diff --git a/CHANGELOG b/CHANGELOG
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--- /dev/null
+++ b/CHANGELOG
@@ -0,0 +1,5 @@
+filepath-bytestring (1.4.2.1.0) unstable; urgency=medium
+
+  * Initial release, based on filepath 1.4.2.1.
+
+ -- Joey Hess <id@joeyh.name>  Tue, 10 Dec 2019 15:21:14 -0400
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright Neil Mitchell 2005-2019.
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Neil Mitchell nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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+++ b/README.md
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+# FilePath [![Hackage version](https://img.shields.io/hackage/v/filepath.svg?label=Hackage)](https://hackage.haskell.org/package/filepath) [![Linux build status](https://img.shields.io/travis/haskell/filepath/master.svg?label=Linux%20build)](https://travis-ci.org/haskell/filepath) [![Windows build status](https://img.shields.io/appveyor/ci/ndmitchell/filepath/master.svg?label=Windows%20build)](https://ci.appveyor.com/project/ndmitchell/filepath)
+
+The `filepath-bytestring` package provides functionality for manipulating `RawFilePath` values (`ByteString`s).
+Its interface is equivilant to the `filepath` package.
+It provides three modules:
+
+* [`System.FilePath.Posix.ByteString`](http://hackage.haskell.org/package/filepath-bytestring/docs/System-FilePath-Posix-ByteString.html) manipulates POSIX/Linux style `RawFilePath` values (with `/` as the path separator).
+* [`System.FilePath.Windows.ByteString`](http://hackage.haskell.org/package/filepath-bytestring/docs/System-FilePath-Windows-ByteString.html) manipulates Windows style `RawFilePath` values (with either `\` or `/` as the path separator, and deals with drives).
+* [`System.FilePath.ByteString`](http://hackage.haskell.org/package/filepath-bytestring/docs/System-FilePath-ByteString.html) is an alias for the module appropriate to your platform.
+
+All three modules provide the same API, and the same documentation (calling out differences in the different variants).
+
+### Developer notes
+
+This package's version should be the same as the `filepath` it's derived
+from, with an added revision number.
+
+Most of the code is in `System/FilePath/Internal.hs` which is `#include`'d into both `System/FilePath/Posix.hs` and `System/FilePath/Windows.hs` with the `IS_WINDOWS` CPP define set to either `True` or `False`. This Internal module is a bit weird in that it isn't really a Haskell module, but is more an include file.
+
+The library has extensive doc tests. Anything starting with `-- >` is transformed into a doc test as a predicate that must evaluate to `True`. These tests follow a few rules:
+
+* Tests prefixed with `Windows:` or `Posix:` are only tested against that specific implementation - otherwise tests are run against both implementations.
+* Any single letter variable, e.g. `x`, is considered universal quantification, and is checked with `QuickCheck`.
+* If `Valid x =>` appears at the start of a doc test, that means the property will only be tested with `x` passing the `isValid` predicate.
+
+Also, all exported functions are quickchecked against the ones from
+`filepath` to make sure thay generate equivilant results.
+
+The tests can be generated by `Generate.hs` in the root of the repo, and will be placed in `tests/TestGen.hs`. The `TestGen.hs` file is checked into the repo, and the CI scripts check that `TestGen.hs` is in sync with what would be generated a fresh - if you don't regenerate `TestGen.hs` the CI will fail.
+
+The `.ghci` file is set up to allow you to type `ghci` to open the library, then `:go` will regenerate the tests and run them.
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/System/FilePath/ByteString.hs b/System/FilePath/ByteString.hs
new file mode 100644
--- /dev/null
+++ b/System/FilePath/ByteString.hs
@@ -0,0 +1,30 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__ >= 704
+{-# LANGUAGE Safe #-}
+#endif
+{- |
+Module      :  System.FilePath.ByteString
+Copyright   :  (c) Neil Mitchell 2005-2014, (c) Joey Hess 2019
+License     :  BSD3
+
+Maintainer  :  id@joeyh.name
+Stability   :  stable
+Portability :  portable
+
+A library for 'RawFilePath' manipulations, using Posix or Windows filepaths
+depending on the platform.
+
+Both "System.FilePath.Posix.ByteString"
+and "System.FilePath.Windows.ByteString" provide the
+same interface. See either for examples and a list of the available
+functions.
+-}
+
+
+#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
+module System.FilePath.ByteString(module System.FilePath.Windows.ByteString) where
+import System.FilePath.Windows.ByteString
+#else
+module System.FilePath.ByteString(module System.FilePath.Posix.ByteString) where
+import System.FilePath.Posix.ByteString
+#endif
diff --git a/System/FilePath/Internal.hs b/System/FilePath/Internal.hs
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--- /dev/null
+++ b/System/FilePath/Internal.hs
@@ -0,0 +1,1083 @@
+#if __GLASGOW_HASKELL__ >= 704
+{-# LANGUAGE Safe #-}
+#endif
+{-# LANGUAGE OverloadedStrings #-}
+
+-- This template expects CPP definitions for:
+--     MODULE_NAME = Posix | Windows
+--     IS_WINDOWS  = False | True
+
+-- |
+-- Module      :  System.FilePath.MODULE_NAME.ByteString
+-- Copyright   :  (c) Neil Mitchell 2005-2014, (c) Joey Hess 2019
+-- License     :  BSD3
+--
+-- Maintainer  :  id@joeyh.name
+-- Stability   :  stable
+-- Portability :  portable
+--
+-- A library for 'RawFilePath' manipulations, using MODULE_NAME style paths on
+-- all platforms. Importing "System.FilePath.ByteString" is usually better.
+--
+-- This module is the same as System.FilePath.MODULE_NAME from the filepath
+-- library, except it uses 'RawFilePath'.
+--
+-- Given the example 'RawFilePath': @\/directory\/file.ext@
+--
+-- We can use the following functions to extract pieces.
+--
+-- * 'takeFileName' gives @\"file.ext\"@
+--
+-- * 'takeDirectory' gives @\"\/directory\"@
+--
+-- * 'takeExtension' gives @\".ext\"@
+--
+-- * 'dropExtension' gives @\"\/directory\/file\"@
+--
+-- * 'takeBaseName' gives @\"file\"@
+--
+-- And we could have built an equivalent path with the following expressions:
+--
+-- * @\"\/directory\" '</>' \"file.ext\"@.
+--
+-- * @\"\/directory\/file" '<.>' \"ext\"@.
+--
+-- * @\"\/directory\/file.txt" '-<.>' \"ext\"@.
+--
+-- Each function in this module is documented with several examples,
+-- which are also used as tests.
+--
+-- Here are a few examples of using the @filepath@ functions together:
+--
+-- /Example 1:/ Find the possible locations of a Haskell module @Test@ imported from module @Main@:
+--
+-- @['replaceFileName' path_to_main \"Test\" '<.>' ext | ext <- [\"hs\",\"lhs\"] ]@
+--
+-- /Example 2:/ Compile a Haskell file, putting the @.hi@ file under @interface@:
+--
+-- @'takeDirectory' file '</>' \"interface\" '</>' ('takeFileName' file '-<.>' \"hi\")@
+--
+-- References:
+-- [1] <http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx Naming Files, Paths and Namespaces> (Microsoft MSDN)
+module System.FilePath.MODULE_NAME.ByteString
+    (
+    -- * Types
+    RawFilePath,
+    -- * Separator predicates
+    pathSeparator, pathSeparators, isPathSeparator,
+    searchPathSeparator, isSearchPathSeparator,
+    extSeparator, isExtSeparator,
+
+    -- * @$PATH@ methods
+    --splitSearchPath, getSearchPath,
+
+    -- * Extension functions
+    splitExtension,
+    takeExtension, replaceExtension, (-<.>), dropExtension, addExtension, hasExtension, (<.>),
+    splitExtensions, dropExtensions, takeExtensions, replaceExtensions, isExtensionOf,
+    stripExtension,
+
+    -- * Filename\/directory functions
+    splitFileName,
+    takeFileName, replaceFileName, dropFileName,
+    takeBaseName, replaceBaseName,
+    takeDirectory, replaceDirectory,
+    combine, (</>),
+    splitPath, joinPath, splitDirectories,
+
+    -- * Drive functions
+    splitDrive, joinDrive,
+    takeDrive, hasDrive, dropDrive, isDrive,
+
+    -- * Trailing slash functions
+    hasTrailingPathSeparator,
+    addTrailingPathSeparator,
+    dropTrailingPathSeparator,
+
+    -- * File name manipulations
+    --normalise, equalFilePath,
+    --makeRelative,
+    isRelative, isAbsolute,
+    isValid, -- makeValid
+    )
+    where
+
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Char8 as B8
+import Data.Char(ord, chr, toUpper, isAsciiLower, isAsciiUpper)
+import Data.Maybe(isJust)
+import Data.Word(Word8)
+
+#ifndef mingw32_HOST_OS
+-- Import from unix, rather than redefining, so users who import both
+-- will not get an ambiguous occurance of RawFilePath.
+import System.Posix.ByteString(RawFilePath)
+#else
+-- | A literal file path
+type RawFilePath = ByteString
+#endif
+
+
+infixr 7  <.>, -<.>
+infixr 5  </>
+
+
+---------------------------------------------------------------------
+-- Platform Abstraction Methods (private)
+
+-- | Is the operating system Unix or Linux like
+isPosix :: Bool
+isPosix = not isWindows
+
+-- | Is the operating system Windows like
+isWindows :: Bool
+isWindows = IS_WINDOWS
+
+
+---------------------------------------------------------------------
+-- The basic functions
+
+-- | The character that separates directories. In the case where more than
+--   one character is possible, 'pathSeparator' is the \'ideal\' one.
+--
+-- > Windows: pathSeparator == fromIntegral (ord '\\')
+-- > Posix:   pathSeparator == fromIntegral (ord '/')
+-- > isPathSeparator pathSeparator
+pathSeparator :: Word8
+pathSeparator = if isWindows then fromIntegral (ord '\\') else fromIntegral (ord '/')
+
+-- | The list of all possible separators.
+--
+-- > Windows: pathSeparators == [fromIntegral (ord '\\'), fromIntegral (ord '/')]
+-- > Posix:   pathSeparators == [fromIntegral (ord '/')]
+-- > pathSeparator `elem` pathSeparators
+pathSeparators :: [Word8]
+pathSeparators = if isWindows then [fromIntegral (ord '\\'), fromIntegral (ord '/')] else [fromIntegral (ord '/')]
+
+-- | Rather than using @(== 'pathSeparator')@, use this. Test if something
+--   is a path separator.
+--
+-- > isPathSeparator a == (a `elem` pathSeparators)
+isPathSeparator :: Word8 -> Bool
+isPathSeparator 47 = True
+isPathSeparator 92 = isWindows
+isPathSeparator _ = False
+
+
+-- | The character that is used to separate the entries in the $PATH environment variable.
+--
+-- > Windows: searchPathSeparator == fromIntegral (ord ';')
+-- > Posix:   searchPathSeparator == fromIntegral (ord ':')
+searchPathSeparator :: Word8
+searchPathSeparator = if isWindows then fromIntegral (ord ';') else fromIntegral (ord ':')
+
+-- | Is the character a file separator?
+--
+-- > isSearchPathSeparator a == (a == searchPathSeparator)
+isSearchPathSeparator :: Word8 -> Bool
+isSearchPathSeparator = (== searchPathSeparator)
+
+
+-- | File extension character
+--
+-- > extSeparator == fromIntegral (ord '.')
+extSeparator :: Word8
+extSeparator = fromIntegral (ord '.')
+
+-- | Is the character an extension character?
+--
+-- > isExtSeparator a == (a == extSeparator)
+isExtSeparator :: Word8 -> Bool
+isExtSeparator = (== extSeparator)
+
+{-
+
+---------------------------------------------------------------------
+-- Path methods (environment $PATH)
+
+-- | Take a string, split it on the 'searchPathSeparator' character.
+--   Blank items are ignored on Windows, and converted to @.@ on Posix.
+--   On Windows path elements are stripped of quotes.
+--
+--   Follows the recommendations in
+--   <http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html>
+--
+-- > untested Posix:   splitSearchPath "File1:File2:File3"  == ["File1","File2","File3"]
+-- > untested Posix:   splitSearchPath "File1::File2:File3" == ["File1",".","File2","File3"]
+-- > untested Windows: splitSearchPath "File1;File2;File3"  == ["File1","File2","File3"]
+-- > untested Windows: splitSearchPath "File1;;File2;File3" == ["File1","File2","File3"]
+-- > untested Windows: splitSearchPath "File1;\"File2\";File3" == ["File1","File2","File3"]
+splitSearchPath :: String -> [FilePath]
+splitSearchPath = f
+    where
+    f xs = case break isSearchPathSeparator xs of
+           (pre, []    ) -> g pre
+           (pre, _:post) -> g pre ++ f post
+
+    g "" = ["." | isPosix]
+    g ('\"':x@(_:_)) | isWindows && last x == '\"' = [init x]
+    g x = [x]
+
+
+-- | Get a list of 'FilePath's in the $PATH variable.
+getSearchPath :: IO [FilePath]
+getSearchPath = fmap splitSearchPath (getEnv "PATH")
+
+-}
+
+---------------------------------------------------------------------
+-- Extension methods
+
+-- | Split on the extension. 'addExtension' is the inverse.
+--
+-- > splitExtension "/directory/path.ext" == ("/directory/path",".ext")
+-- > uncurry (<>) (splitExtension x) == x
+-- > Valid 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/","")
+splitExtension :: RawFilePath -> (ByteString, ByteString)
+splitExtension x = if B.null nameDot
+        then (x,mempty)
+        else (dir <> B.init nameDot, extSeparator `B.cons` ext)
+    where
+        (dir,file) = splitFileName_ x
+        (nameDot,ext) = B.breakEnd isExtSeparator file
+
+-- | Get the extension of a file, returns @\"\"@ for no extension, @.ext@ otherwise.
+--
+-- > takeExtension "/directory/path.ext" == ".ext"
+-- > takeExtension x == snd (splitExtension x)
+-- > Valid x => takeExtension (addExtension x "ext") == ".ext"
+-- > Valid x => takeExtension (replaceExtension x "ext") == ".ext"
+takeExtension :: RawFilePath -> ByteString
+takeExtension = snd . splitExtension
+
+-- | Remove the current extension and add another, equivalent to 'replaceExtension'.
+--
+-- > "/directory/path.txt" -<.> "ext" == "/directory/path.ext"
+-- > "/directory/path.txt" -<.> ".ext" == "/directory/path.ext"
+-- > "foo.o" -<.> "c" == "foo.c"
+(-<.>) :: RawFilePath -> ByteString -> RawFilePath
+(-<.>) = replaceExtension
+
+-- | Set the extension of a file, overwriting one if already present, equivalent to '-<.>'.
+--
+-- > replaceExtension "/directory/path.txt" "ext" == "/directory/path.ext"
+-- > replaceExtension "/directory/path.txt" ".ext" == "/directory/path.ext"
+-- > 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"
+-- > replaceExtension x y == addExtension (dropExtension x) y
+replaceExtension :: RawFilePath -> ByteString -> RawFilePath
+replaceExtension x y = dropExtension x <.> y
+
+-- | Add an extension, even if there is already one there, equivalent to 'addExtension'.
+--
+-- > "/directory/path" <.> "ext" == "/directory/path.ext"
+-- > "/directory/path" <.> ".ext" == "/directory/path.ext"
+(<.>) :: RawFilePath -> ByteString -> RawFilePath
+(<.>) = addExtension
+
+-- | Remove last extension, and the \".\" preceding it.
+--
+-- > dropExtension "/directory/path.ext" == "/directory/path"
+-- > dropExtension x == fst (splitExtension x)
+dropExtension :: RawFilePath -> RawFilePath
+dropExtension = fst . splitExtension
+
+-- | Add an extension, even if there is already one there, equivalent to '<.>'.
