAbsolute, then it returns the second.

Valid x => combine (takeDirectory x) (takeFileName x) `equalFilePath` x
combine "/" "test" == "/test"
combine "home" "bob" == "home/bob"

(</>) :: FilePath -> FilePath -> FilePath infixr 5

A nice alias for combine.

splitPath :: FilePath -> [FilePath]

Split a path by the directory separator.

concat (splitPath x) == x
splitPath "test//item/" == ["test//","item/"]
splitPath "test/item/file" == ["test/","item/","file"]
splitPath "" == []
Windows: splitPath "c:/test/path" == ["c:/","test/","path"]
Posix:   splitPath "/file/test" == ["/","file/","test"]

joinPath :: [FilePath] -> FilePath

Join path elements back together.

Valid x => joinPath (splitPath x) == x
joinPath [] == ""
Posix: joinPath ["test","file","path"] == "test/file/path"

splitDirectories :: FilePath -> [FilePath]

Just as splitPath, but don't add the trailing slashes to each element.

splitDirectories "test/file" == ["test","file"]
splitDirectories "/test/file" == ["/","test","file"]
Valid x => joinPath (splitDirectories x) `equalFilePath` x
splitDirectories "" == []

Low level FilePath operators

hasTrailingPathSeparator :: FilePath -> Bool

Is an item either a directory or the last character a path separator?

hasTrailingPathSeparator "test" == False
hasTrailingPathSeparator "test/" == True

addTrailingPathSeparator :: FilePath -> FilePath

Add a trailing file path separator if one is not already present.

hasTrailingPathSeparator (addTrailingPathSeparator x)
hasTrailingPathSeparator x ==> addTrailingPathSeparator x == x
addTrailingPathSeparator "test/rest" == "test/rest/"

dropTrailingPathSeparator :: FilePath -> FilePath

Remove any trailing path separators

dropTrailingPathSeparator "file/test/" == "file/test"
not (hasTrailingPathSeparator (dropTrailingPathSeparator x)) || isDrive x
dropTrailingPathSeparator "/" == "/"

File name manipulators

normalise :: FilePath -> FilePath

Normalise a file

  • // outside of the drive can be made blank
  • / -> pathSeparator
  • ./ -> ""
Posix:   normalise "/file/\\test////" == "/file/\\test/"
Posix:   normalise "/file/./test" == "/file/test"
Posix:   normalise "/test/file/../bob/fred/" == "/test/file/../bob/fred/"
Posix:   normalise "../bob/fred/" == "../bob/fred/"
Posix:   normalise "./bob/fred/" == "bob/fred/"
Windows: normalise "c:\\file/bob\\" == "C:/file/bob/"
Windows: normalise "c:/" == "C:/"
Windows: normalise "\\\\server\\test" == "\\\\server\\test" -- xxx
Windows: normalise "." == "."
Posix:   normalise "./" == "./"

equalFilePath :: FilePath -> FilePath -> Bool

Equality of two FilePaths. If you call System.Directory.canonicalizePath first this has a much better chance of working. Note that this doesn't follow symlinks or DOSNAM~1s.

         x == y ==> equalFilePath x y
         normalise x == normalise y ==> equalFilePath x y
Posix:   equalFilePath "foo" "foo/"
Posix:   not (equalFilePath "foo" "/foo")
Posix:   not (equalFilePath "foo" "FOO")
Windows: equalFilePath "foo" "FOO"

makeRelative :: FilePath -> FilePath -> FilePath

Contract a filename, based on a relative path.

There is no corresponding makeAbsolute function, instead use System.Directory.canonicalizePath which has the same effect.

         Valid y => equalFilePath x y || (isRelative x && makeRelative y x == x) || equalFilePath (y </> makeRelative y x) x
         makeRelative x x == "."
         null y || equalFilePath (makeRelative x (x </> y)) y || null (takeFileName x)
Windows: makeRelative "C:/Home" "c:/home/bob" == "bob"
Windows: makeRelative "C:/Home" "D:/Home/Bob" == "D:/Home/Bob"
Windows: makeRelative "C:/Home" "C:Home/Bob" == "C:Home/Bob"
Windows: makeRelative "/Home" "/home/bob" == "bob"
Posix:   makeRelative "/Home" "/home/bob" == "/home/bob"
Posix:   makeRelative "/home/" "/home/bob/foo/bar" == "bob/foo/bar"
Posix:   makeRelative "/fred" "bob" == "bob"
Posix:   makeRelative "/file/test" "/file/test/fred" == "fred"
Posix:   makeRelative "/file/test" "/file/test/fred/" == "fred/"
Posix:   makeRelative "some/path" "some/path/a/b/c" == "a/b/c"

isRelative :: FilePath -> Bool

Is a path relative, or is it fixed to the root?

Windows: isRelative "path\\test" == True
Windows: isRelative "c:\\test" == False
Windows: isRelative "c:test" == True
Windows: isRelative "c:" == True
Windows: isRelative "\\\\foo" == False
Windows: isRelative "/foo" == True
Posix:   isRelative "test/path" == True
Posix:   isRelative "/test" == False

isAbsolute :: FilePath -> Bool

not . isRelative
isAbsolute x == not (isRelative x)