X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FMaybe.hs;h=4b7b67e305445c9c4f3201fd7282d78a393b5ce0;hb=f7a485978f04e84b086f1974b88887cc72d832d0;hp=06c7a25398d39db56e13dddf52d3b1830261b498;hpb=7f1f4e7a695c402ddd3a1dc2cc7114e649a78ebc;p=ghc-base.git

diff --git a/Data/Maybe.hs b/Data/Maybe.hs
index 06c7a25..4b7b67e 100644
--- a/Data/Maybe.hs
+++ b/Data/Maybe.hs
@@ -1,15 +1,13 @@
 {-# OPTIONS -fno-implicit-prelude #-}
 -----------------------------------------------------------------------------
--- 
+-- |
 -- Module      :  Data.Maybe
 -- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
 -- 
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
--- Portability :  non-portable
---
--- $Id: Maybe.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
+-- Portability :  portable
 --
 -- The Maybe type, and associated operations.
 --
@@ -33,12 +31,36 @@ module Data.Maybe
    ) where
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.Err	( error )
-import GHC.List
-import GHC.Maybe
+import {-# SOURCE #-} GHC.Err ( error )
 import GHC.Base
 #endif
 
+-- ---------------------------------------------------------------------------
+-- The Maybe type, and instances
+
+data  Maybe a  =  Nothing | Just a	deriving (Eq, Ord)
+
+instance  Functor Maybe  where
+    fmap _ Nothing       = Nothing
+    fmap f (Just a)      = Just (f a)
+
+instance  Monad Maybe  where
+    (Just x) >>= k      = k x
+    Nothing  >>= _      = Nothing
+
+    (Just _) >>  k      = k
+    Nothing  >>  _      = Nothing
+
+    return              = Just
+    fail _		= Nothing
+
+-- ---------------------------------------------------------------------------
+-- Functions over Maybe
+
+maybe :: b -> (a -> b) -> Maybe a -> b
+maybe n _ Nothing  = n
+maybe _ f (Just x) = f x
+
 isJust         :: Maybe a -> Bool
 isJust Nothing = False
 isJust _       = True