+--
+-- > addExtension "/directory/path" "ext" == "/directory/path.ext"
+-- > addExtension "file.txt" "bib" == "file.txt.bib"
+-- > addExtension "file." ".bib" == "file..bib"
+-- > addExtension "file" ".bib" == "file.bib"
+-- > addExtension "/" "x" == "/.x"
+-- > addExtension x "" == x
+-- > Valid x => takeFileName (addExtension (addTrailingPathSeparator x) "ext") == ".ext"
+-- > Windows: addExtension "\\\\share" ".txt" == "\\\\share\\.txt"
+addExtension :: RawFilePath -> ByteString -> RawFilePath
+addExtension file ext = case B.uncons ext of
+        Nothing -> file
+        Just (x,_xs) -> joinDrive a $
+                if isExtSeparator x then b <> ext
+                else b <> (extSeparator `B.cons` ext)
+    where
+        (a,b) = splitDrive file
+
+-- | Does the given filename have an extension?
+--
+-- > hasExtension "/directory/path.ext" == True
+-- > hasExtension "/directory/path" == False
+-- > null (takeExtension x) == not (hasExtension x)
+hasExtension :: RawFilePath -> Bool
+hasExtension = B.any isExtSeparator . takeFileName
+
+
+-- | Does the given filename have the specified extension?
+--
+-- > "png" `isExtensionOf` "/directory/file.png" == True
+-- > ".png" `isExtensionOf` "/directory/file.png" == True
+-- > ".tar.gz" `isExtensionOf` "bar/foo.tar.gz" == True
+-- > "ar.gz" `isExtensionOf` "bar/foo.tar.gz" == False
+-- > "png" `isExtensionOf` "/directory/file.png.jpg" == False
+-- > "csv/table.csv" `isExtensionOf` "/data/csv/table.csv" == False
+isExtensionOf :: ByteString -> RawFilePath -> Bool
+isExtensionOf ext = B.isSuffixOf ext' . takeExtensions
+  where
+    ext' = case B.uncons ext of
+        Just (h, _) | isExtSeparator h -> ext
+        _ -> extSeparator `B.cons` ext
+
+-- | Drop the given extension from a FilePath, and the @\".\"@ preceding it.
+--   Returns 'Nothing' if the FilePath does not have the given extension, or
+--   'Just' and the part before the extension if it does.
+--
+--   This function can be more predictable than 'dropExtensions', especially if the filename
+--   might itself contain @.@ characters.
+--
+-- > stripExtension "hs.o" "foo.x.hs.o" == Just "foo.x"
+-- > stripExtension "hi.o" "foo.x.hs.o" == Nothing
+-- > dropExtension x == fromJust (stripExtension (takeExtension x) x)
+-- > dropExtensions x == fromJust (stripExtension (takeExtensions x) x)
+-- > stripExtension ".c.d" "a.b.c.d"  == Just "a.b"
+-- > stripExtension ".c.d" "a.b..c.d" == Just "a.b."
+-- > stripExtension "baz"  "foo.bar"  == Nothing
+-- > stripExtension "bar"  "foobar"   == Nothing
+-- > stripExtension ""     x          == Just x
+stripExtension :: ByteString -> RawFilePath -> Maybe RawFilePath
+stripExtension ext path = case B.uncons ext of
+        Nothing -> Just path
+        Just (x, _) -> 
+                let dotExt = if isExtSeparator x
+                        then ext
+                        else extSeparator `B.cons` ext
+                in B.stripSuffix dotExt path
+
+
+-- | Split on all extensions.
+--
+-- > splitExtensions "/directory/path.ext" == ("/directory/path",".ext")
+-- > splitExtensions "file.tar.gz" == ("file",".tar.gz")
+-- > uncurry (<>) (splitExtensions x) == x
+-- > Valid x => uncurry addExtension (splitExtensions x) == x
+-- > splitExtensions "file.tar.gz" == ("file",".tar.gz")
+splitExtensions :: RawFilePath -> (RawFilePath, ByteString)
+splitExtensions x = (a <> c, d)
+    where
+        (a,b) = splitFileName_ x
+        (c,d) = B.break isExtSeparator b
+
+-- | Drop all extensions.
+--
+-- > dropExtensions "/directory/path.ext" == "/directory/path"
+-- > dropExtensions "file.tar.gz" == "file"
+-- > not $ hasExtension $ dropExtensions x
+-- > not $ any isExtSeparator $ takeFileName $ dropExtensions x
+dropExtensions :: RawFilePath -> RawFilePath
+dropExtensions = fst . splitExtensions
+
+-- | Get all extensions.
+--
+-- > takeExtensions "/directory/path.ext" == ".ext"
+-- > takeExtensions "file.tar.gz" == ".tar.gz"
+takeExtensions :: RawFilePath -> ByteString
+takeExtensions = snd . splitExtensions
+
+
+-- | Replace all extensions of a file with a new extension. Note
+--   that 'replaceExtension' and 'addExtension' both work for adding
+--   multiple extensions, so only required when you need to drop
+--   all extensions first.
+--
+-- > replaceExtensions "file.fred.bob" "txt" == "file.txt"
+-- > replaceExtensions "file.fred.bob" "tar.gz" == "file.tar.gz"
+replaceExtensions :: RawFilePath -> ByteString -> RawFilePath
+replaceExtensions x y = dropExtensions x <.> y
+
+
+
+---------------------------------------------------------------------
+-- Drive methods
+
+-- | Is the given character a valid drive letter?
+-- only a-z and A-Z are letters, not isAlpha which is more unicodey
+isLetter :: Word8 -> Bool
+isLetter x = isAsciiLower c || isAsciiUpper c
+  where c = chr (fromIntegral x)
+
+-- | Split a path into a drive and a path.
+--   On Posix, \/ is a Drive.
+--
+-- > uncurry (<>) (splitDrive x) == x
+-- > Windows: splitDrive "file" == ("","file")
+-- > Windows: splitDrive "c:/file" == ("c:/","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")
+-- > Posix:   splitDrive "/test" == ("/","test")
+-- > Posix:   splitDrive "//test" == ("//","test")
+-- > Posix:   splitDrive "test/file" == ("","test/file")
+-- > Posix:   splitDrive "file" == ("","file")
+splitDrive :: RawFilePath -> (RawFilePath, RawFilePath)
+splitDrive x | isPosix = B.span (== fromIntegral (ord '/')) x
+splitDrive x | Just y <- readDriveLetter x = y
+splitDrive x | Just y <- readDriveUNC x = y
+splitDrive x | Just y <- readDriveShare x = y
+splitDrive x = (B.empty,x)
+
+addSlash :: RawFilePath -> RawFilePath -> (RawFilePath, RawFilePath)
+addSlash a xs = (a <> c,d)
+    where (c,d) = B.span isPathSeparator xs
+
+-- See [1].
+-- "\\?\D:\<path>" or "\\?\UNC\<server>\<share>"
+readDriveUNC :: RawFilePath -> Maybe (RawFilePath, RawFilePath)
+readDriveUNC p = do
+        (s1, p') <- B.uncons p
+        (s2, p'') <- B.uncons p'
+        (q, p''') <- B.uncons p''
+        (s3, rest) <- B.uncons p'''
+        if q == fromIntegral (ord '?') && all isPathSeparator [s1,s2,s3]
+                then case breakunc rest of
+                        Just (unc,r) -> 
+                                let (a,b) = readDriveShareName r
+                                in Just (B.pack [s1,s2,q,s3] <> unc <> a, b)
+                        Nothing -> case readDriveLetter rest of
+                                -- Extended-length path.
+                                Just (a,b) -> Just (B.pack [s1,s2,q,s3] <> a, b)
+                                Nothing -> Nothing
+                else Nothing
+  where
+        breakunc b = do
+                (u, b') <- B.uncons b
+                (n, b'') <- B.uncons b'
+                (c, b''') <- B.uncons b''
+                (s, rest) <- B.uncons b'''
+                let isup v ch = toUpper (chr (fromIntegral v)) == ch
+                if isPathSeparator s && isup u 'U' && isup n 'N' && isup c 'C'
+                        then Just (B.take 4 b, rest)
+                        else Nothing
+
+{- c:\ -}
+readDriveLetter :: RawFilePath -> Maybe (RawFilePath, RawFilePath)
+readDriveLetter p = case B.uncons p of
+        Just (x, t) | isLetter x -> case B.uncons t of
+                Just (c, t') | c == colon -> case B.uncons t' of
+                        Just (y, _) | isPathSeparator y ->
+                                Just $ addSlash (B.pack [x, colon]) t'
+                        _ -> Just (B.pack [x, colon], t')
+                _ -> Nothing
+        _ -> Nothing
+  where colon = fromIntegral (ord ':')
+
+{- \\sharename\ -}
+readDriveShare :: ByteString -> Maybe (RawFilePath, RawFilePath)
+readDriveShare p = do
+        (s1, p') <- B.uncons p
+        (s2, p'') <- B.uncons p'
+        let (a,b) = readDriveShareName p''
+        if isPathSeparator s1 && isPathSeparator s2
+                then Just (s1 `B.cons` s2 `B.cons` a,b)
+                else Nothing
+
+{- assume you have already seen \\ -}
+{- share\bob -> "share\", "bob" -}
+readDriveShareName :: ByteString -> (RawFilePath, RawFilePath)
+readDriveShareName name = addSlash a b
+    where (a,b) = B.break isPathSeparator name
+
+
+-- | Join a drive and the rest of the path.
+--
+-- > Valid x => uncurry joinDrive (splitDrive x) == x
+-- > Windows: joinDrive "C:" "foo" == "C:foo"
+-- > Windows: joinDrive "C:\\" "bar" == "C:\\bar"
+-- > Windows: joinDrive "\\\\share" "foo" == "\\\\share\\foo"
+-- > Windows: joinDrive "/:" "foo" == "/:\\foo"
+joinDrive :: RawFilePath -> RawFilePath -> RawFilePath
+joinDrive = combineAlways
+
+-- | Get the drive from a filepath.
+--
+-- > takeDrive x == fst (splitDrive x)
+takeDrive :: RawFilePath -> RawFilePath
+takeDrive = fst . splitDrive
+
+-- | Delete the drive, if it exists.
+--
+-- > dropDrive x == snd (splitDrive x)
+dropDrive :: RawFilePath -> RawFilePath
+dropDrive = snd . splitDrive
+
+-- | Does a path have a drive.
+--
+-- > not (hasDrive x) == null (takeDrive x)
+-- > Posix:   hasDrive "/foo" == True
+-- > Windows: hasDrive "C:\\foo" == True
+-- > Windows: hasDrive "C:foo" == True
+-- >          hasDrive "foo" == False
+-- >          hasDrive "" == False
+hasDrive :: RawFilePath -> Bool
+hasDrive = not . B.null . takeDrive
+
+-- | Is an element a drive
+--
+-- > Posix:   isDrive "/" == True
+-- > Posix:   isDrive "/foo" == False
+-- > Windows: isDrive "C:\\" == True
+-- > Windows: isDrive "C:\\foo" == False
+-- >          isDrive "" == False
+isDrive :: RawFilePath -> Bool
+isDrive x = not (B.null x) && B.null (dropDrive x)
+
+---------------------------------------------------------------------
+-- Operations on a filepath, as a list of directories
+
+-- | Split a filename into directory and file. '</>' is the inverse.
+--   The first component will often end with a trailing slash.
+--
+-- > splitFileName "/directory/file.ext" == ("/directory/","file.ext")
+-- > Valid x => uncurry (</>) (splitFileName x) == x || fst (splitFileName x) == "./"
+-- > Valid x => isValid (fst (splitFileName x))
+-- > splitFileName "file/bob.txt" == ("file/", "bob.txt")
+-- > splitFileName "file/" == ("file/", "")
+-- > splitFileName "bob" == ("./", "bob")
+-- > Posix:   splitFileName "/" == ("/","")
+-- > Windows: splitFileName "c:" == ("c:","")
+splitFileName :: RawFilePath -> (ByteString, ByteString)
+splitFileName x = (if B.null dir then "./" else dir, name)
+    where
+        (dir, name) = splitFileName_ x
+
+-- version of splitFileName where, if the FilePath has no directory
+-- component, the returned directory is "" rather than "./".  This
+-- is used in cases where we are going to combine the returned
+-- directory to make a valid FilePath, and having a "./" appear would
+-- look strange and upset simple equality properties.  See
+-- e.g. replaceFileName.
+splitFileName_ :: RawFilePath -> (ByteString, ByteString)
+splitFileName_ x = (drv <> dir, file)
+    where
+        (drv,pth) = splitDrive x
+        (dir,file) = B.breakEnd isPathSeparator pth
+
+-- | Set the filename.
+--
+-- > replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext"
+-- > Valid x => replaceFileName x (takeFileName x) == x
+replaceFileName :: RawFilePath -> ByteString -> RawFilePath
+replaceFileName x y = a </> y where (a,_) = splitFileName_ x
+
+-- | Drop the filename. Unlike 'takeDirectory', this function will leave
+--   a trailing path separator on the directory.
+--
+-- > dropFileName "/directory/file.ext" == "/directory/"
+-- > dropFileName x == fst (splitFileName x)
+dropFileName :: RawFilePath -> RawFilePath
+dropFileName = fst . splitFileName
+
+-- | Get the file name.
+--
+-- > takeFileName "/directory/file.ext" == "file.ext"
+-- > 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)
+takeFileName :: RawFilePath -> RawFilePath
+takeFileName = snd . splitFileName
+
+-- | Get the base name, without an extension or path.
+--
+-- > takeBaseName "/directory/file.ext" == "file"
+-- > takeBaseName "file/test.txt" == "test"
+-- > takeBaseName "dave.ext" == "dave"
+-- > takeBaseName "" == ""
+-- > takeBaseName "test" == "test"
+-- > takeBaseName (addTrailingPathSeparator x) == ""
+-- > takeBaseName "file/file.tar.gz" == "file.tar"
+takeBaseName :: RawFilePath -> ByteString
+takeBaseName = dropExtension . takeFileName
+
+-- | Set the base name.
+--
+-- > replaceBaseName "/directory/other.ext" "file" == "/directory/file.ext"
+-- > replaceBaseName "file/test.txt" "bob" == "file/bob.txt"
+-- > replaceBaseName "fred" "bill" == "bill"
+-- > replaceBaseName "/dave/fred/bob.gz.tar" "new" == "/dave/fred/new.tar"
+-- > Valid x => replaceBaseName x (takeBaseName x) == x
+replaceBaseName :: RawFilePath -> ByteString -> RawFilePath
+replaceBaseName pth nam = combineAlways a (nam <.> ext)
+    where
+        (a,b) = splitFileName_ pth
+        ext = takeExtension b
+
+-- | Is an item either a directory or the last character a path separator?
+--
+-- > hasTrailingPathSeparator "test" == False
+-- > hasTrailingPathSeparator "test/" == True
+hasTrailingPathSeparator :: RawFilePath -> Bool
+hasTrailingPathSeparator x = case B.unsnoc x of
+        Nothing -> False
+        Just (_i, l) -> isPathSeparator l
+
+
+hasLeadingPathSeparator :: RawFilePath -> Bool
+hasLeadingPathSeparator x = case B.uncons x of
+        Nothing -> False
+        Just (h,_t) -> isPathSeparator h
+
+-- | Add a trailing file path separator if one is not already present.
+--
+-- > hasTrailingPathSeparator (addTrailingPathSeparator x)
+-- > hasTrailingPathSeparator x ==> addTrailingPathSeparator x == x
+-- > Posix:    addTrailingPathSeparator "test/rest" == "test/rest/"
+addTrailingPathSeparator :: RawFilePath -> RawFilePath
+addTrailingPathSeparator x
+        | hasTrailingPathSeparator x = x
+        | otherwise = B.snoc x pathSeparator
+
+
+-- | Remove any trailing path separators
+--
+-- > dropTrailingPathSeparator "file/test/" == "file/test"
+-- >           dropTrailingPathSeparator "/" == "/"
+-- > Windows:  dropTrailingPathSeparator "\\" == "\\"
+-- > Posix:    not (hasTrailingPathSeparator (dropTrailingPathSeparator x)) || isDrive x
+dropTrailingPathSeparator :: RawFilePath -> RawFilePath
+dropTrailingPathSeparator x =
+    if hasTrailingPathSeparator x && not (isDrive x)
+    then let x' = dropWhileEnd isPathSeparator x
+         in if B.null x' then B.singleton (B.last x) else x'
+    else x
+
+
+-- | Get the directory name, move up one level.
+--
+-- >           takeDirectory "/directory/other.ext" == "/directory"
+-- >           takeDirectory x `isPrefixOf` x || takeDirectory x == "."
+-- >           takeDirectory "foo" == "."
