diff --git a/Hclip.cabal b/Hclip.cabal
--- a/Hclip.cabal
+++ b/Hclip.cabal
@@ -1,81 +1,63 @@
--- Initial Hclip.cabal generated by cabal init.  For further documentation,
---  see http://haskell.org/cabal/users-guide/
-
--- The name of the package.
-name:                Hclip
-
--- The package version.  See the Haskell package versioning policy (PVP) 
--- for standards guiding when and how versions should be incremented.
--- http://www.haskell.org/haskellwiki/Package_versioning_policy
--- PVP summary:      +-+------- breaking API changes
---                   | | +----- non-breaking API additions
---                   | | | +--- code changes with no API change
-version:             2.0.0.1
-
--- A short (one-line) description of the package.
-synopsis:            A small cross-platform library for reading and modifying the system clipboard.
-
--- A longer description of the package.
--- description:         
-
--- URL for the project homepage or repository.
-homepage:            https://github.com/jetho/Hclip
-
--- The license under which the package is released.
-license:             BSD3
-
--- The file containing the license text.
-license-file:        LICENSE
-
--- The package author(s).
-author:              Jens Thomas
-
--- An email address to which users can send suggestions, bug reports, and 
--- patches.
-maintainer:          jetho@gmx.de
-
--- A copyright notice.
--- copyright:           
-
-category:            System
-
-Description:
-        A small cross-platform library for reading and modifying the system clipboard.
-        .
-        Hclip works on Windows, Mac OS X and Linux (but see the requirements below!).
-        .
-        Requirements:
-        .
-        * Windows: No additional requirements.
-        .
-        * Mac OS X: Requires the pbcopy and pbpaste commands, which ship with Mac OS X.
-        .
-        * Linux: Requires xclip or xsel installed.
-		
-build-type:          Simple
-
--- Constraint on the version of Cabal needed to build this package.
-cabal-version:       >=1.8
-
-
-library
-  -- Modules exported by the library.
-  exposed-modules:     System.Hclip
-  Extensions:          CPP, DeriveDataTypeable
-  
-  -- Modules included in this library but not exported.
-  -- other-modules:       
-  
-  -- Other library packages from which modules are imported.
-  build-depends:       base >= 3 && < 5, 
-                       process, 
-                       mtl, 
-                       strict 
-  
-  if os(windows)
-    Build-depends:     Win32
-
-
-source-repository head
-  type: git
-  location: git://github.com/jetho/Hclip.git
+
+name:                Hclip
+
+-- The package version.  See the Haskell package versioning policy (PVP) 
+-- for standards guiding when and how versions should be incremented.
+-- http://www.haskell.org/haskellwiki/Package_versioning_policy
+-- PVP summary:      +-+------- breaking API changes
+--                   | | +----- non-breaking API additions
+--                   | | | +--- code changes with no API change
+version:             3.0.0.0
+
+synopsis:            A small cross-platform library for reading and modifying the system clipboard.
+
+homepage:            https://github.com/jetho/Hclip
+
+license:             BSD3
+
+license-file:        LICENSE
+
+author:              Jens Thomas
+
+maintainer:          jetho@gmx.de
+
+category:            System
+
+description:
+        A small cross-platform library for reading and modifying the system clipboard.
+        .
+        Hclip works on Windows, Mac OS X and Linux (but see the requirements below!).
+        .
+        Requirements:
+        .
+        * Windows: No additional requirements.
+        .
+        * Mac OS X: Requires the pbcopy and pbpaste commands, which ship with Mac OS X.
+        .
+        * Linux: Requires xclip or xsel installed.
+		
+build-type:          Simple
+
+cabal-version:       >=1.10
+
+
+library
+  exposed-modules:   System.Hclip
+  other-extensions:  CPP, DeriveDataTypeable, GADTs
+  default-language:  Haskell2010
+  build-depends:     base >= 3 && < 5, process, mtl, strict 
+  if os(windows)
+    build-depends:   Win32
+
+Test-suite Tasty
+  default-language:  Haskell2010
+  type:              exitcode-stdio-1.0
+  hs-source-dirs:    tests
+  main-is:           Tasty.hs
+  build-depends:     base >= 3 && < 5, tasty, tasty-hunit, Hclip
+                    
+
+source-repository head
+  type:              git
+  location:          git://github.com/jetho/Hclip.git
+
diff --git a/System/Hclip.hs b/System/Hclip.hs
--- a/System/Hclip.hs
+++ b/System/Hclip.hs
@@ -1,172 +1,194 @@
-
-{-# LANGUAGE CPP #-}
-{-# LANGUAGE DeriveDataTypeable #-}
-
---------------------------------------------------------------------
--- |
--- Module : System.Hclip
--- Copyright : (c) Jens Thomas
--- License : BSD3
---
--- Maintainer: Jens Thomas <jetho@gmx.de>
--- Stability : experimental
--- Portability: 
---
--- A small cross-platform library for reading and modifying the system clipboard. 
