| Copyright | (c) The University of Glasgow 1992-2002 |
|---|---|
| License | see libraries/base/LICENSE |
| Maintainer | cvs-ghc@haskell.org |
| Stability | internal |
| Portability | non-portable (GHC extensions) |
| Safe Haskell | Unsafe |
| Language | Haskell2010 |
GHC.Base
Description
Basic data types and classes.
Synopsis
- class Applicative m => Monad m where
- class Functor f => Applicative f where
- class Applicative f => Alternative f where
- class Functor f where
- class (Alternative m, Monad m) => MonadPlus m where
- type String = [Char]
- class Semigroup a => Monoid a where
- data NonEmpty a = a :| [a]
- class Semigroup a where
- data Void
- data Opaque = forall a. O a
- ord :: Char -> Int
- (.) :: (b -> c) -> (a -> b) -> a -> c
- (<**>) :: 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
- id :: a -> a
- when :: Applicative f => Bool -> f () -> f ()
- assert :: Bool -> a -> a
- mapM :: Monad m => (a -> m b) -> [a] -> m [b]
- sequence :: Monad m => [m a] -> m [a]
- (=<<) :: Monad m => (a -> m b) -> m a -> m b
- join :: Monad m => m (m a) -> m a
- liftM :: Monad m => (a1 -> r) -> m a1 -> m r
- liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
- liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r
- liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r
- liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r
- ap :: Monad m => m (a -> b) -> m a -> m b
- failIO :: String -> IO a
- ($) :: forall r a (b :: TYPE r). (a -> b) -> a -> b
- otherwise :: Bool
- foldr :: (a -> b -> b) -> b -> [a] -> b
- ($!) :: forall r a (b :: TYPE r). (a -> b) -> a -> b
- flip :: (a -> b -> c) -> b -> a -> c
- const :: a -> b -> a
- (++) :: [a] -> [a] -> [a]
- map :: (a -> b) -> [a] -> [b]
- absurd :: Void -> a
- vacuous :: Functor f => f Void -> f a
- shiftL# :: Word# -> Int# -> Word#
- shiftRL# :: Word# -> Int# -> Word#
- iShiftL# :: Int# -> Int# -> Int#
- iShiftRA# :: Int# -> Int# -> Int#
- iShiftRL# :: Int# -> Int# -> Int#
- build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
- augment :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a] -> [a]
- breakpoint :: a -> a
- breakpointCond :: Bool -> a -> a
- unIO :: IO a -> State# RealWorld -> (# State# RealWorld, a #)
- until :: (a -> Bool) -> (a -> a) -> a -> a
- asTypeOf :: a -> a -> a
- eqString :: String -> String -> Bool
- returnIO :: a -> IO a
- bindIO :: IO a -> (a -> IO b) -> IO b
- thenIO :: IO a -> IO b -> IO b
- mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
- unsafeChr :: Int -> Char
- maxInt :: Int
- minInt :: Int
- getTag :: a -> Int#
- quotInt :: Int -> Int -> Int
- remInt :: Int -> Int -> Int
- divInt :: Int -> Int -> Int
- modInt :: Int -> Int -> Int
- quotRemInt :: Int -> Int -> (Int, Int)
- divModInt :: Int -> Int -> (Int, Int)
- shift_mask :: Int# -> Int# -> Int#
- module GHC.Classes
- module GHC.CString
- module GHC.Magic
- module GHC.Magic.Dict
- module GHC.Types
- module GHC.Prim
- module GHC.Prim.Ext
- module GHC.Prim.PtrEq
- module GHC.Err
- module GHC.Maybe
Documentation
class Applicative m => Monad m where Source #
The Monad class defines the basic operations over a monad,
a concept from a branch of mathematics known as category theory.
From the perspective of a Haskell programmer, however, it is best to
think of a monad as an abstract datatype of actions.
Haskell's do expressions provide a convenient syntax for writing
monadic expressions.
Instances of Monad should satisfy the following:
- Left identity
returna>>=k = k a- Right identity
m>>=return= m- Associativity
m>>=(\x -> k x>>=h) = (m>>=k)>>=h
Furthermore, the Monad and Applicative operations should relate as follows:
The above laws imply:
and that pure and (<*>) satisfy the applicative functor laws.
The instances of Monad for lists, Maybe and IO
defined in the Prelude satisfy these laws.
Minimal complete definition
Methods
(>>=) :: forall a b. m a -> (a -> m b) -> m b infixl 1 Source #
Sequentially compose two actions, passing any value produced by the first as an argument to the second.
'as ' can be understood as the >>= bsdo expression
do a <- as bs a
(>>) :: forall a b. m a -> m b -> m b infixl 1 Source #
Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.
'as ' can be understood as the >> bsdo expression
do as bs
Inject a value into the monadic type.
Instances
| Monad Complex Source # | Since: base-4.9.0.0 |
| Monad Identity Source # | Since: base-4.8.0.0 |
| Monad First Source # | Since: base-4.8.0.0 |
| Monad Last Source # | Since: base-4.8.0.0 |
| Monad Down Source # | Since: base-4.11.0.0 |
| Monad First Source # | Since: base-4.9.0.0 |
| Monad Last Source # | Since: base-4.9.0.0 |
| Monad Max Source # | Since: base-4.9.0.0 |
| Monad Min Source # | Since: base-4.9.0.0 |
| Monad Dual Source # | Since: base-4.8.0.0 |
| Monad Product Source # | Since: base-4.8.0.0 |
| Monad Sum Source # | Since: base-4.8.0.0 |
| Monad NonEmpty Source # | Since: base-4.9.0.0 |
| Monad STM Source # | Since: base-4.3.0.0 |
| Monad NoIO Source # | Since: base-4.4.0.0 |
| Monad Par1 Source # | Since: base-4.9.0.0 |
| Monad ReadP Source # | Since: base-2.1 |
| Monad ReadPrec Source # | Since: base-2.1 |
| Monad IO Source # | Since: base-2.1 |
| Monad Maybe Source # | Since: base-2.1 |
| Monad Solo Source # | Since: base-4.15 |
| Monad List Source # | Since: base-2.1 |
| Monad m => Monad (WrappedMonad m) Source # | Since: base-4.7.0.0 |
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 # | |
| ArrowApply a => Monad (ArrowMonad a) Source # | Since: base-2.1 |
Defined in Control.Arrow Methods (>>=) :: ArrowMonad a a0 -> (a0 -> ArrowMonad a b) -> ArrowMonad a b Source # (>>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b Source # return :: a0 -> ArrowMonad a a0 Source # | |
| Monad (ST s) Source # | Since: base-2.1 |
| Monad (Either e) Source # | Since: base-4.4.0.0 |
| Monad (Proxy :: Type -> Type) Source # | Since: base-4.7.0.0 |
| Monad (U1 :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Monad (ST s) Source # | Since: base-2.1 |
| Monoid a => Monad ((,) a) Source # | Since: base-4.9.0.0 |
| Monad m => Monad (Kleisli m a) Source # | Since: base-4.14.0.0 |
| Monad f => Monad (Ap f) Source # | Since: base-4.12.0.0 |
| Monad f => Monad (Alt f) Source # | Since: base-4.8.0.0 |
| Monad f => Monad (Rec1 f) Source # | Since: base-4.9.0.0 |
| (Monoid a, Monoid b) => Monad ((,,) a b) Source # | Since: base-4.14.0.0 |
| (Monad f, Monad g) => Monad (Product f g) Source # | Since: base-4.9.0.0 |
| (Monad f, Monad g) => Monad (f :*: g) Source # | Since: base-4.9.0.0 |
| (Monoid a, Monoid b, Monoid c) => Monad ((,,,) a b c) Source # | Since: base-4.14.0.0 |
| Monad ((->) r) Source # | Since: base-2.1 |
| Monad f => Monad (M1 i c f) Source # | Since: base-4.9.0.0 |
class Functor f => Applicative f where Source #
A functor with application, providing operations to
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:
(<*>) =liftA2id
liftA2f x y = f<$>x<*>y
Further, any definition must satisfy the following:
- Identity
pureid<*>v = v- Composition
pure(.)<*>u<*>v<*>w = u<*>(v<*>w)- Homomorphism
puref<*>purex =pure(f x)- Interchange
u
<*>purey =pure($y)<*>u
The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:
As a consequence of these laws, the Functor instance for f will satisfy
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
liftA2p (liftA2q u v) =liftA2f u .liftA2g v
If f is also a Monad, it should satisfy
(which implies that pure and <*> satisfy the applicative functor laws).