+-- >           takeDirectory "/" == "/"
+-- >           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"
+-- > Windows:  takeDirectory "foo\\bar\\\\" == "foo\\bar"
+-- > Windows:  takeDirectory "C:\\" == "C:\\"
+takeDirectory :: RawFilePath -> RawFilePath
+takeDirectory = dropTrailingPathSeparator . dropFileName
+
+-- | Set the directory, keeping the filename the same.
+--
+-- > replaceDirectory "root/file.ext" "/directory/" == "/directory/file.ext"
+-- > untested Valid x => replaceDirectory x (takeDirectory x) `equalFilePath` x
+replaceDirectory :: RawFilePath -> ByteString -> RawFilePath
+replaceDirectory x dir = combineAlways dir (takeFileName x)
+
+-- | An alias for '</>'.
+combine :: RawFilePath -> RawFilePath -> RawFilePath
+combine a b | hasLeadingPathSeparator b || hasDrive b = b
+            | otherwise = combineAlways a b
+
+-- | Combine two paths, assuming rhs is NOT absolute.
+combineAlways :: RawFilePath -> RawFilePath -> RawFilePath
+combineAlways a b | B.null a = b
+                  | B.null b = a
+                  | hasTrailingPathSeparator a = a <> b
+                  | isWindows && B.length a == 2
+                      && B.last a == fromIntegral (ord ':')
+                      && isLetter (B.head a) = a <> b
+                  | otherwise = a <> B.singleton pathSeparator <> b
+
+-- | Combine two paths with a path separator.
+--   If the second path starts with a path separator or a drive letter, then it returns the second.
+--   The intention is that @readFile (dir '</>' file)@ will access the same file as
+--   @setCurrentDirectory dir; readFile file@.
+--
+-- > Posix:   "/directory" </> "file.ext" == "/directory/file.ext"
+-- > Windows: "/directory" </> "file.ext" == "/directory\\file.ext"
+-- >          "directory" </> "/file.ext" == "/file.ext"
+-- > untested Valid x => (takeDirectory x </> takeFileName x) `equalFilePath` x
+--
+--   Combined:
+--
+-- > Posix:   "/" </> "test" == "/test"
+-- > Posix:   "home" </> "bob" == "home/bob"
+-- > Posix:   "x:" </> "foo" == "x:/foo"
+-- > Windows: "C:\\foo" </> "bar" == "C:\\foo\\bar"
+-- > Windows: "home" </> "bob" == "home\\bob"
+--
+--   Not combined:
+--
+-- > Posix:   "home" </> "/bob" == "/bob"
+-- > Windows: "home" </> "C:\\bob" == "C:\\bob"
+--
+--   Not combined (tricky):
+--
+--   On Windows, if a filepath starts with a single slash, it is relative to the
+--   root of the current drive. In [1], this is (confusingly) referred to as an
+--   absolute path.
+--   The current behavior of '</>' is to never combine these forms.
+--
+-- > Windows: "home" </> "/bob" == "/bob"
+-- > Windows: "home" </> "\\bob" == "\\bob"
+-- > Windows: "C:\\home" </> "\\bob" == "\\bob"
+--
+--   On Windows, from [1]: "If a file name begins with only a disk designator
+--   but not the backslash after the colon, it is interpreted as a relative path
+--   to the current directory on the drive with the specified letter."
+--   The current behavior of '</>' is to never combine these forms.
+--
+-- > Windows: "D:\\foo" </> "C:bar" == "C:bar"
+-- > Windows: "C:\\foo" </> "C:bar" == "C:bar"
+(</>) :: RawFilePath -> RawFilePath -> RawFilePath
+(</>) = combine
+
+-- | Split a path by the directory separator.
+--
+-- > splitPath "/directory/file.ext" == ["/","directory/","file.ext"]
+-- > mconcat (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"]
+splitPath :: RawFilePath -> [RawFilePath]
+splitPath x = [drive | not (B.null drive)] ++ f path
+    where
+        (drive,path) = splitDrive x
+
+        f y
+                | B.null y = []
+                | otherwise = (a<>c) : f d
+            where
+                (a,b) = B.break isPathSeparator y
+                (c,d) = B.span  isPathSeparator b
+
+-- | Just as 'splitPath', but don't add the trailing slashes to each element.
+--
+-- >          splitDirectories "/directory/file.ext" == ["/","directory","file.ext"]
+-- >          splitDirectories "test/file" == ["test","file"]
+-- >          splitDirectories "/test/file" == ["/","test","file"]
+-- > Windows: splitDirectories "C:\\test\\file" == ["C:\\", "test", "file"]
+-- > untested          Valid x => joinPath (splitDirectories x) `equalFilePath` x
+-- >          splitDirectories "" == []
+-- > Windows: splitDirectories "C:\\test\\\\\\file" == ["C:\\", "test", "file"]
+-- >          splitDirectories "/test///file" == ["/","test","file"]
+splitDirectories :: RawFilePath -> [RawFilePath]
+splitDirectories = map dropTrailingPathSeparator . splitPath
+
+
+-- | Join path elements back together.
+--
+-- > joinPath ["/","directory/","file.ext"] == "/directory/file.ext"
+-- > Valid x => joinPath (splitPath x) == x
+-- > joinPath [] == ""
+-- > Posix: joinPath ["test","file","path"] == "test/file/path"
+joinPath :: [RawFilePath] -> RawFilePath
+-- Note that this definition on c:\\c:\\, join then split will give c:\\.
+joinPath = foldr combine mempty
+
+{-
+
+
+---------------------------------------------------------------------
+-- File name manipulators
+
+-- | Equality of two 'FilePath's.
+--   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.
+--
+-- > untested          x == y ==> equalFilePath x y
+-- > untested          normalise x == normalise y ==> equalFilePath x y
+-- > untested          equalFilePath "foo" "foo/"
+-- > untested          not (equalFilePath "foo" "/foo")
+-- > untested Posix:   not (equalFilePath "foo" "FOO")
+-- > untested Windows: equalFilePath "foo" "FOO"
+-- > untested Windows: not (equalFilePath "C:" "C:/")
+equalFilePath :: FilePath -> FilePath -> Bool
+equalFilePath a b = f a == f b
+    where
+        f x | isWindows = dropTrailingPathSeparator $ map toLower $ normalise x
+            | otherwise = dropTrailingPathSeparator $ normalise x
+
+
+-- | Contract a filename, based on a relative path. Note that the resulting path
+--   will never introduce @..@ paths, as the presence of symlinks means @..\/b@
+--   may not reach @a\/b@ if it starts from @a\/c@. For a worked example see
+--   <http://neilmitchell.blogspot.co.uk/2015/10/filepaths-are-subtle-symlinks-are-hard.html this blog post>.
+--
+--   The corresponding @makeAbsolute@ function can be found in
+--   @System.Directory@.
+--
+-- > untested          makeRelative "/directory" "/directory/file.ext" == "file.ext"
+-- > untested          Valid x => makeRelative (takeDirectory x) x `equalFilePath` takeFileName x
+-- > untested          makeRelative x x == "."
+-- > untested          Valid x y => equalFilePath x y || (isRelative x && makeRelative y x == x) || equalFilePath (y </> makeRelative y x) x
+-- > untested Windows: makeRelative "C:\\Home" "c:\\home\\bob" == "bob"
+-- > untested Windows: makeRelative "C:\\Home" "c:/home/bob" == "bob"
+-- > untested Windows: makeRelative "C:\\Home" "D:\\Home\\Bob" == "D:\\Home\\Bob"
+-- > untested Windows: makeRelative "C:\\Home" "C:Home\\Bob" == "C:Home\\Bob"
+-- > untested Windows: makeRelative "/Home" "/home/bob" == "bob"
+-- > untested Windows: makeRelative "/" "//" == "//"
+-- > untested Posix:   makeRelative "/Home" "/home/bob" == "/home/bob"
+-- > untested Posix:   makeRelative "/home/" "/home/bob/foo/bar" == "bob/foo/bar"
+-- > untested Posix:   makeRelative "/fred" "bob" == "bob"
+-- > untested Posix:   makeRelative "/file/test" "/file/test/fred" == "fred"
+-- > untested Posix:   makeRelative "/file/test" "/file/test/fred/" == "fred/"
+-- > untested Posix:   makeRelative "some/path" "some/path/a/b/c" == "a/b/c"
+makeRelative :: FilePath -> FilePath -> FilePath
+makeRelative root path
+ | equalFilePath root path = "."
+ | takeAbs root /= takeAbs path = path
+ | otherwise = f (dropAbs root) (dropAbs path)
+    where
+        f "" y = dropWhile isPathSeparator y
+        f x y = let (x1,x2) = g x
+                    (y1,y2) = g y
+                in if equalFilePath x1 y1 then f x2 y2 else path
+
+        g x = (dropWhile isPathSeparator a, dropWhile isPathSeparator b)
+            where (a,b) = break isPathSeparator $ dropWhile isPathSeparator x
+
+        -- on windows, need to drop '/' which is kind of absolute, but not a drive
+        dropAbs x | hasLeadingPathSeparator x && not (hasDrive x) = tail x
+        dropAbs x = dropDrive x
+
+        takeAbs x | hasLeadingPathSeparator x && not (hasDrive x) = [pathSeparator]
+        takeAbs x = map (\y -> if isPathSeparator y then pathSeparator else toLower y) $ takeDrive x
+
+-- | Normalise a file
+--
+-- * \/\/ outside of the drive can be made blank
+--
+-- * \/ -> 'pathSeparator'
+--
+-- * .\/ -> \"\"
+--
+-- > untested Posix:   normalise "/file/\\test////" == "/file/\\test/"
+-- > untested Posix:   normalise "/file/./test" == "/file/test"
+-- > untested Posix:   normalise "/test/file/../bob/fred/" == "/test/file/../bob/fred/"
+-- > untested Posix:   normalise "../bob/fred/" == "../bob/fred/"
+-- > untested Posix:   normalise "./bob/fred/" == "bob/fred/"
+-- > untested Windows: normalise "c:\\file/bob\\" == "C:\\file\\bob\\"
+-- > untested Windows: normalise "c:\\" == "C:\\"
+-- > untested Windows: normalise "C:.\\" == "C:"
+-- > untested Windows: normalise "\\\\server\\test" == "\\\\server\\test"
+-- > untested Windows: normalise "//server/test" == "\\\\server\\test"
+-- > untested Windows: normalise "c:/file" == "C:\\file"
+-- > untested Windows: normalise "/file" == "\\file"
+-- > untested Windows: normalise "\\" == "\\"
+-- > untested Windows: normalise "/./" == "\\"
+-- > untested          normalise "." == "."
+-- > untested Posix:   normalise "./" == "./"
+-- > untested Posix:   normalise "./." == "./"
+-- > untested Posix:   normalise "/./" == "/"
+-- > untested Posix:   normalise "/" == "/"
+-- > untested Posix:   normalise "bob/fred/." == "bob/fred/"
+-- > untested Posix:   normalise "//home" == "/home"
+normalise :: FilePath -> FilePath
+normalise path = result ++ [pathSeparator | addPathSeparator]
+    where
+        (drv,pth) = splitDrive path
+        result = joinDrive' (normaliseDrive drv) (f pth)
+
+        joinDrive' "" "" = "."
+        joinDrive' d p = joinDrive d p
+
+        addPathSeparator = isDirPath pth
+            && not (hasTrailingPathSeparator result)
+            && not (isRelativeDrive drv)
+
+        isDirPath xs = hasTrailingPathSeparator xs
+            || not (null xs) && last xs == '.' && hasTrailingPathSeparator (init xs)
+
+        f = joinPath . dropDots . propSep . splitDirectories
+
+        propSep (x:xs) | all isPathSeparator x = [pathSeparator] : xs
+                       | otherwise = x : xs
+        propSep [] = []
+
+        dropDots = filter ("." /=)
+
+normaliseDrive :: FilePath -> FilePath
+normaliseDrive "" = ""
+normaliseDrive _ | isPosix = [pathSeparator]
+normaliseDrive drive = if isJust $ readDriveLetter x2
+                       then map toUpper x2
+                       else x2
+    where
+        x2 = map repSlash drive
+
+        repSlash x = if isPathSeparator x then pathSeparator else x
+
+-}
+
+-- Information for validity functions on Windows. See [1].
+isBadCharacter :: Word8 -> Bool
+isBadCharacter x = x >= 0 && x <= 31 || x `elem` l
+  where
+        l = map (fromIntegral . ord) ":*?><|\""
+
+badElements :: [FilePath]
+badElements =
+    ["CON","PRN","AUX","NUL","CLOCK$"
+    ,"COM1","COM2","COM3","COM4","COM5","COM6","COM7","COM8","COM9"
+    ,"LPT1","LPT2","LPT3","LPT4","LPT5","LPT6","LPT7","LPT8","LPT9"]
+
+-- | Is a RawFilePath valid, i.e. could you create a file like it? This function checks for invalid names,
+--   and invalid characters, but does not check if length limits are exceeded, as these are typically
+--   filesystem dependent.
+--
+-- >          isValid "" == False
+-- >          isValid "\0" == False
+-- > Posix:   isValid "/random_ path:*" == True
+-- > Posix:   isValid x == (x /= mempty)
+-- > Windows: isValid "c:\\test" == True
+-- > Windows: isValid "c:\\test:of_test" == False
+-- > Windows: isValid "test*" == False
+-- > Windows: isValid "c:\\test\\nul" == False
+-- > Windows: isValid "c:\\test\\prn.txt" == False
+-- > Windows: isValid "c:\\nul\\file" == False
+-- > Windows: isValid "\\\\" == False
+-- > Windows: isValid "\\\\\\foo" == False
+-- > Windows: isValid "\\\\?\\D:file" == False
+-- > Windows: isValid "foo\tbar" == False
+-- > Windows: isValid "nul .txt" == False
+-- > Windows: isValid " nul.txt" == True
+isValid :: RawFilePath -> Bool
+isValid path
+        | B.null path = False
+        | B.elem 0 path = False
+        | isPosix = True
+        | otherwise = 
+                not (B.any isBadCharacter x2) &&
+                not (any f $ splitDirectories x2) &&
+                not (isJust (readDriveShare x1) && B.all isPathSeparator x1) &&
+                not (isJust (readDriveUNC x1) && not (hasTrailingPathSeparator x1))
+    where
+        (x1,x2) = splitDrive path
+        f x = map toUpper (B8.unpack $ dropWhileEnd (== 32) $ dropExtensions x) `elem` badElements
+
+{-
+
+-- | Take a FilePath and make it valid; does not change already valid FilePaths.
+--
+-- > untested isValid (makeValid x)
+-- > untested isValid x ==> makeValid x == x
+-- > untested makeValid "" == "_"
+-- > untested makeValid "file\0name" == "file_name"
+-- > untested Windows: makeValid "c:\\already\\/valid" == "c:\\already\\/valid"
+-- > untested Windows: makeValid "c:\\test:of_test" == "c:\\test_of_test"
+-- > untested Windows: makeValid "test*" == "test_"
+-- > untested Windows: makeValid "c:\\test\\nul" == "c:\\test\\nul_"
+-- > untested Windows: makeValid "c:\\test\\prn.txt" == "c:\\test\\prn_.txt"
+-- > untested Windows: makeValid "c:\\test/prn.txt" == "c:\\test/prn_.txt"
+-- > untested Windows: makeValid "c:\\nul\\file" == "c:\\nul_\\file"
+-- > untested Windows: makeValid "\\\\\\foo" == "\\\\drive"
+-- > untested Windows: makeValid "\\\\?\\D:file" == "\\\\?\\D:\\file"
+-- > untested Windows: makeValid "nul .txt" == "nul _.txt"
+makeValid :: FilePath -> FilePath
+makeValid "" = "_"
+makeValid path
+        | isPosix = map (\x -> if x == '\0' then '_' else x) path
+        | isJust (readDriveShare drv) && all isPathSeparator drv = take 2 drv ++ "drive"
+        | isJust (readDriveUNC drv) && not (hasTrailingPathSeparator drv) =
+            makeValid (drv ++ [pathSeparator] ++ pth)
+        | otherwise = joinDrive drv $ validElements $ validChars pth
+    where
+        (drv,pth) = splitDrive path
+
+        validChars = map f
+        f x = if isBadCharacter x then '_' else x
+
+        validElements x = joinPath $ map g $ splitPath x
+        g x = h a ++ b
+            where (a,b) = break isPathSeparator x
+        h x = if map toUpper (dropWhileEnd (== ' ') a) `elem` badElements then a ++ "_" <.> b else x
+            where (a,b) = splitExtensions x
+
+-}
+
+-- | 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:\\" == False
+-- > Windows: isRelative "c:/" == False
+-- > Windows: isRelative "c:" == True
+-- > Windows: isRelative "\\\\foo" == False
+-- > Windows: isRelative "\\\\?\\foo" == False
+-- > Windows: isRelative "\\\\?\\UNC\\foo" == False
+-- > Windows: isRelative "/foo" == True
+-- > Windows: isRelative "\\foo" == True
+-- > Posix:   isRelative "test/path" == True
+-- > Posix:   isRelative "/test" == False
+-- > Posix:   isRelative "/" == False
+--
+-- According to [1]:
+--
+-- * "A UNC name of any format [is never relative]."
