    {-# OPTIONS_GHC -fno-implicit-prelude #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Either
    -- Copyright   :  (c) The University of Glasgow 2001
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  experimental
    -- Portability :  portable
    --
    -- The Either type, and associated operations.
    --
    -----------------------------------------------------------------------------

    module Data.Either (
       Either(..),
       either       -- :: (a -> c) -> (b -> c) -> Either a b -> c
     ) where

    #ifdef __GLASGOW_HASKELL__
    import GHC.Base

    {-|

    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__ */