Copyright	Conor McBride and Ross Paterson 2005
License	BSD-style (see the LICENSE file in the distribution)
Maintainer	libraries@haskell.org
Stability	experimental
Portability	portable
Safe Haskell	Trustworthy
Language	Haskell2010

Control.Applicative

Contents

Applicative functors
Alternatives
Instances
Utility functions

Description

This module describes a structure intermediate between a functor and a monad (technically, a strong lax monoidal functor). Compared with monads, this interface lacks the full power of the binding operation >>=, but

it has more instances.
it is sufficient for many uses, e.g. context-free parsing, or the Traversable class.
instances can perform analysis of computations before they are executed, and thus produce shared optimizations.

This interface was introduced for parsers by Niklas Röjemo, because it admits more sharing than the monadic interface. The names here are mostly based on parsing work by Doaitse Swierstra.

For more details, see Applicative Programming with Effects, by Conor McBride and Ross Paterson.

Synopsis

class Functor f => Applicative f where
- pure :: a -> f a
- (<*>) :: f (a -> b) -> f a -> f b
- liftA2 :: (a -> b -> c) -> f a -> f b -> f c
- (*>) :: f a -> f b -> f b
- (<*) :: f a -> f b -> f a
class Applicative f => Alternative f where
- empty :: f a
- (<|>) :: f a -> f a -> f a
- some :: f a -> f [a]
- many :: f a -> f [a]
newtype Const a b = Const {
- getConst :: a
}
newtype WrappedMonad m a = WrapMonad {
- unwrapMonad :: m a
}
newtype WrappedArrow a b c = WrapArrow {
- unwrapArrow :: a b c
}
newtype ZipList a = ZipList {
- getZipList :: [a]
}
(<$>) :: Functor f => (a -> b) -> f a -> f b
(<$) :: Functor f => a -> f b -> f a
(<**>) :: Applicative f => f a -> f (a -> b) -> f b
liftA :: Applicative f => (a -> b) -> f a -> f b
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
optional :: Alternative f => f a -> f (Maybe a)

Applicative functors

class Functor f => Applicative f where Source #

A functor with application, providing operations to

embed pure expressions (pure), and
sequence computations and combine their results (<*> and liftA2).

A minimal complete definition must include implementations of pure and of either <*> or liftA2. If it defines both, then they must behave the same as their default definitions:

(<*>) = liftA2 id

liftA2 f x y = f <$> x <*> y

Further, any definition must satisfy the following:

Identity

pure id <*> v = v

Composition

pure (.) <*> u <*> v <*> w = u <*> (v <*> w)

Homomorphism

pure f <*> pure x = pure (f x)

Interchange

u <*> pure y = pure ($ y) <*> u

The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:

```
u *> v = (id <$ u) <*> v
```
```
u <* v = liftA2 const u v
```

As a consequence of these laws, the Functor instance for f will satisfy

```
fmap f x = pure f <*> x
```

It may be useful to note that supposing

forall x y. p (q x y) = f x . g y

it follows from the above that

liftA2 p (liftA2 q u v) = liftA2 f u . liftA2 g v

If f is also a Monad, it should satisfy

```
pure = return
```

m1 <*> m2 = m1 >>= (x1 -> m2 >>= (x2 -> return (x1 x2)))

```
(*>) = (>>)
```

(which implies that pure and <*> satisfy the applicative functor laws).

Minimal complete definition

pure, ((<*>) | liftA2)

Methods

pure :: a -> f a Source #

Lift a value.

(<*>) :: f (a -> b) -> f a -> f b infixl 4 Source #

Sequential application.

A few functors support an implementation of <*> that is more efficient than the default one.

Using ApplicativeDo: 'fs <*> as' can be understood as the do expression

do f <- fs
   a <- as
   pure (f a)

liftA2 :: (a -> b -> c) -> f a -> f b -> f c Source #

Lift a binary function to actions.

Some functors support an implementation of liftA2 that is more efficient than the default one. In particular, if fmap is an expensive operation, it is likely better to use liftA2 than to fmap over the structure and then use <*>.

This became a typeclass method in 4.10.0.0. Prior to that, it was a function defined in terms of <*> and fmap.

Using ApplicativeDo: 'liftA2 f as bs' can be understood as the do expression

do a <- as
   b <- bs
   pure (f a b)

(*>) :: f a -> f b -> f b infixl 4 Source #

Sequence actions, discarding the value of the first argument.

'as *> bs' can be understood as the do expression

do as
   bs

This is a tad complicated for our ApplicativeDo extension which will give it a Monad constraint. For an Applicative constraint we write it of the form

do _ <- as
   b <- bs
   pure b

(<*) :: f a -> f b -> f a infixl 4 Source #

Sequence actions, discarding the value of the second argument.

