Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell2010 |
Reexports from base
.
Synopsis
- class Functor f => Applicative (f :: Type -> Type) where
- newtype ZipList a = ZipList {
- getZipList :: [a]
- optional :: Alternative f => f a -> f (Maybe a)
- newtype Const a (b :: k) = Const {
- getConst :: a
- class Applicative f => Alternative (f :: Type -> Type) where
- liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
- (<**>) :: Applicative f => f a -> f (a -> b) -> f b
- (&&&) :: Arrow a => a b c -> a b c' -> a b (c, c')
- (>>>) :: forall {k} cat (a :: k) (b :: k) (c :: k). Category cat => cat a b -> cat b c -> cat a c
- (<<<) :: forall {k} cat (b :: k) (c :: k) (a :: k). Category cat => cat b c -> cat a b -> cat a c
- module Control.Concurrent.MVar
- class (Typeable e, Show e) => Exception e
- data SomeException = Exception e => SomeException e
- guard :: Alternative f => Bool -> f ()
- join :: Monad m => m (m a) -> m a
- class Applicative m => Monad (m :: Type -> Type) where
- zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m ()
- zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c]
- unless :: Applicative f => Bool -> f () -> f ()
- replicateM_ :: Applicative m => Int -> m a -> m ()
- replicateM :: Applicative m => Int -> m a -> m [a]
- mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a
- forever :: Applicative f => f a -> f b
- filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a]
- (>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c
- (<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c
- (<$!>) :: Monad m => (a -> b) -> m a -> m b
- class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where
- when :: Applicative f => Bool -> f () -> f ()
- (=<<) :: Monad m => (a -> m b) -> m a -> m b
- class Monad m => MonadFail (m :: Type -> Type) where
- module Control.Monad.IO.Class
- class Bifunctor (p :: Type -> Type -> Type) where
- xor :: Bits a => a -> a -> a
- toIntegralSized :: (Integral a, Integral b, Bits a, Bits b) => a -> Maybe b
- otherwise :: Bool
- data Bool
- bool :: a -> a -> Bool -> a
- (&&) :: Bool -> Bool -> Bool
- not :: Bool -> Bool
- (||) :: Bool -> Bool -> Bool
- data Char
- chr :: Int -> Char
- coerce :: forall {k :: RuntimeRep} (a :: TYPE k) (b :: TYPE k). Coercible a b => a -> b
- class a ~R# b => Coercible (a :: k) (b :: k)
- module Data.Either
- class Eq a where
- ($) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b
- on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
- fix :: (a -> a) -> a
- (&) :: a -> (a -> b) -> b
- id :: a -> a
- flip :: (a -> b -> c) -> b -> a -> c
- const :: a -> b -> a
- (.) :: (b -> c) -> (a -> b) -> a -> c
- class Functor (f :: Type -> Type) where
- void :: Functor f => f a -> f ()
- (<&>) :: Functor f => f a -> (a -> b) -> f b
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- ($>) :: Functor f => f a -> b -> f b
- newtype Compose (f :: k -> Type) (g :: k1 -> k) (a :: k1) = Compose {
- getCompose :: f (g a)
- class Contravariant (f :: Type -> Type) where
- (>$<) :: Contravariant f => (a -> b) -> f b -> f a
- newtype Identity a = Identity {
- runIdentity :: a
- data Int
- data Int8
- data Int16
- data Int32
- data Int64
- type Type = TYPE LiftedRep
- data Constraint
- (++) :: [a] -> [a] -> [a]
- filter :: (a -> Bool) -> [a] -> [a]
- zip :: [a] -> [b] -> [(a, b)]
- map :: (a -> b) -> [a] -> [b]
- unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
- transpose :: [[a]] -> [[a]]
- tails :: [a] -> [[a]]
- subsequences :: [a] -> [[a]]
- sortOn :: Ord b => (a -> b) -> [a] -> [a]
- sortBy :: (a -> a -> Ordering) -> [a] -> [a]
- sort :: Ord a => [a] -> [a]
- permutations :: [a] -> [[a]]
- isPrefixOf :: Eq a => [a] -> [a] -> Bool
- intersperse :: a -> [a] -> [a]
- intercalate :: [a] -> [[a]] -> [a]
- inits :: [a] -> [[a]]
- group :: Eq a => [a] -> [[a]]
- genericTake :: Integral i => i -> [a] -> [a]
- genericSplitAt :: Integral i => i -> [a] -> ([a], [a])
- genericReplicate :: Integral i => i -> a -> [a]
- genericLength :: Num i => [a] -> i
- genericDrop :: Integral i => i -> [a] -> [a]
- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
- zip3 :: [a] -> [b] -> [c] -> [(a, b, c)]
- unzip3 :: [(a, b, c)] -> ([a], [b], [c])
- unzip :: [(a, b)] -> ([a], [b])
- uncons :: [a] -> Maybe (a, [a])
- takeWhile :: (a -> Bool) -> [a] -> [a]
- take :: Int -> [a] -> [a]
- splitAt :: Int -> [a] -> ([a], [a])
- span :: (a -> Bool) -> [a] -> ([a], [a])
- scanr1 :: (a -> a -> a) -> [a] -> [a]
- scanr :: (a -> b -> b) -> b -> [a] -> [b]
