[project @ 2002-07-16 15:47:25 by ross]
[packages/old-time.git] / Data / Either.hs
1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
3 -- |
4 -- Module : Data.Either
5 -- Copyright : (c) The University of Glasgow 2001
6 -- License : BSD-style (see the file libraries/base/LICENSE)
7 --
8 -- Maintainer : libraries@haskell.org
9 -- Stability : experimental
10 -- Portability : portable
11 --
12 -- The Either type, and associated operations.
13 --
14 -----------------------------------------------------------------------------
15
16 module Data.Either (
17 Either(..),
18 either -- :: (a -> c) -> (b -> c) -> Either a b -> c
19 ) where
20
21 #ifdef __GLASGOW_HASKELL__
22 import GHC.Base
23 #endif
24
25 #ifndef __HUGS__
26 {-|
27
28 The 'Either' type represents values with two possibilities: a value of
29 type @'Either' a b@ is either @'Left' a@ or @'Right' b@.
30
31 The 'Either' type is sometimes used to represent a value which is
32 either correct or an error; by convention, the 'Left' constructor is
33 used to hold an error value and the 'Right' constructor is used to
34 hold a correct value (mnemonic: \"right\" also means \"correct\").
35 -}
36 data Either a b = Left a | Right b deriving (Eq, Ord )
37
38 either :: (a -> c) -> (b -> c) -> Either a b -> c
39 either f _ (Left x) = f x
40 either _ g (Right y) = g y
41 #endif /* __HUGS__ */