{-# 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__ */