- scanl1 :: (a -> a -> a) -> [a] -> [a]
- scanl' :: (b -> a -> b) -> b -> [a] -> [b]
- scanl :: (b -> a -> b) -> b -> [a] -> [b]
- reverse :: [a] -> [a]
- replicate :: Int -> a -> [a]
- repeat :: a -> [a]
- iterate :: (a -> a) -> a -> [a]
- dropWhile :: (a -> Bool) -> [a] -> [a]
- drop :: Int -> [a] -> [a]
- break :: (a -> Bool) -> [a] -> ([a], [a])
- data NonEmpty a = a :| [a]
- nonEmpty :: [a] -> Maybe (NonEmpty a)
- data Maybe a
- maybeToList :: Maybe a -> [a]
- maybe :: b -> (a -> b) -> Maybe a -> b
- mapMaybe :: (a -> Maybe b) -> [a] -> [b]
- listToMaybe :: [a] -> Maybe a
- isNothing :: Maybe a -> Bool
- isJust :: Maybe a -> Bool
- fromMaybe :: a -> Maybe a -> a
- catMaybes :: [Maybe a] -> [a]
- class Semigroup a => Monoid a where
- class Eq a => Ord a where
- data Ordering
- newtype Down a = Down {
- getDown :: a
- comparing :: Ord a => (b -> a) -> b -> b -> Ordering
- data Proxy (t :: k) = Proxy
- class Semigroup a where
- class (Functor t, Foldable t) => Traversable (t :: Type -> Type) where
- traverse :: Applicative f => (a -> f b) -> t a -> f (t b)
- sequenceA :: Applicative f => t (f a) -> f (t a)
- mapM :: Monad m => (a -> m b) -> t a -> m (t b)
- sequence :: Monad m => t (m a) -> m (t a)
- mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
- mapAccumL :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
- forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)
- for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b)
- fst :: (a, b) -> a
- snd :: (a, b) -> b
- uncurry :: (a -> b -> c) -> (a, b) -> c
- swap :: (a, b) -> (b, a)
- curry :: ((a, b) -> c) -> a -> b -> c
- class Typeable (a :: k)
- data Void
- data Word
- data Word8
- data Word16
- data Word32
- data Word64
- seq :: forall {r :: RuntimeRep} a (b :: TYPE r). a -> b -> b
- ord :: Char -> Int
- minInt :: Int
- maxInt :: Int
- ($!) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b
- class Bounded a where
- class Enum a where
- succ :: a -> a
- pred :: a -> a
- toEnum :: Int -> a
- fromEnum :: a -> Int
- enumFrom :: a -> [a]
- enumFromThen :: a -> a -> [a]
- enumFromTo :: a -> a -> [a]
- enumFromThenTo :: a -> a -> a -> [a]
- undefined :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => a
- error :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => [Char] -> a
- data Double = D# Double#
- data Float = F# Float#
- class Generic a
- class Num a where
- data Integer
- subtract :: Num a => a -> a -> a
- class IsLabel (x :: Symbol) a where
- fromLabel :: a
- fromIntegral :: (Integral a, Num b) => a -> b
- realToFrac :: (Real a, Fractional b) => a -> b
- class Num a => Fractional a where
- fromRational :: Rational -> a
- class (Real a, Enum a) => Integral a where
- class (Num a, Ord a) => Real a where
- toRational :: a -> Rational
- class (Real a, Fractional a) => RealFrac a where
- data Ratio a
- type Rational = Ratio Integer
- odd :: Integral a => a -> Bool
- numerator :: Ratio a -> a
- lcm :: Integral a => a -> a -> a
- gcd :: Integral a => a -> a -> a
- even :: Integral a => a -> Bool
- denominator :: Ratio a -> a
- (^^) :: (Fractional a, Integral b) => a -> b -> a
- (^) :: (Num a, Integral b) => a -> b -> a
- class Show a
- withFrozenCallStack :: HasCallStack => (HasCallStack => a) -> a
- type HasCallStack = ?callStack :: CallStack
- class KnownNat (n :: Nat)
- class KnownSymbol (n :: Symbol)
- class KnownChar (n :: Char)
- data Natural
- type family TypeError (a :: ErrorMessage) :: b where ...
- type family AppendSymbol (a :: Symbol) (b :: Symbol) :: Symbol where ...
- data Symbol
- type family (a :: Natural) + (b :: Natural) :: Natural where ...
- type family (a :: Natural) * (b :: Natural) :: Natural where ...
- type family (a :: Natural) ^ (b :: Natural) :: Natural where ...
- type family (a :: Natural) - (b :: Natural) :: Natural where ...
- type family CmpSymbol (a :: Symbol) (b :: Symbol) :: Ordering where ...
- type family CmpNat (a :: Natural) (b :: Natural) :: Ordering where ...
- type family CmpChar (a :: Char) (b :: Char) :: Ordering where ...
- type family Div (a :: Natural) (b :: Natural) :: Natural where ...
- type family Mod (a :: Natural) (b :: Natural) :: Natural where ...
- type family Log2 (a :: Natural) :: Natural where ...
- type family ConsSymbol (a :: Char) (b :: Symbol) :: Symbol where ...
- type family UnconsSymbol (a :: Symbol) :: Maybe (Char, Symbol) where ...
- type family CharToNat (a :: Char) :: Natural where ...
- type family NatToChar (a :: Natural) :: Char where ...