+--
+-- * "You cannot use the "\\?\" prefix with a relative path."
+isRelative :: RawFilePath -> Bool
+isRelative x = B.null drive || isRelativeDrive drive
+    where drive = takeDrive x
+
+
+{- c:foo -}
+-- From [1]: "If a file name begins with only a disk designator but not the
+-- backslash after the colon, it is interpreted as a relative path to the
+-- current directory on the drive with the specified letter."
+isRelativeDrive :: RawFilePath -> Bool
+isRelativeDrive x =
+    maybe False (not . hasTrailingPathSeparator . fst) (readDriveLetter x)
+
+-- | @not . 'isRelative'@
+--
+-- > isAbsolute x == not (isRelative x)
+isAbsolute :: RawFilePath -> Bool
+isAbsolute = not . isRelative
+
+-----------------------------------------------------------------------------
+-- dropWhileEnd (/= 32) "foo bar" == "foo ")
+dropWhileEnd :: (Word8 -> Bool) -> ByteString -> ByteString
+dropWhileEnd p = fst . B.spanEnd p
+
+{-
+
+-- takeWhileEnd (>2) [1,2,3,4,1,2,3,4] == [3,4])
+takeWhileEnd :: (a -> Bool) -> [a] -> [a]
+takeWhileEnd p = reverse . takeWhile p . reverse
+
+-- spanEnd (>2) [1,2,3,4,1,2,3,4] = ([1,2,3,4,1,2], [3,4])
+spanEnd :: (a -> Bool) -> [a] -> ([a], [a])
+spanEnd p xs = (dropWhileEnd p xs, takeWhileEnd p xs)
+
+-- breakEnd (< 2) [1,2,3,4,1,2,3,4] == ([1,2,3,4,1],[2,3,4])
+breakEnd :: (a -> Bool) -> [a] -> ([a], [a])
+breakEnd p = spanEnd (not . p)
+
+-- | The stripSuffix function drops the given suffix from a list. It returns
+-- Nothing if the list did not end with the suffix given, or Just the list
+-- before the suffix, if it does.
+stripSuffix :: Eq a => [a] -> [a] -> Maybe [a]
+stripSuffix xs ys = fmap reverse $ stripPrefix (reverse xs) (reverse ys)
+
+-}
diff --git a/System/FilePath/Posix/ByteString.hs b/System/FilePath/Posix/ByteString.hs
new file mode 100644
--- /dev/null
+++ b/System/FilePath/Posix/ByteString.hs
@@ -0,0 +1,4 @@
+{-# LANGUAGE CPP #-}
+#define MODULE_NAME     Posix
+#define IS_WINDOWS      False
+#include "../Internal.hs"
diff --git a/System/FilePath/Windows/ByteString.hs b/System/FilePath/Windows/ByteString.hs
new file mode 100644
--- /dev/null
+++ b/System/FilePath/Windows/ByteString.hs
@@ -0,0 +1,4 @@
+{-# LANGUAGE CPP #-}
+#define MODULE_NAME     Windows
+#define IS_WINDOWS      True
+#include "../Internal.hs"
diff --git a/TODO b/TODO
new file mode 100644
--- /dev/null
+++ b/TODO
@@ -0,0 +1,11 @@
+* Some functions have not been ported from FilePath and are commented out:
+  splitSearchPath, getSearchPath, normalise, equalFilePath, makeRelative,
+  makeValid. Implementations would be accepted if you need any of these.
+* combine checks hasDrive on posix, this is unnecessary
+  since hasLeadingPathSeparator checks the same thing
+  there. isWindows && hasDrive would cover windows while
+  avoiding that overhead. Benchmark to see if it improves.
+* Test suite may not build on Windows due to its use of
+  getFileSystemEncoding.
+* How filename encoding even works in this ByteString library should perhaps be
+  documented.
diff --git a/filepath-bytestring.cabal b/filepath-bytestring.cabal
new file mode 100644
--- /dev/null
+++ b/filepath-bytestring.cabal
@@ -0,0 +1,75 @@
+cabal-version:  >= 1.18
+name:           filepath-bytestring
+version:        1.4.2.1.0
+-- NOTE: Don't forget to update CHANGELOG and the filepath version below
+license:        BSD3
+license-file:   LICENSE
+author:         Neil Mitchell <ndmitchell@gmail.com>
+maintainer:     Joey Hess <id@joeyh.name>
+copyright:      Neil Mitchell 2005-2019
+                Joey Hess 2019
+category:       System
+build-type:     Simple
+synopsis:       Library for manipulating RawFilePaths in a cross platform way.
+description:
+    This package provides functionality for manipulating @RawFilePath@
+    values. It can be used as a drop in replacement for the filepath library
+    to get the benefits of using ByteStrings. It provides three modules:
+    .
+    * "System.FilePath.Posix.ByteString" manipulates POSIX\/Linux style @RawFilePath@ values (with @\/@ as the path separator).
+    .
+    * "System.FilePath.Windows.ByteString" manipulates Windows style @RawFilePath@ values (with either @\\@ or @\/@ as the path separator, and deals with drives).
+    .
+    * "System.FilePath.ByteString" is an alias for the module appropriate to your platform.
+    .
+    All three modules provide the same API, and the same documentation (calling out differences in the different variants).
+
+extra-source-files:
+    System/FilePath/Internal.hs
+extra-doc-files:
+    README.md
+    CHANGELOG
+    TODO
+
+source-repository head
+    type:     git
+    location: git://git.joeyh.name/haskell-filepath-bytestring.git
+
+library
+    default-language: Haskell2010
+    other-extensions:
+        CPP
+        PatternGuards
+    if impl(GHC >= 7.2)
+        other-extensions: Safe
+
+    exposed-modules:
+        System.FilePath.ByteString
+        System.FilePath.Posix.ByteString
+        System.FilePath.Windows.ByteString
+
+    build-depends:
+        base >= 4 && < 4.15,
+        bytestring
+    if !os(Windows)
+        build-depends: unix
+
+    ghc-options: -Wall
+
+test-suite filepath-tests
+    type: exitcode-stdio-1.0
+    default-language: Haskell2010
+    main-is: Test.hs
+    ghc-options: -main-is Test
+    hs-source-dirs: tests
+    other-modules:
+        TestEquiv
+        TestGen
+        TestUtil
+    build-depends:
+        filepath-bytestring,
+        base,
+        bytestring,
+        QuickCheck >= 2.7 && < 2.14,
+	-- filepath same version as this library, to test equivilance
+        filepath == 1.4.2.1
diff --git a/tests/Test.hs b/tests/Test.hs
new file mode 100644
--- /dev/null
+++ b/tests/Test.hs
@@ -0,0 +1,32 @@
+
+module Test(main) where
+
+import System.Environment
+import TestGen
+import TestEquiv
+import Control.Monad
+import Data.Maybe
+import Test.QuickCheck
+
+
+main :: IO ()
+main = do
+    args <- getArgs
+    let count = case args of i:_ -> read i; _ -> 10000
+    putStrLn $ "Testing with " ++ show count ++ " repetitions"
+    let alltests = equivtests ++ tests
+    let total = length alltests
+    let showOutput x = show x{output=""} ++ "\n" ++ output x
+    bad <- fmap catMaybes $ forM (zip [1..] alltests) $ \(i,(msg,prop)) -> do
+        putStrLn $ "Test " ++ show i ++ " of " ++ show total ++ ": " ++ msg
+        res <- quickCheckWithResult stdArgs{chatty=False, maxSuccess=count} prop
+        case res of
+            Success{} -> return Nothing
+            bad -> do putStrLn $ showOutput bad; putStrLn "TEST FAILURE!"; return $ Just (msg,bad)
+    if null bad then
+        putStrLn $ "Success, " ++ show total ++ " tests passed"
+     else do
+        putStrLn $ show (length bad) ++ " FAILURES\n"
+        forM_ (zip [1..] bad) $ \(i,(a,b)) ->
+            putStrLn $ "FAILURE " ++ show i ++ ": " ++ a ++ "\n" ++ showOutput b ++ "\n"
+        fail $ "FAILURE, failed " ++ show (length bad) ++ " of " ++ show total ++ " tests"
diff --git a/tests/TestEquiv.hs b/tests/TestEquiv.hs
new file mode 100644
--- /dev/null
+++ b/tests/TestEquiv.hs
@@ -0,0 +1,83 @@
+-- GENERATED CODE: See ../Generate.hs
+module TestEquiv(equivtests) where
+import TestUtil
+import System.FilePath.ByteString (RawFilePath)
+import qualified System.FilePath.Windows.ByteString as OurWindows
+import qualified System.FilePath.Windows as TheirWindows
+import qualified System.FilePath.Posix.ByteString as OurPosix
+import qualified System.FilePath.Posix as TheirPosix
+equivtests :: [(String, Property)]
+equivtests =
+    [("equiv Posix.isPathSeparator", equiv_0 OurPosix.isPathSeparator TheirPosix.isPathSeparator)
+    ,("equiv Posix.isSearchPathSeparator", equiv_0 OurPosix.isSearchPathSeparator TheirPosix.isSearchPathSeparator)
+    ,("equiv Posix.isExtSeparator", equiv_0 OurPosix.isExtSeparator TheirPosix.isExtSeparator)
+    ,("equiv Posix.splitExtension", equiv_1 OurPosix.splitExtension TheirPosix.splitExtension)
+    ,("equiv Posix.takeExtension", equiv_1 OurPosix.takeExtension TheirPosix.takeExtension)
+    ,("equiv Posix.replaceExtension", equiv_2 OurPosix.replaceExtension TheirPosix.replaceExtension)
+    ,("equiv Posix.dropExtension", equiv_1 OurPosix.dropExtension TheirPosix.dropExtension)
+    ,("equiv Posix.addExtension", equiv_2 OurPosix.addExtension TheirPosix.addExtension)
+    ,("equiv Posix.hasExtension", equiv_1 OurPosix.hasExtension TheirPosix.hasExtension)
+    ,("equiv Posix.splitExtensions", equiv_1 OurPosix.splitExtensions TheirPosix.splitExtensions)
+    ,("equiv Posix.dropExtensions", equiv_1 OurPosix.dropExtensions TheirPosix.dropExtensions)
+    ,("equiv Posix.takeExtensions", equiv_1 OurPosix.takeExtensions TheirPosix.takeExtensions)
+    ,("equiv Posix.replaceExtensions", equiv_2 OurPosix.replaceExtensions TheirPosix.replaceExtensions)
+    ,("equiv Posix.isExtensionOf", equiv_2 OurPosix.isExtensionOf TheirPosix.isExtensionOf)
+    ,("equiv Posix.stripExtension", equiv_2 OurPosix.stripExtension TheirPosix.stripExtension)
+    ,("equiv Posix.splitFileName", equiv_1 OurPosix.splitFileName TheirPosix.splitFileName)
+    ,("equiv Posix.takeFileName", equiv_1 OurPosix.takeFileName TheirPosix.takeFileName)
+    ,("equiv Posix.replaceFileName", equiv_2 OurPosix.replaceFileName TheirPosix.replaceFileName)
+    ,("equiv Posix.dropFileName", equiv_1 OurPosix.dropFileName TheirPosix.dropFileName)
+    ,("equiv Posix.takeBaseName", equiv_1 OurPosix.takeBaseName TheirPosix.takeBaseName)
+    ,("equiv Posix.replaceBaseName", equiv_2 OurPosix.replaceBaseName TheirPosix.replaceBaseName)
+    ,("equiv Posix.takeDirectory", equiv_1 OurPosix.takeDirectory TheirPosix.takeDirectory)
+    ,("equiv Posix.replaceDirectory", equiv_2 OurPosix.replaceDirectory TheirPosix.replaceDirectory)
+    ,("equiv Posix.combine", equiv_2 OurPosix.combine TheirPosix.combine)
+    ,("equiv Posix.splitPath", equiv_1 OurPosix.splitPath TheirPosix.splitPath)
+    ,("equiv Posix.joinPath", equiv_3 OurPosix.joinPath TheirPosix.joinPath)
+    ,("equiv Posix.splitDirectories", equiv_1 OurPosix.splitDirectories TheirPosix.splitDirectories)
+    ,("equiv Posix.splitDrive", equiv_1 OurPosix.splitDrive TheirPosix.splitDrive)
+    ,("equiv Posix.joinDrive", equiv_2 OurPosix.joinDrive TheirPosix.joinDrive)
+    ,("equiv Posix.takeDrive", equiv_1 OurPosix.takeDrive TheirPosix.takeDrive)
+    ,("equiv Posix.hasDrive", equiv_1 OurPosix.hasDrive TheirPosix.hasDrive)
+    ,("equiv Posix.dropDrive", equiv_1 OurPosix.dropDrive TheirPosix.dropDrive)
+    ,("equiv Posix.isDrive", equiv_1 OurPosix.isDrive TheirPosix.isDrive)
+    ,("equiv Posix.hasTrailingPathSeparator", equiv_1 OurPosix.hasTrailingPathSeparator TheirPosix.hasTrailingPathSeparator)
+    ,("equiv Posix.addTrailingPathSeparator", equiv_1 OurPosix.addTrailingPathSeparator TheirPosix.addTrailingPathSeparator)
+    ,("equiv Posix.dropTrailingPathSeparator", equiv_1 OurPosix.dropTrailingPathSeparator TheirPosix.dropTrailingPathSeparator)
+    ,("equiv Windows.isPathSeparator", equiv_0 OurWindows.isPathSeparator TheirWindows.isPathSeparator)
+    ,("equiv Windows.isSearchPathSeparator", equiv_0 OurWindows.isSearchPathSeparator TheirWindows.isSearchPathSeparator)
+    ,("equiv Windows.isExtSeparator", equiv_0 OurWindows.isExtSeparator TheirWindows.isExtSeparator)
+    ,("equiv Windows.splitExtension", equiv_1 OurWindows.splitExtension TheirWindows.splitExtension)
+    ,("equiv Windows.takeExtension", equiv_1 OurWindows.takeExtension TheirWindows.takeExtension)
+    ,("equiv Windows.replaceExtension", equiv_2 OurWindows.replaceExtension TheirWindows.replaceExtension)
+    ,("equiv Windows.dropExtension", equiv_1 OurWindows.dropExtension TheirWindows.dropExtension)
+    ,("equiv Windows.addExtension", equiv_2 OurWindows.addExtension TheirWindows.addExtension)
+    ,("equiv Windows.hasExtension", equiv_1 OurWindows.hasExtension TheirWindows.hasExtension)
+    ,("equiv Windows.splitExtensions", equiv_1 OurWindows.splitExtensions TheirWindows.splitExtensions)
+    ,("equiv Windows.dropExtensions", equiv_1 OurWindows.dropExtensions TheirWindows.dropExtensions)
+    ,("equiv Windows.takeExtensions", equiv_1 OurWindows.takeExtensions TheirWindows.takeExtensions)
+    ,("equiv Windows.replaceExtensions", equiv_2 OurWindows.replaceExtensions TheirWindows.replaceExtensions)
+    ,("equiv Windows.isExtensionOf", equiv_2 OurWindows.isExtensionOf TheirWindows.isExtensionOf)
+    ,("equiv Windows.stripExtension", equiv_2 OurWindows.stripExtension TheirWindows.stripExtension)
+    ,("equiv Windows.splitFileName", equiv_1 OurWindows.splitFileName TheirWindows.splitFileName)
+    ,("equiv Windows.takeFileName", equiv_1 OurWindows.takeFileName TheirWindows.takeFileName)
+    ,("equiv Windows.replaceFileName", equiv_2 OurWindows.replaceFileName TheirWindows.replaceFileName)
+    ,("equiv Windows.dropFileName", equiv_1 OurWindows.dropFileName TheirWindows.dropFileName)
+    ,("equiv Windows.takeBaseName", equiv_1 OurWindows.takeBaseName TheirWindows.takeBaseName)