--- 
---------------------------------------------------------------------
-
-module System.Hclip (
-        getClipboard, 
-        setClipboard, 
-        modifyClipboard,
-        ClipboardException(..)
-  ) where
-
-import System.Process (runInteractiveCommand, readProcessWithExitCode, waitForProcess)
-import System.Info (os)
-import System.IO (Handle, hPutStr, hClose)
-import Data.Monoid 
-import Control.Exception (Exception, throwIO, bracket, bracket_)
-import System.IO.Strict (hGetContents) -- see http://hackage.haskell.org/package/strict
-import System.Exit (ExitCode(..))
-import Control.Monad ((>=>), liftM)
-import Data.List (intercalate, genericLength)
-import Data.Typeable (Typeable)
-
--- | for Windows support
-#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
-import System.Win32.Mem (globalAlloc, globalLock, globalUnlock, copyMemory, gHND)
-import Graphics.Win32.GDI.Clip (openClipboard, closeClipboard, emptyClipboard, getClipboardData, 
-                                setClipboardData, ClipboardFormat, isClipboardFormatAvailable, cF_TEXT)
-import Foreign.C (withCAString, peekCAString)
-import Foreign.Ptr (castPtr, nullPtr)
-#endif
-
-
--- | Clipboard Actions
-data Command = GetClipboard 
-             | SetClipboard String 
-
-
--- | Supported Operating Systems
-data Platform = Linux
-              | Darwin
-              | Windows
-              deriving (Show)
-
-
--- | Exceptions
-data ClipboardException = UnsupportedOS String
-                        | NoTextualData
-                        | MissingCommands [String]
-                        deriving (Typeable)
-                    
-instance Exception ClipboardException
-
-instance Show ClipboardException where
-  show (UnsupportedOS os)     = "Unsupported Operating System: " ++ os
-  show NoTextualData          = "Clipboard doesn't contain textual data."
-  show (MissingCommands cmds) = "Hclip requires " ++ apps ++ " installed."
-    where apps = intercalate " or " cmds
-
-
--- | Read clipboard contents.
-getClipboard :: IO String 
-getClipboard = dispatchCommand GetClipboard
-
-
--- | Set clipboard contents.
-setClipboard :: String -> IO String
-setClipboard = dispatchCommand . SetClipboard
-
-
--- | Apply function to clipboard and return its new contents.
-modifyClipboard :: (String -> String) -> IO String
-modifyClipboard = flip liftM getClipboard >=> setClipboard
-
-
--- | Select the supported operating system.
-dispatchCommand :: Command -> IO String
-dispatchCommand = case os of
-  "linux"   -> clipboard Linux
-  "darwin"  -> clipboard Darwin
-#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
-  "mingw32" -> clipboard Windows 
-#endif
-  unknownOS -> const . throwIO $ UnsupportedOS unknownOS
-
-
--- | MAC OS: use pbcopy and pbpaste    
-clipboard Darwin command = withExternalCommand extCmd command
-  where extCmd = case command of
-                   GetClipboard   -> "pbpaste"
-                   SetClipboard _ -> "pbcopy"
-
-
--- | Linux: use xsel or xclip
-clipboard Linux command = do
-  prog <- chooseFirstCommand ["xsel", "xclip"]
-  withExternalCommand (decode prog command) command
-  where
-    decode "xsel" GetClipboard      = "xsel -o"
-    decode "xsel" (SetClipboard _)  = "xsel -i"
-    decode "xclip" GetClipboard     = "xclip -selection c -o"
-    decode "xclip" (SetClipboard _) = "xclip -selection c"
-    
-
--- | Windows: use WinAPI
-#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
-clipboard Windows GetClipboard = 
-  bracket_ (openClipboard nullPtr) closeClipboard $ do
-    isText <- isClipboardFormatAvailable cF_TEXT
-    if isText
-      then do 
-        h <- getClipboardData cF_TEXT
-        bracket (globalLock h) globalUnlock $ peekCAString . castPtr
-      else throwIO NoTextualData
-
-clipboard Windows (SetClipboard s) = 
-  withCAString s $ \cstr -> do
-    mem <- globalAlloc gHND memSize
-    bracket (globalLock mem) globalUnlock $ \space -> do
-      copyMemory space (castPtr cstr) memSize
-      bracket_ (openClipboard nullPtr) closeClipboard $ do
-        emptyClipboard
-        setClipboardData cF_TEXT space
-        return s
-  where
-    memSize = genericLength s + 1
-#endif
-
-
--- | Run external command for accessing the system clipboard.