Methods
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.
Example
Used in combination with (, <$>)( can be used to build a record.<*>)
>>>data MyState = MyState {arg1 :: Foo, arg2 :: Bar, arg3 :: Baz}
>>>produceFoo :: Applicative f => f Foo
>>>produceBar :: Applicative f => f Bar>>>produceBaz :: Applicative f => f Baz
>>>mkState :: Applicative f => f MyState>>>mkState = MyState <$> produceFoo <*> produceBar <*> produceBaz
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.
Example
>>>liftA2 (,) (Just 3) (Just 5)Just (3,5)
(*>) :: f a -> f b -> f b infixl 4 Source #
Sequence actions, discarding the value of the first argument.
Examples
If used in conjunction with the Applicative instance for Maybe,
you can chain Maybe computations, with a possible "early return"
in case of Nothing.
>>>Just 2 *> Just 3Just 3
>>>Nothing *> Just 3Nothing
Of course a more interesting use case would be to have effectful computations instead of just returning pure values.
>>>import Data.Char>>>import Text.ParserCombinators.ReadP>>>let p = string "my name is " *> munch1 isAlpha <* eof>>>readP_to_S p "my name is Simon"[("Simon","")]
(<*) :: f a -> f b -> f a infixl 4 Source #
Sequence actions, discarding the value of the second argument.
Instances
| Applicative ZipList Source # | f <$> ZipList xs1 <*> ... <*> ZipList xsN
= ZipList (zipWithN f xs1 ... xsN)where (\a b c -> stimes c [a, b]) <$> 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 |
Defined in Control.Applicative | |
| Applicative Complex Source # | Since: base-4.9.0.0 |
| Applicative Identity Source # | Since: base-4.8.0.0 |
Defined in Data.Functor.Identity | |
| Applicative First Source # | Since: base-4.8.0.0 |
| Applicative Last Source # | Since: base-4.8.0.0 |
| Applicative Down Source # | Since: base-4.11.0.0 |
| Applicative First Source # | Since: base-4.9.0.0 |
| Applicative Last Source # | Since: base-4.9.0.0 |
| Applicative Max Source # | Since: base-4.9.0.0 |
| Applicative Min Source # | Since: base-4.9.0.0 |
| Applicative Dual Source # | Since: base-4.8.0.0 |
| Applicative Product Source # | Since: base-4.8.0.0 |
Defined in Data.Semigroup.Internal | |
| Applicative Sum Source # | Since: base-4.8.0.0 |
| Applicative NonEmpty Source # | Since: base-4.9.0.0 |
Defined in GHC.Base | |
| Applicative STM Source # | Since: base-4.8.0.0 |
| Applicative NoIO Source # | Since: base-4.8.0.0 |
| Applicative Par1 Source # | Since: base-4.9.0.0 |
| Applicative ReadP Source # | Since: base-4.6.0.0 |
| Applicative ReadPrec Source # | Since: base-4.6.0.0 |
Defined in Text.ParserCombinators.ReadPrec | |
| Applicative IO Source # | Since: base-2.1 |
| Applicative Maybe Source # | Since: base-2.1 |
| Applicative Solo Source # | Since: base-4.15 |
| Applicative List Source # | Since: base-2.1 |
| Monad m => Applicative (WrappedMonad m) Source # | Since: base-2.1 |
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 # | |
| Arrow a => Applicative (ArrowMonad a) Source # | Since: base-4.6.0.0 |
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 # | |
| Applicative (ST s) Source # | Since: base-2.1 |
| Applicative (Either e) Source # | Since: base-3.0 |
Defined in Data.Either | |
| Applicative (Proxy :: Type -> Type) Source # | Since: base-4.7.0.0 |
| Applicative (U1 :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Applicative (ST s) Source # | Since: base-4.4.0.0 |
| Monoid a => Applicative ((,) a) Source # | For tuples, the ("hello ", (+15)) <*> ("world!", 2002)
("hello world!",2017)Since: base-2.1 |
| Arrow a => Applicative (WrappedArrow a b) Source # | Since: base-2.1 |
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 # | |
| Applicative m => Applicative (Kleisli m a) Source # | Since: base-4.14.0.0 |
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 # | |
| Monoid m => Applicative (Const m :: Type -> Type) Source # | Since: base-2.0.1 |
Defined in Data.Functor.Const | |
| Applicative f => Applicative (Ap f) Source # | Since: base-4.12.0.0 |
| Applicative f => Applicative (Alt f) Source # | Since: base-4.8.0.0 |
| (Generic1 f, Applicative (Rep1 f)) => Applicative (Generically1 f) Source # | Since: base-4.17.0.0 |
Defined in GHC.Generics Methods pure :: a -> Generically1 f a Source # (<*>) :: Generically1 f (a -> b) -> Generically1 f a -> Generically1 f b Source # liftA2 :: (a -> b -> c) -> Generically1 f a -> Generically1 f b -> Generically1 f c Source # (*>) :: Generically1 f a -> Generically1 f b -> Generically1 f b Source # (<*) :: Generically1 f a -> Generically1 f b -> Generically1 f a Source # | |
| Applicative f => Applicative (Rec1 f) Source # | Since: base-4.9.0.0 |
| (Monoid a, Monoid b) => Applicative ((,,) a b) Source # | Since: base-4.14.0.0 |
Defined in GHC.Base | |
| (Applicative f, Applicative g) => Applicative (Product f g) Source # | Since: base-4.9.0.0 |
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 g) => Applicative (f :*: g) Source # | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
| Monoid c => Applicative (K1 i c :: Type -> Type) Source # | Since: base-4.12.0.0 |
| (Monoid a, Monoid b, Monoid c) => Applicative ((,,,) a b c) Source # | Since: base-4.14.0.0 |
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 ((->) r) Source # | Since: base-2.1 |
| (Applicative f, Applicative g) => Applicative (Compose f g) Source # | Since: base-4.9.0.0 |
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 # | |
| (Applicative f, Applicative g) => Applicative (f :.: g) Source # | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
| Applicative f => Applicative (M1 i c f) Source # | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
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:
Methods
The identity of <|>
(<|>) :: f a -> f a -> f a infixl 3 Source #
An associative binary operation
One or more.