+    ,("equiv Windows.replaceBaseName", equiv_2 OurWindows.replaceBaseName TheirWindows.replaceBaseName)
+    ,("equiv Windows.takeDirectory", equiv_1 OurWindows.takeDirectory TheirWindows.takeDirectory)
+    ,("equiv Windows.replaceDirectory", equiv_2 OurWindows.replaceDirectory TheirWindows.replaceDirectory)
+    ,("equiv Windows.combine", equiv_2 OurWindows.combine TheirWindows.combine)
+    ,("equiv Windows.splitPath", equiv_1 OurWindows.splitPath TheirWindows.splitPath)
+    ,("equiv Windows.joinPath", equiv_3 OurWindows.joinPath TheirWindows.joinPath)
+    ,("equiv Windows.splitDirectories", equiv_1 OurWindows.splitDirectories TheirWindows.splitDirectories)
+    ,("equiv Windows.splitDrive", equiv_1 OurWindows.splitDrive TheirWindows.splitDrive)
+    ,("equiv Windows.joinDrive", equiv_2 OurWindows.joinDrive TheirWindows.joinDrive)
+    ,("equiv Windows.takeDrive", equiv_1 OurWindows.takeDrive TheirWindows.takeDrive)
+    ,("equiv Windows.hasDrive", equiv_1 OurWindows.hasDrive TheirWindows.hasDrive)
+    ,("equiv Windows.dropDrive", equiv_1 OurWindows.dropDrive TheirWindows.dropDrive)
+    ,("equiv Windows.isDrive", equiv_1 OurWindows.isDrive TheirWindows.isDrive)
+    ,("equiv Windows.hasTrailingPathSeparator", equiv_1 OurWindows.hasTrailingPathSeparator TheirWindows.hasTrailingPathSeparator)
+    ,("equiv Windows.addTrailingPathSeparator", equiv_1 OurWindows.addTrailingPathSeparator TheirWindows.addTrailingPathSeparator)
+    ,("equiv Windows.dropTrailingPathSeparator", equiv_1 OurWindows.dropTrailingPathSeparator TheirWindows.dropTrailingPathSeparator)
+    ]
diff --git a/tests/TestGen.hs b/tests/TestGen.hs
new file mode 100644
--- /dev/null
+++ b/tests/TestGen.hs
@@ -0,0 +1,382 @@
+-- GENERATED CODE: See ../Generate.hs
+{-# LANGUAGE OverloadedStrings #-}
+module TestGen(tests) where
+import TestUtil
+import Data.Char
+import qualified System.FilePath.Windows.ByteString as W
+import qualified System.FilePath.Posix.ByteString as P
+import Data.ByteString (isPrefixOf, isSuffixOf, null, any)
+import Prelude hiding (isPrefixOf, isSuffixOf, null, any)
+tests :: [(String, Property)]
+tests =
+    [("W.pathSeparator == fromIntegral (ord '\\\\')", property $ W.pathSeparator == fromIntegral (ord '\\'))
+    ,("P.pathSeparator == fromIntegral (ord '/')", property $ P.pathSeparator == fromIntegral (ord '/'))
+    ,("P.isPathSeparator P.pathSeparator", property $ P.isPathSeparator P.pathSeparator)
+    ,("W.isPathSeparator W.pathSeparator", property $ W.isPathSeparator W.pathSeparator)
+    ,("W.pathSeparators == [fromIntegral (ord '\\\\'), fromIntegral (ord '/')]", property $ W.pathSeparators == [fromIntegral (ord '\\'), fromIntegral (ord '/')])
+    ,("P.pathSeparators == [fromIntegral (ord '/')]", property $ P.pathSeparators == [fromIntegral (ord '/')])
+    ,("P.pathSeparator `elem` P.pathSeparators", property $ P.pathSeparator `elem` P.pathSeparators)
+    ,("W.pathSeparator `elem` W.pathSeparators", property $ W.pathSeparator `elem` W.pathSeparators)
+    ,("P.isPathSeparator a == (a `elem` P.pathSeparators)", property $ \a -> P.isPathSeparator a == (a `elem` P.pathSeparators))
+    ,("W.isPathSeparator a == (a `elem` W.pathSeparators)", property $ \a -> W.isPathSeparator a == (a `elem` W.pathSeparators))
+    ,("W.searchPathSeparator == fromIntegral (ord ';')", property $ W.searchPathSeparator == fromIntegral (ord ';'))
+    ,("P.searchPathSeparator == fromIntegral (ord ':')", property $ P.searchPathSeparator == fromIntegral (ord ':'))
+    ,("P.isSearchPathSeparator a == (a == P.searchPathSeparator)", property $ \a -> P.isSearchPathSeparator a == (a == P.searchPathSeparator))
+    ,("W.isSearchPathSeparator a == (a == W.searchPathSeparator)", property $ \a -> W.isSearchPathSeparator a == (a == W.searchPathSeparator))
+    ,("P.extSeparator == fromIntegral (ord '.')", property $ P.extSeparator == fromIntegral (ord '.'))
+    ,("W.extSeparator == fromIntegral (ord '.')", property $ W.extSeparator == fromIntegral (ord '.'))
+    ,("P.isExtSeparator a == (a == P.extSeparator)", property $ \a -> P.isExtSeparator a == (a == P.extSeparator))
+    ,("W.isExtSeparator a == (a == W.extSeparator)", property $ \a -> W.isExtSeparator a == (a == W.extSeparator))
+    ,("P.splitExtension \"/directory/path.ext\" == (\"/directory/path\", \".ext\")", property $ P.splitExtension "/directory/path.ext" == ("/directory/path", ".ext"))
+    ,("W.splitExtension \"/directory/path.ext\" == (\"/directory/path\", \".ext\")", property $ W.splitExtension "/directory/path.ext" == ("/directory/path", ".ext"))
+    ,("uncurry (<>) (P.splitExtension x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in uncurry (<>) (P.splitExtension x) == x)
+    ,("uncurry (<>) (W.splitExtension x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in uncurry (<>) (W.splitExtension x) == x)
+    ,("uncurry P.addExtension (P.splitExtension x) == x", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in uncurry P.addExtension (P.splitExtension x) == x)
+    ,("uncurry W.addExtension (W.splitExtension x) == x", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in uncurry W.addExtension (W.splitExtension x) == x)
+    ,("P.splitExtension \"file.txt\" == (\"file\", \".txt\")", property $ P.splitExtension "file.txt" == ("file", ".txt"))
+    ,("W.splitExtension \"file.txt\" == (\"file\", \".txt\")", property $ W.splitExtension "file.txt" == ("file", ".txt"))
+    ,("P.splitExtension \"file\" == (\"file\", \"\")", property $ P.splitExtension "file" == ("file", ""))
+    ,("W.splitExtension \"file\" == (\"file\", \"\")", property $ W.splitExtension "file" == ("file", ""))
+    ,("P.splitExtension \"file/file.txt\" == (\"file/file\", \".txt\")", property $ P.splitExtension "file/file.txt" == ("file/file", ".txt"))
+    ,("W.splitExtension \"file/file.txt\" == (\"file/file\", \".txt\")", property $ W.splitExtension "file/file.txt" == ("file/file", ".txt"))
+    ,("P.splitExtension \"file.txt/boris\" == (\"file.txt/boris\", \"\")", property $ P.splitExtension "file.txt/boris" == ("file.txt/boris", ""))
+    ,("W.splitExtension \"file.txt/boris\" == (\"file.txt/boris\", \"\")", property $ W.splitExtension "file.txt/boris" == ("file.txt/boris", ""))
+    ,("P.splitExtension \"file.txt/boris.ext\" == (\"file.txt/boris\", \".ext\")", property $ P.splitExtension "file.txt/boris.ext" == ("file.txt/boris", ".ext"))
+    ,("W.splitExtension \"file.txt/boris.ext\" == (\"file.txt/boris\", \".ext\")", property $ W.splitExtension "file.txt/boris.ext" == ("file.txt/boris", ".ext"))
+    ,("P.splitExtension \"file/path.txt.bob.fred\" == (\"file/path.txt.bob\", \".fred\")", property $ P.splitExtension "file/path.txt.bob.fred" == ("file/path.txt.bob", ".fred"))
+    ,("W.splitExtension \"file/path.txt.bob.fred\" == (\"file/path.txt.bob\", \".fred\")", property $ W.splitExtension "file/path.txt.bob.fred" == ("file/path.txt.bob", ".fred"))
+    ,("P.splitExtension \"file/path.txt/\" == (\"file/path.txt/\", \"\")", property $ P.splitExtension "file/path.txt/" == ("file/path.txt/", ""))
+    ,("W.splitExtension \"file/path.txt/\" == (\"file/path.txt/\", \"\")", property $ W.splitExtension "file/path.txt/" == ("file/path.txt/", ""))
+    ,("P.takeExtension \"/directory/path.ext\" == \".ext\"", property $ P.takeExtension "/directory/path.ext" == ".ext")
+    ,("W.takeExtension \"/directory/path.ext\" == \".ext\"", property $ W.takeExtension "/directory/path.ext" == ".ext")
+    ,("P.takeExtension x == snd (P.splitExtension x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.takeExtension x == snd (P.splitExtension x))
+    ,("W.takeExtension x == snd (W.splitExtension x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.takeExtension x == snd (W.splitExtension x))
+    ,("P.takeExtension (P.addExtension x \"ext\") == \".ext\"", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.takeExtension (P.addExtension x "ext") == ".ext")
+    ,("W.takeExtension (W.addExtension x \"ext\") == \".ext\"", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.takeExtension (W.addExtension x "ext") == ".ext")
+    ,("P.takeExtension (P.replaceExtension x \"ext\") == \".ext\"", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.takeExtension (P.replaceExtension x "ext") == ".ext")
+    ,("W.takeExtension (W.replaceExtension x \"ext\") == \".ext\"", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.takeExtension (W.replaceExtension x "ext") == ".ext")
+    ,("\"/directory/path.txt\" P.-<.> \"ext\" == \"/directory/path.ext\"", property $ "/directory/path.txt" P.-<.> "ext" == "/directory/path.ext")
+    ,("\"/directory/path.txt\" W.-<.> \"ext\" == \"/directory/path.ext\"", property $ "/directory/path.txt" W.-<.> "ext" == "/directory/path.ext")
+    ,("\"/directory/path.txt\" P.-<.> \".ext\" == \"/directory/path.ext\"", property $ "/directory/path.txt" P.-<.> ".ext" == "/directory/path.ext")
+    ,("\"/directory/path.txt\" W.-<.> \".ext\" == \"/directory/path.ext\"", property $ "/directory/path.txt" W.-<.> ".ext" == "/directory/path.ext")
+    ,("\"foo.o\" P.-<.> \"c\" == \"foo.c\"", property $ "foo.o" P.-<.> "c" == "foo.c")
+    ,("\"foo.o\" W.-<.> \"c\" == \"foo.c\"", property $ "foo.o" W.-<.> "c" == "foo.c")
+    ,("P.replaceExtension \"/directory/path.txt\" \"ext\" == \"/directory/path.ext\"", property $ P.replaceExtension "/directory/path.txt" "ext" == "/directory/path.ext")
+    ,("W.replaceExtension \"/directory/path.txt\" \"ext\" == \"/directory/path.ext\"", property $ W.replaceExtension "/directory/path.txt" "ext" == "/directory/path.ext")
+    ,("P.replaceExtension \"/directory/path.txt\" \".ext\" == \"/directory/path.ext\"", property $ P.replaceExtension "/directory/path.txt" ".ext" == "/directory/path.ext")
+    ,("W.replaceExtension \"/directory/path.txt\" \".ext\" == \"/directory/path.ext\"", property $ W.replaceExtension "/directory/path.txt" ".ext" == "/directory/path.ext")
+    ,("P.replaceExtension \"file.txt\" \".bob\" == \"file.bob\"", property $ P.replaceExtension "file.txt" ".bob" == "file.bob")
+    ,("W.replaceExtension \"file.txt\" \".bob\" == \"file.bob\"", property $ W.replaceExtension "file.txt" ".bob" == "file.bob")
+    ,("P.replaceExtension \"file.txt\" \"bob\" == \"file.bob\"", property $ P.replaceExtension "file.txt" "bob" == "file.bob")
+    ,("W.replaceExtension \"file.txt\" \"bob\" == \"file.bob\"", property $ W.replaceExtension "file.txt" "bob" == "file.bob")
+    ,("P.replaceExtension \"file\" \".bob\" == \"file.bob\"", property $ P.replaceExtension "file" ".bob" == "file.bob")
+    ,("W.replaceExtension \"file\" \".bob\" == \"file.bob\"", property $ W.replaceExtension "file" ".bob" == "file.bob")
+    ,("P.replaceExtension \"file.txt\" \"\" == \"file\"", property $ P.replaceExtension "file.txt" "" == "file")
+    ,("W.replaceExtension \"file.txt\" \"\" == \"file\"", property $ W.replaceExtension "file.txt" "" == "file")
+    ,("P.replaceExtension \"file.fred.bob\" \"txt\" == \"file.fred.txt\"", property $ P.replaceExtension "file.fred.bob" "txt" == "file.fred.txt")
+    ,("W.replaceExtension \"file.fred.bob\" \"txt\" == \"file.fred.txt\"", property $ W.replaceExtension "file.fred.bob" "txt" == "file.fred.txt")
+    ,("P.replaceExtension x y == P.addExtension (P.dropExtension x) y", property $ \(QFilePath vx) (QFilePath vy) -> let y = toRawFilePath vy in let x = toRawFilePath vx in P.replaceExtension x y == P.addExtension (P.dropExtension x) y)
+    ,("W.replaceExtension x y == W.addExtension (W.dropExtension x) y", property $ \(QFilePath vx) (QFilePath vy) -> let y = toRawFilePath vy in let x = toRawFilePath vx in W.replaceExtension x y == W.addExtension (W.dropExtension x) y)
+    ,("\"/directory/path\" P.<.> \"ext\" == \"/directory/path.ext\"", property $ "/directory/path" P.<.> "ext" == "/directory/path.ext")
+    ,("\"/directory/path\" W.<.> \"ext\" == \"/directory/path.ext\"", property $ "/directory/path" W.<.> "ext" == "/directory/path.ext")
+    ,("\"/directory/path\" P.<.> \".ext\" == \"/directory/path.ext\"", property $ "/directory/path" P.<.> ".ext" == "/directory/path.ext")
+    ,("\"/directory/path\" W.<.> \".ext\" == \"/directory/path.ext\"", property $ "/directory/path" W.<.> ".ext" == "/directory/path.ext")
+    ,("P.dropExtension \"/directory/path.ext\" == \"/directory/path\"", property $ P.dropExtension "/directory/path.ext" == "/directory/path")
+    ,("W.dropExtension \"/directory/path.ext\" == \"/directory/path\"", property $ W.dropExtension "/directory/path.ext" == "/directory/path")
+    ,("P.dropExtension x == fst (P.splitExtension x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.dropExtension x == fst (P.splitExtension x))
+    ,("W.dropExtension x == fst (W.splitExtension x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.dropExtension x == fst (W.splitExtension x))
+    ,("P.addExtension \"/directory/path\" \"ext\" == \"/directory/path.ext\"", property $ P.addExtension "/directory/path" "ext" == "/directory/path.ext")
+    ,("W.addExtension \"/directory/path\" \"ext\" == \"/directory/path.ext\"", property $ W.addExtension "/directory/path" "ext" == "/directory/path.ext")
