Make Control.Exception buildable by nhc98.

[haskell-directory.git] / Control / Monad / Fix.hs

diff --git a/Control/Monad/Fix.hs b/Control/Monad/Fix.hs
index c2b1669..ea481d8 100644 (file)
--- a/Control/Monad/Fix.hs
+++ b/Control/Monad/Fix.hs
@@ -24,11 +24,8 @@ module Control.Monad.Fix (
 
 import Prelude
 import System.IO
-
--- | @'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
+import Control.Monad.Instances ()
+import Data.Function (fix)
 
 -- | Monads having fixed points with a \'knot-tying\' semantics.
 -- Instances of 'MonadFix' should satisfy the following laws:
@@ -37,7 +34,7 @@ fix f = let x = f x in x
 --     @'mfix' ('return' . h)  =  'return' ('fix' h)@
 --
 -- [/left shrinking/ (or /tightening/)]
---     @'mfix' (\\x -> a >>= \\y -> f x y)  =  \\y -> 'mfix' (\\x -> f x y)@
+--     @'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))@,
@@ -71,3 +68,6 @@ instance MonadFix [] where
 -- IO:
 instance MonadFix IO where
     mfix = fixIO 
+
+instance MonadFix ((->) r) where
+    mfix f = \ r -> let a = f a r in a