Data.Functor.Alt

Documentation

class Functor f => Alt f where

Laws:

<!> is associative:             (a <!> b) <!> c = a <!> (b <!> c)
<$> left-distributes over <!>:  f <$> (a <!> b) = (f <$> a) <!> (f <$> b)

If extended to an Alternative then <!> should equal <|>.

Ideally, an instance of Alt also satisfies the "left distribution" law of MonadPlus with respect to <.>:

<.> right-distributes over <!>: (a <!> b) <.> c = (a <.> c) <!> (b <.> c)

IO, Either a, ExceptT e m and STM instead satisfy the "left catch" law:

pure a <!> b = pure a

Maybe and Identity satisfy both "left distribution" and "left catch".

These variations cannot be stated purely in terms of the dependencies of Alt.

When and if MonadPlus is successfully refactored, this class should also be refactored to remove these instances.

The right distributive law should extend in the cases where the a Bind or Monad is provided to yield variations of the right distributive law:

(m <!> n) >>- f = (m >>- f) <!> (m >>- f)
(m <!> n) >>= f = (m >>= f) <!> (m >>= f)

Minimal complete definition

(<!>)

Methods

(<!>) :: f a -> f a -> f a infixl 3

<|> without a required empty

some :: Applicative f => f a -> f [a]

many :: Applicative f => f a -> f [a]

Instances

Alt Identity

Choose the first option every time. While 'choose the last option' every time is also valid, this instance satisfies more laws.

Since: 5.3.6

Defined in Data.Functor.Alt

Methods

(<!>) :: Identity a -> Identity a -> Identity a

some :: Applicative Identity => Identity a -> Identity [a]

many :: Applicative Identity => Identity a -> Identity [a]

Alt First

Defined in Data.Functor.Alt

Methods

(<!>) :: First a -> First a -> First a

some :: Applicative First => First a -> First [a]

many :: Applicative First => First a -> First [a]

Alt Last

Defined in Data.Functor.Alt

Methods

(<!>) :: Last a -> Last a -> Last a

some :: Applicative Last => Last a -> Last [a]

many :: Applicative Last => Last a -> Last [a]

Alt First

Defined in Data.Functor.Alt

Methods

(<!>) :: First a -> First a -> First a

some :: Applicative First => First a -> First [a]

many :: Applicative First => First a -> First [a]

Alt Last

Defined in Data.Functor.Alt

Methods

(<!>) :: Last a -> Last a -> Last a

some :: Applicative Last => Last a -> Last [a]

many :: Applicative Last => Last a -> Last [a]

Alt IntMap

Defined in Data.Functor.Alt

Methods

(<!>) :: IntMap a -> IntMap a -> IntMap a

some :: Applicative IntMap => IntMap a -> IntMap [a]

many :: Applicative IntMap => IntMap a -> IntMap [a]

Alt Seq

Defined in Data.Functor.Alt

Methods

(<!>) :: Seq a -> Seq a -> Seq a

some :: Applicative Seq => Seq a -> Seq [a]

many :: Applicative Seq => Seq a -> Seq [a]

Alt IO

This instance does not actually satisfy the (<.>) right distributive law It instead satisfies the "left catch" law

Defined in Data.Functor.Alt

Methods

(<!>) :: IO a -> IO a -> IO a

some :: Applicative IO => IO a -> IO [a]

many :: Applicative IO => IO a -> IO [a]

Alt NonEmpty

Defined in Data.Functor.Alt

Methods

(<!>) :: NonEmpty a -> NonEmpty a -> NonEmpty a

some :: Applicative NonEmpty => NonEmpty a -> NonEmpty [a]

many :: Applicative NonEmpty => NonEmpty a -> NonEmpty [a]

Alt Maybe

Defined in Data.Functor.Alt

Methods

(<!>) :: Maybe a -> Maybe a -> Maybe a

some :: Applicative Maybe => Maybe a -> Maybe [a]

many :: Applicative Maybe => Maybe a -> Maybe [a]

Alt []

Defined in Data.Functor.Alt

Methods

(<!>) :: [a] -> [a] -> [a]

some :: Applicative [] => [a] -> [[a]]

many :: Applicative [] => [a] -> [[a]]

