diff --git a/.travis.yml b/.travis.yml
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,13 +6,17 @@
 
   # Try installing some of the build-deps with apt-get for speed.
   - travis/cabal-apt-install $mode
+  - cabal install packdeps packunused
 
 install:
   - cabal configure -flib-Werror $mode
-  - cabal build
+  - cabal build --ghc-options=-ddump-minimal-imports
 
 script:
-  - $script && hlint src --cpp-define HLINT
+  - $script
+  - hlint src --cpp-define HLINT
+  - packdeps comonad.cabal
+  - packunused
 
 notifications:
   irc:
diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,11 @@
+4.2
+---
+* `transformers 0.4` compatibility
+
+4.1
+---
+* Fixed the 'Typeable' instance for 'Cokleisli on GHC 7.8.1
+
 4.0.1
 -----
 * Fixes to avoid warnings on GHC 7.8.1
diff --git a/comonad.cabal b/comonad.cabal
--- a/comonad.cabal
+++ b/comonad.cabal
@@ -1,6 +1,6 @@
 name:          comonad
 category:      Control, Comonads
-version:       4.0.1
+version:       4.2
 license:       BSD3
 cabal-version: >= 1.10
 license-file:  LICENSE
@@ -45,10 +45,9 @@
     containers    >= 0.3     && < 0.6,
     contravariant >= 0.2.0.1 && < 1,
     distributive  >= 0.2.2   && < 1,
-    mtl           >= 2.0     && < 2.2,
     semigroups    >= 0.8.3.1 && < 1,
     tagged        >= 0.1     && < 1,
-    transformers  >= 0.2     && < 0.4
+    transformers  >= 0.2     && < 0.5
 
   exposed-modules:
     Control.Comonad
diff --git a/src/Control/Comonad.hs b/src/Control/Comonad.hs
--- a/src/Control/Comonad.hs
+++ b/src/Control/Comonad.hs
@@ -59,11 +59,7 @@
 import Data.Tree
 import Prelude hiding (id, (.))
 import Control.Monad.Fix
-#if __GLASGOW_HASKELL__ >= 707
--- Data.Typeable is redundant
-#else
 import Data.Typeable
-#endif
 
 infixl 4 <@, @>, <@@>, <@>, $>
 infixl 1 =>>
@@ -76,9 +72,11 @@
 I. Provide definitions for 'extract' and 'extend'
 satisfying these laws:
 
-> extend extract      = id
-> extract . extend f  = f
-> extend f . extend g = extend (f . extend g)
+@
+'extend' 'extract'      = 'id'
+'extract' . 'extend' f  = f
+'extend' f . 'extend' g = 'extend' (f . 'extend' g)
+@
 
 In this case, you may simply set 'fmap' = 'liftW'.
 
@@ -87,16 +85,20 @@
 that Cokleisli composition must be associative, and has extract for
 a unit:
 
-> f =>= extract   = f
-> extract =>= f   = f
-> (f =>= g) =>= h = f =>= (g =>= h)
+@
+f '=>=' 'extract'   = f
+'extract' '=>=' f   = f
+(f '=>=' g) '=>=' h = f '=>=' (g '=>=' h)
+@
 
 II. Alternately, you may choose to provide definitions for 'fmap',
 'extract', and 'duplicate' satisfying these laws:
 
-> extract . duplicate      = id
-> fmap extract . duplicate = id
-> duplicate . duplicate    = fmap duplicate . duplicate
+@
+'extract' . 'duplicate'      = 'id'
+'fmap' 'extract' . 'duplicate' = 'id'
+'duplicate' . 'duplicate'    = 'fmap' 'duplicate' . 'duplicate'
+@
 
 In this case you may not rely on the ability to define 'fmap' in
 terms of 'liftW'.
@@ -104,9 +106,11 @@
 You may of course, choose to define both 'duplicate' /and/ 'extend'.
 In that case you must also satisfy these laws:
 
-> extend f  = fmap f . duplicate
-> duplicate = extend id
-> fmap f    = extend (f . extract)
+@
+'extend' f  = 'fmap' f . 'duplicate'
+'duplicate' = 'extend' id
+'fmap' f    = 'extend' (f . 'extract')
+@
 
 These are the default definitions of 'extend' and 'duplicate' and
 the definition of 'liftW' respectively.
@@ -115,17 +119,23 @@
 
 class Functor w => Comonad w where
   -- |
-  -- > extract . fmap f = f . extract
+  -- @
+  -- 'extract' . 'fmap' f = f . 'extract'
+  -- @
   extract :: w a -> a
 
   -- |
-  -- > duplicate = extend id
-  -- > fmap (fmap f) . duplicate = duplicate . fmap f
+  -- @
+  -- 'duplicate' = 'extend' 'id'
+  -- 'fmap' ('fmap' f) . 'duplicate' = 'duplicate' . 'fmap' f
+  -- @
   duplicate :: w a -> w (w a)
   duplicate = extend id
 
