[Word8] to filesystem encoded String

My, GHC makes this hard.

Utility/FileSystemEncoding.hs

@@ -13,6 +13,8 @@ import Foreign.C
 import System.IO
 import System.IO.Unsafe
 import qualified Data.Hash.MD5 as MD5
+import Data.Word
+import Data.Bits.Utils
 
 {- Sets a Handle to use the filesystem encoding. This causes data
  - written or read from it to be encoded/decoded the same
@@ -29,7 +31,7 @@ withFilePath :: FilePath -> (CString -> IO a) -> IO a
 withFilePath fp f = Encoding.getFileSystemEncoding
 	>>= \enc -> GHC.withCString enc fp f
 
-{- Encodes a FilePath into a Str, applying the filesystem encoding.
+{- Encodes a FilePath into a Md5.Str, applying the filesystem encoding.
  -
  - This use of unsafePerformIO is belived to be safe; GHC's interface
  - only allows doing this conversion with CStrings, and the CString buffer
@@ -41,3 +43,15 @@ encodeFilePath :: FilePath -> MD5.Str
 encodeFilePath fp = MD5.Str $ unsafePerformIO $ do
 	enc <- Encoding.getFileSystemEncoding
 	GHC.withCString enc fp $ GHC.peekCString Encoding.char8
+
+{- Converts a [Word8] to a FilePath, encoding using the filesystem encoding.
+ -
+ - w82c produces a String, which may contain Chars that are invalid
+ - unicode. From there, this is really a simple matter of applying the
+ - file system encoding, only complicated by GHC's interface to doing so.
+ -}
+{-# NOINLINE encodeW8 #-}
+encodeW8 :: [Word8] -> FilePath
+encodeW8 w8 = unsafePerformIO $ do
+	enc <- Encoding.getFileSystemEncoding
+	GHC.withCString Encoding.char8 (w82s w8) $ GHC.peekCString enc