MonadPlus m => Alt (WrappedMonad m)

Defined in Data.Functor.Alt

Methods

(<!>) :: WrappedMonad m a -> WrappedMonad m a -> WrappedMonad m a

some :: Applicative (WrappedMonad m) => WrappedMonad m a -> WrappedMonad m [a]

many :: Applicative (WrappedMonad m) => WrappedMonad m a -> WrappedMonad m [a]

Alt (Either a)

Defined in Data.Functor.Alt

Methods

(<!>) :: Either a a0 -> Either a a0 -> Either a a0

some :: Applicative (Either a) => Either a a0 -> Either a [a0]

many :: Applicative (Either a) => Either a a0 -> Either a [a0]

Alt (Proxy :: Type -> Type)

Defined in Data.Functor.Alt

Methods

(<!>) :: Proxy a -> Proxy a -> Proxy a

some :: Applicative Proxy => Proxy a -> Proxy [a]

many :: Applicative Proxy => Proxy a -> Proxy [a]

Alt (U1 :: Type -> Type)

Defined in Data.Functor.Alt

Methods

(<!>) :: U1 a -> U1 a -> U1 a

some :: Applicative U1 => U1 a -> U1 [a]

many :: Applicative U1 => U1 a -> U1 [a]

Alt (V1 :: Type -> Type)

Defined in Data.Functor.Alt

Methods

(<!>) :: V1 a -> V1 a -> V1 a

some :: Applicative V1 => V1 a -> V1 [a]

many :: Applicative V1 => V1 a -> V1 [a]

Ord k => Alt (Map k)

Defined in Data.Functor.Alt

Methods

(<!>) :: Map k a -> Map k a -> Map k a

some :: Applicative (Map k) => Map k a -> Map k [a]

many :: Applicative (Map k) => Map k a -> Map k [a]

Alternative f => Alt (WrappedApplicative f)

Defined in Data.Functor.Alt

Methods

(<!>) :: WrappedApplicative f a -> WrappedApplicative f a -> WrappedApplicative f a

some :: Applicative (WrappedApplicative f) => WrappedApplicative f a -> WrappedApplicative f [a]

many :: Applicative (WrappedApplicative f) => WrappedApplicative f a -> WrappedApplicative f [a]

Alt f => Alt (Lift f)

Defined in Data.Functor.Alt

Methods

(<!>) :: Lift f a -> Lift f a -> Lift f a

some :: Applicative (Lift f) => Lift f a -> Lift f [a]

many :: Applicative (Lift f) => Lift f a -> Lift f [a]

Apply f => Alt (ListT f)

Defined in Data.Functor.Alt

Methods

(<!>) :: ListT f a -> ListT f a -> ListT f a

some :: Applicative (ListT f) => ListT f a -> ListT f [a]

many :: Applicative (ListT f) => ListT f a -> ListT f [a]

(Functor f, Monad f) => Alt (MaybeT f)

Defined in Data.Functor.Alt

Methods

(<!>) :: MaybeT f a -> MaybeT f a -> MaybeT f a

some :: Applicative (MaybeT f) => MaybeT f a -> MaybeT f [a]

many :: Applicative (MaybeT f) => MaybeT f a -> MaybeT f [a]

(Hashable k, Eq k) => Alt (HashMap k)

Defined in Data.Functor.Alt

Methods

(<!>) :: HashMap k a -> HashMap k a -> HashMap k a

some :: Applicative (HashMap k) => HashMap k a -> HashMap k [a]

many :: Applicative (HashMap k) => HashMap k a -> HashMap k [a]

ArrowPlus a => Alt (WrappedArrow a b)

Defined in Data.Functor.Alt

Methods

(<!>) :: WrappedArrow a b a0 -> WrappedArrow a b a0 -> WrappedArrow a b a0

some :: Applicative (WrappedArrow a b) => WrappedArrow a b a0 -> WrappedArrow a b [a0]

many :: Applicative (WrappedArrow a b) => WrappedArrow a b a0 -> WrappedArrow a b [a0]

Alt f => Alt (Rec1 f)