Zero or more.
Instances
class Functor f where Source #
A type f is a Functor if it provides a function fmap which, given any types a and b
lets you apply any function from (a -> b) to turn an f a into an f b, preserving the
structure of f. Furthermore f needs to adhere to the following:
Note, that the second law follows from the free theorem of the type fmap and
the first law, so you need only check that the former condition holds.
See https://www.schoolofhaskell.com/user/edwardk/snippets/fmap or
https://github.com/quchen/articles/blob/master/second_functor_law.md
for an explanation.
Minimal complete definition
Methods
fmap :: (a -> b) -> f a -> f b Source #
fmap is used to apply a function of type (a -> b) to a value of type f a,
where f is a functor, to produce a value of type f b.
Note that for any type constructor with more than one parameter (e.g., Either),
only the last type parameter can be modified with fmap (e.g., b in `Either a b`).
Some type constructors with two parameters or more have a Bifunctor
Examples
Convert from a Maybe IntMaybe String
using show:
>>>fmap show NothingNothing>>>fmap show (Just 3)Just "3"
Convert from an Either Int IntEither Int String using show:
>>>fmap show (Left 17)Left 17>>>fmap show (Right 17)Right "17"
Double each element of a list:
>>>fmap (*2) [1,2,3][2,4,6]
Apply even to the second element of a pair:
>>>fmap even (2,2)(2,True)
It may seem surprising that the function is only applied to the last element of the tuple
compared to the list example above which applies it to every element in the list.
To understand, remember that tuples are type constructors with multiple type parameters:
a tuple of 3 elements (a,b,c) can also be written (,,) a b c and its Functor instance
is defined for Functor ((,,) a b) (i.e., only the third parameter is free to be mapped over
with fmap).
It explains why fmap can be used with tuples containing values of different types as in the
following example:
>>>fmap even ("hello", 1.0, 4)("hello",1.0,True)
Instances
| Functor ZipList Source # | Since: base-2.1 |
| Functor Handler Source # | Since: base-4.6.0.0 |
| Functor Complex Source # | Since: base-4.9.0.0 |
| Functor Identity Source # | Since: base-4.8.0.0 |
| Functor First Source # | Since: base-4.8.0.0 |
| Functor Last Source # | Since: base-4.8.0.0 |
| Functor Down Source # | Since: base-4.11.0.0 |
| Functor First Source # | Since: base-4.9.0.0 |
| Functor Last Source # | Since: base-4.9.0.0 |
| Functor Max Source # | Since: base-4.9.0.0 |
| Functor Min Source # | Since: base-4.9.0.0 |
| Functor Dual Source # | Since: base-4.8.0.0 |
| Functor Product Source # | Since: base-4.8.0.0 |
| Functor Sum Source # | Since: base-4.8.0.0 |
| Functor NonEmpty Source # | Since: base-4.9.0.0 |
| Functor STM Source # | Since: base-4.3.0.0 |
| Functor NoIO Source # | Since: base-4.8.0.0 |
| Functor Par1 Source # | Since: base-4.9.0.0 |
| Functor ArgDescr Source # | Since: base-4.7.0.0 |
| Functor ArgOrder Source # | Since: base-4.7.0.0 |
| Functor OptDescr Source # | Since: base-4.7.0.0 |
| Functor ReadP Source # | Since: base-2.1 |
| Functor ReadPrec Source # | Since: base-2.1 |
| Functor IO Source # | Since: base-2.1 |
| Functor Maybe Source # | Since: base-2.1 |
| Functor Solo Source # | Since: base-4.15 |
| Functor List Source # | Since: base-2.1 |
| Monad m => Functor (WrappedMonad m) Source # | Since: base-2.1 |
Defined in Control.Applicative Methods fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source # (<$) :: a -> WrappedMonad m b -> WrappedMonad m a Source # | |
| Arrow a => Functor (ArrowMonad a) Source # | Since: base-4.6.0.0 |
Defined in Control.Arrow Methods fmap :: (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b Source # (<$) :: a0 -> ArrowMonad a b -> ArrowMonad a a0 Source # | |
| Functor (ST s) Source # | Since: base-2.1 |
| Functor (Either a) Source # | Since: base-3.0 |
| Functor (Proxy :: Type -> Type) Source # | Since: base-4.7.0.0 |
| Functor (Arg a) Source # | Since: base-4.9.0.0 |
| Functor (Array i) Source # | Since: base-2.1 |
| Functor (U1 :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor (V1 :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor (ST s) Source # | Since: base-2.1 |
| Functor ((,) a) Source # | Since: base-2.1 |
| Arrow a => Functor (WrappedArrow a b) Source # | Since: base-2.1 |
Defined in Control.Applicative Methods fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 Source # (<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 Source # | |
| Functor m => Functor (Kleisli m a) Source # | Since: base-4.14.0.0 |
| Functor (Const m :: Type -> Type) Source # | Since: base-2.1 |
| Functor f => Functor (Ap f) Source # | Since: base-4.12.0.0 |
| Functor f => Functor (Alt f) Source # | Since: base-4.8.0.0 |
| (Generic1 f, Functor (Rep1 f)) => Functor (Generically1 f) Source # | Since: base-4.17.0.0 |
Defined in GHC.Generics Methods fmap :: (a -> b) -> Generically1 f a -> Generically1 f b Source # (<$) :: a -> Generically1 f b -> Generically1 f a Source # | |
| Functor f => Functor (Rec1 f) Source # | Since: base-4.9.0.0 |
| Functor (URec (Ptr ()) :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor (URec Char :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor (URec Double :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor (URec Float :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor (URec Int :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor (URec Word :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor ((,,) a b) Source # | Since: base-4.14.0.0 |
| (Functor f, Functor g) => Functor (Product f g) Source # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (Sum f g) Source # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (f :*: g) Source # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (f :+: g) Source # | Since: base-4.9.0.0 |
| Functor (K1 i c :: Type -> Type) Source # | Since: base-4.9.0.0 |
| Functor ((,,,) a b c) Source # | Since: base-4.14.0.0 |
| Functor ((->) r) Source # | Since: base-2.1 |
| (Functor f, Functor g) => Functor (Compose f g) Source # | Since: base-4.9.0.0 |
| (Functor f, Functor g) => Functor (f :.: g) Source # | Since: base-4.9.0.0 |
| Functor f => Functor (M1 i c f) Source # | Since: base-4.9.0.0 |
| Functor ((,,,,) a b c d) Source # | Since: base-4.18.0.0 |
| Functor ((,,,,,) a b c d e) Source # | Since: base-4.18.0.0 |
| Functor ((,,,,,,) a b c d e f) Source # | Since: base-4.18.0.0 |
class (Alternative m, Monad m) => MonadPlus m where Source #
Monads that also support choice and failure.