- data SomeSymbol = KnownSymbol n => SomeSymbol (Proxy n)
- data SomeChar = KnownChar n => SomeChar (Proxy n)
- pattern ShowType :: t -> ErrorMessage
- pattern (:<>:) :: ErrorMessage -> ErrorMessage -> ErrorMessage
- pattern (:$$:) :: ErrorMessage -> ErrorMessage -> ErrorMessage
- symbolVal' :: forall (n :: Symbol). KnownSymbol n => Proxy# n -> String
- symbolVal :: forall (n :: Symbol) proxy. KnownSymbol n => proxy n -> String
- someSymbolVal :: String -> SomeSymbol
- someNatVal :: Integer -> Maybe SomeNat
- someCharVal :: Char -> SomeChar
- sameSymbol :: forall (a :: Symbol) (b :: Symbol) proxy1 proxy2. (KnownSymbol a, KnownSymbol b) => proxy1 a -> proxy2 b -> Maybe (a :~: b)
- sameChar :: forall (a :: Char) (b :: Char) proxy1 proxy2. (KnownChar a, KnownChar b) => proxy1 a -> proxy2 b -> Maybe (a :~: b)
- natVal' :: forall (n :: Nat). KnownNat n => Proxy# n -> Integer
- natVal :: forall (n :: Nat) proxy. KnownNat n => proxy n -> Integer
- cmpSymbol :: forall (a :: Symbol) (b :: Symbol) proxy1 proxy2. (KnownSymbol a, KnownSymbol b) => proxy1 a -> proxy2 b -> OrderingI a b
- cmpChar :: forall (a :: Char) (b :: Char) proxy1 proxy2. (KnownChar a, KnownChar b) => proxy1 a -> proxy2 b -> OrderingI a b
- charVal' :: forall (n :: Char). KnownChar n => Proxy# n -> Char
- charVal :: forall (n :: Char) proxy. KnownChar n => proxy n -> Char
- data SomeNat = KnownNat n => SomeNat (Proxy n)
- type Nat = Natural
- sameNat :: forall (a :: Nat) (b :: Nat) proxy1 proxy2. (KnownNat a, KnownNat b) => proxy1 a -> proxy2 b -> Maybe (a :~: b)
- cmpNat :: forall (a :: Nat) (b :: Nat) proxy1 proxy2. (KnownNat a, KnownNat b) => proxy1 a -> proxy2 b -> OrderingI a b
- data OrderingI (a :: k) (b :: k) where
- type (<=?) (m :: k) (n :: k) = OrdCond (Compare m n) 'True 'True 'False
- type (<=) (x :: k) (y :: k) = (x <=? y) ~ 'True
- module Incipit.Fixed
- module Incipit.Foldable
- module Incipit.Fractional
- quot :: Integral a => a -> a -> Maybe a
- rem :: Integral a => a -> a -> Maybe a
- div :: Integral a => a -> a -> Maybe a
- mod :: Integral a => a -> a -> Maybe a
- quotRem :: Integral a => a -> a -> Maybe (a, a)
- divMod :: Integral a => a -> a -> Maybe (a, a)
- data Natural
- print :: Show a => a -> IO ()
- data IO a
- putStrLn :: String -> IO ()
- putStr :: String -> IO ()
- type FilePath = String
- showsPrec :: Show a => Int -> a -> ShowS
- showString :: String -> ShowS
- showParen :: Bool -> ShowS -> ShowS
Documentation
class Functor f => Applicative (f :: Type -> Type) where #
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:
(<*>
) =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:
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
liftA2
p (liftA2
q u v) =liftA2
f u .liftA2
g v
If f
is also a Monad
, it should satisfy
(which implies that pure
and <*>
satisfy the applicative functor laws).
Lift a value.
(<*>) :: f (a -> b) -> f a -> f b infixl 4 #
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 #
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 #
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 3
Just 3
>>>
Nothing *> Just 3
Nothing
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 #
Sequence actions, discarding the value of the second argument.
Instances
Applicative ZipList | 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 |
Applicative Complex | Since: base-4.9.0.0 |
Applicative Identity | Since: base-4.8.0.0 |
Applicative First | Since: base-4.8.0.0 |
Applicative Last | Since: base-4.8.0.0 |
Applicative Down | Since: base-4.11.0.0 |
Applicative First | Since: base-4.9.0.0 |
Applicative Last | Since: base-4.9.0.0 |
Applicative Max | Since: base-4.9.0.0 |
Applicative Min | Since: base-4.9.0.0 |
Applicative Par1 | Since: base-4.9.0.0 |
Applicative P | Since: base-4.5.0.0 |
Applicative ReadP | Since: base-4.6.0.0 |
Applicative Seq | Since: containers-0.5.4 |
Applicative DList | |
Applicative IO | Since: base-2.1 |
Applicative Q | |
Applicative NonEmpty | Since: base-4.9.0.0 |
Applicative Maybe | Since: base-2.1 |
Applicative Solo | Since: base-4.15 |
Applicative [] | Since: base-2.1 |
Monad m => Applicative (WrappedMonad m) | Since: base-2.1 |
Defined in Control.Applicative pure :: a -> WrappedMonad m a # (<*>) :: WrappedMonad m (a -> b) -> WrappedMonad m a -> WrappedMonad m b # liftA2 :: (a -> b -> c) -> WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m c # (*>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b # (<*) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m a # | |
Arrow a => Applicative (ArrowMonad a) | Since: base-4.6.0.0 |
Defined in Control.Arrow pure :: a0 -> ArrowMonad a a0 # (<*>) :: ArrowMonad a (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b # liftA2 :: (a0 -> b -> c) -> ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a c # (*>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b # (<*) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a a0 # | |
Applicative (Either e) | Since: base-3.0 |
Applicative (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
Applicative (U1 :: Type -> Type) | Since: base-4.9.0.0 |