+    ,("P.addExtension \"file.txt\" \"bib\" == \"file.txt.bib\"", property $ P.addExtension "file.txt" "bib" == "file.txt.bib")
+    ,("W.addExtension \"file.txt\" \"bib\" == \"file.txt.bib\"", property $ W.addExtension "file.txt" "bib" == "file.txt.bib")
+    ,("P.addExtension \"file.\" \".bib\" == \"file..bib\"", property $ P.addExtension "file." ".bib" == "file..bib")
+    ,("W.addExtension \"file.\" \".bib\" == \"file..bib\"", property $ W.addExtension "file." ".bib" == "file..bib")
+    ,("P.addExtension \"file\" \".bib\" == \"file.bib\"", property $ P.addExtension "file" ".bib" == "file.bib")
+    ,("W.addExtension \"file\" \".bib\" == \"file.bib\"", property $ W.addExtension "file" ".bib" == "file.bib")
+    ,("P.addExtension \"/\" \"x\" == \"/.x\"", property $ P.addExtension "/" "x" == "/.x")
+    ,("W.addExtension \"/\" \"x\" == \"/.x\"", property $ W.addExtension "/" "x" == "/.x")
+    ,("P.addExtension x \"\" == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.addExtension x "" == x)
+    ,("W.addExtension x \"\" == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.addExtension x "" == x)
+    ,("P.takeFileName (P.addExtension (P.addTrailingPathSeparator x) \"ext\") == \".ext\"", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.takeFileName (P.addExtension (P.addTrailingPathSeparator x) "ext") == ".ext")
+    ,("W.takeFileName (W.addExtension (W.addTrailingPathSeparator x) \"ext\") == \".ext\"", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.takeFileName (W.addExtension (W.addTrailingPathSeparator x) "ext") == ".ext")
+    ,("W.addExtension \"\\\\\\\\share\" \".txt\" == \"\\\\\\\\share\\\\.txt\"", property $ W.addExtension "\\\\share" ".txt" == "\\\\share\\.txt")
+    ,("P.hasExtension \"/directory/path.ext\" == True", property $ P.hasExtension "/directory/path.ext" == True)
+    ,("W.hasExtension \"/directory/path.ext\" == True", property $ W.hasExtension "/directory/path.ext" == True)
+    ,("P.hasExtension \"/directory/path\" == False", property $ P.hasExtension "/directory/path" == False)
+    ,("W.hasExtension \"/directory/path\" == False", property $ W.hasExtension "/directory/path" == False)
+    ,("null (P.takeExtension x) == not (P.hasExtension x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in null (P.takeExtension x) == not (P.hasExtension x))
+    ,("null (W.takeExtension x) == not (W.hasExtension x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in null (W.takeExtension x) == not (W.hasExtension x))
+    ,("\"png\" `P.isExtensionOf` \"/directory/file.png\" == True", property $ "png" `P.isExtensionOf` "/directory/file.png" == True)
+    ,("\"png\" `W.isExtensionOf` \"/directory/file.png\" == True", property $ "png" `W.isExtensionOf` "/directory/file.png" == True)
+    ,("\".png\" `P.isExtensionOf` \"/directory/file.png\" == True", property $ ".png" `P.isExtensionOf` "/directory/file.png" == True)
+    ,("\".png\" `W.isExtensionOf` \"/directory/file.png\" == True", property $ ".png" `W.isExtensionOf` "/directory/file.png" == True)
+    ,("\".tar.gz\" `P.isExtensionOf` \"bar/foo.tar.gz\" == True", property $ ".tar.gz" `P.isExtensionOf` "bar/foo.tar.gz" == True)
+    ,("\".tar.gz\" `W.isExtensionOf` \"bar/foo.tar.gz\" == True", property $ ".tar.gz" `W.isExtensionOf` "bar/foo.tar.gz" == True)
+    ,("\"ar.gz\" `P.isExtensionOf` \"bar/foo.tar.gz\" == False", property $ "ar.gz" `P.isExtensionOf` "bar/foo.tar.gz" == False)
+    ,("\"ar.gz\" `W.isExtensionOf` \"bar/foo.tar.gz\" == False", property $ "ar.gz" `W.isExtensionOf` "bar/foo.tar.gz" == False)
+    ,("\"png\" `P.isExtensionOf` \"/directory/file.png.jpg\" == False", property $ "png" `P.isExtensionOf` "/directory/file.png.jpg" == False)
+    ,("\"png\" `W.isExtensionOf` \"/directory/file.png.jpg\" == False", property $ "png" `W.isExtensionOf` "/directory/file.png.jpg" == False)
+    ,("\"csv/table.csv\" `P.isExtensionOf` \"/data/csv/table.csv\" == False", property $ "csv/table.csv" `P.isExtensionOf` "/data/csv/table.csv" == False)
+    ,("\"csv/table.csv\" `W.isExtensionOf` \"/data/csv/table.csv\" == False", property $ "csv/table.csv" `W.isExtensionOf` "/data/csv/table.csv" == False)
+    ,("P.stripExtension \"hs.o\" \"foo.x.hs.o\" == Just \"foo.x\"", property $ P.stripExtension "hs.o" "foo.x.hs.o" == Just "foo.x")
+    ,("W.stripExtension \"hs.o\" \"foo.x.hs.o\" == Just \"foo.x\"", property $ W.stripExtension "hs.o" "foo.x.hs.o" == Just "foo.x")
+    ,("P.stripExtension \"hi.o\" \"foo.x.hs.o\" == Nothing", property $ P.stripExtension "hi.o" "foo.x.hs.o" == Nothing)
+    ,("W.stripExtension \"hi.o\" \"foo.x.hs.o\" == Nothing", property $ W.stripExtension "hi.o" "foo.x.hs.o" == Nothing)
+    ,("P.dropExtension x == fromJust (P.stripExtension (P.takeExtension x) x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.dropExtension x == fromJust (P.stripExtension (P.takeExtension x) x))
+    ,("W.dropExtension x == fromJust (W.stripExtension (W.takeExtension x) x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.dropExtension x == fromJust (W.stripExtension (W.takeExtension x) x))
+    ,("P.dropExtensions x == fromJust (P.stripExtension (P.takeExtensions x) x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.dropExtensions x == fromJust (P.stripExtension (P.takeExtensions x) x))
+    ,("W.dropExtensions x == fromJust (W.stripExtension (W.takeExtensions x) x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.dropExtensions x == fromJust (W.stripExtension (W.takeExtensions x) x))
+    ,("P.stripExtension \".c.d\" \"a.b.c.d\" == Just \"a.b\"", property $ P.stripExtension ".c.d" "a.b.c.d" == Just "a.b")
+    ,("W.stripExtension \".c.d\" \"a.b.c.d\" == Just \"a.b\"", property $ W.stripExtension ".c.d" "a.b.c.d" == Just "a.b")
+    ,("P.stripExtension \".c.d\" \"a.b..c.d\" == Just \"a.b.\"", property $ P.stripExtension ".c.d" "a.b..c.d" == Just "a.b.")
+    ,("W.stripExtension \".c.d\" \"a.b..c.d\" == Just \"a.b.\"", property $ W.stripExtension ".c.d" "a.b..c.d" == Just "a.b.")
+    ,("P.stripExtension \"baz\" \"foo.bar\" == Nothing", property $ P.stripExtension "baz" "foo.bar" == Nothing)
+    ,("W.stripExtension \"baz\" \"foo.bar\" == Nothing", property $ W.stripExtension "baz" "foo.bar" == Nothing)
+    ,("P.stripExtension \"bar\" \"foobar\" == Nothing", property $ P.stripExtension "bar" "foobar" == Nothing)
+    ,("W.stripExtension \"bar\" \"foobar\" == Nothing", property $ W.stripExtension "bar" "foobar" == Nothing)
+    ,("P.stripExtension \"\" x == Just x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.stripExtension "" x == Just x)
+    ,("W.stripExtension \"\" x == Just x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.stripExtension "" x == Just x)
+    ,("P.splitExtensions \"/directory/path.ext\" == (\"/directory/path\", \".ext\")", property $ P.splitExtensions "/directory/path.ext" == ("/directory/path", ".ext"))
+    ,("W.splitExtensions \"/directory/path.ext\" == (\"/directory/path\", \".ext\")", property $ W.splitExtensions "/directory/path.ext" == ("/directory/path", ".ext"))
+    ,("P.splitExtensions \"file.tar.gz\" == (\"file\", \".tar.gz\")", property $ P.splitExtensions "file.tar.gz" == ("file", ".tar.gz"))
+    ,("W.splitExtensions \"file.tar.gz\" == (\"file\", \".tar.gz\")", property $ W.splitExtensions "file.tar.gz" == ("file", ".tar.gz"))
+    ,("uncurry (<>) (P.splitExtensions x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in uncurry (<>) (P.splitExtensions x) == x)
+    ,("uncurry (<>) (W.splitExtensions x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in uncurry (<>) (W.splitExtensions x) == x)
+    ,("uncurry P.addExtension (P.splitExtensions x) == x", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in uncurry P.addExtension (P.splitExtensions x) == x)
+    ,("uncurry W.addExtension (W.splitExtensions x) == x", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in uncurry W.addExtension (W.splitExtensions x) == x)
+    ,("P.splitExtensions \"file.tar.gz\" == (\"file\", \".tar.gz\")", property $ P.splitExtensions "file.tar.gz" == ("file", ".tar.gz"))
+    ,("W.splitExtensions \"file.tar.gz\" == (\"file\", \".tar.gz\")", property $ W.splitExtensions "file.tar.gz" == ("file", ".tar.gz"))
+    ,("P.dropExtensions \"/directory/path.ext\" == \"/directory/path\"", property $ P.dropExtensions "/directory/path.ext" == "/directory/path")
+    ,("W.dropExtensions \"/directory/path.ext\" == \"/directory/path\"", property $ W.dropExtensions "/directory/path.ext" == "/directory/path")
+    ,("P.dropExtensions \"file.tar.gz\" == \"file\"", property $ P.dropExtensions "file.tar.gz" == "file")
+    ,("W.dropExtensions \"file.tar.gz\" == \"file\"", property $ W.dropExtensions "file.tar.gz" == "file")
+    ,("not $ P.hasExtension $ P.dropExtensions x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in not $ P.hasExtension $ P.dropExtensions x)
+    ,("not $ W.hasExtension $ W.dropExtensions x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in not $ W.hasExtension $ W.dropExtensions x)
+    ,("not $ any P.isExtSeparator $ P.takeFileName $ P.dropExtensions x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in not $ any P.isExtSeparator $ P.takeFileName $ P.dropExtensions x)
+    ,("not $ any W.isExtSeparator $ W.takeFileName $ W.dropExtensions x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in not $ any W.isExtSeparator $ W.takeFileName $ W.dropExtensions x)
+    ,("P.takeExtensions \"/directory/path.ext\" == \".ext\"", property $ P.takeExtensions "/directory/path.ext" == ".ext")
+    ,("W.takeExtensions \"/directory/path.ext\" == \".ext\"", property $ W.takeExtensions "/directory/path.ext" == ".ext")
+    ,("P.takeExtensions \"file.tar.gz\" == \".tar.gz\"", property $ P.takeExtensions "file.tar.gz" == ".tar.gz")
+    ,("W.takeExtensions \"file.tar.gz\" == \".tar.gz\"", property $ W.takeExtensions "file.tar.gz" == ".tar.gz")
+    ,("P.replaceExtensions \"file.fred.bob\" \"txt\" == \"file.txt\"", property $ P.replaceExtensions "file.fred.bob" "txt" == "file.txt")
+    ,("W.replaceExtensions \"file.fred.bob\" \"txt\" == \"file.txt\"", property $ W.replaceExtensions "file.fred.bob" "txt" == "file.txt")
+    ,("P.replaceExtensions \"file.fred.bob\" \"tar.gz\" == \"file.tar.gz\"", property $ P.replaceExtensions "file.fred.bob" "tar.gz" == "file.tar.gz")
+    ,("W.replaceExtensions \"file.fred.bob\" \"tar.gz\" == \"file.tar.gz\"", property $ W.replaceExtensions "file.fred.bob" "tar.gz" == "file.tar.gz")
+    ,("uncurry (<>) (P.splitDrive x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in uncurry (<>) (P.splitDrive x) == x)
+    ,("uncurry (<>) (W.splitDrive x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in uncurry (<>) (W.splitDrive x) == x)
+    ,("W.splitDrive \"file\" == (\"\", \"file\")", property $ W.splitDrive "file" == ("", "file"))
+    ,("W.splitDrive \"c:/file\" == (\"c:/\", \"file\")", property $ W.splitDrive "c:/file" == ("c:/", "file"))
+    ,("W.splitDrive \"c:\\\\file\" == (\"c:\\\\\", \"file\")", property $ W.splitDrive "c:\\file" == ("c:\\", "file"))
+    ,("W.splitDrive \"\\\\\\\\shared\\\\test\" == (\"\\\\\\\\shared\\\\\", \"test\")", property $ W.splitDrive "\\\\shared\\test" == ("\\\\shared\\", "test"))
+    ,("W.splitDrive \"\\\\\\\\shared\" == (\"\\\\\\\\shared\", \"\")", property $ W.splitDrive "\\\\shared" == ("\\\\shared", ""))
+    ,("W.splitDrive \"\\\\\\\\?\\\\UNC\\\\shared\\\\file\" == (\"\\\\\\\\?\\\\UNC\\\\shared\\\\\", \"file\")", property $ W.splitDrive "\\\\?\\UNC\\shared\\file" == ("\\\\?\\UNC\\shared\\", "file"))
+    ,("W.splitDrive \"\\\\\\\\?\\\\UNCshared\\\\file\" == (\"\\\\\\\\?\\\\\", \"UNCshared\\\\file\")", property $ W.splitDrive "\\\\?\\UNCshared\\file" == ("\\\\?\\", "UNCshared\\file"))
+    ,("W.splitDrive \"\\\\\\\\?\\\\d:\\\\file\" == (\"\\\\\\\\?\\\\d:\\\\\", \"file\")", property $ W.splitDrive "\\\\?\\d:\\file" == ("\\\\?\\d:\\", "file"))
+    ,("W.splitDrive \"/d\" == (\"\", \"/d\")", property $ W.splitDrive "/d" == ("", "/d"))
+    ,("P.splitDrive \"/test\" == (\"/\", \"test\")", property $ P.splitDrive "/test" == ("/", "test"))
+    ,("P.splitDrive \"//test\" == (\"//\", \"test\")", property $ P.splitDrive "//test" == ("//", "test"))
+    ,("P.splitDrive \"test/file\" == (\"\", \"test/file\")", property $ P.splitDrive "test/file" == ("", "test/file"))
+    ,("P.splitDrive \"file\" == (\"\", \"file\")", property $ P.splitDrive "file" == ("", "file"))
+    ,("uncurry P.joinDrive (P.splitDrive x) == x", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in uncurry P.joinDrive (P.splitDrive x) == x)
+    ,("uncurry W.joinDrive (W.splitDrive x) == x", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in uncurry W.joinDrive (W.splitDrive x) == x)
+    ,("W.joinDrive \"C:\" \"foo\" == \"C:foo\"", property $ W.joinDrive "C:" "foo" == "C:foo")
+    ,("W.joinDrive \"C:\\\\\" \"bar\" == \"C:\\\\bar\"", property $ W.joinDrive "C:\\" "bar" == "C:\\bar")
