Remove non-directory stuff (of base), and rename package to "directory"

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

diff --git a/Control/Monad/Fix.hs b/Control/Monad/Fix.hs
deleted file mode 100644 (file)
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--- a/Control/Monad/Fix.hs
+++ /dev/null
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------------------------------------------------------------------------------
--- |
--- Module      :  Control.Monad.Fix
--- Copyright   :  (c) Andy Gill 2001,
---               (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
---
--- Monadic fixpoints.
---
--- For a detailed discussion, see Levent Erkok's thesis,
--- /Value Recursion in Monadic Computations/, Oregon Graduate Institute, 2002.
---
------------------------------------------------------------------------------
-
-module Control.Monad.Fix (
-       MonadFix(
-          mfix -- :: (a -> m a) -> m a
-         ),
-       fix     -- :: (a -> a) -> a
-  ) where
-
-import Prelude
-import System.IO
-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:
---
--- [/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 (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 
-
-instance MonadFix ((->) r) where
-    mfix f = \ r -> let a = f a r in a