diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2015, Alej Cabrera
+Copyright (c) 2016, Allele Dev
 
 All rights reserved.
 
@@ -13,7 +13,7 @@
       disclaimer in the documentation and/or other materials provided
       with the distribution.
 
-    * Neither the name of Alej Cabrera nor the names of other
+    * Neither the name of Allele Dev nor the names of other
       contributors may be used to endorse or promote products derived
       from this software without specific prior written permission.
 
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -57,25 +57,26 @@
 --------------------------------------------------------------------------------
 runTeletype :: Eff '[Teletype] w -> IO w
 runTeletype (Val x) = return x
-runTeletype (E u q) = case decomp u of
-              Right (PutStrLn msg) -> putStrLn msg  >> runTeletype (qApp q ())
-              Right GetLine        -> getLine      >>= \s -> runTeletype (qApp q s)
-              Right ExitSuccess    -> exitSuccess
-              Left  _              -> error "This cannot happen"
+runTeletype (E u q) = case extract u of
+              (PutStrLn msg) -> putStrLn msg  >> runTeletype (qApp q ())
+              GetLine        -> getLine      >>= \s -> runTeletype (qApp q s)
+              ExitSuccess    -> exitSuccess
 
 --------------------------------------------------------------------------------
                         -- Pure Interpreter --
 --------------------------------------------------------------------------------
 runTeletypePure :: [String] -> Eff '[Teletype] w -> [String]
-runTeletypePure inputs req = reverse (go inputs req [])
-  where go :: [String] -> Eff '[Teletype] w -> [String] -> [String]
-        go _      (Val _) acc = acc
-        go []     _       acc = acc
-        go (x:xs) (E u q) acc = case decomp u of
-          Right (PutStrLn msg) -> go (x:xs) (qApp q ()) (msg:acc)
-          Right GetLine        -> go xs     (qApp q x) acc
-          Right ExitSuccess    -> go xs     (Val ())   acc
-          Left _               -> go xs     (Val ())   acc
+runTeletypePure inputs req =
+  reverse . snd $ run (handleRelayS (inputs, []) (\s _ -> pure s) go req)
+  where
+    go :: ([String], [String])
+       -> Teletype v
+       -> (([String], [String]) -> Arr '[] v ([String], [String]))
+       -> Eff '[] ([String], [String])
+    go (is, os) (PutStrLn msg) q = q (is, msg : os) ()
+    go (i:is, os) GetLine q = q (is, os) i
+    go ([], _) GetLine _ = error "Not enough lines"
+    go (_, os) ExitSuccess _ = pure ([], os)
 ```
 
 # Contributing
diff --git a/bench/Core.hs b/bench/Core.hs
--- a/bench/Core.hs
+++ b/bench/Core.hs
@@ -5,8 +5,16 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE CPP #-}
 module Main where
 
+#if __GLASGOW_HASKELL__ <= 708
+import Control.Applicative
+import qualified Control.Monad.Error as MTL
+#else
+import qualified Control.Monad.Except as MTL
+#endif
+
 import Control.Monad
 import Control.Monad.Freer
 import Control.Monad.Freer.Internal
@@ -17,7 +25,6 @@
 import Criterion
 import Criterion.Main
 import qualified Control.Monad.State as MTL
-import qualified Control.Monad.Except as MTL
 import qualified Control.Monad.Free as Free
 
 --------------------------------------------------------------------------------
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,9 @@
+# 0.2.4.0 (November 25, 2016)
+
+* Internal reorg
+  * In particular, hide implementation details in Union.Internal
+  * Rewrite interpreters in terms of `extract` instead of `decomp`
+
 # 0.2.3.0 (June 25, 2016)
 
 * Add GHC 8 support
diff --git a/examples/src/Main.hs b/examples/src/Main.hs
--- a/examples/src/Main.hs
+++ b/examples/src/Main.hs
@@ -1,18 +1,22 @@
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
 module Main where
 
 import Control.Monad.Freer
 import Teletype
 
-runner :: Eff '[Teletype] ()
+runner :: (Member Teletype r) => Eff r ()
 runner = do
   x <- getLine'
+  _ <- getLine'
   putStrLn' x
-  y <- getLine'
-  putStrLn' y
+  z <- getLine'
+  putStrLn' z
+  putStrLn' x
+  putStrLn' x
 
 main :: IO ()