Monoid a => Applicative ((,) a) | For tuples, the ("hello ", (+15)) <*> ("world!", 2002) ("hello world!",2017) Since: base-2.1 |
Arrow a => Applicative (WrappedArrow a b) | Since: base-2.1 |
Defined in Control.Applicative pure :: a0 -> WrappedArrow a b a0 # (<*>) :: WrappedArrow a b (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 # liftA2 :: (a0 -> b0 -> c) -> WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b c # (*>) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b b0 # (<*) :: WrappedArrow a b a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 # | |
Applicative m => Applicative (Kleisli m a) | Since: base-4.14.0.0 |
Defined in Control.Arrow | |
Monoid m => Applicative (Const m :: Type -> Type) | Since: base-2.0.1 |
Applicative f => Applicative (Ap f) | Since: base-4.12.0.0 |
Applicative f => Applicative (Rec1 f) | Since: base-4.9.0.0 |
(Applicative f, Monad f) => Applicative (WhenMissing f x) | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal pure :: a -> WhenMissing f x a # (<*>) :: WhenMissing f x (a -> b) -> WhenMissing f x a -> WhenMissing f x b # liftA2 :: (a -> b -> c) -> WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x c # (*>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b # (<*) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x a # | |
(Monoid a, Monoid b) => Applicative ((,,) a b) | Since: base-4.14.0.0 |
(Applicative f, Applicative g) => Applicative (Product f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Product | |
(Applicative f, Applicative g) => Applicative (f :*: g) | Since: base-4.9.0.0 |
Monoid c => Applicative (K1 i c :: Type -> Type) | Since: base-4.12.0.0 |
(Monad f, Applicative f) => Applicative (WhenMatched f x y) | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal pure :: a -> WhenMatched f x y a # (<*>) :: WhenMatched f x y (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b # liftA2 :: (a -> b -> c) -> WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y c # (*>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b # (<*) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y a # | |
(Applicative f, Monad f) => Applicative (WhenMissing f k x) | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal pure :: a -> WhenMissing f k x a # (<*>) :: WhenMissing f k x (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b # liftA2 :: (a -> b -> c) -> WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x c # (*>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b # (<*) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x a # | |
(Monoid a, Monoid b, Monoid c) => Applicative ((,,,) a b c) | Since: base-4.14.0.0 |
Defined in GHC.Base | |
Applicative ((->) r) | Since: base-2.1 |
(Applicative f, Applicative g) => Applicative (Compose f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose | |
(Applicative f, Applicative g) => Applicative (f :.: g) | Since: base-4.9.0.0 |
Applicative f => Applicative (M1 i c f) | Since: base-4.9.0.0 |
(Monad f, Applicative f) => Applicative (WhenMatched f k x y) | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal pure :: a -> WhenMatched f k x y a # (<*>) :: WhenMatched f k x y (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b # liftA2 :: (a -> b -> c) -> WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y c # (*>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b # (<*) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y a # |
Lists, but with an Applicative
functor based on zipping.
ZipList | |
|
Instances
Foldable ZipList | Since: base-4.9.0.0 |
Defined in Control.Applicative fold :: Monoid m => ZipList m -> m # foldMap :: Monoid m => (a -> m) -> ZipList a -> m # foldMap' :: Monoid m => (a -> m) -> ZipList a -> m # foldr :: (a -> b -> b) -> b -> ZipList a -> b # foldr' :: (a -> b -> b) -> b -> ZipList a -> b # foldl :: (b -> a -> b) -> b -> ZipList a -> b # foldl' :: (b -> a -> b) -> b -> ZipList a -> b # foldr1 :: (a -> a -> a) -> ZipList a -> a # foldl1 :: (a -> a -> a) -> ZipList a -> a # elem :: Eq a => a -> ZipList a -> Bool # maximum :: Ord a => ZipList a -> a # minimum :: Ord a => ZipList a -> a # | |
Traversable ZipList | Since: base-4.9.0.0 |
Alternative ZipList | Since: base-4.11.0.0 |
Applicative ZipList | 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 |
Functor ZipList | Since: base-2.1 |
Generic1 ZipList | |
IsList (ZipList a) | Since: base-4.15.0.0 |
Generic (ZipList a) | |
Read a => Read (ZipList a) | Since: base-4.7.0.0 |
Show a => Show (ZipList a) | Since: base-4.7.0.0 |
Eq a => Eq (ZipList a) | Since: base-4.7.0.0 |
Ord a => Ord (ZipList a) | Since: base-4.7.0.0 |
Defined in Control.Applicative | |
type Rep1 ZipList | Since: base-4.7.0.0 |
Defined in Control.Applicative | |
type Item (ZipList a) | |
type Rep (ZipList a) | Since: base-4.7.0.0 |
Defined in Control.Applicative |
optional :: Alternative f => f a -> f (Maybe a) #
One or none.
It is useful for modelling any computation that is allowed to fail.
Examples
Using the Alternative
instance of Control.Monad.Except, the following functions:
>>>
import Control.Monad.Except
>>>
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
The Const
functor.