Using ApplicativeDo: 'as <* bs' can be understood as the do expression

do a <- as
   bs
   pure a

Instances

Instances details

Applicative [] #	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> [a] Source # (<>) :: [a -> b] -> [a] -> [b] Source # liftA2 :: (a -> b -> c) -> [a] -> [b] -> [c] Source # (>) :: [a] -> [b] -> [b] Source # (<*) :: [a] -> [b] -> [a] Source #
Applicative Maybe #	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> Maybe a Source # (<>) :: Maybe (a -> b) -> Maybe a -> Maybe b Source # liftA2 :: (a -> b -> c) -> Maybe a -> Maybe b -> Maybe c Source # (>) :: Maybe a -> Maybe b -> Maybe b Source # (<*) :: Maybe a -> Maybe b -> Maybe a Source #
Applicative IO #	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> IO a Source # (<>) :: IO (a -> b) -> IO a -> IO b Source # liftA2 :: (a -> b -> c) -> IO a -> IO b -> IO c Source # (>) :: IO a -> IO b -> IO b Source # (<*) :: IO a -> IO b -> IO a Source #
Applicative Par1 #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> Par1 a Source # (<>) :: Par1 (a -> b) -> Par1 a -> Par1 b Source # liftA2 :: (a -> b -> c) -> Par1 a -> Par1 b -> Par1 c Source # (>) :: Par1 a -> Par1 b -> Par1 b Source # (<*) :: Par1 a -> Par1 b -> Par1 a Source #
Applicative NonEmpty #	Since: base-4.9.0.0
Instance details Defined in GHC.Base Methods pure :: a -> NonEmpty a Source # (<>) :: NonEmpty (a -> b) -> NonEmpty a -> NonEmpty b Source # liftA2 :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c Source # (>) :: NonEmpty a -> NonEmpty b -> NonEmpty b Source # (<*) :: NonEmpty a -> NonEmpty b -> NonEmpty a Source #
Applicative NoIO #	Since: base-4.8.0.0
Instance details Defined in GHC.GHCi Methods pure :: a -> NoIO a Source # (<>) :: NoIO (a -> b) -> NoIO a -> NoIO b Source # liftA2 :: (a -> b -> c) -> NoIO a -> NoIO b -> NoIO c Source # (>) :: NoIO a -> NoIO b -> NoIO b Source # (<*) :: NoIO a -> NoIO b -> NoIO a Source #
Applicative ReadP #	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods pure :: a -> ReadP a Source # (<>) :: ReadP (a -> b) -> ReadP a -> ReadP b Source # liftA2 :: (a -> b -> c) -> ReadP a -> ReadP b -> ReadP c Source # (>) :: ReadP a -> ReadP b -> ReadP b Source # (<*) :: ReadP a -> ReadP b -> ReadP a Source #
Applicative ReadPrec #	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadPrec Methods pure :: a -> ReadPrec a Source # (<>) :: ReadPrec (a -> b) -> ReadPrec a -> ReadPrec b Source # liftA2 :: (a -> b -> c) -> ReadPrec a -> ReadPrec b -> ReadPrec c Source # (>) :: ReadPrec a -> ReadPrec b -> ReadPrec b Source # (<*) :: ReadPrec a -> ReadPrec b -> ReadPrec a Source #
Applicative Down #	Since: base-4.11.0.0
Instance details Defined in Data.Ord Methods pure :: a -> Down a Source # (<>) :: Down (a -> b) -> Down a -> Down b Source # liftA2 :: (a -> b -> c) -> Down a -> Down b -> Down c Source # (>) :: Down a -> Down b -> Down b Source # (<*) :: Down a -> Down b -> Down a Source #
Applicative Product #	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Product a Source # (<>) :: Product (a -> b) -> Product a -> Product b Source # liftA2 :: (a -> b -> c) -> Product a -> Product b -> Product c Source # (>) :: Product a -> Product b -> Product b Source # (<*) :: Product a -> Product b -> Product a Source #
Applicative Sum #	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Sum a Source # (<>) :: Sum (a -> b) -> Sum a -> Sum b Source # liftA2 :: (a -> b -> c) -> Sum a -> Sum b -> Sum c Source # (>) :: Sum a -> Sum b -> Sum b Source # (<*) :: Sum a -> Sum b -> Sum a Source #
Applicative Dual #	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Dual a Source # (<>) :: Dual (a -> b) -> Dual a -> Dual b Source # liftA2 :: (a -> b -> c) -> Dual a -> Dual b -> Dual c Source # (>) :: Dual a -> Dual b -> Dual b Source # (<*) :: Dual a -> Dual b -> Dual a Source #
Applicative Last #	Since: base-4.8.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> Last a Source # (<>) :: Last (a -> b) -> Last a -> Last b Source # liftA2 :: (a -> b -> c) -> Last a -> Last b -> Last c Source # (>) :: Last a -> Last b -> Last b Source # (<*) :: Last a -> Last b -> Last a Source #
Applicative First #	Since: base-4.8.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> First a Source # (<>) :: First (a -> b) -> First a -> First b Source # liftA2 :: (a -> b -> c) -> First a -> First b -> First c Source # (>) :: First a -> First b -> First b Source # (<*) :: First a -> First b -> First a Source #
Applicative STM #	Since: base-4.8.0.0
Instance details Defined in GHC.Conc.Sync Methods pure :: a -> STM a Source # (<>) :: STM (a -> b) -> STM a -> STM b Source # liftA2 :: (a -> b -> c) -> STM a -> STM b -> STM c Source # (>) :: STM a -> STM b -> STM b Source # (<*) :: STM a -> STM b -> STM a Source #
Applicative Identity #	Since: base-4.8.0.0
Instance details Defined in Data.Functor.Identity Methods pure :: a -> Identity a Source # (<>) :: Identity (a -> b) -> Identity a -> Identity b Source # liftA2 :: (a -> b -> c) -> Identity a -> Identity b -> Identity c Source # (>) :: Identity a -> Identity b -> Identity b Source # (<*) :: Identity a -> Identity b -> Identity a Source #
Applicative ZipList #	f <$> ZipList xs1 <> ... <> ZipList xsN = ZipList (zipWithN f xs1 ... xsN) where `zipWithN` refers to the `zipWith` function of the appropriate arity (`zipWith`, `zipWith3`, `zipWith4`, ...). For example: (\a b c -> stimes c [a, b]) <$> ZipList "abcd" <> ZipList "567" <> ZipList [1..] = ZipList (zipWith3 (\a b c -> stimes c [a, b]) "abcd" "567" [1..]) = ZipList {getZipList = ["a5","b6b6","c7c7c7"]} Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a -> ZipList a Source # (<>) :: ZipList (a -> b) -> ZipList a -> ZipList b Source # liftA2 :: (a -> b -> c) -> ZipList a -> ZipList b -> ZipList c Source # (>) :: ZipList a -> ZipList b -> ZipList b Source # (<*) :: ZipList a -> ZipList b -> ZipList a Source #
Applicative Option #	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Option a Source # (<>) :: Option (a -> b) -> Option a -> Option b Source # liftA2 :: (a -> b -> c) -> Option a -> Option b -> Option c Source # (>) :: Option a -> Option b -> Option b Source # (<*) :: Option a -> Option b -> Option a Source #
Applicative Last #	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Last a Source # (<>) :: Last (a -> b) -> Last a -> Last b Source # liftA2 :: (a -> b -> c) -> Last a -> Last b -> Last c Source # (>) :: Last a -> Last b -> Last b Source # (<*) :: Last a -> Last b -> Last a Source #
Applicative First #	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> First a Source # (<>) :: First (a -> b) -> First a -> First b Source # liftA2 :: (a -> b -> c) -> First a -> First b -> First c Source # (>) :: First a -> First b -> First b Source # (<*) :: First a -> First b -> First a Source #
Applicative Max #	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Max a Source # (<>) :: Max (a -> b) -> Max a -> Max b Source # liftA2 :: (a -> b -> c) -> Max a -> Max b -> Max c Source # (>) :: Max a -> Max b -> Max b Source # (<*) :: Max a -> Max b -> Max a Source #
Applicative Min #	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods pure :: a -> Min a Source # (<>) :: Min (a -> b) -> Min a -> Min b Source # liftA2 :: (a -> b -> c) -> Min a -> Min b -> Min c Source # (>) :: Min a -> Min b -> Min b Source # (<*) :: Min a -> Min b -> Min a Source #
Applicative Complex #	Since: base-4.9.0.0
Instance details Defined in Data.Complex Methods pure :: a -> Complex a Source # (<>) :: Complex (a -> b) -> Complex a -> Complex b Source # liftA2 :: (a -> b -> c) -> Complex a -> Complex b -> Complex c Source # (>) :: Complex a -> Complex b -> Complex b Source # (<*) :: Complex a -> Complex b -> Complex a Source #
Applicative (Either e) #	Since: base-3.0
Instance details Defined in Data.Either Methods pure :: a -> Either e a Source # (<>) :: Either e (a -> b) -> Either e a -> Either e b Source # liftA2 :: (a -> b -> c) -> Either e a -> Either e b -> Either e c Source # (>) :: Either e a -> Either e b -> Either e b Source # (<*) :: Either e a -> Either e b -> Either e a Source #
Applicative (U1 :: Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> U1 a Source # (<>) :: U1 (a -> b) -> U1 a -> U1 b Source # liftA2 :: (a -> b -> c) -> U1 a -> U1 b -> U1 c Source # (>) :: U1 a -> U1 b -> U1 b Source # (<*) :: U1 a -> U1 b -> U1 a Source #