 main = do
-  let xs = runTeletypePure ["cat", "fish"] runner
+  let xs = runTeletypePure ["cat", "fish", "dog", "bird"] runner
   print xs
   runTeletype runner
diff --git a/examples/src/Teletype.hs b/examples/src/Teletype.hs
--- a/examples/src/Teletype.hs
+++ b/examples/src/Teletype.hs
@@ -5,7 +5,6 @@
 module Teletype where
 
 import Control.Monad.Freer
-import Control.Monad.Freer.Internal
 import System.Exit hiding (ExitSuccess)
 
 --------------------------------------------------------------------------------
@@ -28,24 +27,27 @@
 --------------------------------------------------------------------------------
                      -- Effectful Interpreter --
 --------------------------------------------------------------------------------
-runTeletype :: Eff '[Teletype] w -> IO w
-runTeletype (Val x) = return x
-runTeletype (E u q) = case decomp u of
-              Right (PutStrLn msg) -> putStrLn msg  >> runTeletype (qApp q ())
-              Right GetLine        -> getLine      >>= \s -> runTeletype (qApp q s)
-              Right ExitSuccess    -> exitSuccess
-              Left  _              -> error "This cannot happen"
+runTeletype :: Eff '[Teletype, IO] w -> IO w
+runTeletype req = runM (handleRelay pure go req)
+  where
+   go :: Teletype v -> Arr '[IO] v w -> Eff '[IO] w
+   go (PutStrLn msg) q = send (putStrLn msg) >>= q
+   go GetLine q = send getLine >>= q
+   go ExitSuccess q = send exitSuccess >>= q
 
 --------------------------------------------------------------------------------
                         -- Pure Interpreter --
 --------------------------------------------------------------------------------
 runTeletypePure :: [String] -> Eff '[Teletype] w -> [String]
-runTeletypePure inputs req = reverse (go inputs req [])
-  where go :: [String] -> Eff '[Teletype] w -> [String] -> [String]
-        go _      (Val _) acc = acc
-        go []     _       acc = acc
-        go (x:xs) (E u q) acc = case decomp u of
-          Right (PutStrLn msg) -> go (x:xs) (qApp q ()) (msg:acc)
-          Right GetLine        -> go xs     (qApp q x) acc
-          Right ExitSuccess    -> go xs     (Val ())   acc
-          Left _               -> go xs     (Val ())   acc
+runTeletypePure inputs req =
+  reverse . snd $ run (handleRelayS (inputs, []) (\s _ -> pure s) go req)
+  where
+    go
+      :: ([String], [String])
+      -> Teletype v
+      -> (([String], [String]) -> Arr '[] v ([String], [String]))
+      -> Eff '[] ([String], [String])
+    go (is, os) (PutStrLn msg) q = q (is, msg : os) ()
+    go (i:is, os) GetLine q = q (is, os) i
+    go ([], _) GetLine _ = error "Not enough lines"
+    go (_, os) ExitSuccess _ = pure ([], os)
diff --git a/freer.cabal b/freer.cabal
--- a/freer.cabal
+++ b/freer.cabal
@@ -1,5 +1,5 @@
 name:                freer
-version:             0.2.3.0
+version:             0.2.4.0
 synopsis:            Implementation of the Freer Monad
 license:             BSD3
 license-file:        LICENSE
@@ -48,13 +48,14 @@
                      , Control.Monad.Freer.Writer
                      , Data.FTCQueue
                      , Data.Open.Union
+                     , Data.Open.Union.Internal
 
   build-depends:       base >=4.7 && <5
   hs-source-dirs:      src
   ghc-options:         -Wall
   default-language:    Haskell2010
 
-executable examples
+executable freer-examples
   main-is:             Main.hs
   other-modules:       Common
                      , Coroutine
diff --git a/src/Control/Monad/Freer.hs b/src/Control/Monad/Freer.hs
--- a/src/Control/Monad/Freer.hs
+++ b/src/Control/Monad/Freer.hs
@@ -1,9 +1,12 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE RankNTypes #-}
 {-|
 Module      : Control.Monad.Freer
 Description : Freer - an extensible effects library
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
@@ -13,7 +16,12 @@
   Members,
   Eff,
   run,
+  runM,
+  runNat,
+  handleRelay,
+  handleRelayS,
   send,
+  Arr,
 
   NonDetEff(..),
   makeChoiceA,
@@ -21,3 +29,9 @@
 ) where
 
 import Control.Monad.Freer.Internal
+
+runNat
+  :: forall m r e w.