Instances
Generic1 (Const a :: k -> Type) | |
Bifunctor (Const :: Type -> Type -> Type) | Since: base-4.8.0.0 |
Foldable (Const m :: TYPE LiftedRep -> Type) | Since: base-4.7.0.0 |
Defined in Data.Functor.Const fold :: Monoid m0 => Const m m0 -> m0 # foldMap :: Monoid m0 => (a -> m0) -> Const m a -> m0 # foldMap' :: Monoid m0 => (a -> m0) -> Const m a -> m0 # foldr :: (a -> b -> b) -> b -> Const m a -> b # foldr' :: (a -> b -> b) -> b -> Const m a -> b # foldl :: (b -> a -> b) -> b -> Const m a -> b # foldl' :: (b -> a -> b) -> b -> Const m a -> b # foldr1 :: (a -> a -> a) -> Const m a -> a # foldl1 :: (a -> a -> a) -> Const m a -> a # elem :: Eq a => a -> Const m a -> Bool # maximum :: Ord a => Const m a -> a # minimum :: Ord a => Const m a -> a # | |
Contravariant (Const a :: Type -> Type) | |
Traversable (Const m :: Type -> Type) | Since: base-4.7.0.0 |
Monoid m => Applicative (Const m :: Type -> Type) | Since: base-2.0.1 |
Functor (Const m :: Type -> Type) | Since: base-2.1 |
IsString a => IsString (Const a b) | Since: base-4.9.0.0 |
Defined in Data.String fromString :: String -> Const a b # | |
Storable a => Storable (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
Monoid a => Monoid (Const a b) | Since: base-4.9.0.0 |
Semigroup a => Semigroup (Const a b) | Since: base-4.9.0.0 |
Bits a => Bits (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const (.&.) :: Const a b -> Const a b -> Const a b # (.|.) :: Const a b -> Const a b -> Const a b # xor :: Const a b -> Const a b -> Const a b # complement :: Const a b -> Const a b # shift :: Const a b -> Int -> Const a b # rotate :: Const a b -> Int -> Const a b # setBit :: Const a b -> Int -> Const a b # clearBit :: Const a b -> Int -> Const a b # complementBit :: Const a b -> Int -> Const a b # testBit :: Const a b -> Int -> Bool # bitSizeMaybe :: Const a b -> Maybe Int # isSigned :: Const a b -> Bool # shiftL :: Const a b -> Int -> Const a b # unsafeShiftL :: Const a b -> Int -> Const a b # shiftR :: Const a b -> Int -> Const a b # unsafeShiftR :: Const a b -> Int -> Const a b # rotateL :: Const a b -> Int -> Const a b # | |
FiniteBits a => FiniteBits (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const finiteBitSize :: Const a b -> Int # countLeadingZeros :: Const a b -> Int # countTrailingZeros :: Const a b -> Int # | |
Bounded a => Bounded (Const a b) | Since: base-4.9.0.0 |
Enum a => Enum (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const succ :: Const a b -> Const a b # pred :: Const a b -> Const a b # fromEnum :: Const a b -> Int # enumFrom :: Const a b -> [Const a b] # enumFromThen :: Const a b -> Const a b -> [Const a b] # enumFromTo :: Const a b -> Const a b -> [Const a b] # enumFromThenTo :: Const a b -> Const a b -> Const a b -> [Const a b] # | |
Floating a => Floating (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const exp :: Const a b -> Const a b # log :: Const a b -> Const a b # sqrt :: Const a b -> Const a b # (**) :: Const a b -> Const a b -> Const a b # logBase :: Const a b -> Const a b -> Const a b # sin :: Const a b -> Const a b # cos :: Const a b -> Const a b # tan :: Const a b -> Const a b # asin :: Const a b -> Const a b # acos :: Const a b -> Const a b # atan :: Const a b -> Const a b # sinh :: Const a b -> Const a b # cosh :: Const a b -> Const a b # tanh :: Const a b -> Const a b # asinh :: Const a b -> Const a b # acosh :: Const a b -> Const a b # atanh :: Const a b -> Const a b # log1p :: Const a b -> Const a b # expm1 :: Const a b -> Const a b # | |
RealFloat a => RealFloat (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const floatRadix :: Const a b -> Integer # floatDigits :: Const a b -> Int # floatRange :: Const a b -> (Int, Int) # decodeFloat :: Const a b -> (Integer, Int) # encodeFloat :: Integer -> Int -> Const a b # exponent :: Const a b -> Int # significand :: Const a b -> Const a b # scaleFloat :: Int -> Const a b -> Const a b # isInfinite :: Const a b -> Bool # isDenormalized :: Const a b -> Bool # isNegativeZero :: Const a b -> Bool # | |
Generic (Const a b) | |
Ix a => Ix (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const range :: (Const a b, Const a b) -> [Const a b] # index :: (Const a b, Const a b) -> Const a b -> Int # unsafeIndex :: (Const a b, Const a b) -> Const a b -> Int # inRange :: (Const a b, Const a b) -> Const a b -> Bool # rangeSize :: (Const a b, Const a b) -> Int # unsafeRangeSize :: (Const a b, Const a b) -> Int # | |
Num a => Num (Const a b) | Since: base-4.9.0.0 |
Read a => Read (Const a b) | This instance would be equivalent to the derived instances of the
Since: base-4.8.0.0 |
Fractional a => Fractional (Const a b) | Since: base-4.9.0.0 |
Integral a => Integral (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
Real a => Real (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const toRational :: Const a b -> Rational # | |
RealFrac a => RealFrac (Const a b) | Since: base-4.9.0.0 |
Show a => Show (Const a b) | This instance would be equivalent to the derived instances of the
Since: base-4.8.0.0 |
Eq a => Eq (Const a b) | Since: base-4.9.0.0 |
Ord a => Ord (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
type Rep1 (Const a :: k -> Type) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
type Rep (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const |
class Applicative f => Alternative (f :: Type -> Type) where #
A monoid on applicative functors.
If defined, some
and many
should be the least solutions
of the equations:
The identity of <|>
(<|>) :: f a -> f a -> f a infixl 3 #
An associative binary operation
One or more.
Zero or more.
Instances
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d #
Lift a ternary function to actions.
(<**>) :: Applicative f => f a -> f (a -> b) -> f b infixl 4 #
A variant of <*>
with the arguments reversed.
(&&&) :: Arrow a => a b c -> a b c' -> a b (c, c') infixr 3 #
Fanout: send the input to both argument arrows and combine their output.