Monoid a => Applicative ((,) a) #	For tuples, the `Monoid` constraint on `a` determines how the first values merge. For example, `String`s concatenate: ("hello ", (+15)) <> ("world!", 2002) ("hello world!",2017) Since: base-2.1*
Instance details Defined in GHC.Base Methods pure :: a0 -> (a, a0) Source # (<>) :: (a, a0 -> b) -> (a, a0) -> (a, b) Source # liftA2 :: (a0 -> b -> c) -> (a, a0) -> (a, b) -> (a, c) Source # (>) :: (a, a0) -> (a, b) -> (a, b) Source # (<*) :: (a, a0) -> (a, b) -> (a, a0) Source #
Applicative (ST s) #	Since: base-4.4.0.0
Instance details Defined in GHC.ST Methods pure :: a -> ST s a Source # (<>) :: ST s (a -> b) -> ST s a -> ST s b Source # liftA2 :: (a -> b -> c) -> ST s a -> ST s b -> ST s c Source # (>) :: ST s a -> ST s b -> ST s b Source # (<*) :: ST s a -> ST s b -> ST s a Source #
Applicative (Proxy :: Type -> Type) #	Since: base-4.7.0.0
Instance details Defined in Data.Proxy Methods pure :: a -> Proxy a Source # (<>) :: Proxy (a -> b) -> Proxy a -> Proxy b Source # liftA2 :: (a -> b -> c) -> Proxy a -> Proxy b -> Proxy c Source # (>) :: Proxy a -> Proxy b -> Proxy b Source # (<*) :: Proxy a -> Proxy b -> Proxy a Source #
Arrow a => Applicative (ArrowMonad a) #	Since: base-4.6.0.0
Instance details Defined in Control.Arrow Methods pure :: a0 -> ArrowMonad a a0 Source # (<>) :: ArrowMonad a (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b Source # liftA2 :: (a0 -> b -> c) -> ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a c Source # (>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b Source # (<*) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a a0 Source #
Monad m => Applicative (WrappedMonad m) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a -> WrappedMonad m a Source # (<>) :: WrappedMonad m (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source # liftA2 :: (a -> b -> c) -> WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m c Source # (>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b Source # (<*) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m a Source #
Applicative (ST s) #	Since: base-2.1
Instance details Defined in Control.Monad.ST.Lazy.Imp Methods pure :: a -> ST s a Source # (<>) :: ST s (a -> b) -> ST s a -> ST s b Source # liftA2 :: (a -> b -> c) -> ST s a -> ST s b -> ST s c Source # (>) :: ST s a -> ST s b -> ST s b Source # (<*) :: ST s a -> ST s b -> ST s a Source #
Applicative f => Applicative (Rec1 f) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> Rec1 f a Source # (<>) :: Rec1 f (a -> b) -> Rec1 f a -> Rec1 f b Source # liftA2 :: (a -> b -> c) -> Rec1 f a -> Rec1 f b -> Rec1 f c Source # (>) :: Rec1 f a -> Rec1 f b -> Rec1 f b Source # (<*) :: Rec1 f a -> Rec1 f b -> Rec1 f a Source #
(Monoid a, Monoid b) => Applicative ((,,) a b) #	Since: base-4.14.0.0
Instance details Defined in GHC.Base Methods pure :: a0 -> (a, b, a0) Source # (<>) :: (a, b, a0 -> b0) -> (a, b, a0) -> (a, b, b0) Source # liftA2 :: (a0 -> b0 -> c) -> (a, b, a0) -> (a, b, b0) -> (a, b, c) Source # (>) :: (a, b, a0) -> (a, b, b0) -> (a, b, b0) Source # (<*) :: (a, b, a0) -> (a, b, b0) -> (a, b, a0) Source #
Applicative f => Applicative (Alt f) #	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods pure :: a -> Alt f a Source # (<>) :: Alt f (a -> b) -> Alt f a -> Alt f b Source # liftA2 :: (a -> b -> c) -> Alt f a -> Alt f b -> Alt f c Source # (>) :: Alt f a -> Alt f b -> Alt f b Source # (<*) :: Alt f a -> Alt f b -> Alt f a Source #
Applicative f => Applicative (Ap f) #	Since: base-4.12.0.0
Instance details Defined in Data.Monoid Methods pure :: a -> Ap f a Source # (<>) :: Ap f (a -> b) -> Ap f a -> Ap f b Source # liftA2 :: (a -> b -> c) -> Ap f a -> Ap f b -> Ap f c Source # (>) :: Ap f a -> Ap f b -> Ap f b Source # (<*) :: Ap f a -> Ap f b -> Ap f a Source #
Monoid m => Applicative (Const m :: Type -> Type) #	Since: base-2.0.1
Instance details Defined in Data.Functor.Const Methods pure :: a -> Const m a Source # (<>) :: Const m (a -> b) -> Const m a -> Const m b Source # liftA2 :: (a -> b -> c) -> Const m a -> Const m b -> Const m c Source # (>) :: Const m a -> Const m b -> Const m b Source # (<*) :: Const m a -> Const m b -> Const m a Source #
Applicative m => Applicative (Kleisli m a) #	Since: base-4.14.0.0
Instance details Defined in Control.Arrow Methods pure :: a0 -> Kleisli m a a0 Source # (<>) :: Kleisli m a (a0 -> b) -> Kleisli m a a0 -> Kleisli m a b Source # liftA2 :: (a0 -> b -> c) -> Kleisli m a a0 -> Kleisli m a b -> Kleisli m a c Source # (>) :: Kleisli m a a0 -> Kleisli m a b -> Kleisli m a b Source # (<*) :: Kleisli m a a0 -> Kleisli m a b -> Kleisli m a a0 Source #
Arrow a => Applicative (WrappedArrow a b) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a0 -> WrappedArrow a b a0 Source # (<>) :: WrappedArrow a b (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 Source # liftA2 :: (a0 -> b0 -> c) -> WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b c Source # (>) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b b0 Source # (<*) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 Source #
Monoid c => Applicative (K1 i c :: Type -> Type) #	Since: base-4.12.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> K1 i c a Source # (<>) :: K1 i c (a -> b) -> K1 i c a -> K1 i c b Source # liftA2 :: (a -> b -> c0) -> K1 i c a -> K1 i c b -> K1 i c c0 Source # (>) :: K1 i c a -> K1 i c b -> K1 i c b Source # (<*) :: K1 i c a -> K1 i c b -> K1 i c a Source #
(Applicative f, Applicative g) => Applicative (f :*: g) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> (f :: g) a Source # (<>) :: (f :: g) (a -> b) -> (f :: g) a -> (f :: g) b Source # liftA2 :: (a -> b -> c) -> (f :: g) a -> (f :: g) b -> (f :: g) c Source # (>) :: (f :: g) a -> (f :: g) b -> (f :: g) b Source # (<) :: (f :: g) a -> (f :: g) b -> (f :: g) a Source #
Applicative ((->) r) #	Since: base-2.1
Instance details Defined in GHC.Base Methods pure :: a -> r -> a Source # (<>) :: (r -> (a -> b)) -> (r -> a) -> r -> b Source # liftA2 :: (a -> b -> c) -> (r -> a) -> (r -> b) -> r -> c Source # (>) :: (r -> a) -> (r -> b) -> r -> b Source # (<*) :: (r -> a) -> (r -> b) -> r -> a Source #
(Monoid a, Monoid b, Monoid c) => Applicative ((,,,) a b c) #	Since: base-4.14.0.0
Instance details Defined in GHC.Base Methods pure :: a0 -> (a, b, c, a0) Source # (<>) :: (a, b, c, a0 -> b0) -> (a, b, c, a0) -> (a, b, c, b0) Source # liftA2 :: (a0 -> b0 -> c0) -> (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, c0) Source # (>) :: (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, b0) Source # (<*) :: (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, a0) Source #
(Applicative f, Applicative g) => Applicative (Product f g) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods pure :: a -> Product f g a Source # (<>) :: Product f g (a -> b) -> Product f g a -> Product f g b Source # liftA2 :: (a -> b -> c) -> Product f g a -> Product f g b -> Product f g c Source # (>) :: Product f g a -> Product f g b -> Product f g b Source # (<*) :: Product f g a -> Product f g b -> Product f g a Source #
Applicative f => Applicative (M1 i c f) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> M1 i c f a Source # (<>) :: M1 i c f (a -> b) -> M1 i c f a -> M1 i c f b Source # liftA2 :: (a -> b -> c0) -> M1 i c f a -> M1 i c f b -> M1 i c f c0 Source # (>) :: M1 i c f a -> M1 i c f b -> M1 i c f b Source # (<*) :: M1 i c f a -> M1 i c f b -> M1 i c f a Source #
(Applicative f, Applicative g) => Applicative (f :.: g) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods pure :: a -> (f :.: g) a Source # (<>) :: (f :.: g) (a -> b) -> (f :.: g) a -> (f :.: g) b Source # liftA2 :: (a -> b -> c) -> (f :.: g) a -> (f :.: g) b -> (f :.: g) c Source # (>) :: (f :.: g) a -> (f :.: g) b -> (f :.: g) b Source # (<*) :: (f :.: g) a -> (f :.: g) b -> (f :.: g) a Source #
(Applicative f, Applicative g) => Applicative (Compose f g) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Compose Methods pure :: a -> Compose f g a Source # (<>) :: Compose f g (a -> b) -> Compose f g a -> Compose f g b Source # liftA2 :: (a -> b -> c) -> Compose f g a -> Compose f g b -> Compose f g c Source # (>) :: Compose f g a -> Compose f g b -> Compose f g b Source # (<*) :: Compose f g a -> Compose f g b -> Compose f g a Source #

