X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FEither.hs;h=0c5e15347883878eca0ee28534ecd727d1ef24b5;hb=b875ec7b3b799bf19841ca1adf23f6d3e8b3a8f6;hp=20dfe47ef5f745ed7b8d0a28dec615fac03e4ed8;hpb=d9e5fa673b75cdffbcd0e85cdcc98d706acbb29a;p=haskell-directory.git

diff --git a/Data/Either.hs b/Data/Either.hs
index 20dfe47..0c5e153 100644
--- a/Data/Either.hs
+++ b/Data/Either.hs
@@ -1,16 +1,14 @@
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -fno-implicit-prelude #-}
 -----------------------------------------------------------------------------
--- 
+-- |
 -- Module      :  Data.Either
 -- 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 :  portable
 --
--- $Id: Either.hs,v 1.3 2001/07/03 14:13:32 simonmar Exp $
---
 -- The Either type, and associated operations.
 --
 -----------------------------------------------------------------------------
@@ -22,10 +20,23 @@ module Data.Either (
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Base
-#endif
 
+{-|
+
+The 'Either' type represents values with two possibilities: a value of
+type @'Either' a b@ is either @'Left' a@ or @'Right' b@.
+
+The 'Either' type is sometimes used to represent a value which is
+either correct or an error; by convention, the 'Left' constructor is
+used to hold an error value and the 'Right' constructor is used to
+hold a correct value (mnemonic: \"right\" also means \"correct\").
+-}
 data  Either a b  =  Left a | Right b	deriving (Eq, Ord )
 
+-- | Case analysis for the 'Either' type.
+-- If the value is @'Left' a@, apply the first function to @a@;
+-- if it is @'Right' b@, apply the second function to @b@.
 either                  :: (a -> c) -> (b -> c) -> Either a b -> c
 either f _ (Left x)     =  f x
 either _ g (Right y)    =  g y
+#endif  /* __GLASGOW_HASKELL__ */