Safe Haskell	Safe

Eta.Types.Either

Description

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").

Synopsis

Documentation

data Either a b :: * -> * -> * #

Constructors

Left a
Right b

Instances

Monad (Either e)
Methods (>>=) :: Either e a -> (a -> Either e b) -> Either e b # (>>) :: Either e a -> Either e b -> Either e b return :: a -> Either e a fail :: String -> Either e a
Functor (Either a)
Methods fmap :: (a -> b) -> Either a a -> Either a b # (<$) :: a -> Either a b -> Either a a
Applicative (Either e)
Methods pure :: a -> Either e a # (<>) :: Either e (a -> b) -> Either e a -> Either e b # (>) :: Either e a -> Either e b -> Either e b (<*) :: Either e a -> Either e b -> Either e a
Foldable (Either a)
Methods fold :: Monoid m => Either a m -> m foldMap :: Monoid m => (a -> m) -> Either a a -> m # foldr :: (a -> b -> b) -> b -> Either a a -> b # foldr' :: (a -> b -> b) -> b -> Either a a -> b foldl :: (b -> a -> b) -> b -> Either a a -> b foldl' :: (b -> a -> b) -> b -> Either a a -> b foldr1 :: (a -> a -> a) -> Either a a -> a foldl1 :: (a -> a -> a) -> Either a a -> a toList :: Either a a -> [a] null :: Either a a -> Bool length :: Either a a -> Int elem :: Eq a => a -> Either a a -> Bool maximum :: Ord a => Either a a -> a minimum :: Ord a => Either a a -> a sum :: Num a => Either a a -> a product :: Num a => Either a a -> a
Traversable (Either a)
Methods traverse :: Applicative f => (a -> f b) -> Either a a -> f (Either a b) # sequenceA :: Applicative f => Either a (f a) -> f (Either a a) # mapM :: Monad m => (a -> m b) -> Either a a -> m (Either a b) sequence :: Monad m => Either a (m a) -> m (Either a a)
Generic1 (Either a)
Associated Types type Rep1 (Either a :: * -> ) :: -> * Methods from1 :: Either a a -> Rep1 (Either a) a to1 :: Rep1 (Either a) a -> Either a a
(Eq b, Eq a) => Eq (Either a b)
Methods (==) :: Either a b -> Either a b -> Bool # (/=) :: Either a b -> Either a b -> Bool #
(Ord b, Ord a) => Ord (Either a b)
Methods compare :: Either a b -> Either a b -> Ordering # (<) :: Either a b -> Either a b -> Bool # (<=) :: Either a b -> Either a b -> Bool # (>) :: Either a b -> Either a b -> Bool # (>=) :: Either a b -> Either a b -> Bool # max :: Either a b -> Either a b -> Either a b # min :: Either a b -> Either a b -> Either a b #
(Read b, Read a) => Read (Either a b)
Methods readsPrec :: Int -> ReadS (Either a b) # readList :: ReadS [Either a b] readPrec :: ReadPrec (Either a b) readListPrec :: ReadPrec [Either a b]
(Show b, Show a) => Show (Either a b)
Methods showsPrec :: Int -> Either a b -> ShowS # show :: Either a b -> String # showList :: [Either a b] -> ShowS #
Generic (Either a b)
Associated Types type Rep (Either a b) :: * -> * Methods from :: Either a b -> Rep (Either a b) x to :: Rep (Either a b) x -> Either a b
type Rep1 (Either a)
type Rep1 (Either a) = D1 (MetaData "Either" "Data.Either" "base" False) ((:+:) (C1 (MetaCons "Left" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 a))) (C1 (MetaCons "Right" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) Par1)))
type Rep (Either a b)
type Rep (Either a b) = D1 (MetaData "Either" "Data.Either" "base" False) ((:+:) (C1 (MetaCons "Left" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 a))) (C1 (MetaCons "Right" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 b))))
type (==) (Either k k1) a b
type (==) (Either k k1) a b = EqEither k k1 a b

lefts :: [Either a b] -> [a] #

rights :: [Either a b] -> [b] #

isLeft :: Either a b -> Bool #

isRight :: Either a b -> Bool #

partitionEithers :: [Either a b] -> ([a], [b]) #

fromLeftOrElse :: Either a b -> a -> a #

Return the contents of a Left or a default value

>>> Left 4 `fromLeftOrElse` 0
4
>>> Right 4 `fromLeftOrElse` 0
0

fromRightOrElse :: Either a b -> b -> b #

Return the contents of a Right or a default value

>>> Right 4 `fromRightOrElse` 0
4
>>> Left 4 `fromRightOrElse` 0
0

handleEither :: (a -> c) -> (b -> c) -> Either a b -> c #

Handler for the Either type Takes two functions and an Either.

If the value is a 'Left a' apply the first function to a. If the value is a 'Right b' apply the first function to b.