Minimal complete definition
Nothing
Methods
The identity of mplus. It should also satisfy the equations
mzero >>= f = mzero v >> mzero = mzero
The default definition is
mzero = empty
mplus :: m a -> m a -> m a Source #
An associative operation. The default definition is
mplus = (<|>)
Instances
| MonadPlus STM Source # | Takes the first non- Since: base-4.3.0.0 |
| MonadPlus ReadP Source # | Since: base-2.1 |
| MonadPlus ReadPrec Source # | Since: base-2.1 |
| MonadPlus IO Source # | Takes the first non-throwing Since: base-4.9.0.0 |
| MonadPlus Maybe Source # | Picks the leftmost Since: base-2.1 |
| MonadPlus List Source # | Combines lists by concatenation, starting from the empty list. Since: base-2.1 |
| (ArrowApply a, ArrowPlus a) => MonadPlus (ArrowMonad a) Source # | Since: base-4.6.0.0 |
Defined in Control.Arrow Methods mzero :: ArrowMonad a a0 Source # mplus :: ArrowMonad a a0 -> ArrowMonad a a0 -> ArrowMonad a a0 Source # | |
| MonadPlus (Proxy :: Type -> Type) Source # | Since: base-4.9.0.0 |
| MonadPlus (U1 :: Type -> Type) Source # | Since: base-4.9.0.0 |
| MonadPlus m => MonadPlus (Kleisli m a) Source # | Since: base-4.14.0.0 |
| MonadPlus f => MonadPlus (Ap f) Source # | Since: base-4.12.0.0 |
| MonadPlus f => MonadPlus (Alt f) Source # | Since: base-4.8.0.0 |
| MonadPlus f => MonadPlus (Rec1 f) Source # | Since: base-4.9.0.0 |
| (MonadPlus f, MonadPlus g) => MonadPlus (Product f g) Source # | Since: base-4.9.0.0 |
| (MonadPlus f, MonadPlus g) => MonadPlus (f :*: g) Source # | Since: base-4.9.0.0 |
| MonadPlus f => MonadPlus (M1 i c f) Source # | Since: base-4.9.0.0 |
String is an alias for a list of characters.
String constants in Haskell are values of type String.
That means if you write a string literal like "hello world",
it will have the type [Char], which is the same as String.
Note: You can ask the compiler to automatically infer different types
with the -XOverloadedStrings language extension, for example
"hello world" :: Text. See IsString for more information.
Because String is just a list of characters, you can use normal list functions
to do basic string manipulation. See Data.List for operations on lists.
Performance considerations
[Char] is a relatively memory-inefficient type.
It is a linked list of boxed word-size characters, internally it looks something like:
╭─────┬───┬──╮ ╭─────┬───┬──╮ ╭─────┬───┬──╮ ╭────╮
│ (:) │ │ ─┼─>│ (:) │ │ ─┼─>│ (:) │ │ ─┼─>│ [] │
╰─────┴─┼─┴──╯ ╰─────┴─┼─┴──╯ ╰─────┴─┼─┴──╯ ╰────╯
v v v
'a' 'b' 'c'The String "abc" will use 5*3+1 = 16 (in general 5n+1)
words of space in memory.
Furthermore, operations like (++) (string concatenation) are O(n)
(in the left argument).
For historical reasons, the base library uses String in a lot of places
for the conceptual simplicity, but library code dealing with user-data
should use the text
package for Unicode text, or the the
bytestring package
for binary data.
class Semigroup a => Monoid a where Source #
The class of monoids (types with an associative binary operation that has an identity). Instances should satisfy the following:
- Right identity
x<>mempty= x- Left identity
mempty<>x = x- Associativity
x(<>(y<>z) = (x<>y)<>zSemigrouplaw)- Concatenation
mconcat=foldr(<>)mempty
You can alternatively define mconcat instead of mempty, in which case the
laws are:
- Unit
mconcat(purex) = x- Multiplication
mconcat(joinxss) =mconcat(fmapmconcatxss)- Subclass
mconcat(toListxs) =sconcatxs
The method names refer to the monoid of lists under concatenation, but there are many other instances.
Some types can be viewed as a monoid in more than one way,
e.g. both addition and multiplication on numbers.
In such cases we often define newtypes and make those instances
of Monoid, e.g. Sum and Product.
NOTE: Semigroup is a superclass of Monoid since base-4.11.0.0.
Methods
Identity of mappend
>>>"Hello world" <> mempty"Hello world"
mappend :: a -> a -> a Source #
An associative operation
NOTE: This method is redundant and has the default
implementation mappend = (<>)mappend is a synonym for
(<>), it is expected that the two functions are defined the same
way. In a future GHC release mappend will be removed from Monoid.
Fold a list using the monoid.
For most types, the default definition for mconcat will be
used, but the function is included in the class definition so
that an optimized version can be provided for specific types.
>>>mconcat ["Hello", " ", "Haskell", "!"]"Hello Haskell!"