+     (Member m r)
+  => (forall a. e a -> m a) -> Eff (e ': r) w -> Eff r w
+runNat f = handleRelay pure (\v -> (send (f v) >>=))
diff --git a/src/Control/Monad/Freer/Coroutine.hs b/src/Control/Monad/Freer/Coroutine.hs
--- a/src/Control/Monad/Freer/Coroutine.hs
+++ b/src/Control/Monad/Freer/Coroutine.hs
@@ -6,9 +6,9 @@
 {-|
 Module      : Control.Monad.Freer.Coroutine
 Description : Composable coroutine effects layer.
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : broken
 Portability : POSIX
 
diff --git a/src/Control/Monad/Freer/Cut.hs b/src/Control/Monad/Freer/Cut.hs
--- a/src/Control/Monad/Freer/Cut.hs
+++ b/src/Control/Monad/Freer/Cut.hs
@@ -5,9 +5,9 @@
 {-|
 Module      : Control.Monad.Freer.Cut
 Description : An implementation of logical Cut
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : broken
 Portability : POSIX
 
diff --git a/src/Control/Monad/Freer/Exception.hs b/src/Control/Monad/Freer/Exception.hs
--- a/src/Control/Monad/Freer/Exception.hs
+++ b/src/Control/Monad/Freer/Exception.hs
@@ -5,9 +5,9 @@
 {-|
 Module      : Control.Monad.Freer.Exception
 Description : An Exception effect and handler.
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
diff --git a/src/Control/Monad/Freer/Fresh.hs b/src/Control/Monad/Freer/Fresh.hs
--- a/src/Control/Monad/Freer/Fresh.hs
+++ b/src/Control/Monad/Freer/Fresh.hs
@@ -6,9 +6,9 @@
 {-|
 Module      : Control.Monad.Freer.Fresh
 Description : Generation of fresh integers as an effect.
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : broken
 Portability : POSIX
 
diff --git a/src/Control/Monad/Freer/Internal.hs b/src/Control/Monad/Freer/Internal.hs
--- a/src/Control/Monad/Freer/Internal.hs
+++ b/src/Control/Monad/Freer/Internal.hs
@@ -14,9 +14,9 @@
 {-|
 Module      : Control.Monad.Freer.Internal
 Description : Mechanisms to make effects work
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
@@ -44,6 +44,7 @@
 
   decomp,
   tsingleton,
+  extract,
 
   qApp,
   qComp,
@@ -137,9 +138,8 @@
 -- This is useful for plugging in traditional transformer stacks.
 runM :: Monad m => Eff '[m] w -> m w
 runM (Val x) = return x
-runM (E u q) = case decomp u of
-  Right mb -> mb >>= runM . qApp q
-  Left _   -> error "Internal:runM - This (Left) should never happen"
+runM (E u q) = case extract u of
+  mb -> mb >>= runM . qApp q
 
 -- the other case is unreachable since Union [] a cannot be
 -- constructed. Therefore, run is a total function if its argument
diff --git a/src/Control/Monad/Freer/Reader.hs b/src/Control/Monad/Freer/Reader.hs
--- a/src/Control/Monad/Freer/Reader.hs
+++ b/src/Control/Monad/Freer/Reader.hs
@@ -7,9 +7,9 @@
 {-|
 Module      : Control.Monad.Freer.Reader
 Description : Reader effects, for encapsulating an environment
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
diff --git a/src/Control/Monad/Freer/State.hs b/src/Control/Monad/Freer/State.hs
--- a/src/Control/Monad/Freer/State.hs
+++ b/src/Control/Monad/Freer/State.hs
@@ -7,9 +7,9 @@
 {-|
 Module      : Control.Monad.Freer.State
 Description : State effects, for state-carrying computations.