The default definition may be overridden with a more efficient version if desired.
(>>>) :: forall {k} cat (a :: k) (b :: k) (c :: k). Category cat => cat a b -> cat b c -> cat a c infixr 1 #
Left-to-right composition
(<<<) :: forall {k} cat (b :: k) (c :: k) (a :: k). Category cat => cat b c -> cat a b -> cat a c infixr 1 #
Right-to-left composition
module Control.Concurrent.MVar
class (Typeable e, Show e) => Exception e #
Any type that you wish to throw or catch as an exception must be an
instance of the Exception
class. The simplest case is a new exception
type directly below the root:
data MyException = ThisException | ThatException deriving Show instance Exception MyException
The default method definitions in the Exception
class do what we need
in this case. You can now throw and catch ThisException
and
ThatException
as exceptions:
*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException)) Caught ThisException
In more complicated examples, you may wish to define a whole hierarchy of exceptions:
--------------------------------------------------------------------- -- Make the root exception type for all the exceptions in a compiler data SomeCompilerException = forall e . Exception e => SomeCompilerException e instance Show SomeCompilerException where show (SomeCompilerException e) = show e instance Exception SomeCompilerException compilerExceptionToException :: Exception e => e -> SomeException compilerExceptionToException = toException . SomeCompilerException compilerExceptionFromException :: Exception e => SomeException -> Maybe e compilerExceptionFromException x = do SomeCompilerException a <- fromException x cast a --------------------------------------------------------------------- -- Make a subhierarchy for exceptions in the frontend of the compiler data SomeFrontendException = forall e . Exception e => SomeFrontendException e instance Show SomeFrontendException where show (SomeFrontendException e) = show e instance Exception SomeFrontendException where toException = compilerExceptionToException fromException = compilerExceptionFromException frontendExceptionToException :: Exception e => e -> SomeException frontendExceptionToException = toException . SomeFrontendException frontendExceptionFromException :: Exception e => SomeException -> Maybe e frontendExceptionFromException x = do SomeFrontendException a <- fromException x cast a --------------------------------------------------------------------- -- Make an exception type for a particular frontend compiler exception data MismatchedParentheses = MismatchedParentheses deriving Show instance Exception MismatchedParentheses where toException = frontendExceptionToException fromException = frontendExceptionFromException
We can now catch a MismatchedParentheses
exception as
MismatchedParentheses
, SomeFrontendException
or
SomeCompilerException
, but not other types, e.g. IOException
:
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses)) Caught MismatchedParentheses *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException)) Caught MismatchedParentheses *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException)) Caught MismatchedParentheses *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException)) *** Exception: MismatchedParentheses
Instances
Exception Void | Since: base-4.8.0.0 |
Defined in Data.Void toException :: Void -> SomeException # fromException :: SomeException -> Maybe Void # displayException :: Void -> String # | |
Exception ArithException | Since: base-4.0.0.0 |
Defined in GHC.Exception.Type | |
Exception SomeException | Since: base-3.0 |
Defined in GHC.Exception.Type | |
Exception UnicodeException | |
Defined in Data.Text.Encoding.Error |
data SomeException #
The SomeException
type is the root of the exception type hierarchy.
When an exception of type e
is thrown, behind the scenes it is
encapsulated in a SomeException
.
Exception e => SomeException e |
Instances
Exception SomeException | Since: base-3.0 |
Defined in GHC.Exception.Type | |
Show SomeException | Since: base-3.0 |
Defined in GHC.Exception.Type showsPrec :: Int -> SomeException -> ShowS # show :: SomeException -> String # showList :: [SomeException] -> ShowS # |
guard :: Alternative f => Bool -> f () #
Conditional failure of Alternative
computations. Defined by
guard True =pure
() guard False =empty
Examples
Common uses of guard
include conditionally signaling an error in
an error monad and conditionally rejecting the current choice in an
Alternative
-based parser.
As an example of signaling an error in the error monad Maybe
,
consider a safe division function safeDiv x y
that returns
Nothing
when the denominator y
is zero and
otherwise. For example:Just
(x `div`
y)
>>>
safeDiv 4 0
Nothing
>>>
safeDiv 4 2
Just 2
A definition of safeDiv
using guards, but not guard
:
safeDiv :: Int -> Int -> Maybe Int safeDiv x y | y /= 0 = Just (x `div` y) | otherwise = Nothing
A definition of safeDiv
using guard
and Monad
do
-notation:
safeDiv :: Int -> Int -> Maybe Int safeDiv x y = do guard (y /= 0) return (x `div` y)
join :: Monad m => m (m a) -> m a #
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.
'
' can be understood as the 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
class Applicative m => Monad (m :: Type -> Type) where #
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
return
a>>=
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.