Instances
| Monoid ByteArray Source # | Since: base-4.17.0.0 |
| Monoid All Source # | Since: base-2.1 |
| Monoid Any Source # | Since: base-2.1 |
| Monoid Event Source # | Since: base-4.4.0.0 |
| Monoid Lifetime Source # |
Since: base-4.8.0.0 |
| Monoid Ordering Source # | Since: base-2.1 |
| Monoid () Source # | Since: base-2.1 |
| FiniteBits a => Monoid (And a) Source # | This constraint is arguably too strong. However,
as some types (such as Since: base-4.16 |
| FiniteBits a => Monoid (Iff a) Source # | This constraint is arguably
too strong. However, as some types (such as Since: base-4.16 |
| Bits a => Monoid (Ior a) Source # | Since: base-4.16 |
| Bits a => Monoid (Xor a) Source # | Since: base-4.16 |
| Monoid (Comparison a) Source # |
mempty :: Comparison a mempty = Comparison _ _ -> EQ |
Defined in Data.Functor.Contravariant Methods mempty :: Comparison a Source # mappend :: Comparison a -> Comparison a -> Comparison a Source # mconcat :: [Comparison a] -> Comparison a Source # | |
| Monoid (Equivalence a) Source # |
mempty :: Equivalence a mempty = Equivalence _ _ -> True |
Defined in Data.Functor.Contravariant Methods mempty :: Equivalence a Source # mappend :: Equivalence a -> Equivalence a -> Equivalence a Source # mconcat :: [Equivalence a] -> Equivalence a Source # | |
| Monoid (Predicate a) Source # |
mempty :: Predicate a mempty = _ -> True |
| Monoid a => Monoid (Identity a) Source # | Since: base-4.9.0.0 |
| Monoid (First a) Source # | Since: base-2.1 |
| Monoid (Last a) Source # | Since: base-2.1 |
| Monoid a => Monoid (Down a) Source # | Since: base-4.11.0.0 |
| (Ord a, Bounded a) => Monoid (Max a) Source # | Since: base-4.9.0.0 |
| (Ord a, Bounded a) => Monoid (Min a) Source # | Since: base-4.9.0.0 |
| Monoid m => Monoid (WrappedMonoid m) Source # | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods mempty :: WrappedMonoid m Source # mappend :: WrappedMonoid m -> WrappedMonoid m -> WrappedMonoid m Source # mconcat :: [WrappedMonoid m] -> WrappedMonoid m Source # | |
| Monoid a => Monoid (Dual a) Source # | Since: base-2.1 |
| Monoid (Endo a) Source # | Since: base-2.1 |
| Num a => Monoid (Product a) Source # | Since: base-2.1 |
| Num a => Monoid (Sum a) Source # | Since: base-2.1 |
| Monoid a => Monoid (STM a) Source # | Since: base-4.17.0.0 |
| (Generic a, Monoid (Rep a ())) => Monoid (Generically a) Source # | Since: base-4.17.0.0 |
Defined in GHC.Generics Methods mempty :: Generically a Source # mappend :: Generically a -> Generically a -> Generically a Source # mconcat :: [Generically a] -> Generically a Source # | |
| Monoid p => Monoid (Par1 p) Source # | Since: base-4.12.0.0 |
| Monoid a => Monoid (IO a) Source # | Since: base-4.9.0.0 |
| Semigroup a => Monoid (Maybe a) Source # | Lift a semigroup into Since 4.11.0: constraint on inner Since: base-2.1 |
| Monoid a => Monoid (a) Source # | Since: base-4.15 |
| Monoid [a] Source # | Since: base-2.1 |
| Monoid a => Monoid (Op a b) Source # |
mempty :: Op a b mempty = Op _ -> mempty |
| Monoid (Proxy s) Source # | Since: base-4.7.0.0 |
| Monoid (U1 p) Source # | Since: base-4.12.0.0 |
| Monoid a => Monoid (ST s a) Source # | Since: base-4.11.0.0 |
| (Monoid a, Monoid b) => Monoid (a, b) Source # | Since: base-2.1 |
| Monoid b => Monoid (a -> b) Source # | Since: base-2.1 |
| Monoid a => Monoid (Const a b) Source # | Since: base-4.9.0.0 |
| (Applicative f, Monoid a) => Monoid (Ap f a) Source # | Since: base-4.12.0.0 |
| Alternative f => Monoid (Alt f a) Source # | Since: base-4.8.0.0 |
| Monoid (f p) => Monoid (Rec1 f p) Source # | Since: base-4.12.0.0 |
| (Monoid a, Monoid b, Monoid c) => Monoid (a, b, c) Source # | Since: base-2.1 |
| (Monoid (f a), Monoid (g a)) => Monoid (Product f g a) Source # | Since: base-4.16.0.0 |
| (Monoid (f p), Monoid (g p)) => Monoid ((f :*: g) p) Source # | Since: base-4.12.0.0 |
| Monoid c => Monoid (K1 i c p) Source # | Since: base-4.12.0.0 |
| (Monoid a, Monoid b, Monoid c, Monoid d) => Monoid (a, b, c, d) Source # | Since: base-2.1 |
| Monoid (f (g a)) => Monoid (Compose f g a) Source # | Since: base-4.16.0.0 |
| Monoid (f (g p)) => Monoid ((f :.: g) p) Source # | Since: base-4.12.0.0 |
| Monoid (f p) => Monoid (M1 i c f p) Source # | Since: base-4.12.0.0 |
| (Monoid a, Monoid b, Monoid c, Monoid d, Monoid e) => Monoid (a, b, c, d, e) Source # | Since: base-2.1 |
Non-empty (and non-strict) list type.
Since: base-4.9.0.0
Constructors
| a :| [a] infixr 5 |
Instances
| MonadFix NonEmpty Source # | Since: base-4.9.0.0 |
| MonadZip NonEmpty Source # | Since: base-4.9.0.0 |
| Foldable NonEmpty Source # | Since: base-4.9.0.0 |
Defined in Data.Foldable Methods fold :: Monoid m => NonEmpty m -> m Source # foldMap :: Monoid m => (a -> m) -> NonEmpty a -> m Source # foldMap' :: Monoid m => (a -> m) -> NonEmpty a -> m Source # foldr :: (a -> b -> b) -> b -> NonEmpty a -> b Source # foldr' :: (a -> b -> b) -> b -> NonEmpty a -> b Source # foldl :: (b -> a -> b) -> b -> NonEmpty a -> b Source # foldl' :: (b -> a -> b) -> b -> NonEmpty a -> b Source # foldr1 :: (a -> a -> a) -> NonEmpty a -> a Source # foldl1 :: (a -> a -> a) -> NonEmpty a -> a Source # toList :: NonEmpty a -> [a] Source # null :: NonEmpty a -> Bool Source # length :: NonEmpty a -> Int Source # elem :: Eq a => a -> NonEmpty a -> Bool Source # maximum :: Ord a => NonEmpty a -> a Source # minimum :: Ord a => NonEmpty a -> a Source # | |
| Foldable1 NonEmpty Source # | Since: base-4.18.0.0 |
Defined in Data.Foldable1 Methods fold1 :: Semigroup m => NonEmpty m -> m Source # foldMap1 :: Semigroup m => (a -> m) -> NonEmpty a -> m Source # foldMap1' :: Semigroup m => (a -> m) -> NonEmpty a -> m Source # toNonEmpty :: NonEmpty a -> NonEmpty a Source # maximum :: Ord a => NonEmpty a -> a Source # minimum :: Ord a => NonEmpty a -> a Source # head :: NonEmpty a -> a Source # last :: NonEmpty a -> a Source # foldrMap1 :: (a -> b) -> (a -> b -> b) -> NonEmpty a -> b Source # foldlMap1' :: (a -> b) -> (b -> a -> b) -> NonEmpty a -> b Source # foldlMap1 :: (a -> b) -> (b -> a -> b) -> NonEmpty a -> b Source # foldrMap1' :: (a -> b) -> (a -> b -> b) -> NonEmpty a -> b Source # | |