-withExternalCommand :: String -> Command -> IO String
-withExternalCommand prog command = 
-  bracket (runInteractiveCommand prog)
-          (\(inp, outp, stderr, pid) -> mapM_ hClose [inp, outp, stderr] >> waitForProcess pid)
-          (\(inp, outp, _, _)        -> action command (inp, outp))
-  where
-    action GetClipboard = hGetContents . stdout
-    action (SetClipboard text) = (flip hPutStr text >=> const (return text)) . stdin
-    stdin = fst
-    stdout = snd
-
-
--- | Search for installed programs and return the first match.
-chooseFirstCommand :: [String] -> IO String
-chooseFirstCommand cmds = do
-  results <- mapM whichCommand cmds
-  maybe (throwIO $ MissingCommands cmds)
-        return
-        (getFirst . mconcat $ map First results)
-
-
--- | Check if cmd is installed using the which command.
-whichCommand :: String -> IO (Maybe String)
-whichCommand cmd = do
-  (exitCode,_,_) <- readProcessWithExitCode "which" [cmd] ""
-  case exitCode of
-    ExitSuccess   -> return $ Just cmd
-    ExitFailure _ -> return Nothing
-
+
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+
+--------------------------------------------------------------------
+-- |
+-- Module : System.Hclip
+-- Copyright : (c) Jens Thomas
+-- License : BSD3
+--
+-- Maintainer: Jens Thomas <jetho@gmx.de>
+-- Stability : experimental
+-- Portability:
+--
+-- A small cross-platform library for reading and modifying the system clipboard.
+-- 
+--------------------------------------------------------------------
+
+module System.Hclip (
+        getClipboard,
+        setClipboard,
+        modifyClipboard,
+        modifyClipboard_,
+        clearClipboard,
+        ClipboardException(..)
+  ) where
+
+
+import System.Info (os)
+import System.Process (runInteractiveCommand, readProcessWithExitCode, waitForProcess)
+import System.IO (Handle, hPutStr, hClose)
+import Data.Monoid 
+import System.IO.Strict (hGetContents) -- see http://hackage.haskell.org/package/strict
+import System.Exit (ExitCode(..))
+import Data.List (intercalate)
+import Control.Exception (Exception, throw, throwIO, bracket, bracket_)
+import Data.Typeable (Typeable)
+import Control.Applicative ((<$>))
+import Control.Monad ((>=>), liftM)
+
+-- | for Windows support
+#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
+import System.Win32.Mem (globalAlloc, globalLock, globalUnlock, copyMemory, gHND)
+import Graphics.Win32.GDI.Clip (openClipboard, closeClipboard, emptyClipboard, getClipboardData,
+                                setClipboardData, ClipboardFormat, isClipboardFormatAvailable, cF_TEXT)
+import Foreign.C (withCAString, peekCAString)
+import Foreign.Ptr (castPtr, nullPtr)
+#endif
+
+
+type StdIn      = Handle
+type StdOut     = Handle
+type IOAction a = (StdIn, StdOut) -> IO a
+
+
+-- | Clipboard Commands
+data Command a where
+    GetClipboard   :: Command (IO String)
+    SetClipboard   :: String -> Command (IO ())
+
+
+-- | Supported Platforms
+data Platform = Linux
+              | Darwin
+              | Windows
+
+
+-- | Exceptions
+data ClipboardException = UnsupportedOS String
+                        | NoTextualData
+                        | MissingCommands [String]
+                        deriving (Typeable)
+                    
+instance Exception ClipboardException
+
+instance Show ClipboardException where
+    show (UnsupportedOS s)     = "Unsupported Operating System: " ++ s
+    show NoTextualData          = "Clipboard doesn't contain textual data."
+    show (MissingCommands cmds) = "Hclip requires " ++ apps ++ " installed."
+        where apps = intercalate " or " cmds
+
+
+-- | Read clipboard contents.
+getClipboard :: IO String
+getClipboard = dispatch GetClipboard
+
+-- | Set clipboard contents.
+setClipboard :: String -> IO ()
+setClipboard = dispatch . SetClipboard
+
+-- | Apply function to clipboard and return its new contents.
+modifyClipboard :: (String -> String) -> IO String
+modifyClipboard f = do
+    modified <- f <$> getClipboard
+    setClipboard modified
+    return modified
+
+-- | Apply function to clipboard.
+modifyClipboard_ :: (String -> String) -> IO ()
+modifyClipboard_ = flip liftM getClipboard >=> setClipboard
+
+-- | Delete Clipboard contents.
+clearClipboard :: IO ()
+clearClipboard = setClipboard ""
+
+
+-- | Dispatch on the type of the Operating System.
+dispatch cmd = execute (resolveOS os) cmd
+    where
+        resolveOS "linux"   = Linux
+        resolveOS "darwin"  = Darwin
+#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
+        resolveOS "mingw32" = Windows
+#endif
+        resolveOS unknownOS = throw . UnsupportedOS $ unknownOS
+
+
+-- | Platform-specific execution.
