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diff --git a/users/wpcarro/haskell-file/f.hs b/users/wpcarro/haskell-file/f.hs
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+module F
+  ( join
+  , split
+  ) where
+
+--------------------------------------------------------------------------------
+-- Dependencies
+--------------------------------------------------------------------------------
+
+import Data.List (span)
+import System.FilePath (FilePath, pathSeparator)
+import System.FilePath.Posix (FilePath)
+import qualified System.FilePath.Posix as F
+
+-- TODO: Move this to a misc.hs, prelude.hs, operators.hs; somewhere.
+(|>) :: a -> (a -> b) -> b
+(|>) a f = f a
+infixl 1 |>
+
+-- TODO: Move this to a test_utils.hs or elsewhere.
+simpleAssert :: (Eq a) => a -> a -> ()
+simpleAssert x y =
+  if x == y then
+    ()
+  else
+    error "Assertion error"
+
+--------------------------------------------------------------------------------
+-- Library
+--------------------------------------------------------------------------------
+
+join :: [FilePath] -> FilePath
+join = F.joinPath
+
+-- | Split path and return  list containing parts.
+split :: FilePath -> [String]
+split = splitJoin . span (/= pathSeparator)
+  where
+    splitJoin :: (String, String) -> [String]
+    splitJoin ([], []) = []
+    splitJoin (a, []) = [a]
+    splitJoin (a, [_]) = [a]
+    splitJoin (a, _:b) = a : split b
+
+--------------------------------------------------------------------------------
+-- Tests
+--------------------------------------------------------------------------------
+
+expected :: [([FilePath], FilePath)]
+expected = [ (["path"], "path")
+           , (["/path"], "/path")
+           , (["path", "to", "file"], "path/to/file")
+           , (["/path", "to", "file"], "/path/to/file")
+           , (["/"], "/")
+           ]
+
+runTests :: [()]
+runTests =
+  fmap (\(input, expected) -> simpleAssert (join input) expected) expected
+
+main :: IO ()
+main = do
+  print runTests
+  pure ()