| Eq1 NonEmpty Source # | Since: base-4.10.0.0 |
| Ord1 NonEmpty Source # | Since: base-4.10.0.0 |
Defined in Data.Functor.Classes | |
| Read1 NonEmpty Source # | Since: base-4.10.0.0 |
Defined in Data.Functor.Classes Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (NonEmpty a) Source # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [NonEmpty a] Source # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (NonEmpty a) Source # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [NonEmpty a] Source # | |
| Show1 NonEmpty Source # | Since: base-4.10.0.0 |
| Traversable NonEmpty Source # | Since: base-4.9.0.0 |
Defined in Data.Traversable | |
| Applicative NonEmpty Source # | Since: base-4.9.0.0 |
Defined in GHC.Base | |
| Functor NonEmpty Source # | Since: base-4.9.0.0 |
| Monad NonEmpty Source # | Since: base-4.9.0.0 |
| Generic1 NonEmpty Source # | |
| Data a => Data (NonEmpty a) Source # | Since: base-4.9.0.0 |
Defined in Data.Data Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> NonEmpty a -> c (NonEmpty a) Source # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (NonEmpty a) Source # toConstr :: NonEmpty a -> Constr Source # dataTypeOf :: NonEmpty a -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (NonEmpty a)) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (NonEmpty a)) Source # gmapT :: (forall b. Data b => b -> b) -> NonEmpty a -> NonEmpty a Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> NonEmpty a -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> NonEmpty a -> r Source # gmapQ :: (forall d. Data d => d -> u) -> NonEmpty a -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> NonEmpty a -> u Source # gmapM :: Monad m => (forall d. Data d => d -> m d) -> NonEmpty a -> m (NonEmpty a) Source # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> NonEmpty a -> m (NonEmpty a) Source # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> NonEmpty a -> m (NonEmpty a) Source # | |
| Semigroup (NonEmpty a) Source # | Since: base-4.9.0.0 |
| Generic (NonEmpty a) Source # | |
| IsList (NonEmpty a) Source # | Since: base-4.9.0.0 |
| Read a => Read (NonEmpty a) Source # | Since: base-4.11.0.0 |
| Show a => Show (NonEmpty a) Source # | Since: base-4.11.0.0 |
| Eq a => Eq (NonEmpty a) Source # | Since: base-4.9.0.0 |
| Ord a => Ord (NonEmpty a) Source # | Since: base-4.9.0.0 |
Defined in GHC.Base Methods compare :: NonEmpty a -> NonEmpty a -> Ordering Source # (<) :: NonEmpty a -> NonEmpty a -> Bool Source # (<=) :: NonEmpty a -> NonEmpty a -> Bool Source # (>) :: NonEmpty a -> NonEmpty a -> Bool Source # (>=) :: NonEmpty a -> NonEmpty a -> Bool Source # | |
| type Rep1 NonEmpty Source # | Since: base-4.6.0.0 |
Defined in GHC.Generics type Rep1 NonEmpty = D1 ('MetaData "NonEmpty" "GHC.Base" "base" 'False) (C1 ('MetaCons ":|" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1 :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 List))) | |
| type Rep (NonEmpty a) Source # | Since: base-4.6.0.0 |
Defined in GHC.Generics type Rep (NonEmpty a) = D1 ('MetaData "NonEmpty" "GHC.Base" "base" 'False) (C1 ('MetaCons ":|" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 [a]))) | |
| type Item (NonEmpty a) Source # | |
Defined in GHC.IsList | |
class Semigroup a where Source #
The class of semigroups (types with an associative binary operation).
Instances should satisfy the following:
You can alternatively define sconcat instead of (<>), in which case the
laws are:
Since: base-4.9.0.0
Methods
(<>) :: a -> a -> a infixr 6 Source #
An associative operation.
>>>[1,2,3] <> [4,5,6][1,2,3,4,5,6]
sconcat :: NonEmpty a -> a Source #
Reduce a non-empty list with <>
The default definition should be sufficient, but this can be overridden for efficiency.
>>>import Data.List.NonEmpty (NonEmpty (..))>>>sconcat $ "Hello" :| [" ", "Haskell", "!"]"Hello Haskell!"
stimes :: Integral b => b -> a -> a Source #
Repeat a value n times.
Given that this works on a Semigroup it is allowed to fail if
you request 0 or fewer repetitions, and the default definition
will do so.
By making this a member of the class, idempotent semigroups
and monoids can upgrade this to execute in \(\mathcal{O}(1)\) by
picking stimes = or stimesIdempotentstimes =
respectively.stimesIdempotentMonoid
>>>stimes 4 [1][1,1,1,1]
Instances
| Semigroup ByteArray Source # | Since: base-4.17.0.0 |
| Semigroup All Source # | Since: base-4.9.0.0 |
| Semigroup Any Source # | Since: base-4.9.0.0 |
| Semigroup Void Source # | Since: base-4.9.0.0 |
| Semigroup Event Source # | Since: base-4.10.0.0 |
| Semigroup Lifetime Source # | Since: base-4.10.0.0 |
| Semigroup Ordering Source # | Since: base-4.9.0.0 |
| Semigroup () Source # | Since: base-4.9.0.0 |
| Bits a => Semigroup (And a) Source # | Since: base-4.16 |
| FiniteBits a => Semigroup (Iff a) Source # | This constraint is arguably
too strong. However, as some types (such as Since: base-4.16 |
| Bits a => Semigroup (Ior a) Source # | Since: base-4.16 |
| Bits a => Semigroup (Xor a) Source # | Since: base-4.16 |
| Semigroup (Comparison a) Source # |
(<>) :: Comparison a -> Comparison a -> Comparison a Comparison cmp <> Comparison cmp' = Comparison a a' -> cmp a a' <> cmp a a' |
Defined in Data.Functor.Contravariant Methods (<>) :: Comparison a -> Comparison a -> Comparison a Source # sconcat :: NonEmpty (Comparison a) -> Comparison a Source # stimes :: Integral b => b -> Comparison a -> Comparison a Source # | |
| Semigroup (Equivalence a) Source # |
(<>) :: Equivalence a -> Equivalence a -> Equivalence a Equivalence equiv <> Equivalence equiv' = Equivalence a b -> equiv a b && equiv' a b |
Defined in Data.Functor.Contravariant Methods (<>) :: Equivalence a -> Equivalence a -> Equivalence a Source # sconcat :: NonEmpty (Equivalence a) -> Equivalence a Source # stimes :: Integral b => b -> Equivalence a -> Equivalence a Source # | |
| Semigroup (Predicate a) Source # |
(<>) :: Predicate a -> Predicate a -> Predicate a Predicate pred <> Predicate pred' = Predicate a -> pred a && pred' a |
| Semigroup a => Semigroup (Identity a) Source # | Since: base-4.9.0.0 |
| Semigroup (First a) Source # | Since: base-4.9.0.0 |