Alternatives

class Applicative f => Alternative f where Source #

A monoid on applicative functors.

If defined, some and many should be the least solutions of the equations:

```
some v = (:) <$> v <*> many v
```
```
many v = some v <|> pure []
```

Minimal complete definition

empty, (<|>)

Methods

empty :: f a Source #

The identity of <|>

(<|>) :: f a -> f a -> f a infixl 3 Source #

An associative binary operation

some :: f a -> f [a] Source #

One or more.

many :: f a -> f [a] Source #

Zero or more.

Instances

Instances details

Alternative [] #	Since: base-2.1
Instance details Defined in GHC.Base Methods empty :: [a] Source # (<\|>) :: [a] -> [a] -> [a] Source # some :: [a] -> [[a]] Source # many :: [a] -> [[a]] Source #
Alternative Maybe #	Since: base-2.1
Instance details Defined in GHC.Base Methods empty :: Maybe a Source # (<\|>) :: Maybe a -> Maybe a -> Maybe a Source # some :: Maybe a -> Maybe [a] Source # many :: Maybe a -> Maybe [a] Source #
Alternative IO #	Since: base-4.9.0.0
Instance details Defined in GHC.Base Methods empty :: IO a Source # (<\|>) :: IO a -> IO a -> IO a Source # some :: IO a -> IO [a] Source # many :: IO a -> IO [a] Source #
Alternative ReadP #	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods empty :: ReadP a Source # (<\|>) :: ReadP a -> ReadP a -> ReadP a Source # some :: ReadP a -> ReadP [a] Source # many :: ReadP a -> ReadP [a] Source #
Alternative ReadPrec #	Since: base-4.6.0.0
Instance details Defined in Text.ParserCombinators.ReadPrec Methods empty :: ReadPrec a Source # (<\|>) :: ReadPrec a -> ReadPrec a -> ReadPrec a Source # some :: ReadPrec a -> ReadPrec [a] Source # many :: ReadPrec a -> ReadPrec [a] Source #
Alternative STM #	Since: base-4.8.0.0
Instance details Defined in GHC.Conc.Sync Methods empty :: STM a Source # (<\|>) :: STM a -> STM a -> STM a Source # some :: STM a -> STM [a] Source # many :: STM a -> STM [a] Source #
Alternative ZipList #	Since: base-4.11.0.0
Instance details Defined in Control.Applicative Methods empty :: ZipList a Source # (<\|>) :: ZipList a -> ZipList a -> ZipList a Source # some :: ZipList a -> ZipList [a] Source # many :: ZipList a -> ZipList [a] Source #
Alternative Option #	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods empty :: Option a Source # (<\|>) :: Option a -> Option a -> Option a Source # some :: Option a -> Option [a] Source # many :: Option a -> Option [a] Source #
Alternative (U1 :: Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods empty :: U1 a Source # (<\|>) :: U1 a -> U1 a -> U1 a Source # some :: U1 a -> U1 [a] Source # many :: U1 a -> U1 [a] Source #
Alternative (Proxy :: Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Proxy Methods empty :: Proxy a Source # (<\|>) :: Proxy a -> Proxy a -> Proxy a Source # some :: Proxy a -> Proxy [a] Source # many :: Proxy a -> Proxy [a] Source #
ArrowPlus a => Alternative (ArrowMonad a) #	Since: base-4.6.0.0
Instance details Defined in Control.Arrow Methods empty :: ArrowMonad a a0 Source # (<\|>) :: ArrowMonad a a0 -> ArrowMonad a a0 -> ArrowMonad a a0 Source # some :: ArrowMonad a a0 -> ArrowMonad a [a0] Source # many :: ArrowMonad a a0 -> ArrowMonad a [a0] Source #
MonadPlus m => Alternative (WrappedMonad m) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods empty :: WrappedMonad m a Source # (<\|>) :: WrappedMonad m a -> WrappedMonad m a -> WrappedMonad m a Source # some :: WrappedMonad m a -> WrappedMonad m [a] Source # many :: WrappedMonad m a -> WrappedMonad m [a] Source #
Alternative f => Alternative (Rec1 f) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods empty :: Rec1 f a Source # (<\|>) :: Rec1 f a -> Rec1 f a -> Rec1 f a Source # some :: Rec1 f a -> Rec1 f [a] Source # many :: Rec1 f a -> Rec1 f [a] Source #
Alternative f => Alternative (Alt f) #	Since: base-4.8.0.0
Instance details Defined in Data.Semigroup.Internal Methods empty :: Alt f a Source # (<\|>) :: Alt f a -> Alt f a -> Alt f a Source # some :: Alt f a -> Alt f [a] Source # many :: Alt f a -> Alt f [a] Source #
Alternative f => Alternative (Ap f) #	Since: base-4.12.0.0
Instance details Defined in Data.Monoid Methods empty :: Ap f a Source # (<\|>) :: Ap f a -> Ap f a -> Ap f a Source # some :: Ap f a -> Ap f [a] Source # many :: Ap f a -> Ap f [a] Source #
Alternative m => Alternative (Kleisli m a) #	Since: base-4.14.0.0
Instance details Defined in Control.Arrow Methods empty :: Kleisli m a a0 Source # (<\|>) :: Kleisli m a a0 -> Kleisli m a a0 -> Kleisli m a a0 Source # some :: Kleisli m a a0 -> Kleisli m a [a0] Source # many :: Kleisli m a a0 -> Kleisli m a [a0] Source #
(ArrowZero a, ArrowPlus a) => Alternative (WrappedArrow a b) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods empty :: WrappedArrow a b a0 Source # (<\|>) :: WrappedArrow a b a0 -> WrappedArrow a b a0 -> WrappedArrow a b a0 Source # some :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source # many :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source #
(Alternative f, Alternative g) => Alternative (f :*: g) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods empty :: (f :: g) a Source # (<\|>) :: (f :: g) a -> (f :: g) a -> (f :: g) a Source # some :: (f :: g) a -> (f :: g) [a] Source # many :: (f :: g) a -> (f :: g) [a] Source #
(Alternative f, Alternative g) => Alternative (Product f g) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods empty :: Product f g a Source # (<\|>) :: Product f g a -> Product f g a -> Product f g a Source # some :: Product f g a -> Product f g [a] Source # many :: Product f g a -> Product f g [a] Source #
Alternative f => Alternative (M1 i c f) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods empty :: M1 i c f a Source # (<\|>) :: M1 i c f a -> M1 i c f a -> M1 i c f a Source # some :: M1 i c f a -> M1 i c f [a] Source # many :: M1 i c f a -> M1 i c f [a] Source #
(Alternative f, Applicative g) => Alternative (f :.: g) #	Since: base-4.9.0.0
Instance details Defined in GHC.Generics Methods empty :: (f :.: g) a Source # (<\|>) :: (f :.: g) a -> (f :.: g) a -> (f :.: g) a Source # some :: (f :.: g) a -> (f :.: g) [a] Source # many :: (f :.: g) a -> (f :.: g) [a] Source #
(Alternative f, Applicative g) => Alternative (Compose f g) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Compose Methods empty :: Compose f g a Source # (<\|>) :: Compose f g a -> Compose f g a -> Compose f g a Source # some :: Compose f g a -> Compose f g [a] Source # many :: Compose f g a -> Compose f g [a] Source #

Instances

newtype Const a b Source #

The Const functor.

