1 files changed, 75 insertions, 0 deletions
diff --git a/libraries/base/Data/Maybe.hs b/libraries/base/Data/Maybe.hs
new file mode 100644
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+++ b/libraries/base/Data/Maybe.hs
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+{-# OPTIONS -fno-implicit-prelude #-}
+-----------------------------------------------------------------------------
+-- 
+-- Module      :  Data.Maybe
+-- Copyright   :  (c) The University of Glasgow 2001
+-- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- 
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  experimental
+-- Portability :  non-portable
+--
+-- $Id: Maybe.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
+--
+-- The Maybe type, and associated operations.
+--
+-----------------------------------------------------------------------------
+
+module Data.Maybe
+   (
+     Maybe(Nothing,Just)-- instance of: Eq, Ord, Show, Read,
+			--		Functor, Monad, MonadPlus
+
+   , maybe		-- :: b -> (a -> b) -> Maybe a -> b
+
+   , isJust		-- :: Maybe a -> Bool
+   , isNothing		-- :: Maybe a -> Bool
+   , fromJust		-- :: Maybe a -> a
+   , fromMaybe		-- :: a -> Maybe a -> a
+   , listToMaybe        -- :: [a] -> Maybe a
+   , maybeToList	-- :: Maybe a -> [a]
+   , catMaybes		-- :: [Maybe a] -> [a]
+   , mapMaybe		-- :: (a -> Maybe b) -> [a] -> [b]
+   ) where
+
+#ifdef __GLASGOW_HASKELL__
+import GHC.Err	( error )
+import GHC.List
+import GHC.Maybe
+import GHC.Base
+#endif
+
+isJust         :: Maybe a -> Bool
+isJust Nothing = False
+isJust _       = True
+
+isNothing         :: Maybe a -> Bool
+isNothing Nothing = True
+isNothing _       = False
+
+fromJust          :: Maybe a -> a
+fromJust Nothing  = error "Maybe.fromJust: Nothing" -- yuck
+fromJust (Just x) = x
+
+fromMaybe     :: a -> Maybe a -> a
+fromMaybe d x = case x of {Nothing -> d;Just v  -> v}
+
+maybeToList            :: Maybe a -> [a]
+maybeToList  Nothing   = []
+maybeToList  (Just x)  = [x]
+
+listToMaybe           :: [a] -> Maybe a
+listToMaybe []        =  Nothing
+listToMaybe (a:_)     =  Just a
+ 
+catMaybes              :: [Maybe a] -> [a]
+catMaybes ls = [x | Just x <- ls]
+
+mapMaybe          :: (a -> Maybe b) -> [a] -> [b]
+mapMaybe _ []     = []
+mapMaybe f (x:xs) =
+ let rs = mapMaybe f xs in
+ case f x of
+  Nothing -> rs
+  Just r  -> r:rs
+