+    ,("W.joinDrive \"\\\\\\\\share\" \"foo\" == \"\\\\\\\\share\\\\foo\"", property $ W.joinDrive "\\\\share" "foo" == "\\\\share\\foo")
+    ,("W.joinDrive \"/:\" \"foo\" == \"/:\\\\foo\"", property $ W.joinDrive "/:" "foo" == "/:\\foo")
+    ,("P.takeDrive x == fst (P.splitDrive x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.takeDrive x == fst (P.splitDrive x))
+    ,("W.takeDrive x == fst (W.splitDrive x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.takeDrive x == fst (W.splitDrive x))
+    ,("P.dropDrive x == snd (P.splitDrive x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.dropDrive x == snd (P.splitDrive x))
+    ,("W.dropDrive x == snd (W.splitDrive x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.dropDrive x == snd (W.splitDrive x))
+    ,("not (P.hasDrive x) == null (P.takeDrive x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in not (P.hasDrive x) == null (P.takeDrive x))
+    ,("not (W.hasDrive x) == null (W.takeDrive x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in not (W.hasDrive x) == null (W.takeDrive x))
+    ,("P.hasDrive \"/foo\" == True", property $ P.hasDrive "/foo" == True)
+    ,("W.hasDrive \"C:\\\\foo\" == True", property $ W.hasDrive "C:\\foo" == True)
+    ,("W.hasDrive \"C:foo\" == True", property $ W.hasDrive "C:foo" == True)
+    ,("P.hasDrive \"foo\" == False", property $ P.hasDrive "foo" == False)
+    ,("W.hasDrive \"foo\" == False", property $ W.hasDrive "foo" == False)
+    ,("P.hasDrive \"\" == False", property $ P.hasDrive "" == False)
+    ,("W.hasDrive \"\" == False", property $ W.hasDrive "" == False)
+    ,("P.isDrive \"/\" == True", property $ P.isDrive "/" == True)
+    ,("P.isDrive \"/foo\" == False", property $ P.isDrive "/foo" == False)
+    ,("W.isDrive \"C:\\\\\" == True", property $ W.isDrive "C:\\" == True)
+    ,("W.isDrive \"C:\\\\foo\" == False", property $ W.isDrive "C:\\foo" == False)
+    ,("P.isDrive \"\" == False", property $ P.isDrive "" == False)
+    ,("W.isDrive \"\" == False", property $ W.isDrive "" == False)
+    ,("P.splitFileName \"/directory/file.ext\" == (\"/directory/\", \"file.ext\")", property $ P.splitFileName "/directory/file.ext" == ("/directory/", "file.ext"))
+    ,("W.splitFileName \"/directory/file.ext\" == (\"/directory/\", \"file.ext\")", property $ W.splitFileName "/directory/file.ext" == ("/directory/", "file.ext"))
+    ,("uncurry (P.</>) (P.splitFileName x) == x || fst (P.splitFileName x) == \"./\"", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in uncurry (P.</>) (P.splitFileName x) == x || fst (P.splitFileName x) == "./")
+    ,("uncurry (W.</>) (W.splitFileName x) == x || fst (W.splitFileName x) == \"./\"", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in uncurry (W.</>) (W.splitFileName x) == x || fst (W.splitFileName x) == "./")
+    ,("P.isValid (fst (P.splitFileName x))", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.isValid (fst (P.splitFileName x)))
+    ,("W.isValid (fst (W.splitFileName x))", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.isValid (fst (W.splitFileName x)))
+    ,("P.splitFileName \"file/bob.txt\" == (\"file/\", \"bob.txt\")", property $ P.splitFileName "file/bob.txt" == ("file/", "bob.txt"))
+    ,("W.splitFileName \"file/bob.txt\" == (\"file/\", \"bob.txt\")", property $ W.splitFileName "file/bob.txt" == ("file/", "bob.txt"))
+    ,("P.splitFileName \"file/\" == (\"file/\", \"\")", property $ P.splitFileName "file/" == ("file/", ""))
+    ,("W.splitFileName \"file/\" == (\"file/\", \"\")", property $ W.splitFileName "file/" == ("file/", ""))
+    ,("P.splitFileName \"bob\" == (\"./\", \"bob\")", property $ P.splitFileName "bob" == ("./", "bob"))
+    ,("W.splitFileName \"bob\" == (\"./\", \"bob\")", property $ W.splitFileName "bob" == ("./", "bob"))
+    ,("P.splitFileName \"/\" == (\"/\", \"\")", property $ P.splitFileName "/" == ("/", ""))
+    ,("W.splitFileName \"c:\" == (\"c:\", \"\")", property $ W.splitFileName "c:" == ("c:", ""))
+    ,("P.replaceFileName \"/directory/other.txt\" \"file.ext\" == \"/directory/file.ext\"", property $ P.replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext")
+    ,("W.replaceFileName \"/directory/other.txt\" \"file.ext\" == \"/directory/file.ext\"", property $ W.replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext")
+    ,("P.replaceFileName x (P.takeFileName x) == x", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.replaceFileName x (P.takeFileName x) == x)
+    ,("W.replaceFileName x (W.takeFileName x) == x", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.replaceFileName x (W.takeFileName x) == x)
+    ,("P.dropFileName \"/directory/file.ext\" == \"/directory/\"", property $ P.dropFileName "/directory/file.ext" == "/directory/")
+    ,("W.dropFileName \"/directory/file.ext\" == \"/directory/\"", property $ W.dropFileName "/directory/file.ext" == "/directory/")
+    ,("P.dropFileName x == fst (P.splitFileName x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.dropFileName x == fst (P.splitFileName x))
+    ,("W.dropFileName x == fst (W.splitFileName x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.dropFileName x == fst (W.splitFileName x))
+    ,("P.takeFileName \"/directory/file.ext\" == \"file.ext\"", property $ P.takeFileName "/directory/file.ext" == "file.ext")
+    ,("W.takeFileName \"/directory/file.ext\" == \"file.ext\"", property $ W.takeFileName "/directory/file.ext" == "file.ext")
+    ,("P.takeFileName \"test/\" == \"\"", property $ P.takeFileName "test/" == "")
+    ,("W.takeFileName \"test/\" == \"\"", property $ W.takeFileName "test/" == "")
+    ,("P.takeFileName x `isSuffixOf` x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.takeFileName x `isSuffixOf` x)
+    ,("W.takeFileName x `isSuffixOf` x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.takeFileName x `isSuffixOf` x)
+    ,("P.takeFileName x == snd (P.splitFileName x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.takeFileName x == snd (P.splitFileName x))
+    ,("W.takeFileName x == snd (W.splitFileName x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.takeFileName x == snd (W.splitFileName x))
+    ,("P.takeFileName (P.replaceFileName x \"fred\") == \"fred\"", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.takeFileName (P.replaceFileName x "fred") == "fred")
+    ,("W.takeFileName (W.replaceFileName x \"fred\") == \"fred\"", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.takeFileName (W.replaceFileName x "fred") == "fred")
+    ,("P.takeFileName (x P.</> \"fred\") == \"fred\"", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.takeFileName (x P.</> "fred") == "fred")
+    ,("W.takeFileName (x W.</> \"fred\") == \"fred\"", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.takeFileName (x W.</> "fred") == "fred")
+    ,("P.isRelative (P.takeFileName x)", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.isRelative (P.takeFileName x))
+    ,("W.isRelative (W.takeFileName x)", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.isRelative (W.takeFileName x))
+    ,("P.takeBaseName \"/directory/file.ext\" == \"file\"", property $ P.takeBaseName "/directory/file.ext" == "file")
+    ,("W.takeBaseName \"/directory/file.ext\" == \"file\"", property $ W.takeBaseName "/directory/file.ext" == "file")
+    ,("P.takeBaseName \"file/test.txt\" == \"test\"", property $ P.takeBaseName "file/test.txt" == "test")
+    ,("W.takeBaseName \"file/test.txt\" == \"test\"", property $ W.takeBaseName "file/test.txt" == "test")
+    ,("P.takeBaseName \"dave.ext\" == \"dave\"", property $ P.takeBaseName "dave.ext" == "dave")
+    ,("W.takeBaseName \"dave.ext\" == \"dave\"", property $ W.takeBaseName "dave.ext" == "dave")
+    ,("P.takeBaseName \"\" == \"\"", property $ P.takeBaseName "" == "")
+    ,("W.takeBaseName \"\" == \"\"", property $ W.takeBaseName "" == "")
+    ,("P.takeBaseName \"test\" == \"test\"", property $ P.takeBaseName "test" == "test")
+    ,("W.takeBaseName \"test\" == \"test\"", property $ W.takeBaseName "test" == "test")
+    ,("P.takeBaseName (P.addTrailingPathSeparator x) == \"\"", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.takeBaseName (P.addTrailingPathSeparator x) == "")
+    ,("W.takeBaseName (W.addTrailingPathSeparator x) == \"\"", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.takeBaseName (W.addTrailingPathSeparator x) == "")
+    ,("P.takeBaseName \"file/file.tar.gz\" == \"file.tar\"", property $ P.takeBaseName "file/file.tar.gz" == "file.tar")
+    ,("W.takeBaseName \"file/file.tar.gz\" == \"file.tar\"", property $ W.takeBaseName "file/file.tar.gz" == "file.tar")
+    ,("P.replaceBaseName \"/directory/other.ext\" \"file\" == \"/directory/file.ext\"", property $ P.replaceBaseName "/directory/other.ext" "file" == "/directory/file.ext")
+    ,("W.replaceBaseName \"/directory/other.ext\" \"file\" == \"/directory/file.ext\"", property $ W.replaceBaseName "/directory/other.ext" "file" == "/directory/file.ext")
+    ,("P.replaceBaseName \"file/test.txt\" \"bob\" == \"file/bob.txt\"", property $ P.replaceBaseName "file/test.txt" "bob" == "file/bob.txt")
+    ,("W.replaceBaseName \"file/test.txt\" \"bob\" == \"file/bob.txt\"", property $ W.replaceBaseName "file/test.txt" "bob" == "file/bob.txt")
+    ,("P.replaceBaseName \"fred\" \"bill\" == \"bill\"", property $ P.replaceBaseName "fred" "bill" == "bill")
+    ,("W.replaceBaseName \"fred\" \"bill\" == \"bill\"", property $ W.replaceBaseName "fred" "bill" == "bill")
+    ,("P.replaceBaseName \"/dave/fred/bob.gz.tar\" \"new\" == \"/dave/fred/new.tar\"", property $ P.replaceBaseName "/dave/fred/bob.gz.tar" "new" == "/dave/fred/new.tar")
+    ,("W.replaceBaseName \"/dave/fred/bob.gz.tar\" \"new\" == \"/dave/fred/new.tar\"", property $ W.replaceBaseName "/dave/fred/bob.gz.tar" "new" == "/dave/fred/new.tar")
+    ,("P.replaceBaseName x (P.takeBaseName x) == x", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.replaceBaseName x (P.takeBaseName x) == x)
+    ,("W.replaceBaseName x (W.takeBaseName x) == x", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.replaceBaseName x (W.takeBaseName x) == x)
+    ,("P.hasTrailingPathSeparator \"test\" == False", property $ P.hasTrailingPathSeparator "test" == False)
+    ,("W.hasTrailingPathSeparator \"test\" == False", property $ W.hasTrailingPathSeparator "test" == False)
+    ,("P.hasTrailingPathSeparator \"test/\" == True", property $ P.hasTrailingPathSeparator "test/" == True)
+    ,("W.hasTrailingPathSeparator \"test/\" == True", property $ W.hasTrailingPathSeparator "test/" == True)
+    ,("P.hasTrailingPathSeparator (P.addTrailingPathSeparator x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.hasTrailingPathSeparator (P.addTrailingPathSeparator x))
+    ,("W.hasTrailingPathSeparator (W.addTrailingPathSeparator x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.hasTrailingPathSeparator (W.addTrailingPathSeparator x))
+    ,("P.hasTrailingPathSeparator x ==> P.addTrailingPathSeparator x == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.hasTrailingPathSeparator x ==> P.addTrailingPathSeparator x == x)
+    ,("W.hasTrailingPathSeparator x ==> W.addTrailingPathSeparator x == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.hasTrailingPathSeparator x ==> W.addTrailingPathSeparator x == x)
+    ,("P.addTrailingPathSeparator \"test/rest\" == \"test/rest/\"", property $ P.addTrailingPathSeparator "test/rest" == "test/rest/")
+    ,("P.dropTrailingPathSeparator \"file/test/\" == \"file/test\"", property $ P.dropTrailingPathSeparator "file/test/" == "file/test")
+    ,("W.dropTrailingPathSeparator \"file/test/\" == \"file/test\"", property $ W.dropTrailingPathSeparator "file/test/" == "file/test")
+    ,("P.dropTrailingPathSeparator \"/\" == \"/\"", property $ P.dropTrailingPathSeparator "/" == "/")
+    ,("W.dropTrailingPathSeparator \"/\" == \"/\"", property $ W.dropTrailingPathSeparator "/" == "/")
+    ,("W.dropTrailingPathSeparator \"\\\\\" == \"\\\\\"", property $ W.dropTrailingPathSeparator "\\" == "\\")
+    ,("not (P.hasTrailingPathSeparator (P.dropTrailingPathSeparator x)) || P.isDrive x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in not (P.hasTrailingPathSeparator (P.dropTrailingPathSeparator x)) || P.isDrive x)
+    ,("P.takeDirectory \"/directory/other.ext\" == \"/directory\"", property $ P.takeDirectory "/directory/other.ext" == "/directory")
+    ,("W.takeDirectory \"/directory/other.ext\" == \"/directory\"", property $ W.takeDirectory "/directory/other.ext" == "/directory")
+    ,("P.takeDirectory x `isPrefixOf` x || P.takeDirectory x == \".\"", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.takeDirectory x `isPrefixOf` x || P.takeDirectory x == ".")
+    ,("W.takeDirectory x `isPrefixOf` x || W.takeDirectory x == \".\"", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.takeDirectory x `isPrefixOf` x || W.takeDirectory x == ".")
+    ,("P.takeDirectory \"foo\" == \".\"", property $ P.takeDirectory "foo" == ".")
+    ,("W.takeDirectory \"foo\" == \".\"", property $ W.takeDirectory "foo" == ".")
