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{-# 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__ */
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