Constructors

Const
Fields getConst :: a

Instances

Instances details

Generic1 (Const a :: k -> Type) #
Instance details Defined in Data.Functor.Const Associated Types type Rep1 (Const a) :: k -> Type Source # Methods from1 :: forall (a0 :: k0). Const a a0 -> Rep1 (Const a) a0 Source # to1 :: forall (a0 :: k0). Rep1 (Const a) a0 -> Const a a0 Source #
Show2 (Const :: Type -> Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftShowsPrec2 :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> (Int -> b -> ShowS) -> ([b] -> ShowS) -> Int -> Const a b -> ShowS Source # liftShowList2 :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> (Int -> b -> ShowS) -> ([b] -> ShowS) -> [Const a b] -> ShowS Source #
Read2 (Const :: Type -> Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftReadsPrec2 :: (Int -> ReadS a) -> ReadS [a] -> (Int -> ReadS b) -> ReadS [b] -> Int -> ReadS (Const a b) Source # liftReadList2 :: (Int -> ReadS a) -> ReadS [a] -> (Int -> ReadS b) -> ReadS [b] -> ReadS [Const a b] Source # liftReadPrec2 :: ReadPrec a -> ReadPrec [a] -> ReadPrec b -> ReadPrec [b] -> ReadPrec (Const a b) Source # liftReadListPrec2 :: ReadPrec a -> ReadPrec [a] -> ReadPrec b -> ReadPrec [b] -> ReadPrec [Const a b] Source #
Ord2 (Const :: Type -> Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftCompare2 :: (a -> b -> Ordering) -> (c -> d -> Ordering) -> Const a c -> Const b d -> Ordering Source #
Eq2 (Const :: Type -> Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftEq2 :: (a -> b -> Bool) -> (c -> d -> Bool) -> Const a c -> Const b d -> Bool Source #
Bifunctor (Const :: Type -> Type -> Type) #	Since: base-4.8.0.0
Instance details Defined in Data.Bifunctor Methods bimap :: (a -> b) -> (c -> d) -> Const a c -> Const b d Source # first :: (a -> b) -> Const a c -> Const b c Source # second :: (b -> c) -> Const a b -> Const a c Source #
Bifoldable (Const :: Type -> Type -> Type) #	Since: base-4.10.0.0
Instance details Defined in Data.Bifoldable Methods bifold :: Monoid m => Const m m -> m Source # bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> Const a b -> m Source # bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> Const a b -> c Source # bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> Const a b -> c Source #
Bitraversable (Const :: Type -> Type -> Type) #	Since: base-4.10.0.0
Instance details Defined in Data.Bitraversable Methods bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Const a b -> f (Const c d) Source #
Functor (Const m :: Type -> Type) #	Since: base-2.1
Instance details Defined in Data.Functor.Const Methods fmap :: (a -> b) -> Const m a -> Const m b Source # (<$) :: a -> Const m b -> Const m a Source #
Monoid m => Applicative (Const m :: Type -> Type) #	Since: base-2.0.1
Instance details Defined in Data.Functor.Const Methods pure :: a -> Const m a Source # (<>) :: Const m (a -> b) -> Const m a -> Const m b Source # liftA2 :: (a -> b -> c) -> Const m a -> Const m b -> Const m c Source # (>) :: Const m a -> Const m b -> Const m b Source # (<*) :: Const m a -> Const m b -> Const m a Source #
Foldable (Const m :: Type -> Type) #	Since: base-4.7.0.0
Instance details Defined in Data.Functor.Const Methods fold :: Monoid m0 => Const m m0 -> m0 Source # foldMap :: Monoid m0 => (a -> m0) -> Const m a -> m0 Source # foldMap' :: Monoid m0 => (a -> m0) -> Const m a -> m0 Source # foldr :: (a -> b -> b) -> b -> Const m a -> b Source # foldr' :: (a -> b -> b) -> b -> Const m a -> b Source # foldl :: (b -> a -> b) -> b -> Const m a -> b Source # foldl' :: (b -> a -> b) -> b -> Const m a -> b Source # foldr1 :: (a -> a -> a) -> Const m a -> a Source # foldl1 :: (a -> a -> a) -> Const m a -> a Source # toList :: Const m a -> [a] Source # null :: Const m a -> Bool Source # length :: Const m a -> Int Source # elem :: Eq a => a -> Const m a -> Bool Source # maximum :: Ord a => Const m a -> a Source # minimum :: Ord a => Const m a -> a Source # sum :: Num a => Const m a -> a Source # product :: Num a => Const m a -> a Source #
Traversable (Const m :: Type -> Type) #	Since: base-4.7.0.0
Instance details Defined in Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Const m a -> f (Const m b) Source # sequenceA :: Applicative f => Const m (f a) -> f (Const m a) Source # mapM :: Monad m0 => (a -> m0 b) -> Const m a -> m0 (Const m b) Source # sequence :: Monad m0 => Const m (m0 a) -> m0 (Const m a) Source #
Show a => Show1 (Const a :: Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftShowsPrec :: (Int -> a0 -> ShowS) -> ([a0] -> ShowS) -> Int -> Const a a0 -> ShowS Source # liftShowList :: (Int -> a0 -> ShowS) -> ([a0] -> ShowS) -> [Const a a0] -> ShowS Source #
Read a => Read1 (Const a :: Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftReadsPrec :: (Int -> ReadS a0) -> ReadS [a0] -> Int -> ReadS (Const a a0) Source # liftReadList :: (Int -> ReadS a0) -> ReadS [a0] -> ReadS [Const a a0] Source # liftReadPrec :: ReadPrec a0 -> ReadPrec [a0] -> ReadPrec (Const a a0) Source # liftReadListPrec :: ReadPrec a0 -> ReadPrec [a0] -> ReadPrec [Const a a0] Source #
Ord a => Ord1 (Const a :: Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftCompare :: (a0 -> b -> Ordering) -> Const a a0 -> Const a b -> Ordering Source #
Eq a => Eq1 (Const a :: Type -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftEq :: (a0 -> b -> Bool) -> Const a a0 -> Const a b -> Bool Source #
Contravariant (Const a :: Type -> Type) #
Instance details Defined in Data.Functor.Contravariant Methods contramap :: (a' -> a0) -> Const a a0 -> Const a a' Source # (>$) :: b -> Const a b -> Const a a0 Source #
Bounded a => Bounded (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods minBound :: Const a b Source # maxBound :: Const a b Source #
Enum a => Enum (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods succ :: Const a b -> Const a b Source # pred :: Const a b -> Const a b Source # toEnum :: Int -> Const a b Source # fromEnum :: Const a b -> Int Source # enumFrom :: Const a b -> [Const a b] Source # enumFromThen :: Const a b -> Const a b -> [Const a b] Source # enumFromTo :: Const a b -> Const a b -> [Const a b] Source # enumFromThenTo :: Const a b -> Const a b -> Const a b -> [Const a b] Source #
Eq a => Eq (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods (==) :: Const a b -> Const a b -> Bool Source # (/=) :: Const a b -> Const a b -> Bool Source #
Floating a => Floating (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods pi :: Const a b Source # exp :: Const a b -> Const a b Source # log :: Const a b -> Const a b Source # sqrt :: Const a b -> Const a b Source # (**) :: Const a b -> Const a b -> Const a b Source # logBase :: Const a b -> Const a b -> Const a b Source # sin :: Const a b -> Const a b Source # cos :: Const a b -> Const a b Source # tan :: Const a b -> Const a b Source # asin :: Const a b -> Const a b Source # acos :: Const a b -> Const a b Source # atan :: Const a b -> Const a b Source # sinh :: Const a b -> Const a b Source # cosh :: Const a b -> Const a b Source # tanh :: Const a b -> Const a b Source # asinh :: Const a b -> Const a b Source # acosh :: Const a b -> Const a b Source # atanh :: Const a b -> Const a b Source # log1p :: Const a b -> Const a b Source # expm1 :: Const a b -> Const a b Source # log1pexp :: Const a b -> Const a b Source # log1mexp :: Const a b -> Const a b Source #
Fractional a => Fractional (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods (/) :: Const a b -> Const a b -> Const a b Source # recip :: Const a b -> Const a b Source # fromRational :: Rational -> Const a b Source #
Integral a => Integral (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods quot :: Const a b -> Const a b -> Const a b Source # rem :: Const a b -> Const a b -> Const a b Source # div :: Const a b -> Const a b -> Const a b Source # mod :: Const a b -> Const a b -> Const a b Source # quotRem :: Const a b -> Const a b -> (Const a b, Const a b) Source # divMod :: Const a b -> Const a b -> (Const a b, Const a b) Source # toInteger :: Const a b -> Integer Source #
