diff options
Diffstat (limited to 'libraries/base/Data/Either.hs')
| -rw-r--r-- | libraries/base/Data/Either.hs | 30 |
1 files changed, 18 insertions, 12 deletions
diff --git a/libraries/base/Data/Either.hs b/libraries/base/Data/Either.hs index 2469e78511..58987a3910 100644 --- a/libraries/base/Data/Either.hs +++ b/libraries/base/Data/Either.hs @@ -1,3 +1,4 @@ +{-# LANGUAGE CPP #-} {-# LANGUAGE Trustworthy #-} {-# LANGUAGE NoImplicitPrelude #-} {-# LANGUAGE StandaloneDeriving #-} @@ -33,8 +34,6 @@ import GHC.Base import GHC.Show import GHC.Read -import Data.Type.Equality - -- $setup -- Allow the use of some Prelude functions in doctests. -- >>> import Prelude ( (+), (*), length, putStrLn ) @@ -124,13 +123,28 @@ Left "parse error" -} data Either a b = Left a | Right b - deriving (Eq, Ord, Read, Show) + deriving ( Eq -- ^ @since 2.01 + , Ord -- ^ @since 2.01 + , Read -- ^ @since 3.0 + , Show -- ^ @since 3.0 + ) -- | @since 3.0 instance Functor (Either a) where fmap _ (Left x) = Left x fmap f (Right y) = Right (f y) +-- | @since 4.9.0.0 +instance Semigroup (Either a b) where + Left _ <> b = b + a <> _ = a +#if !defined(__HADDOCK_VERSION__) + -- workaround https://github.com/haskell/haddock/issues/680 + stimes n x + | n <= 0 = errorWithoutStackTrace "stimes: positive multiplier expected" + | otherwise = x +#endif + -- | @since 3.0 instance Applicative (Either e) where pure = Right @@ -150,7 +164,7 @@ instance Monad (Either e) where -- -- We create two values of type @'Either' 'String' 'Int'@, one using the -- 'Left' constructor and another using the 'Right' constructor. Then --- we apply \"either\" the 'length' function (if we have a 'String') +-- we apply \"either\" the 'Prelude.length' function (if we have a 'String') -- or the \"times-two\" function (if we have an 'Int'): -- -- >>> let s = Left "foo" :: Either String Int @@ -318,13 +332,6 @@ fromRight :: b -> Either a b -> b fromRight _ (Right b) = b fromRight b _ = b --- instance for the == Boolean type-level equality operator -type family EqEither a b where - EqEither ('Left x) ('Left y) = x == y - EqEither ('Right x) ('Right y) = x == y - EqEither a b = 'False -type instance a == b = EqEither a b - {- {-------------------------------------------------------------------- Testing @@ -333,4 +340,3 @@ prop_partitionEithers :: [Either Int Int] -> Bool prop_partitionEithers x = partitionEithers x == (lefts x, rights x) -} - |