(>>=) :: m a -> (a -> m b) -> m b infixl 1 #
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
(>>) :: m a -> m b -> m b infixl 1 #
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
Instances
Monad Complex | Since: base-4.9.0.0 |
Monad Identity | Since: base-4.8.0.0 |
Monad First | Since: base-4.8.0.0 |
Monad Last | Since: base-4.8.0.0 |
Monad Down | Since: base-4.11.0.0 |
Monad First | Since: base-4.9.0.0 |
Monad Last | Since: base-4.9.0.0 |
Monad Max | Since: base-4.9.0.0 |
Monad Min | Since: base-4.9.0.0 |
Monad Par1 | Since: base-4.9.0.0 |
Monad P | Since: base-2.1 |
Monad ReadP | Since: base-2.1 |
Monad Seq | |
Monad DList | |
Monad IO | Since: base-2.1 |
Monad Q | |
Monad NonEmpty | Since: base-4.9.0.0 |
Monad Maybe | Since: base-2.1 |
Monad Solo | Since: base-4.15 |
Monad [] | Since: base-2.1 |
Monad m => Monad (WrappedMonad m) | Since: base-4.7.0.0 |
Defined in Control.Applicative (>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b # (>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b # return :: a -> WrappedMonad m a # | |
ArrowApply a => Monad (ArrowMonad a) | Since: base-2.1 |
Defined in Control.Arrow (>>=) :: ArrowMonad a a0 -> (a0 -> ArrowMonad a b) -> ArrowMonad a b # (>>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b # return :: a0 -> ArrowMonad a a0 # | |
Monad (Either e) | Since: base-4.4.0.0 |
Monad (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
Monad (U1 :: Type -> Type) | Since: base-4.9.0.0 |
Monoid a => Monad ((,) a) | Since: base-4.9.0.0 |
Monad m => Monad (Kleisli m a) | Since: base-4.14.0.0 |
Monad f => Monad (Ap f) | Since: base-4.12.0.0 |
Monad f => Monad (Rec1 f) | Since: base-4.9.0.0 |
(Applicative f, Monad f) => Monad (WhenMissing f x) | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal (>>=) :: WhenMissing f x a -> (a -> WhenMissing f x b) -> WhenMissing f x b # (>>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b # return :: a -> WhenMissing f x a # | |
(Monoid a, Monoid b) => Monad ((,,) a b) | Since: base-4.14.0.0 |
(Monad f, Monad g) => Monad (Product f g) | Since: base-4.9.0.0 |
(Monad f, Monad g) => Monad (f :*: g) | Since: base-4.9.0.0 |
(Monad f, Applicative f) => Monad (WhenMatched f x y) | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal (>>=) :: WhenMatched f x y a -> (a -> WhenMatched f x y b) -> WhenMatched f x y b # (>>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b # return :: a -> WhenMatched f x y a # | |
(Applicative f, Monad f) => Monad (WhenMissing f k x) | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal (>>=) :: WhenMissing f k x a -> (a -> WhenMissing f k x b) -> WhenMissing f k x b # (>>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b # return :: a -> WhenMissing f k x a # | |
(Monoid a, Monoid b, Monoid c) => Monad ((,,,) a b c) | Since: base-4.14.0.0 |
Monad ((->) r) | Since: base-2.1 |
Monad f => Monad (M1 i c f) | Since: base-4.9.0.0 |
(Monad f, Applicative f) => Monad (WhenMatched f k x y) | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal (>>=) :: WhenMatched f k x y a -> (a -> WhenMatched f k x y b) -> WhenMatched f k x y b # (>>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b # return :: a -> WhenMatched f k x y a # |
zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () #
zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] #
unless :: Applicative f => Bool -> f () -> f () #
The reverse of when
.
replicateM_ :: Applicative m => Int -> m a -> m () #
replicateM :: Applicative m => Int -> m a -> m [a] #
performs the action replicateM
n actact
n
times,
and then returns the list of results:
Examples
>>>
import Control.Monad.State
>>>
runState (replicateM 3 $ state $ \s -> (s, s + 1)) 1
([1,2,3],4)
forever :: Applicative f => f a -> f b #
Repeat an action indefinitely.
Examples
A common use of forever
is to process input from network sockets,
Handle
s, and channels
(e.g. MVar
and
Chan
).
For example, here is how we might implement an echo
server, using
forever
both to listen for client connections on a network socket
and to echo client input on client connection handles:
echoServer :: Socket -> IO () echoServer socket =forever
$ do client <- accept socketforkFinally
(echo client) (\_ -> hClose client) where echo :: Handle -> IO () echo client =forever
$ hGetLine client >>= hPutStrLn client
Note that "forever" isn't necessarily non-terminating.
If the action is in a
and short-circuits after some number of iterations.
then MonadPlus
actually returns forever
mzero
, effectively short-circuiting its caller.
filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] #
This generalizes the list-based filter
function.
(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1 #
Left-to-right composition of Kleisli arrows.
'(bs
' can be understood as the >=>
cs) ado
expression
do b <- bs a cs b
class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where #
Monads that also support choice and failure.
Nothing
The identity of mplus
. It should also satisfy the equations
mzero >>= f = mzero v >> mzero = mzero
The default definition is
mzero = empty
An associative operation. The default definition is
mplus = (<|>
)
Instances
MonadPlus P | Since: base-2.1 |
Defined in Text.ParserCombinators.ReadP | |
MonadPlus ReadP | Since: base-2.1 |
MonadPlus Seq | |
MonadPlus DList | |
MonadPlus IO | Since: base-4.9.0.0 |
MonadPlus Maybe | Since: base-2.1 |
MonadPlus [] | Since: base-2.1 |
(ArrowApply a, ArrowPlus a) => MonadPlus (ArrowMonad a) | Since: base-4.6.0.0 |
Defined in Control.Arrow mzero :: ArrowMonad a a0 # mplus :: ArrowMonad a a0 -> ArrowMonad a a0 -> ArrowMonad a a0 # | |
MonadPlus (Proxy :: Type -> Type) | Since: base-4.9.0.0 |
MonadPlus (U1 :: Type -> Type) | Since: base-4.9.0.0 |
MonadPlus m => MonadPlus (Kleisli m a) | Since: base-4.14.0.0 |
MonadPlus f => MonadPlus (Ap f) | Since: base-4.12.0.0 |
MonadPlus f => MonadPlus (Rec1 f) | Since: base-4.9.0.0 |
(MonadPlus f, MonadPlus g) => MonadPlus (Product f g) | Since: base-4.9.0.0 |
(MonadPlus f, MonadPlus g) => MonadPlus (f :*: g) | Since: base-4.9.0.0 |
MonadPlus f => MonadPlus (M1 i c f) | Since: base-4.9.0.0 |
when :: Applicative f => Bool -> f () -> f () #
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.