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
diff --git a/src/Control/Monad/Freer/StateRW.hs b/src/Control/Monad/Freer/StateRW.hs
--- a/src/Control/Monad/Freer/StateRW.hs
+++ b/src/Control/Monad/Freer/StateRW.hs
@@ -6,9 +6,9 @@
 {-|
 Module      : Control.Monad.Freer.StateRW
 Description : State effects in terms of Reader/Writer
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
diff --git a/src/Control/Monad/Freer/Trace.hs b/src/Control/Monad/Freer/Trace.hs
--- a/src/Control/Monad/Freer/Trace.hs
+++ b/src/Control/Monad/Freer/Trace.hs
@@ -6,9 +6,9 @@
 {-|
 Module      : Control.Monad.Freer.Trace
 Description : Composable Trace effects
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
@@ -38,6 +38,5 @@
 -- | An IO handler for Trace effects
 runTrace :: Eff '[Trace] w -> IO w
 runTrace (Val x) = return x
-runTrace (E u q) = case decomp u of
-     Right (Trace s) -> putStrLn s >> runTrace (qApp q ())
-     Left _          -> error "runTrace:Left - This should never happen"
+runTrace (E u q) = case extract u of
+     Trace s -> putStrLn s >> runTrace (qApp q ())
diff --git a/src/Control/Monad/Freer/Writer.hs b/src/Control/Monad/Freer/Writer.hs
--- a/src/Control/Monad/Freer/Writer.hs
+++ b/src/Control/Monad/Freer/Writer.hs
@@ -2,13 +2,13 @@
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE DataKinds #-}
-
+{-# LANGUAGE CPP #-}
 {-|
 Module      : Control.Monad.Freer.Writer
 Description : Composable Writer effects -
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
@@ -23,6 +23,10 @@
   tell,
   runWriter
 ) where
+
+#if __GLASGOW_HASKELL__ <= 708
+import Data.Monoid
+#endif
 
 import Control.Monad.Freer.Internal
 
diff --git a/src/Data/FTCQueue.hs b/src/Data/FTCQueue.hs
--- a/src/Data/FTCQueue.hs
+++ b/src/Data/FTCQueue.hs
@@ -3,9 +3,9 @@
 {-|
 Module      : Data.FTCQueue
 Description : Fast type-aligned queue optimized to effectful functions.
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
diff --git a/src/Data/Open/Union.hs b/src/Data/Open/Union.hs
--- a/src/Data/Open/Union.hs
+++ b/src/Data/Open/Union.hs
@@ -10,9 +10,9 @@
 {-|
 Module      : Data.Open.Union
 Description : Open unions (type-indexed co-products) for extensible effects.
-Copyright   : Alej Cabrera 2015
+Copyright   : Allele Dev 2016
 License     : BSD-3
-Maintainer  : cpp.cabrera@gmail.com
+Maintainer  : allele.dev@gmail.com
 Stability   : experimental
 Portability : POSIX
 
@@ -31,72 +31,22 @@
 -}
 
 module Data.Open.Union (
+  module Data.Open.Union,
   Union,
+  Member(..),
   decomp,
   weaken,
-  Member(..),
-  Members
+  extract,
+  Functor(..)
 ) where
 
 import GHC.Exts
+import Data.Open.Union.Internal
 
 --------------------------------------------------------------------------------
                            -- Interface --
 --------------------------------------------------------------------------------
-data Union (r :: [ * -> * ]) v where
-  UNow  :: t v -> Union (t ': r) v
-  UNext :: Union r v -> Union (any ': r) v
-
-{-# INLINE decomp #-}
-decomp :: Union (t ': r) v -> Either (Union r v) (t v)
-decomp (UNow x)  = Right x
-decomp (UNext v) = Left v
-
-{-# INLINE weaken #-}
-weaken :: Union r w -> Union (any ': r) w
-weaken = UNext
-
-class (Member' t r (FindElem t r)) => Member t r where
-  inj :: t v -> Union r v
-  prj :: Union r v -> Maybe (t v)
-
-instance (Member' t r (FindElem t r)) => Member t r where
-  inj = inj' (P :: P (FindElem t r))
-  prj = prj' (P :: P (FindElem t r))
-
 type family Members m r :: Constraint where
   Members (t ': c) r = (Member t r, Members c r)
   Members '[] r = ()
 
---------------------------------------------------------------------------------
-                         -- Implementation --
---------------------------------------------------------------------------------
-data Nat = S Nat | Z
-data P (n :: Nat) = P
-
--- injecting/projecting at a specified position P n
-class Member' t r (n :: Nat) where
-  inj' :: P n -> t v -> Union r v
-  prj' :: P n -> Union r v -> Maybe (t v)
-
-instance (r ~ (t ': r')) => Member' t r 'Z where
-  inj' _ = UNow
-  prj' _ (UNow x) = Just x
-  prj' _ _        = Nothing
-
-instance (r ~ (t' ': r'), Member' t r' n) => Member' t r ('S n) where
-  inj' _ = UNext . inj' (P::P n)