+    ,("P.takeDirectory \"/\" == \"/\"", property $ P.takeDirectory "/" == "/")
+    ,("W.takeDirectory \"/\" == \"/\"", property $ W.takeDirectory "/" == "/")
+    ,("P.takeDirectory \"/foo\" == \"/\"", property $ P.takeDirectory "/foo" == "/")
+    ,("W.takeDirectory \"/foo\" == \"/\"", property $ W.takeDirectory "/foo" == "/")
+    ,("P.takeDirectory \"/foo/bar/baz\" == \"/foo/bar\"", property $ P.takeDirectory "/foo/bar/baz" == "/foo/bar")
+    ,("W.takeDirectory \"/foo/bar/baz\" == \"/foo/bar\"", property $ W.takeDirectory "/foo/bar/baz" == "/foo/bar")
+    ,("P.takeDirectory \"/foo/bar/baz/\" == \"/foo/bar/baz\"", property $ P.takeDirectory "/foo/bar/baz/" == "/foo/bar/baz")
+    ,("W.takeDirectory \"/foo/bar/baz/\" == \"/foo/bar/baz\"", property $ W.takeDirectory "/foo/bar/baz/" == "/foo/bar/baz")
+    ,("P.takeDirectory \"foo/bar/baz\" == \"foo/bar\"", property $ P.takeDirectory "foo/bar/baz" == "foo/bar")
+    ,("W.takeDirectory \"foo/bar/baz\" == \"foo/bar\"", property $ W.takeDirectory "foo/bar/baz" == "foo/bar")
+    ,("W.takeDirectory \"foo\\\\bar\" == \"foo\"", property $ W.takeDirectory "foo\\bar" == "foo")
+    ,("W.takeDirectory \"foo\\\\bar\\\\\\\\\" == \"foo\\\\bar\"", property $ W.takeDirectory "foo\\bar\\\\" == "foo\\bar")
+    ,("W.takeDirectory \"C:\\\\\" == \"C:\\\\\"", property $ W.takeDirectory "C:\\" == "C:\\")
+    ,("P.replaceDirectory \"root/file.ext\" \"/directory/\" == \"/directory/file.ext\"", property $ P.replaceDirectory "root/file.ext" "/directory/" == "/directory/file.ext")
+    ,("W.replaceDirectory \"root/file.ext\" \"/directory/\" == \"/directory/file.ext\"", property $ W.replaceDirectory "root/file.ext" "/directory/" == "/directory/file.ext")
+    ,("\"/directory\" P.</> \"file.ext\" == \"/directory/file.ext\"", property $ "/directory" P.</> "file.ext" == "/directory/file.ext")
+    ,("\"/directory\" W.</> \"file.ext\" == \"/directory\\\\file.ext\"", property $ "/directory" W.</> "file.ext" == "/directory\\file.ext")
+    ,("\"directory\" P.</> \"/file.ext\" == \"/file.ext\"", property $ "directory" P.</> "/file.ext" == "/file.ext")
+    ,("\"directory\" W.</> \"/file.ext\" == \"/file.ext\"", property $ "directory" W.</> "/file.ext" == "/file.ext")
+    ,("\"/\" P.</> \"test\" == \"/test\"", property $ "/" P.</> "test" == "/test")
+    ,("\"home\" P.</> \"bob\" == \"home/bob\"", property $ "home" P.</> "bob" == "home/bob")
+    ,("\"x:\" P.</> \"foo\" == \"x:/foo\"", property $ "x:" P.</> "foo" == "x:/foo")
+    ,("\"C:\\\\foo\" W.</> \"bar\" == \"C:\\\\foo\\\\bar\"", property $ "C:\\foo" W.</> "bar" == "C:\\foo\\bar")
+    ,("\"home\" W.</> \"bob\" == \"home\\\\bob\"", property $ "home" W.</> "bob" == "home\\bob")
+    ,("\"home\" P.</> \"/bob\" == \"/bob\"", property $ "home" P.</> "/bob" == "/bob")
+    ,("\"home\" W.</> \"C:\\\\bob\" == \"C:\\\\bob\"", property $ "home" W.</> "C:\\bob" == "C:\\bob")
+    ,("\"home\" W.</> \"/bob\" == \"/bob\"", property $ "home" W.</> "/bob" == "/bob")
+    ,("\"home\" W.</> \"\\\\bob\" == \"\\\\bob\"", property $ "home" W.</> "\\bob" == "\\bob")
+    ,("\"C:\\\\home\" W.</> \"\\\\bob\" == \"\\\\bob\"", property $ "C:\\home" W.</> "\\bob" == "\\bob")
+    ,("\"D:\\\\foo\" W.</> \"C:bar\" == \"C:bar\"", property $ "D:\\foo" W.</> "C:bar" == "C:bar")
+    ,("\"C:\\\\foo\" W.</> \"C:bar\" == \"C:bar\"", property $ "C:\\foo" W.</> "C:bar" == "C:bar")
+    ,("P.splitPath \"/directory/file.ext\" == [\"/\", \"directory/\", \"file.ext\"]", property $ P.splitPath "/directory/file.ext" == ["/", "directory/", "file.ext"])
+    ,("W.splitPath \"/directory/file.ext\" == [\"/\", \"directory/\", \"file.ext\"]", property $ W.splitPath "/directory/file.ext" == ["/", "directory/", "file.ext"])
+    ,("mconcat (P.splitPath x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in mconcat (P.splitPath x) == x)
+    ,("mconcat (W.splitPath x) == x", property $ \(QFilePath vx) -> let x = toRawFilePath vx in mconcat (W.splitPath x) == x)
+    ,("P.splitPath \"test//item/\" == [\"test//\", \"item/\"]", property $ P.splitPath "test//item/" == ["test//", "item/"])
+    ,("W.splitPath \"test//item/\" == [\"test//\", \"item/\"]", property $ W.splitPath "test//item/" == ["test//", "item/"])
+    ,("P.splitPath \"test/item/file\" == [\"test/\", \"item/\", \"file\"]", property $ P.splitPath "test/item/file" == ["test/", "item/", "file"])
+    ,("W.splitPath \"test/item/file\" == [\"test/\", \"item/\", \"file\"]", property $ W.splitPath "test/item/file" == ["test/", "item/", "file"])
+    ,("P.splitPath \"\" == []", property $ P.splitPath "" == [])
+    ,("W.splitPath \"\" == []", property $ W.splitPath "" == [])
+    ,("W.splitPath \"c:\\\\test\\\\path\" == [\"c:\\\\\", \"test\\\\\", \"path\"]", property $ W.splitPath "c:\\test\\path" == ["c:\\", "test\\", "path"])
+    ,("P.splitPath \"/file/test\" == [\"/\", \"file/\", \"test\"]", property $ P.splitPath "/file/test" == ["/", "file/", "test"])
+    ,("P.splitDirectories \"/directory/file.ext\" == [\"/\", \"directory\", \"file.ext\"]", property $ P.splitDirectories "/directory/file.ext" == ["/", "directory", "file.ext"])
+    ,("W.splitDirectories \"/directory/file.ext\" == [\"/\", \"directory\", \"file.ext\"]", property $ W.splitDirectories "/directory/file.ext" == ["/", "directory", "file.ext"])
+    ,("P.splitDirectories \"test/file\" == [\"test\", \"file\"]", property $ P.splitDirectories "test/file" == ["test", "file"])
+    ,("W.splitDirectories \"test/file\" == [\"test\", \"file\"]", property $ W.splitDirectories "test/file" == ["test", "file"])
+    ,("P.splitDirectories \"/test/file\" == [\"/\", \"test\", \"file\"]", property $ P.splitDirectories "/test/file" == ["/", "test", "file"])
+    ,("W.splitDirectories \"/test/file\" == [\"/\", \"test\", \"file\"]", property $ W.splitDirectories "/test/file" == ["/", "test", "file"])
+    ,("W.splitDirectories \"C:\\\\test\\\\file\" == [\"C:\\\\\", \"test\", \"file\"]", property $ W.splitDirectories "C:\\test\\file" == ["C:\\", "test", "file"])
+    ,("P.splitDirectories \"\" == []", property $ P.splitDirectories "" == [])
+    ,("W.splitDirectories \"\" == []", property $ W.splitDirectories "" == [])
+    ,("W.splitDirectories \"C:\\\\test\\\\\\\\\\\\file\" == [\"C:\\\\\", \"test\", \"file\"]", property $ W.splitDirectories "C:\\test\\\\\\file" == ["C:\\", "test", "file"])
+    ,("P.splitDirectories \"/test///file\" == [\"/\", \"test\", \"file\"]", property $ P.splitDirectories "/test///file" == ["/", "test", "file"])
+    ,("W.splitDirectories \"/test///file\" == [\"/\", \"test\", \"file\"]", property $ W.splitDirectories "/test///file" == ["/", "test", "file"])
+    ,("P.joinPath [\"/\", \"directory/\", \"file.ext\"] == \"/directory/file.ext\"", property $ P.joinPath ["/", "directory/", "file.ext"] == "/directory/file.ext")
+    ,("W.joinPath [\"/\", \"directory/\", \"file.ext\"] == \"/directory/file.ext\"", property $ W.joinPath ["/", "directory/", "file.ext"] == "/directory/file.ext")
+    ,("P.joinPath (P.splitPath x) == x", property $ \(QFilePathValidP vx) -> let x = toRawFilePath vx in P.joinPath (P.splitPath x) == x)
+    ,("W.joinPath (W.splitPath x) == x", property $ \(QFilePathValidW vx) -> let x = toRawFilePath vx in W.joinPath (W.splitPath x) == x)
+    ,("P.joinPath [] == \"\"", property $ P.joinPath [] == "")
+    ,("W.joinPath [] == \"\"", property $ W.joinPath [] == "")
+    ,("P.joinPath [\"test\", \"file\", \"path\"] == \"test/file/path\"", property $ P.joinPath ["test", "file", "path"] == "test/file/path")
+    ,("P.isValid \"\" == False", property $ P.isValid "" == False)
+    ,("W.isValid \"\" == False", property $ W.isValid "" == False)
+    ,("P.isValid \"\\0\" == False", property $ P.isValid "\0" == False)
+    ,("W.isValid \"\\0\" == False", property $ W.isValid "\0" == False)
+    ,("P.isValid \"/random_ path:*\" == True", property $ P.isValid "/random_ path:*" == True)
+    ,("P.isValid x == (x /= mempty)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.isValid x == (x /= mempty))
+    ,("W.isValid \"c:\\\\test\" == True", property $ W.isValid "c:\\test" == True)
+    ,("W.isValid \"c:\\\\test:of_test\" == False", property $ W.isValid "c:\\test:of_test" == False)
+    ,("W.isValid \"test*\" == False", property $ W.isValid "test*" == False)
+    ,("W.isValid \"c:\\\\test\\\\nul\" == False", property $ W.isValid "c:\\test\\nul" == False)
+    ,("W.isValid \"c:\\\\test\\\\prn.txt\" == False", property $ W.isValid "c:\\test\\prn.txt" == False)
+    ,("W.isValid \"c:\\\\nul\\\\file\" == False", property $ W.isValid "c:\\nul\\file" == False)
+    ,("W.isValid \"\\\\\\\\\" == False", property $ W.isValid "\\\\" == False)
+    ,("W.isValid \"\\\\\\\\\\\\foo\" == False", property $ W.isValid "\\\\\\foo" == False)
+    ,("W.isValid \"\\\\\\\\?\\\\D:file\" == False", property $ W.isValid "\\\\?\\D:file" == False)
+    ,("W.isValid \"foo\\tbar\" == False", property $ W.isValid "foo\tbar" == False)
+    ,("W.isValid \"nul .txt\" == False", property $ W.isValid "nul .txt" == False)
+    ,("W.isValid \" nul.txt\" == True", property $ W.isValid " nul.txt" == True)
+    ,("W.isRelative \"path\\\\test\" == True", property $ W.isRelative "path\\test" == True)
+    ,("W.isRelative \"c:\\\\test\" == False", property $ W.isRelative "c:\\test" == False)
+    ,("W.isRelative \"c:test\" == True", property $ W.isRelative "c:test" == True)
+    ,("W.isRelative \"c:\\\\\" == False", property $ W.isRelative "c:\\" == False)
+    ,("W.isRelative \"c:/\" == False", property $ W.isRelative "c:/" == False)
+    ,("W.isRelative \"c:\" == True", property $ W.isRelative "c:" == True)
+    ,("W.isRelative \"\\\\\\\\foo\" == False", property $ W.isRelative "\\\\foo" == False)
+    ,("W.isRelative \"\\\\\\\\?\\\\foo\" == False", property $ W.isRelative "\\\\?\\foo" == False)
+    ,("W.isRelative \"\\\\\\\\?\\\\UNC\\\\foo\" == False", property $ W.isRelative "\\\\?\\UNC\\foo" == False)
+    ,("W.isRelative \"/foo\" == True", property $ W.isRelative "/foo" == True)
+    ,("W.isRelative \"\\\\foo\" == True", property $ W.isRelative "\\foo" == True)
+    ,("P.isRelative \"test/path\" == True", property $ P.isRelative "test/path" == True)
+    ,("P.isRelative \"/test\" == False", property $ P.isRelative "/test" == False)
+    ,("P.isRelative \"/\" == False", property $ P.isRelative "/" == False)
+    ,("P.isAbsolute x == not (P.isRelative x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in P.isAbsolute x == not (P.isRelative x))
+    ,("W.isAbsolute x == not (W.isRelative x)", property $ \(QFilePath vx) -> let x = toRawFilePath vx in W.isAbsolute x == not (W.isRelative x))
+    ]
diff --git a/tests/TestUtil.hs b/tests/TestUtil.hs
new file mode 100644
--- /dev/null
+++ b/tests/TestUtil.hs
@@ -0,0 +1,157 @@
+{-# LANGUAGE TypeSynonymInstances, FlexibleInstances, MultiParamTypeClasses #-}
+
+module TestUtil(
+    (==>), QFilePath(..), QFilePathValidW(..), QFilePathValidP(..),
+    toRawFilePath,
+    equiv_0, equiv_1, equiv_2, equiv_3,
+    module Test.QuickCheck,
+    module Data.Maybe
+    ) where
+
+import Test.QuickCheck hiding ((==>))
+import Data.List
+import Data.Maybe
+import Data.Word
+import Data.Char
+import Control.Monad
+import qualified System.FilePath.Windows as W
+import qualified System.FilePath.Posix as P
+import System.FilePath.ByteString (RawFilePath)
+import qualified GHC.Foreign as GHC
+import qualified GHC.IO.Encoding as Encoding
+import System.IO.Unsafe
+import qualified Data.ByteString as B
+
+infixr 0 ==>
+a ==> b = not a || b
+
+class ToRawFilePath t where
+        toRawFilePath :: t -> RawFilePath
+
+instance ToRawFilePath [Char] where
+        toRawFilePath = B.pack . decodeW8NUL
+
+decodeW8NUL :: String -> [Word8]
+decodeW8NUL = intercalate [c2w8 nul] . map decodeW8 . splitc nul
+  where
+        nul = '\NUL'
+
+c2w8 :: Char -> Word8
+c2w8 = fromIntegral . fromEnum
+
+s2w8 :: String -> [Word8]
+s2w8 = map c2w8
+
+splitc :: Eq c => c -> [c] -> [[c]]
+splitc c s = case break (== c) s of
+        (i, _c:rest) -> i : splitc c rest
+        (i, []) -> i : []
+
+decodeW8 :: FilePath -> [Word8]
+decodeW8 = s2w8 . encodeFilePath
+
+{-# NOINLINE encodeFilePath #-}
+encodeFilePath :: String -> String
+encodeFilePath fp = unsafePerformIO $ do
+        enc <- Encoding.getFileSystemEncoding
+        GHC.withCString enc fp (GHC.peekCString Encoding.char8)
+
+newtype QFilePathValidW = QFilePathValidW FilePath deriving Show
+
+instance ToRawFilePath QFilePathValidW where
+    toRawFilePath (QFilePathValidW p) = toRawFilePath p
+
+instance Arbitrary QFilePathValidW where
+    arbitrary = fmap (QFilePathValidW . W.makeValid) arbitraryFilePath
+    shrink (QFilePathValidW x) = shrinkValid QFilePathValidW W.makeValid x
+
+newtype QFilePathValidP = QFilePathValidP FilePath deriving Show
+
+instance ToRawFilePath QFilePathValidP where
+    toRawFilePath (QFilePathValidP p) = toRawFilePath p
+
+instance Arbitrary QFilePathValidP where
+    arbitrary = fmap (QFilePathValidP . P.makeValid) arbitraryFilePath
+    shrink (QFilePathValidP x) = shrinkValid QFilePathValidP P.makeValid x
+
+newtype QFilePath = QFilePath FilePath deriving Show
+
+instance ToRawFilePath QFilePath where
+    toRawFilePath (QFilePath p) = toRawFilePath p
+
+instance Arbitrary QFilePath where
+    arbitrary = fmap QFilePath arbitraryFilePath
+    shrink (QFilePath x) = shrinkValid QFilePath id x
+
+
+-- | Generate an arbitrary FilePath use a few special (interesting) characters.
+arbitraryFilePath :: Gen FilePath
+arbitraryFilePath = sized $ \n -> do
+    k <- choose (0,n)
+    replicateM k $ elements "?./:\\a ;_"
+
+-- | Shrink, but also apply a validity function. Try and make shorter, or use more
+--   @a@ (since @a@ is pretty dull), but make sure you terminate even after valid.
+shrinkValid :: (FilePath -> a) -> (FilePath -> FilePath) -> FilePath -> [a]
+shrinkValid wrap valid o =
+    [ wrap y
+    | y <- map valid $ shrinkList (\x -> ['a' | x /= 'a']) o
+    , length y < length o || (length y == length o && countA y > countA o)]
+    where countA = length . filter (== 'a')
+
+class EquivResult t1 t2 where
+        equivresult :: t1 -> t2 -> Bool
+
+instance Eq t => EquivResult t t where
+        equivresult a b = a == b
+
+instance (EquivResult a c, EquivResult b d) => EquivResult (a, b) (c, d) where
+        equivresult (a, b) (c, d) = equivresult a c && equivresult b d
+
+instance (EquivResult a b) => EquivResult (Maybe a) (Maybe b) where
+        equivresult Nothing Nothing = True
+        equivresult (Just a) (Just b) = equivresult a b
+
+instance (EquivResult a b) => EquivResult [a] [b] where
+        equivresult a b = and (map (uncurry equivresult) (zip a b))
+
+instance EquivResult FilePath RawFilePath where
+        equivresult a b = toRawFilePath a == b
+
+instance EquivResult RawFilePath FilePath where
+        equivresult a b = toRawFilePath b == a
+
+equiv_0
+        :: EquivResult a b
+        => (Word8 -> a)
+        -> (Char -> b)
+        -> Property
+equiv_0 our their = property $ \w ->
+        our w `equivresult` their (chr (fromIntegral w))
+
+equiv_1
+        :: EquivResult a b
+        => (RawFilePath -> a)
+        -> (FilePath -> b)
+        -> Property
+equiv_1 our their = property $ \(QFilePath f) ->
+        our (toRawFilePath f) `equivresult` their f
+
+equiv_2
+        :: EquivResult a b
+        => (RawFilePath -> RawFilePath -> a)
+        -> (FilePath -> FilePath -> b)
+        -> Property
+equiv_2 our their = property $ \(QFilePath a) (QFilePath b) ->
+        our (toRawFilePath a) (toRawFilePath b) `equivresult` their a b
+
+equiv_3
+        :: EquivResult a b
+        => ([RawFilePath] -> a)
+        -> ([FilePath] -> b)
+        -> Property
+equiv_3 our their = property $ \l ->
+        our (map (\(QFilePath f) -> toRawFilePath f) l)
+                `equivresult`
+        their (map (\(QFilePath f) -> f) l)
+