(Typeable k, Data a, Typeable b) => Data (Const a b) #	Since: base-4.10.0.0
Instance details Defined in Data.Data Methods gfoldl :: (forall d b0. Data d => c (d -> b0) -> d -> c b0) -> (forall g. g -> c g) -> Const a b -> c (Const a b) Source # gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Const a b) Source # toConstr :: Const a b -> Constr Source # dataTypeOf :: Const a b -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Const a b)) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Const a b)) Source # gmapT :: (forall b0. Data b0 => b0 -> b0) -> Const a b -> Const a b Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Const a b -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Const a b -> r Source # gmapQ :: (forall d. Data d => d -> u) -> Const a b -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> Const a b -> u Source # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Const a b -> m (Const a b) Source # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Const a b -> m (Const a b) Source # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Const a b -> m (Const a b) Source #
Num a => Num (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods (+) :: Const a b -> Const a b -> Const a b Source # (-) :: Const a b -> Const a b -> Const a b Source # (*) :: Const a b -> Const a b -> Const a b Source # negate :: Const a b -> Const a b Source # abs :: Const a b -> Const a b Source # signum :: Const a b -> Const a b Source # fromInteger :: Integer -> Const a b Source #
Ord a => Ord (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods compare :: Const a b -> Const a b -> Ordering Source # (<) :: Const a b -> Const a b -> Bool Source # (<=) :: Const a b -> Const a b -> Bool Source # (>) :: Const a b -> Const a b -> Bool Source # (>=) :: Const a b -> Const a b -> Bool Source # max :: Const a b -> Const a b -> Const a b Source # min :: Const a b -> Const a b -> Const a b Source #
Read a => Read (Const a b) #	This instance would be equivalent to the derived instances of the `Const` newtype if the `getConst` field were removed Since: base-4.8.0.0
Instance details Defined in Data.Functor.Const Methods readsPrec :: Int -> ReadS (Const a b) Source # readList :: ReadS [Const a b] Source # readPrec :: ReadPrec (Const a b) Source # readListPrec :: ReadPrec [Const a b] Source #
Real a => Real (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods toRational :: Const a b -> Rational Source #
RealFloat a => RealFloat (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods floatRadix :: Const a b -> Integer Source # floatDigits :: Const a b -> Int Source # floatRange :: Const a b -> (Int, Int) Source # decodeFloat :: Const a b -> (Integer, Int) Source # encodeFloat :: Integer -> Int -> Const a b Source # exponent :: Const a b -> Int Source # significand :: Const a b -> Const a b Source # scaleFloat :: Int -> Const a b -> Const a b Source # isNaN :: Const a b -> Bool Source # isInfinite :: Const a b -> Bool Source # isDenormalized :: Const a b -> Bool Source # isNegativeZero :: Const a b -> Bool Source # isIEEE :: Const a b -> Bool Source # atan2 :: Const a b -> Const a b -> Const a b Source #
RealFrac a => RealFrac (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods properFraction :: Integral b0 => Const a b -> (b0, Const a b) Source # truncate :: Integral b0 => Const a b -> b0 Source # round :: Integral b0 => Const a b -> b0 Source # ceiling :: Integral b0 => Const a b -> b0 Source # floor :: Integral b0 => Const a b -> b0 Source #
Show a => Show (Const a b) #	This instance would be equivalent to the derived instances of the `Const` newtype if the `getConst` field were removed Since: base-4.8.0.0
Instance details Defined in Data.Functor.Const Methods showsPrec :: Int -> Const a b -> ShowS Source # show :: Const a b -> String Source # showList :: [Const a b] -> ShowS Source #
Ix a => Ix (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods range :: (Const a b, Const a b) -> [Const a b] Source # index :: (Const a b, Const a b) -> Const a b -> Int Source # unsafeIndex :: (Const a b, Const a b) -> Const a b -> Int Source # inRange :: (Const a b, Const a b) -> Const a b -> Bool Source # rangeSize :: (Const a b, Const a b) -> Int Source # unsafeRangeSize :: (Const a b, Const a b) -> Int Source #
IsString a => IsString (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.String Methods fromString :: String -> Const a b Source #
Generic (Const a b) #
Instance details Defined in Data.Functor.Const Associated Types type Rep (Const a b) :: Type -> Type Source # Methods from :: Const a b -> Rep (Const a b) x Source # to :: Rep (Const a b) x -> Const a b Source #
Semigroup a => Semigroup (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods (<>) :: Const a b -> Const a b -> Const a b Source # sconcat :: NonEmpty (Const a b) -> Const a b Source # stimes :: Integral b0 => b0 -> Const a b -> Const a b Source #
Monoid a => Monoid (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods mempty :: Const a b Source # mappend :: Const a b -> Const a b -> Const a b Source # mconcat :: [Const a b] -> Const a b Source #
FiniteBits a => FiniteBits (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods finiteBitSize :: Const a b -> Int Source # countLeadingZeros :: Const a b -> Int Source # countTrailingZeros :: Const a b -> Int Source #
Bits a => Bits (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods (.&.) :: Const a b -> Const a b -> Const a b Source # (.\|.) :: Const a b -> Const a b -> Const a b Source # xor :: Const a b -> Const a b -> Const a b Source # complement :: Const a b -> Const a b Source # shift :: Const a b -> Int -> Const a b Source # rotate :: Const a b -> Int -> Const a b Source # zeroBits :: Const a b Source # bit :: Int -> Const a b Source # setBit :: Const a b -> Int -> Const a b Source # clearBit :: Const a b -> Int -> Const a b Source # complementBit :: Const a b -> Int -> Const a b Source # testBit :: Const a b -> Int -> Bool Source # bitSizeMaybe :: Const a b -> Maybe Int Source # bitSize :: Const a b -> Int Source # isSigned :: Const a b -> Bool Source # shiftL :: Const a b -> Int -> Const a b Source # unsafeShiftL :: Const a b -> Int -> Const a b Source # shiftR :: Const a b -> Int -> Const a b Source # unsafeShiftR :: Const a b -> Int -> Const a b Source # rotateL :: Const a b -> Int -> Const a b Source # rotateR :: Const a b -> Int -> Const a b Source # popCount :: Const a b -> Int Source #
Storable a => Storable (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const Methods sizeOf :: Const a b -> Int Source # alignment :: Const a b -> Int Source # peekElemOff :: Ptr (Const a b) -> Int -> IO (Const a b) Source # pokeElemOff :: Ptr (Const a b) -> Int -> Const a b -> IO () Source # peekByteOff :: Ptr b0 -> Int -> IO (Const a b) Source # pokeByteOff :: Ptr b0 -> Int -> Const a b -> IO () Source # peek :: Ptr (Const a b) -> IO (Const a b) Source # poke :: Ptr (Const a b) -> Const a b -> IO () Source #
type Rep1 (Const a :: k -> Type) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const type Rep1 (Const a :: k -> Type) = D1 ('MetaData "Const" "Data.Functor.Const" "base" 'True) (C1 ('MetaCons "Const" 'PrefixI 'True) (S1 ('MetaSel ('Just "getConst") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)))
type Rep (Const a b) #	Since: base-4.9.0.0
Instance details Defined in Data.Functor.Const type Rep (Const a b) = D1 ('MetaData "Const" "Data.Functor.Const" "base" 'True) (C1 ('MetaCons "Const" 'PrefixI 'True) (S1 ('MetaSel ('Just "getConst") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)))