-  prj' _ (UNow _)  = Nothing
-  prj' _ (UNext x) = prj' (P::P n) x
-
--- Find an index of an element in a `list'
--- The element must exist
--- This closed type family disambiguates otherwise overlapping
--- instances
-type family FindElem (t :: * -> *) r :: Nat where
-  FindElem t (t ': r)    = 'Z
-  FindElem t (any ': r)  = 'S (FindElem t r)
-
-type family EQU (a :: k) (b :: k) :: Bool where
-  EQU a a = 'True
-  EQU a b = 'False
diff --git a/src/Data/Open/Union/Internal.hs b/src/Data/Open/Union/Internal.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Open/Union/Internal.hs
@@ -0,0 +1,77 @@
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE DataKinds, PolyKinds #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+module Data.Open.Union.Internal where
+
+data Union (r :: [ * -> * ]) v where
+  UNow  :: t v -> Union (t ': r) v
+  UNext :: Union (t ': r) v -> Union (any ': t ': r) v
+
+data Nat = S Nat | Z
+data P (n :: Nat) = P
+
+-- injecting/projecting at a specified position P n
+class Member' t r (n :: Nat) where
+  inj' :: P n -> t v -> Union r v
+  prj' :: P n -> Union r v -> Maybe (t v)
+
+instance (r ~ (t ': r')) => Member' t r 'Z where
+  inj' _ = UNow
+  prj' _ (UNow x) = Just x
+  prj' _ _        = Nothing
+
+instance (r ~ (t' ': r' : rs'), Member' t (r' : rs') n) => Member' t r ('S n) where
+  inj' _ = UNext . inj' (P::P n)
+  prj' _ (UNow _)  = Nothing
+  prj' _ (UNext x) = prj' (P::P n) x
+
+-- Find an index of an element in a `list'
+-- The element must exist
+-- This closed type family disambiguates otherwise overlapping
+-- instances
+type family FindElem (t :: * -> *) r :: Nat where
+  FindElem t (t ': r)    = 'Z
+  FindElem t (any ': r)  = 'S (FindElem t r)
+
+type family EQU (a :: k) (b :: k) :: Bool where
+  EQU a a = 'True
+  EQU a b = 'False
+
+--------------------------------------------------------------------------------
+                           -- Interface --
+--------------------------------------------------------------------------------
+
+{-# INLINE decomp #-}
+decomp :: Union (t ': r) v -> Either (Union r v) (t v)
+decomp (UNow x)  = Right x
+decomp (UNext v) = Left v
+
+{-# INLINE weaken #-}
+weaken :: Union (t ': r) w -> Union (any ': t ': r) w
+weaken = UNext
+
+{-# INLINE extract #-}
+extract :: Union '[t] v -> t v
+extract (UNow x)  = x
+
+
+class (Member' t r (FindElem t r)) => Member t r where
+  inj :: t v -> Union r v
+  prj :: Union r v -> Maybe (t v)
+
+instance (Member' t r (FindElem t r)) => Member t r where
+  inj = inj' (P :: P (FindElem t r))
+  prj = prj' (P :: P (FindElem t r))
+
+instance (Functor f) => Functor (Union '[f]) where
+  fmap f = inj . fmap f . extract
+instance (Functor f1, Functor (Union (f2 ': fs))) =>
+         Functor (Union (f1 ': f2 ': fs)) where
+  fmap f = either (weaken . fmap f) (inj . fmap f) . decomp
+
+
diff --git a/tests/Tests.hs b/tests/Tests.hs
--- a/tests/Tests.hs
+++ b/tests/Tests.hs
@@ -1,4 +1,9 @@
+{-# LANGUAGE CPP #-}
 module Main where
+
+#if __GLASGOW_HASKELL__ <= 708
+import Control.Applicative
+#endif
 
 import Control.Monad.Freer
 
diff --git a/tests/Tests/Coroutine.hs b/tests/Tests/Coroutine.hs
--- a/tests/Tests/Coroutine.hs
+++ b/tests/Tests/Coroutine.hs
@@ -1,9 +1,14 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE DataKinds #-}
-
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE CPP #-}
 module Tests.Coroutine (
   runTestCoroutine
 ) where
+
+#if __GLASGOW_HASKELL__ <= 708
+import Control.Applicative
+#endif
 
 import Control.Monad
 import Control.Monad.Freer
diff --git a/tests/Tests/Exception.hs b/tests/Tests/Exception.hs
--- a/tests/Tests/Exception.hs
+++ b/tests/Tests/Exception.hs
@@ -1,6 +1,8 @@
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE ConstraintKinds #-}
+
 module Tests.Exception (
   TooBig(..),
 
diff --git a/tests/Tests/Reader.hs b/tests/Tests/Reader.hs
--- a/tests/Tests/Reader.hs
+++ b/tests/Tests/Reader.hs
@@ -1,9 +1,15 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE CPP #-}
 module Tests.Reader (
   testReader,
   testMultiReader,
   testLocal
 ) where
+
+#if __GLASGOW_HASKELL__ <= 708
+import Control.Applicative
+#endif
 
 import Control.Monad.Freer
 import Control.Monad.Freer.Reader