Defined in Data.Functor.Alt

Methods

(<!>) :: Rec1 f a -> Rec1 f a -> Rec1 f a

some :: Applicative (Rec1 f) => Rec1 f a -> Rec1 f [a]

many :: Applicative (Rec1 f) => Rec1 f a -> Rec1 f [a]

Alt f => Alt (Static f a)

Defined in Data.Semigroupoid.Static

Methods

(<!>) :: Static f a a0 -> Static f a a0 -> Static f a a0

some :: Applicative (Static f a) => Static f a a0 -> Static f a [a0]

many :: Applicative (Static f a) => Static f a a0 -> Static f a [a0]

Alt f => Alt (Backwards f)

Defined in Data.Functor.Alt

Methods

(<!>) :: Backwards f a -> Backwards f a -> Backwards f a

some :: Applicative (Backwards f) => Backwards f a -> Backwards f [a]

many :: Applicative (Backwards f) => Backwards f a -> Backwards f [a]

(Functor f, Monad f) => Alt (ErrorT e f)

Defined in Data.Functor.Alt

Methods

(<!>) :: ErrorT e f a -> ErrorT e f a -> ErrorT e f a

some :: Applicative (ErrorT e f) => ErrorT e f a -> ErrorT e f [a]

many :: Applicative (ErrorT e f) => ErrorT e f a -> ErrorT e f [a]

(Functor f, Monad f, Semigroup e) => Alt (ExceptT e f)

Defined in Data.Functor.Alt

Methods

(<!>) :: ExceptT e f a -> ExceptT e f a -> ExceptT e f a

some :: Applicative (ExceptT e f) => ExceptT e f a -> ExceptT e f [a]

many :: Applicative (ExceptT e f) => ExceptT e f a -> ExceptT e f [a]

Alt f => Alt (IdentityT f)

Defined in Data.Functor.Alt

Methods

(<!>) :: IdentityT f a -> IdentityT f a -> IdentityT f a

some :: Applicative (IdentityT f) => IdentityT f a -> IdentityT f [a]

many :: Applicative (IdentityT f) => IdentityT f a -> IdentityT f [a]

Alt f => Alt (ReaderT e f)

Defined in Data.Functor.Alt

Methods

(<!>) :: ReaderT e f a -> ReaderT e f a -> ReaderT e f a

some :: Applicative (ReaderT e f) => ReaderT e f a -> ReaderT e f [a]

many :: Applicative (ReaderT e f) => ReaderT e f a -> ReaderT e f [a]

Alt f => Alt (StateT e f)

Defined in Data.Functor.Alt

Methods

(<!>) :: StateT e f a -> StateT e f a -> StateT e f a

some :: Applicative (StateT e f) => StateT e f a -> StateT e f [a]

many :: Applicative (StateT e f) => StateT e f a -> StateT e f [a]

Alt f => Alt (StateT e f)

Defined in Data.Functor.Alt

Methods

(<!>) :: StateT e f a -> StateT e f a -> StateT e f a

some :: Applicative (StateT e f) => StateT e f a -> StateT e f [a]

many :: Applicative (StateT e f) => StateT e f a -> StateT e f [a]

Alt f => Alt (WriterT w f)

Since: 5.3.6

Defined in Data.Functor.Alt

Methods

(<!>) :: WriterT w f a -> WriterT w f a -> WriterT w f a

some :: Applicative (WriterT w f) => WriterT w f a -> WriterT w f [a]

many :: Applicative (WriterT w f) => WriterT w f a -> WriterT w f [a]

Alt f => Alt (WriterT w f)

Defined in Data.Functor.Alt

Methods

(<!>) :: WriterT w f a -> WriterT w f a -> WriterT w f a

some :: Applicative (WriterT w f) => WriterT w f a -> WriterT w f [a]

many :: Applicative (WriterT w f) => WriterT w f a -> WriterT w f [a]

Alt f => Alt (WriterT w f)

Defined in Data.Functor.Alt

Methods

(<!>) :: WriterT w f a -> WriterT w f a -> WriterT w f a

some :: Applicative (WriterT w f) => WriterT w f a -> WriterT w f [a]

many :: Applicative (WriterT w f) => WriterT w f a -> WriterT w f [a]