newtype WrappedMonad m a Source #

Constructors

WrapMonad
Fields unwrapMonad :: m a

Instances

Instances details

Monad m => Monad (WrappedMonad m) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative Methods (>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b Source # (>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b Source # return :: a -> WrappedMonad m a Source #
Monad m => Functor (WrappedMonad m) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source # (<$) :: a -> WrappedMonad m b -> WrappedMonad m a Source #
Monad m => Applicative (WrappedMonad m) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a -> WrappedMonad m a Source # (<>) :: WrappedMonad m (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source # liftA2 :: (a -> b -> c) -> WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m c Source # (>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b Source # (<*) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m a Source #
MonadPlus m => Alternative (WrappedMonad m) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods empty :: WrappedMonad m a Source # (<\|>) :: WrappedMonad m a -> WrappedMonad m a -> WrappedMonad m a Source # some :: WrappedMonad m a -> WrappedMonad m [a] Source # many :: WrappedMonad m a -> WrappedMonad m [a] Source #
Generic1 (WrappedMonad m :: Type -> Type) #
Instance details Defined in Control.Applicative Associated Types type Rep1 (WrappedMonad m) :: k -> Type Source # Methods from1 :: forall (a :: k). WrappedMonad m a -> Rep1 (WrappedMonad m) a Source # to1 :: forall (a :: k). Rep1 (WrappedMonad m) a -> WrappedMonad m a Source #
(Typeable m, Typeable a, Data (m a)) => Data (WrappedMonad m a) #	Since: base-4.14.0.0
Instance details Defined in Data.Data Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> WrappedMonad m a -> c (WrappedMonad m a) Source # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (WrappedMonad m a) Source # toConstr :: WrappedMonad m a -> Constr Source # dataTypeOf :: WrappedMonad m a -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (WrappedMonad m a)) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (WrappedMonad m a)) Source # gmapT :: (forall b. Data b => b -> b) -> WrappedMonad m a -> WrappedMonad m a Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> WrappedMonad m a -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> WrappedMonad m a -> r Source # gmapQ :: (forall d. Data d => d -> u) -> WrappedMonad m a -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> WrappedMonad m a -> u Source # gmapM :: Monad m0 => (forall d. Data d => d -> m0 d) -> WrappedMonad m a -> m0 (WrappedMonad m a) Source # gmapMp :: MonadPlus m0 => (forall d. Data d => d -> m0 d) -> WrappedMonad m a -> m0 (WrappedMonad m a) Source # gmapMo :: MonadPlus m0 => (forall d. Data d => d -> m0 d) -> WrappedMonad m a -> m0 (WrappedMonad m a) Source #
Generic (WrappedMonad m a) #
Instance details Defined in Control.Applicative Associated Types type Rep (WrappedMonad m a) :: Type -> Type Source # Methods from :: WrappedMonad m a -> Rep (WrappedMonad m a) x Source # to :: Rep (WrappedMonad m a) x -> WrappedMonad m a Source #
type Rep1 (WrappedMonad m :: Type -> Type) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative type Rep1 (WrappedMonad m :: Type -> Type) = D1 ('MetaData "WrappedMonad" "Control.Applicative" "base" 'True) (C1 ('MetaCons "WrapMonad" 'PrefixI 'True) (S1 ('MetaSel ('Just "unwrapMonad") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 m)))
type Rep (WrappedMonad m a) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative type Rep (WrappedMonad m a) = D1 ('MetaData "WrappedMonad" "Control.Applicative" "base" 'True) (C1 ('MetaCons "WrapMonad" 'PrefixI 'True) (S1 ('MetaSel ('Just "unwrapMonad") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m a))))

newtype WrappedArrow a b c Source #

Constructors

WrapArrow
Fields unwrapArrow :: a b c

Instances

Instances details

Generic1 (WrappedArrow a b :: Type -> Type) #
Instance details Defined in Control.Applicative Associated Types type Rep1 (WrappedArrow a b) :: k -> Type Source # Methods from1 :: forall (a0 :: k). WrappedArrow a b a0 -> Rep1 (WrappedArrow a b) a0 Source # to1 :: forall (a0 :: k). Rep1 (WrappedArrow a b) a0 -> WrappedArrow a b a0 Source #
Arrow a => Functor (WrappedArrow a b) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 Source # (<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 Source #
Arrow a => Applicative (WrappedArrow a b) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a0 -> WrappedArrow a b a0 Source # (<>) :: WrappedArrow a b (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 Source # liftA2 :: (a0 -> b0 -> c) -> WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b c Source # (>) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b b0 Source # (<*) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 Source #
(ArrowZero a, ArrowPlus a) => Alternative (WrappedArrow a b) #	Since: base-2.1
Instance details Defined in Control.Applicative Methods empty :: WrappedArrow a b a0 Source # (<\|>) :: WrappedArrow a b a0 -> WrappedArrow a b a0 -> WrappedArrow a b a0 Source # some :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source # many :: WrappedArrow a b a0 -> WrappedArrow a b [a0] Source #
(Typeable a, Typeable b, Typeable c, Data (a b c)) => Data (WrappedArrow a b c) #	Since: base-4.14.0.0
Instance details Defined in Data.Data Methods gfoldl :: (forall d b0. Data d => c0 (d -> b0) -> d -> c0 b0) -> (forall g. g -> c0 g) -> WrappedArrow a b c -> c0 (WrappedArrow a b c) Source # gunfold :: (forall b0 r. Data b0 => c0 (b0 -> r) -> c0 r) -> (forall r. r -> c0 r) -> Constr -> c0 (WrappedArrow a b c) Source # toConstr :: WrappedArrow a b c -> Constr Source # dataTypeOf :: WrappedArrow a b c -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c0 (t d)) -> Maybe (c0 (WrappedArrow a b c)) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c0 (t d e)) -> Maybe (c0 (WrappedArrow a b c)) Source # gmapT :: (forall b0. Data b0 => b0 -> b0) -> WrappedArrow a b c -> WrappedArrow a b c Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> WrappedArrow a b c -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> WrappedArrow a b c -> r Source # gmapQ :: (forall d. Data d => d -> u) -> WrappedArrow a b c -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> WrappedArrow a b c -> u Source # gmapM :: Monad m => (forall d. Data d => d -> m d) -> WrappedArrow a b c -> m (WrappedArrow a b c) Source # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> WrappedArrow a b c -> m (WrappedArrow a b c) Source # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> WrappedArrow a b c -> m (WrappedArrow a b c) Source #
Generic (WrappedArrow a b c) #
Instance details Defined in Control.Applicative Associated Types type Rep (WrappedArrow a b c) :: Type -> Type Source # Methods from :: WrappedArrow a b c -> Rep (WrappedArrow a b c) x Source # to :: Rep (WrappedArrow a b c) x -> WrappedArrow a b c Source #
type Rep1 (WrappedArrow a b :: Type -> Type) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative type Rep1 (WrappedArrow a b :: Type -> Type) = D1 ('MetaData "WrappedArrow" "Control.Applicative" "base" 'True) (C1 ('MetaCons "WrapArrow" 'PrefixI 'True) (S1 ('MetaSel ('Just "unwrapArrow") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 (a b))))
type Rep (WrappedArrow a b c) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative type Rep (WrappedArrow a b c) = D1 ('MetaData "WrappedArrow" "Control.Applicative" "base" 'True) (C1 ('MetaCons "WrapArrow" 'PrefixI 'True) (S1 ('MetaSel ('Just "unwrapArrow") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (a b c))))

newtype ZipList a Source #

Lists, but with an Applicative functor based on zipping.