+execute :: Platform -> Command a -> a
+
+execute Linux cmd@GetClipboard     = resolveLinuxApp cmd >>= flip withExternalApp readOutHandle
+execute Linux cmd@(SetClipboard s) = resolveLinuxApp cmd >>= flip withExternalApp (writeInHandle s)
+
+execute Darwin GetClipboard     = withExternalApp "pbpaste" readOutHandle
+execute Darwin (SetClipboard s) = withExternalApp "pbcopy" $ writeInHandle s
+
+-- | Windows: use WinAPI
+#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
+execute Windows GetClipboard =
+    bracket_ (openClipboard nullPtr) closeClipboard $ do
+        isText <- isClipboardFormatAvailable cF_TEXT
+        if isText
+            then do
+                h <- getClipboardData cF_TEXT
+                bracket (globalLock h) globalUnlock $ peekCAString . castPtr
+            else throwIO NoTextualData
+
+execute Windows (SetClipboard s) =
+    withCAString s $ \cstr -> do
+        mem <- globalAlloc gHND memSize
+        bracket (globalLock mem) globalUnlock $ \space -> do
+            copyMemory space (castPtr cstr) memSize
+            bracket_ (openClipboard nullPtr) closeClipboard $ do
+                emptyClipboard
+                setClipboardData cF_TEXT space
+                return ()
+    where
+        memSize = genericLength s + 1
+#endif
+
+
+-- | Determine the correct Linux command.
+resolveLinuxApp :: Command a -> IO String
+resolveLinuxApp cmd = decode cmd <$> chooseFirstApp ["xsel", "xclip"] 
+    where
+        decode GetClipboard "xsel"      = "xsel -o"
+        decode (SetClipboard _) "xsel"  = "xsel -i"
+        decode GetClipboard "xclip"     = "xclip -selection c -o"
+        decode (SetClipboard _) "xclip" = "xclip -selection c"
+
+-- | Run external app and apply action to the file handles.
+withExternalApp :: String -> IOAction a -> IO a 
+withExternalApp app action = 
+    bracket (runInteractiveCommand app)
+            (\(inp, outp, stderr, pid) -> mapM_ hClose [inp, outp, stderr] >> waitForProcess pid)
+            (\(inp, outp, _, _)        -> action (inp, outp))
+
+-- | Search for installed programs and return the first match.
+chooseFirstApp :: [String] -> IO String
+chooseFirstApp apps = do
+    results <- mapM whichCommand apps
+    maybe (throwIO $ MissingCommands apps)
+          return
+          (getFirst . mconcat $ map First results)
+
+-- | Check if cmd is installed by using the which command.
+whichCommand :: String -> IO (Maybe String)
+whichCommand cmd = do
+  (exitCode,_,_) <- readProcessWithExitCode "which" [cmd] ""
+  case exitCode of
+    ExitSuccess   -> return $ Just cmd
+    ExitFailure _ -> return Nothing
+
+readOutHandle :: IOAction String
+readOutHandle = hGetContents . stdout
+
+writeInHandle :: String -> IOAction ()
+writeInHandle s = flip hPutStr s . stdin
+
+stdin, stdout :: (StdIn, StdOut) -> Handle
+stdin = fst
+stdout = snd
+
diff --git a/tests/Tasty.hs b/tests/Tasty.hs
new file mode 100644
--- /dev/null
+++ b/tests/Tasty.hs
@@ -0,0 +1,45 @@
+import Test.Tasty
+import Test.Tasty.HUnit
+
+import System.Hclip
+
+
+main = defaultMain tests
+
+tests :: TestTree
+tests = testGroup "Tests" [unitTests]
+
+
+unitTests = testGroup "Unit tests"
+  [ testCase "Clear Clipboard" $ do
+      setClipboard "Haskell"
+      clearClipboard 
+      contents <- getClipboard
+      contents @?= ""
+
+  , testCase "Set Clipboard" $ do
+      clearClipboard 
+      setClipboard "Haskell"
+      contents <- getClipboard
+      contents @?= "Haskell"
+
+  , testCase "Get Clipboard" $ do
+      setClipboard "Haskell"
+      contents <- getClipboard
+      contents @?= "Haskell"
+
+  , testCase "Modify Clipboard" $ do
+      let f = reverse
+          s = "Haskell"
+      setClipboard s
+      modifyClipboard_ f
+      contents <- getClipboard
+      contents @?= (f s)
+
+  , testCase "Modify Clipboard and return new contents" $ do
+      let f = reverse
+          s = "Haskell"
+      setClipboard s
+      contents <- modifyClipboard f
+      contents @?= f s
+  ]