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diff --git a/Control/Monad/Fix.hs b/Control/Monad/Fix.hs
index 53d5c42..e04a7f6 100644
--- a/Control/Monad/Fix.hs
+++ b/Control/Monad/Fix.hs
@@ -2,20 +2,17 @@
 -- |
 -- Module      :  Control.Monad.Fix
 -- Copyright   :  (c) Andy Gill 2001,
---		  (c) Oregon Graduate Institute of Science and Technology, 2001
--- License     :  BSD-style (see the file libraries/core/LICENSE)
--- 
+-- 		  (c) Oregon Graduate Institute of Science and Technology, 2002
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
 -- Portability :  portable
 --
--- The Fix monad.
+-- Monadic fixpoints.
+--
+-- For a detailed discussion, see Levent Erkok's thesis,
+-- /Value Recursion in Monadic Computations/, Oregon Graduate Institute, 2002.
 --
---	  Inspired by the paper
---	  /Functional Programming with Overloading and
---	      Higher-Order Polymorphism/, 
---	    Mark P Jones (<http://www.cse.ogi.edu/~mpj>)
---		  Advanced School of Functional Programming, 1995.
 -----------------------------------------------------------------------------
 
 module Control.Monad.Fix (
@@ -27,20 +24,54 @@ module Control.Monad.Fix (
 
 import Prelude
 import System.IO
+import Control.Monad.Instances ()
 
+-- | @'fix' f@ is the least fixed point of the function @f@,
+-- i.e. the least defined @x@ such that @f x = x@.
 fix :: (a -> a) -> a
 fix f = let x = f x in x
 
+-- | Monads having fixed points with a \'knot-tying\' semantics.
+-- Instances of 'MonadFix' should satisfy the following laws:
+--
+-- [/purity/]
+--	@'mfix' ('return' . h)  =  'return' ('fix' h)@
+--
+-- [/left shrinking/ (or /tightening/)]
+--	@'mfix' (\\x -> a >>= \\y -> f x y)  =  a >>= \\y -> 'mfix' (\\x -> f x y)@
+--
+-- [/sliding/]
+--	@'mfix' ('Control.Monad.liftM' h . f)  =  'Control.Monad.liftM' h ('mfix' (f . h))@,
+--	for strict @h@.
+--
+-- [/nesting/]
+--	@'mfix' (\\x -> 'mfix' (\\y -> f x y))  =  'mfix' (\\x -> f x x)@
+--
+-- This class is used in the translation of the recursive @do@ notation
+-- supported by GHC and Hugs.
 class (Monad m) => MonadFix m where
+	-- | The fixed point of a monadic computation.
+	-- @'mfix' f@ executes the action @f@ only once, with the eventual
+	-- output fed back as the input.  Hence @f@ should not be strict,
+	-- for then @'mfix' f@ would diverge.
 	mfix :: (a -> m a) -> m a
 
+-- Instances of MonadFix for Prelude monads
+
+-- Maybe:
 instance MonadFix Maybe where
-	mfix f = let
-		a = f $ case a of
-			Just x -> x
-			_      -> error "empty mfix argument"
-		in a
+    mfix f = let a = f (unJust a) in a
+             where unJust (Just x) = x
+
+-- List:
+instance MonadFix [] where
+    mfix f = case fix (f . head) of
+               []    -> []
+               (x:_) -> x : mfix (tail . f)
 
+-- IO:
 instance MonadFix IO where
-	mfix = fixIO
+    mfix = fixIO 
 
+instance MonadFix ((->) r) where
+    mfix f = \ r -> let a = f a r in a