   -- |
-  -- > extend f = fmap f . duplicate
+  -- @
+  -- 'extend' f = 'fmap' f . 'duplicate'
+  -- @
   extend :: (w a -> b) -> w a -> w b
   extend f = fmap f . duplicate
 
@@ -175,24 +185,30 @@
 --
 -- Mathematically, it is a strong lax symmetric semi-monoidal comonad on the
 -- category @Hask@ of Haskell types. That it to say that @w@ is a strong lax
--- symmetric semi-monoidal functor on Hask, where both extract and duplicate are
+-- symmetric semi-monoidal functor on Hask, where both 'extract' and 'duplicate' are
 -- symmetric monoidal natural transformations.
 --
 -- Laws:
 --
--- > (.) <$> u <@> v <@> w = u <@> (v <@> w)
--- > extract (p <@> q) = extract p (extract q)
--- > duplicate (p <@> q) = (<@>) <$> duplicate p <@> duplicate q
+-- @
+-- ('.') '<$>' u '<@>' v '<@>' w = u '<@>' (v '<@>' w)
+-- 'extract' (p '<@>' q) = 'extract' p ('extract' q)
+-- 'duplicate' (p '<@>' q) = ('<@>') '<$>' 'duplicate' p '<@>' 'duplicate' q
+-- @
 --
--- If our type is both a ComonadApply and Applicative we further require
+-- If our type is both a 'ComonadApply' and 'Applicative' we further require
 --
--- > (<*>) = (<@>)
+-- @
+-- ('<*>') = ('<@>')
+-- @
 --
 -- Finally, if you choose to define ('<@') and ('@>'), the results of your
 -- definitions should match the following laws:
 --
--- > a @> b = const id <$> a <@> b
--- > a <@ b = const <$> a <@> b
+-- @
+-- a '@>' b = 'const' 'id' '<$>' a '<@>' b
+-- a '<@' b = 'const' '<$>' a '<@>' b
+-- @
 
 class Comonad w => ComonadApply w where
   (<@>) :: w (a -> b) -> w a -> w b
@@ -232,7 +248,13 @@
 -- | A suitable default definition for 'fmap' for a 'Comonad'.
 -- Promotes a function to a comonad.
 --
--- > fmap f = liftW f = extend (f . extract)
+-- You can only safely use to define 'fmap' if your 'Comonad'
+-- defined 'extend', not just 'duplicate', since defining
+-- 'extend' in terms of duplicate uses 'fmap'!
+--
+-- @
+-- 'fmap' f = 'liftW' f = 'extend' (f . 'extract')
+-- @
 liftW :: Comonad w => (a -> b) -> w a -> w b
 liftW f = extend (f . extract)
 {-# INLINE liftW #-}
@@ -256,12 +278,12 @@
 (<<=) = extend
 {-# INLINE (<<=) #-}
 
--- | Right-to-left Cokleisli composition
+-- | Right-to-left 'Cokleisli' composition
 (=<=) :: Comonad w => (w b -> c) -> (w a -> b) -> w a -> c
 f =<= g = f . extend g
 {-# INLINE (=<=) #-}
 
--- | Left-to-right Cokleisli composition
+-- | Left-to-right 'Cokleisli' composition
 (=>=) :: Comonad w => (w a -> b) -> (w b -> c) -> w a -> c
 f =>= g = g . extend f
 {-# INLINE (=>=) #-}
@@ -271,21 +293,20 @@
 (<@@>) = liftW2 (flip id)
 {-# INLINE (<@@>) #-}
 
--- | Lift a binary function into a comonad with zipping
+-- | Lift a binary function into a 'Comonad' with zipping
 liftW2 :: ComonadApply w => (a -> b -> c) -> w a -> w b -> w c
 liftW2 f a b = f <$> a <@> b
 {-# INLINE liftW2 #-}
 
--- | Lift a ternary function into a comonad with zipping
+-- | Lift a ternary function into a 'Comonad' with zipping
 liftW3 :: ComonadApply w => (a -> b -> c -> d) -> w a -> w b -> w c -> w d
 liftW3 f a b c = f <$> a <@> b <@> c
 {-# INLINE liftW3 #-}
 
 -- | The 'Cokleisli' 'Arrow's of a given 'Comonad'
 newtype Cokleisli w a b = Cokleisli { runCokleisli :: w a -> b }
-
 #if __GLASGOW_HASKELL__ >= 707
--- instance Typeable (Cokleisli w) derived automatically
+  deriving Typeable
 #else
 #ifdef __GLASGOW_HASKELL__
 instance Typeable1 w => Typeable2 (Cokleisli w) where