Constructors

ZipList
Fields getZipList :: [a]

Instances

Instances details

Functor ZipList #	Since: base-2.1
Instance details Defined in Control.Applicative Methods fmap :: (a -> b) -> ZipList a -> ZipList b Source # (<$) :: a -> ZipList b -> ZipList a Source #
Applicative ZipList #	f <$> ZipList xs1 <> ... <> ZipList xsN = ZipList (zipWithN f xs1 ... xsN) where `zipWithN` refers to the `zipWith` function of the appropriate arity (`zipWith`, `zipWith3`, `zipWith4`, ...). For example: (\a b c -> stimes c [a, b]) <$> ZipList "abcd" <> ZipList "567" <> ZipList [1..] = ZipList (zipWith3 (\a b c -> stimes c [a, b]) "abcd" "567" [1..]) = ZipList {getZipList = ["a5","b6b6","c7c7c7"]} Since: base-2.1
Instance details Defined in Control.Applicative Methods pure :: a -> ZipList a Source # (<>) :: ZipList (a -> b) -> ZipList a -> ZipList b Source # liftA2 :: (a -> b -> c) -> ZipList a -> ZipList b -> ZipList c Source # (>) :: ZipList a -> ZipList b -> ZipList b Source # (<*) :: ZipList a -> ZipList b -> ZipList a Source #
Foldable ZipList #	Since: base-4.9.0.0
Instance details Defined in Control.Applicative Methods fold :: Monoid m => ZipList m -> m Source # foldMap :: Monoid m => (a -> m) -> ZipList a -> m Source # foldMap' :: Monoid m => (a -> m) -> ZipList a -> m Source # foldr :: (a -> b -> b) -> b -> ZipList a -> b Source # foldr' :: (a -> b -> b) -> b -> ZipList a -> b Source # foldl :: (b -> a -> b) -> b -> ZipList a -> b Source # foldl' :: (b -> a -> b) -> b -> ZipList a -> b Source # foldr1 :: (a -> a -> a) -> ZipList a -> a Source # foldl1 :: (a -> a -> a) -> ZipList a -> a Source # toList :: ZipList a -> [a] Source # null :: ZipList a -> Bool Source # length :: ZipList a -> Int Source # elem :: Eq a => a -> ZipList a -> Bool Source # maximum :: Ord a => ZipList a -> a Source # minimum :: Ord a => ZipList a -> a Source # sum :: Num a => ZipList a -> a Source # product :: Num a => ZipList a -> a Source #
Traversable ZipList #	Since: base-4.9.0.0
Instance details Defined in Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> ZipList a -> f (ZipList b) Source # sequenceA :: Applicative f => ZipList (f a) -> f (ZipList a) Source # mapM :: Monad m => (a -> m b) -> ZipList a -> m (ZipList b) Source # sequence :: Monad m => ZipList (m a) -> m (ZipList a) Source #
Alternative ZipList #	Since: base-4.11.0.0
Instance details Defined in Control.Applicative Methods empty :: ZipList a Source # (<\|>) :: ZipList a -> ZipList a -> ZipList a Source # some :: ZipList a -> ZipList [a] Source # many :: ZipList a -> ZipList [a] Source #
IsList (ZipList a) #	Since: base-4.15.0.0
Instance details Defined in GHC.Exts Associated Types type Item (ZipList a) Source # Methods fromList :: [Item (ZipList a)] -> ZipList a Source # fromListN :: Int -> [Item (ZipList a)] -> ZipList a Source # toList :: ZipList a -> [Item (ZipList a)] Source #
Eq a => Eq (ZipList a) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative Methods (==) :: ZipList a -> ZipList a -> Bool Source # (/=) :: ZipList a -> ZipList a -> Bool Source #
Data a => Data (ZipList a) #	Since: base-4.14.0.0
Instance details Defined in Data.Data Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ZipList a -> c (ZipList a) Source # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ZipList a) Source # toConstr :: ZipList a -> Constr Source # dataTypeOf :: ZipList a -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (ZipList a)) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (ZipList a)) Source # gmapT :: (forall b. Data b => b -> b) -> ZipList a -> ZipList a Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ZipList a -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ZipList a -> r Source # gmapQ :: (forall d. Data d => d -> u) -> ZipList a -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> ZipList a -> u Source # gmapM :: Monad m => (forall d. Data d => d -> m d) -> ZipList a -> m (ZipList a) Source # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ZipList a -> m (ZipList a) Source # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ZipList a -> m (ZipList a) Source #
Ord a => Ord (ZipList a) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative Methods compare :: ZipList a -> ZipList a -> Ordering Source # (<) :: ZipList a -> ZipList a -> Bool Source # (<=) :: ZipList a -> ZipList a -> Bool Source # (>) :: ZipList a -> ZipList a -> Bool Source # (>=) :: ZipList a -> ZipList a -> Bool Source # max :: ZipList a -> ZipList a -> ZipList a Source # min :: ZipList a -> ZipList a -> ZipList a Source #
Read a => Read (ZipList a) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative Methods readsPrec :: Int -> ReadS (ZipList a) Source # readList :: ReadS [ZipList a] Source # readPrec :: ReadPrec (ZipList a) Source # readListPrec :: ReadPrec [ZipList a] Source #
Show a => Show (ZipList a) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative Methods showsPrec :: Int -> ZipList a -> ShowS Source # show :: ZipList a -> String Source # showList :: [ZipList a] -> ShowS Source #
Generic (ZipList a) #
Instance details Defined in Control.Applicative Associated Types type Rep (ZipList a) :: Type -> Type Source # Methods from :: ZipList a -> Rep (ZipList a) x Source # to :: Rep (ZipList a) x -> ZipList a Source #
Generic1 ZipList #
Instance details Defined in Control.Applicative Associated Types type Rep1 ZipList :: k -> Type Source # Methods from1 :: forall (a :: k). ZipList a -> Rep1 ZipList a Source # to1 :: forall (a :: k). Rep1 ZipList a -> ZipList a Source #
type Rep (ZipList a) #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative type Rep (ZipList a) = D1 ('MetaData "ZipList" "Control.Applicative" "base" 'True) (C1 ('MetaCons "ZipList" 'PrefixI 'True) (S1 ('MetaSel ('Just "getZipList") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 [a])))
type Item (ZipList a) #
Instance details Defined in GHC.Exts type Item (ZipList a) = a
type Rep1 ZipList #	Since: base-4.7.0.0
Instance details Defined in Control.Applicative type Rep1 ZipList = D1 ('MetaData "ZipList" "Control.Applicative" "base" 'True) (C1 ('MetaCons "ZipList" 'PrefixI 'True) (S1 ('MetaSel ('Just "getZipList") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 [])))

Utility functions

(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 Source #

An infix synonym for fmap.

The name of this operator is an allusion to $. Note the similarities between their types:

 ($)  ::              (a -> b) ->   a ->   b
(<$>) :: Functor f => (a -> b) -> f a -> f b

Whereas $ is function application, <$> is function application lifted over a Functor.

Examples

Expand

Convert from a Maybe Int to a Maybe String using show:

>>> show <$> Nothing
Nothing
>>> show <$> Just 3
Just "3"

Convert from an Either Int Int to an Either Int String using show:

>>> show <$> Left 17
Left 17
>>> show <$> Right 17
Right "17"

Double each element of a list:

>>> (*2) <$> [1,2,3]
[2,4,6]

Apply even to the second element of a pair:

>>> even <$> (2,2)
(2,True)

(<$) :: Functor f => a -> f b -> f a infixl 4 Source #

Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

Using ApplicativeDo: 'a <$ bs' can be understood as the do expression

do bs
   pure a

with an inferred Functor constraint.

(<**>) :: Applicative f => f a -> f (a -> b) -> f b infixl 4 Source #

A variant of <*> with the arguments reversed.

Using ApplicativeDo: 'as <**> fs' can be understood as the do expression

do a <- as
   f <- fs
   pure (f a)

liftA :: Applicative f => (a -> b) -> f a -> f b Source #

Lift a function to actions. This function may be used as a value for fmap in a Functor instance.

Using ApplicativeDo: 'liftA f as' can be understood as the do expression

do a <- as
   pure (f a)

with an inferred Functor constraint, weaker than Applicative.

liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d Source #

Lift a ternary function to actions.

Using ApplicativeDo: 'liftA3 f as bs cs' can be understood as the do expression

do a <- as
   b <- bs
   c <- cs
   pure (f a b c)

optional :: Alternative f => f a -> f (Maybe a) Source #

One or none.

It is useful for modelling any computation that is allowed to fail.

Examples

Expand

Using the Alternative instance of Except, the following functions:

>>> canFail = throwError "it failed" :: Except String Int
>>> final = return 42                :: Except String Int

Can be combined by allowing the first function to fail:

>>> runExcept $ canFail *> final
Left "it failed"
>>> runExcept $ optional canFail *> final
Right 42