Data.Choice

Documentation

data Choice a b

Choice is a version of Either that is strict on both the Left side (called This) and the Right side (called That).

Note: Choice is not used as an error monad. Use Fail for that.

Constructors

This !a

That !b

Instances

Bifunctor Choice

Methods

bimap :: (a -> b) -> (c -> d) -> Choice a c -> Choice b d

first :: (a -> b) -> Choice a c -> Choice b c

second :: (b -> c) -> Choice a b -> Choice a c

Monad (Choice e)

Methods

(>>=) :: Choice e a -> (a -> Choice e b) -> Choice e b

(>>) :: Choice e a -> Choice e b -> Choice e b

return :: a -> Choice e a

fail :: String -> Choice e a

Functor (Choice a)

Methods

fmap :: (a -> b) -> Choice a a -> Choice a b

(<$) :: a -> Choice a b -> Choice a a

Applicative (Choice e)

Methods

pure :: a -> Choice e a

(<*>) :: Choice e (a -> b) -> Choice e a -> Choice e b

(*>) :: Choice e a -> Choice e b -> Choice e b

(<*) :: Choice e a -> Choice e b -> Choice e a

(Eq b, Eq a) => Eq (Choice a b)

Methods

(==) :: Choice a b -> Choice a b -> Bool

(/=) :: Choice a b -> Choice a b -> Bool

(Data b, Data a) => Data (Choice a b)

Methods

gfoldl :: (forall d c. Data d => c (d -> c) -> d -> c c) -> (forall g. g -> c g) -> Choice a b -> c (Choice a b)

gunfold :: (forall c r. Data c => c (c -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Choice a b)

toConstr :: Choice a b -> Constr

dataTypeOf :: Choice a b -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c (Choice a b))

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Choice a b))

gmapT :: (forall c. Data c => c -> c) -> Choice a b -> Choice a b

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Choice a b -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Choice a b -> r

gmapQ :: (forall d. Data d => d -> u) -> Choice a b -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> Choice a b -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Choice a b -> m (Choice a b)

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Choice a b -> m (Choice a b)

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Choice a b -> m (Choice a b)

(Ord b, Ord a) => Ord (Choice a b)

Methods

compare :: Choice a b -> Choice a b -> Ordering

(<) :: Choice a b -> Choice a b -> Bool

(<=) :: Choice a b -> Choice a b -> Bool

(>) :: Choice a b -> Choice a b -> Bool

(>=) :: Choice a b -> Choice a b -> Bool

max :: Choice a b -> Choice a b -> Choice a b

min :: Choice a b -> Choice a b -> Choice a b

(Read b, Read a) => Read (Choice a b)

Methods

readsPrec :: Int -> ReadS (Choice a b)

readList :: ReadS [Choice a b]

readPrec :: ReadPrec (Choice a b)

readListPrec :: ReadPrec [Choice a b]

(Show b, Show a) => Show (Choice a b)

Methods

showsPrec :: Int -> Choice a b -> ShowS

show :: Choice a b -> String

showList :: [Choice a b] -> ShowS

(Arbitrary a, Arbitrary b) => Arbitrary (Choice a b)

Methods

arbitrary :: Gen (Choice a b)

shrink :: Choice a b -> [Choice a b]

(Hashable a, Hashable b) => Hashable (Choice a b)

Methods

hashWithSalt :: Int -> Choice a b -> Int

hash :: Choice a b -> Int

(NFData a, NFData b) => NFData (Choice a b)

Methods

rnf :: Choice a b -> ()

choice :: (a -> c) -> (b -> c) -> Choice a b -> c

Choice's version of either

this :: Monad m => Choice a b -> m a

>>> this (This "foo") :: Maybe String
Just "foo"

>>> this (That "bar") :: Maybe String
Nothing

that :: Monad m => Choice a b -> m b

>>> that (This "foo") :: Maybe String
Nothing

>>> that (That "bar") :: Maybe String
Just "bar"

these :: [Choice a b] -> [a]

>>> these [This "foo", This "bar", That "baz", This "quux"]
["foo","bar","quux"]

those :: [Choice a b] -> [b]

>>> those [This "foo", This "bar", That "baz", This "quux"]
["baz"]

eitherToChoice :: Either a b -> Choice a b

>>> eitherToChoice (Left 1)
This 1

>>> eitherToChoice (Right 5)
That 5

mergeChoice :: Choice a a -> a

>>> mergeChoice (This 5 :: Choice Int Int)
5

>>> mergeChoice (That 'c' :: Choice Char Char)
'c'