Alt f => Alt (Reverse f)

Defined in Data.Functor.Alt

Methods

(<!>) :: Reverse f a -> Reverse f a -> Reverse f a

some :: Applicative (Reverse f) => Reverse f a -> Reverse f [a]

many :: Applicative (Reverse f) => Reverse f a -> Reverse f [a]

(Alt f, Alt g) => Alt (Product f g)

Defined in Data.Functor.Alt

Methods

(<!>) :: Product f g a -> Product f g a -> Product f g a

some :: Applicative (Product f g) => Product f g a -> Product f g [a]

many :: Applicative (Product f g) => Product f g a -> Product f g [a]

(Alt f, Alt g) => Alt (f :*: g)

Defined in Data.Functor.Alt

Methods

(<!>) :: (f :*: g) a -> (f :*: g) a -> (f :*: g) a

some :: Applicative (f :*: g) => (f :*: g) a -> (f :*: g) [a]

many :: Applicative (f :*: g) => (f :*: g) a -> (f :*: g) [a]

Semigroup c => Alt (K1 i c :: Type -> Type)

since 5.3.8

Defined in Data.Functor.Alt

Methods

(<!>) :: K1 i c a -> K1 i c a -> K1 i c a

some :: Applicative (K1 i c) => K1 i c a -> K1 i c [a]

many :: Applicative (K1 i c) => K1 i c a -> K1 i c [a]

(Alt f, Functor g) => Alt (Compose f g)

Defined in Data.Functor.Alt

Methods

(<!>) :: Compose f g a -> Compose f g a -> Compose f g a

some :: Applicative (Compose f g) => Compose f g a -> Compose f g [a]

many :: Applicative (Compose f g) => Compose f g a -> Compose f g [a]

(Alt f, Functor g) => Alt (f :.: g)

Since: 5.3.8

Defined in Data.Functor.Alt

Methods

(<!>) :: (f :.: g) a -> (f :.: g) a -> (f :.: g) a

some :: Applicative (f :.: g) => (f :.: g) a -> (f :.: g) [a]

many :: Applicative (f :.: g) => (f :.: g) a -> (f :.: g) [a]

Alt f => Alt (M1 i c f)

Defined in Data.Functor.Alt

Methods

(<!>) :: M1 i c f a -> M1 i c f a -> M1 i c f a

some :: Applicative (M1 i c f) => M1 i c f a -> M1 i c f [a]

many :: Applicative (M1 i c f) => M1 i c f a -> M1 i c f [a]

Alt f => Alt (RWST r w s f)

Since: 5.3.6

Defined in Data.Functor.Alt

Methods

(<!>) :: RWST r w s f a -> RWST r w s f a -> RWST r w s f a

some :: Applicative (RWST r w s f) => RWST r w s f a -> RWST r w s f [a]

many :: Applicative (RWST r w s f) => RWST r w s f a -> RWST r w s f [a]

Alt f => Alt (RWST r w s f)

Defined in Data.Functor.Alt

Methods

(<!>) :: RWST r w s f a -> RWST r w s f a -> RWST r w s f a

some :: Applicative (RWST r w s f) => RWST r w s f a -> RWST r w s f [a]

many :: Applicative (RWST r w s f) => RWST r w s f a -> RWST r w s f [a]

Alt f => Alt (RWST r w s f)

Defined in Data.Functor.Alt

Methods

(<!>) :: RWST r w s f a -> RWST r w s f a -> RWST r w s f a

some :: Applicative (RWST r w s f) => RWST r w s f a -> RWST r w s f [a]

many :: Applicative (RWST r w s f) => RWST r w s f a -> RWST r w s f [a]

optional :: (Alt f, Applicative f) => f a -> f (Maybe a)

One or none.

galt :: (Generic1 f, Alt (Rep1 f)) => f a -> f a -> f a

Generic (<!>). Caveats:

1. Will not compile if f is a sum type.
2. Any types where the a does not appear must have a Semigroup instance.

Since: 5.3.8

module Data.Functor.Apply