| Semigroup (Last a) Source # | Since: base-4.9.0.0 |
| Semigroup a => Semigroup (Down a) Source # | Since: base-4.11.0.0 |
| Semigroup (First a) Source # | Since: base-4.9.0.0 |
| Semigroup (Last a) Source # | Since: base-4.9.0.0 |
| Ord a => Semigroup (Max a) Source # | Since: base-4.9.0.0 |
| Ord a => Semigroup (Min a) Source # | Since: base-4.9.0.0 |
| Monoid m => Semigroup (WrappedMonoid m) Source # | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods (<>) :: WrappedMonoid m -> WrappedMonoid m -> WrappedMonoid m Source # sconcat :: NonEmpty (WrappedMonoid m) -> WrappedMonoid m Source # stimes :: Integral b => b -> WrappedMonoid m -> WrappedMonoid m Source # | |
| Semigroup a => Semigroup (Dual a) Source # | Since: base-4.9.0.0 |
| Semigroup (Endo a) Source # | Since: base-4.9.0.0 |
| Num a => Semigroup (Product a) Source # | Since: base-4.9.0.0 |
| Num a => Semigroup (Sum a) Source # | Since: base-4.9.0.0 |
| Semigroup (NonEmpty a) Source # | Since: base-4.9.0.0 |
| Semigroup a => Semigroup (STM a) Source # | Since: base-4.17.0.0 |
| (Generic a, Semigroup (Rep a ())) => Semigroup (Generically a) Source # | Since: base-4.17.0.0 |
Defined in GHC.Generics Methods (<>) :: Generically a -> Generically a -> Generically a Source # sconcat :: NonEmpty (Generically a) -> Generically a Source # stimes :: Integral b => b -> Generically a -> Generically a Source # | |
| Semigroup p => Semigroup (Par1 p) Source # | Since: base-4.12.0.0 |
| Semigroup a => Semigroup (IO a) Source # | Since: base-4.10.0.0 |
| Semigroup a => Semigroup (Maybe a) Source # | Since: base-4.9.0.0 |
| Semigroup a => Semigroup (a) Source # | Since: base-4.15 |
| Semigroup [a] Source # | Since: base-4.9.0.0 |
| Semigroup (Either a b) Source # | Since: base-4.9.0.0 |
| Semigroup a => Semigroup (Op a b) Source # |
(<>) :: Op a b -> Op a b -> Op a b Op f <> Op g = Op a -> f a <> g a |
| Semigroup (Proxy s) Source # | Since: base-4.9.0.0 |
| Semigroup (U1 p) Source # | Since: base-4.12.0.0 |
| Semigroup (V1 p) Source # | Since: base-4.12.0.0 |
| Semigroup a => Semigroup (ST s a) Source # | Since: base-4.11.0.0 |
| (Semigroup a, Semigroup b) => Semigroup (a, b) Source # | Since: base-4.9.0.0 |
| Semigroup b => Semigroup (a -> b) Source # | Since: base-4.9.0.0 |
| Semigroup a => Semigroup (Const a b) Source # | Since: base-4.9.0.0 |
| (Applicative f, Semigroup a) => Semigroup (Ap f a) Source # | Since: base-4.12.0.0 |
| Alternative f => Semigroup (Alt f a) Source # | Since: base-4.9.0.0 |
| Semigroup (f p) => Semigroup (Rec1 f p) Source # | Since: base-4.12.0.0 |
| (Semigroup a, Semigroup b, Semigroup c) => Semigroup (a, b, c) Source # | Since: base-4.9.0.0 |
| (Semigroup (f a), Semigroup (g a)) => Semigroup (Product f g a) Source # | Since: base-4.16.0.0 |
| (Semigroup (f p), Semigroup (g p)) => Semigroup ((f :*: g) p) Source # | Since: base-4.12.0.0 |
| Semigroup c => Semigroup (K1 i c p) Source # | Since: base-4.12.0.0 |
| (Semigroup a, Semigroup b, Semigroup c, Semigroup d) => Semigroup (a, b, c, d) Source # | Since: base-4.9.0.0 |
| Semigroup (f (g a)) => Semigroup (Compose f g a) Source # | Since: base-4.16.0.0 |
| Semigroup (f (g p)) => Semigroup ((f :.: g) p) Source # | Since: base-4.12.0.0 |
| Semigroup (f p) => Semigroup (M1 i c f p) Source # | Since: base-4.12.0.0 |
| (Semigroup a, Semigroup b, Semigroup c, Semigroup d, Semigroup e) => Semigroup (a, b, c, d, e) Source # | Since: base-4.9.0.0 |
Uninhabited data type
Since: base-4.8.0.0
Instances
| Data Void Source # | Since: base-4.8.0.0 |
Defined in Data.Data Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Void -> c Void Source # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Void Source # toConstr :: Void -> Constr Source # dataTypeOf :: Void -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Void) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Void) Source # gmapT :: (forall b. Data b => b -> b) -> Void -> Void Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Void -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Void -> r Source # gmapQ :: (forall d. Data d => d -> u) -> Void -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> Void -> u Source # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Void -> m Void Source # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Void -> m Void Source # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Void -> m Void Source # | |
| Semigroup Void Source # | Since: base-4.9.0.0 |
| Exception Void Source # | Since: base-4.8.0.0 |
Defined in GHC.Exception.Type Methods toException :: Void -> SomeException Source # fromException :: SomeException -> Maybe Void Source # displayException :: Void -> String Source # | |
| Generic Void Source # | |
| Ix Void Source # | Since: base-4.8.0.0 |
| Read Void Source # | Reading a Since: base-4.8.0.0 |
| Show Void Source # | Since: base-4.8.0.0 |
| Eq Void Source # | Since: base-4.8.0.0 |
| Ord Void Source # | Since: base-4.8.0.0 |
| type Rep Void Source # | Since: base-4.8.0.0 |
(<**>) :: Applicative f => f a -> f (a -> b) -> f b infixl 4 Source #
A variant of <*> with the arguments reversed.
liftA :: Applicative f => (a -> b) -> f a -> f b Source #
Lift a function to actions.
Equivalent to Functor's fmap but implemented using only Applicative's methods:
liftA f a = pure f <*> a
As such this function may be used to implement a Functor instance from an Applicative one.
Examples
Using the Applicative instance for Lists:
>>>liftA (+1) [1, 2][2,3]
Or the Applicative instance for Maybe
>>>liftA (+1) (Just 3)Just 4
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d Source #
Lift a ternary function to actions.
when :: Applicative f => Bool -> f () -> f () Source #
Conditional execution of Applicative expressions. For example,
when debug (putStrLn "Debugging")
will output the string Debugging if the Boolean value debug
is True, and otherwise do nothing.
assert :: Bool -> a -> a Source #
If the first argument evaluates to True, then the result is the
second argument. Otherwise an AssertionFailed exception
is raised, containing a String with the source file and line number of the
call to assert.
Assertions can normally be turned on or off with a compiler flag
(for GHC, assertions are normally on unless optimisation is turned on
with -O or the -fignore-asserts
option is given). When assertions are turned off, the first
argument to assert is ignored, and the second argument is
returned as the result.
sequence :: Monad m => [m a] -> m [a] Source #
Evaluate each action in the sequence from left to right, and collect the results.
(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 Source #
Same as >>=, but with the arguments interchanged.
join :: Monad m => m (m a) -> m a Source #
The join function is the conventional monad join operator. It
is used to remove one level of monadic structure, projecting its
bound argument into the outer level.
'join bssdo expression
do bs <- bss bs
Examples
A common use of join is to run an IO computation returned from
an STM transaction, since STM transactions
can't perform IO directly. Recall that
atomically :: STM a -> IO a
is used to run STM transactions atomically. So, by
specializing the types of atomically and join to
atomically:: STM (IO b) -> IO (IO b)join:: IO (IO b) -> IO b
we can compose them as
join.atomically:: STM (IO b) -> IO b
liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r Source #
Promote a function to a monad, scanning the monadic arguments from left to right. For example,
liftM2 (+) [0,1] [0,2] = [0,2,1,3] liftM2 (+) (Just 1) Nothing = Nothing
liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r Source #
Promote a function to a monad, scanning the monadic arguments from
left to right (cf. liftM2).
liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r Source #
Promote a function to a monad, scanning the monadic arguments from
left to right (cf. liftM2).
liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r Source #
Promote a function to a monad, scanning the monadic arguments from
left to right (cf. liftM2).
($) :: forall r a (b :: TYPE r). (a -> b) -> a -> b infixr 0 Source #
Application operator. This operator is redundant, since ordinary
application (f x) means the same as (f . However, $ x)$ has
low, right-associative binding precedence, so it sometimes allows
parentheses to be omitted; for example:
f $ g $ h x = f (g (h x))
It is also useful in higher-order situations, such as map ($ 0) xszipWith ($) fs xs
Note that ( is representation-polymorphic in its result type, so that
$)foo where $ Truefoo :: Bool -> Int# is well-typed.
foldr :: (a -> b -> b) -> b -> [a] -> b Source #
foldr, applied to a binary operator, a starting value (typically
the right-identity of the operator), and a list, reduces the list
using the binary operator, from right to left:
foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
($!) :: forall r a (b :: TYPE r). (a -> b) -> a -> b infixr 0 Source #
Strict (call-by-value) application operator. It takes a function and an argument, evaluates the argument to weak head normal form (WHNF), then calls the function with that value.
flip :: (a -> b -> c) -> b -> a -> c Source #
flip ff.
>>>flip (++) "hello" "world""worldhello"
const x y always evaluates to x, ignoring its second argument.
>>>const 42 "hello"42
>>>map (const 42) [0..3][42,42,42,42]
(++) :: [a] -> [a] -> [a] infixr 5 Source #
Append two lists, i.e.,
[x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn] [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
If the first list is not finite, the result is the first list.
WARNING: This function takes linear time in the number of elements of the first list.
map :: (a -> b) -> [a] -> [b] Source #
\(\mathcal{O}(n)\). map f xs is the list obtained by applying f to
each element of xs, i.e.,
map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn] map f [x1, x2, ...] == [f x1, f x2, ...]
>>>map (+1) [1, 2, 3][2,3,4]
Since Void values logically don't exist, this witnesses the
logical reasoning tool of "ex falso quodlibet".
>>>let x :: Either Void Int; x = Right 5>>>:{case x of Right r -> r Left l -> absurd l :} 5
Since: base-4.8.0.0
shiftL# :: Word# -> Int# -> Word# Source #
Shift the argument left by the specified number of bits (which must be non-negative).
shiftRL# :: Word# -> Int# -> Word# Source #
Shift the argument right by the specified number of bits (which must be non-negative). The RL means "right, logical" (as opposed to RA for arithmetic) (although an arithmetic right shift wouldn't make sense for Word#)
iShiftL# :: Int# -> Int# -> Int# Source #
Shift the argument left by the specified number of bits (which must be non-negative).
iShiftRA# :: Int# -> Int# -> Int# Source #
Shift the argument right (signed) by the specified number of bits (which must be non-negative). The RA means "right, arithmetic" (as opposed to RL for logical)
iShiftRL# :: Int# -> Int# -> Int# Source #
Shift the argument right (unsigned) by the specified number of bits (which must be non-negative). The RL means "right, logical" (as opposed to RA for arithmetic)
breakpoint :: a -> a Source #
breakpointCond :: Bool -> a -> a Source #
until :: (a -> Bool) -> (a -> a) -> a -> a Source #
until p ff until p holds.
eqString :: String -> String -> Bool Source #
This String equality predicate is used when desugaring
pattern-matches against strings.
Returns the tag of a constructor application; this function is used by the deriving code for Eq, Ord and Enum.
quotInt :: Int -> Int -> Int Source #
Used to implement quot for the Integral typeclass.
This performs integer division on its two parameters, truncated towards zero.
Example
>>>quotInt 10 25
>>>quot 10 25
remInt :: Int -> Int -> Int Source #
Used to implement rem for the Integral typeclass.
This gives the remainder after integer division of its two parameters, satisfying
((x `quot` y) * y) + (x `rem` y) == x
Example
>>>remInt 3 21
>>>rem 3 21
divInt :: Int -> Int -> Int Source #
Used to implement div for the Integral typeclass.
This performs integer division on its two parameters, truncated towards negative infinity.
Example
>>>10 `divInt` 25
>>>10 `div` 25
modInt :: Int -> Int -> Int Source #
Used to implement mod for the Integral typeclass.
This performs the modulo operation, satisfying
((x `div` y) * y) + (x `mod` y) == x
Example
>>>7 `modInt` 31
>>>7 `mod` 31
quotRemInt :: Int -> Int -> (Int, Int) Source #
Used to implement quotRem for the Integral typeclass.
This gives a tuple equivalent to
(quot x y, mod x y)
Example
>>>quotRemInt 10 2(5,0)
>>>quotRem 10 2(5,0)
divModInt :: Int -> Int -> (Int, Int) Source #
Used to implement divMod for the Integral typeclass.
This gives a tuple equivalent to
(div x y, mod x y)
Example
>>>divModInt 10 2(5,0)
>>>divMod 10 2(5,0)
shift_mask :: Int# -> Int# -> Int# Source #
This function is used to implement branchless shifts. If the number of bits to shift is greater than or equal to the type size in bits, then the shift must return 0. Instead of doing a test, we use a mask obtained via this function which is branchless too.
shift_mask m b | b < m = 0xFF..FF | otherwise = 0
module GHC.Classes
module GHC.CString
module GHC.Magic
module GHC.Magic.Dict
module GHC.Types
module GHC.Prim
module GHC.Prim.Ext
module GHC.Prim.PtrEq
module GHC.Err
module GHC.Maybe