(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 #
Same as >>=
, but with the arguments interchanged.
class Monad m => MonadFail (m :: Type -> Type) where #
When a value is bound in do
-notation, the pattern on the left
hand side of <-
might not match. In this case, this class
provides a function to recover.
A Monad
without a MonadFail
instance may only be used in conjunction
with pattern that always match, such as newtypes, tuples, data types with
only a single data constructor, and irrefutable patterns (~pat
).
Instances of MonadFail
should satisfy the following law: fail s
should
be a left zero for >>=
,
fail s >>= f = fail s
If your Monad
is also MonadPlus
, a popular definition is
fail _ = mzero
Since: base-4.9.0.0
Instances
MonadFail P | Since: base-4.9.0.0 |
Defined in Text.ParserCombinators.ReadP | |
MonadFail ReadP | Since: base-4.9.0.0 |
Defined in Text.ParserCombinators.ReadP | |
MonadFail DList | |
Defined in Data.DList.Internal | |
MonadFail IO | Since: base-4.9.0.0 |
Defined in Control.Monad.Fail | |
MonadFail Q | |
Defined in Language.Haskell.TH.Syntax | |
MonadFail Maybe | Since: base-4.9.0.0 |
Defined in Control.Monad.Fail | |
MonadFail [] | Since: base-4.9.0.0 |
Defined in Control.Monad.Fail | |
MonadFail f => MonadFail (Ap f) | Since: base-4.12.0.0 |
Defined in Data.Monoid |
module Control.Monad.IO.Class
class Bifunctor (p :: Type -> Type -> Type) where #
A bifunctor is a type constructor that takes
two type arguments and is a functor in both arguments. That
is, unlike with Functor
, a type constructor such as Either
does not need to be partially applied for a Bifunctor
instance, and the methods in this class permit mapping
functions over the Left
value or the Right
value,
or both at the same time.
Formally, the class Bifunctor
represents a bifunctor
from Hask
-> Hask
.
Intuitively it is a bifunctor where both the first and second arguments are covariant.
You can define a Bifunctor
by either defining bimap
or by
defining both first
and second
.
If you supply bimap
, you should ensure that:
bimap
id
id
≡id
If you supply first
and second
, ensure:
first
id
≡id
second
id
≡id
If you supply both, you should also ensure:
bimap
f g ≡first
f.
second
g
These ensure by parametricity:
bimap
(f.
g) (h.
i) ≡bimap
f h.
bimap
g ifirst
(f.
g) ≡first
f.
first
gsecond
(f.
g) ≡second
f.
second
g
Since: base-4.8.0.0
bimap :: (a -> b) -> (c -> d) -> p a c -> p b d #
Map over both arguments at the same time.
bimap
f g ≡first
f.
second
g
Examples
>>>
bimap toUpper (+1) ('j', 3)
('J',4)
>>>
bimap toUpper (+1) (Left 'j')
Left 'J'
>>>
bimap toUpper (+1) (Right 3)
Right 4
Instances
Bifunctor Either | Since: base-4.8.0.0 |
Bifunctor Arg | Since: base-4.9.0.0 |
Bifunctor (,) | Since: base-4.8.0.0 |
Bifunctor (Const :: Type -> Type -> Type) | Since: base-4.8.0.0 |
Bifunctor ((,,) x1) | Since: base-4.8.0.0 |
Bifunctor (K1 i :: Type -> Type -> Type) | Since: base-4.9.0.0 |
Bifunctor ((,,,) x1 x2) | Since: base-4.8.0.0 |
Bifunctor ((,,,,) x1 x2 x3) | Since: base-4.8.0.0 |
Bifunctor ((,,,,,) x1 x2 x3 x4) | Since: base-4.8.0.0 |
Bifunctor ((,,,,,,) x1 x2 x3 x4 x5) | Since: base-4.8.0.0 |
toIntegralSized :: (Integral a, Integral b, Bits a, Bits b) => a -> Maybe b #
Attempt to convert an Integral
type a
to an Integral
type b
using
the size of the types as measured by Bits
methods.
A simpler version of this function is:
toIntegral :: (Integral a, Integral b) => a -> Maybe b toIntegral x | toInteger x == y = Just (fromInteger y) | otherwise = Nothing where y = toInteger x
This version requires going through Integer
, which can be inefficient.
However, toIntegralSized
is optimized to allow GHC to statically determine
the relative type sizes (as measured by bitSizeMaybe
and isSigned
) and
avoid going through Integer
for many types. (The implementation uses
fromIntegral
, which is itself optimized with rules for base
types but may
go through Integer
for some type pairs.)
Since: base-4.8.0.0
Instances
Bits Bool | Interpret Since: base-4.7.0.0 |
Defined in GHC.Bits (.&.) :: Bool -> Bool -> Bool # (.|.) :: Bool -> Bool -> Bool # complement :: Bool -> Bool # shift :: Bool -> Int -> Bool # rotate :: Bool -> Int -> Bool # setBit :: Bool -> Int -> Bool # clearBit :: Bool -> Int -> Bool # complementBit :: Bool -> Int -> Bool # testBit :: Bool -> Int -> Bool # bitSizeMaybe :: Bool -> Maybe Int # shiftL :: Bool -> Int -> Bool # unsafeShiftL :: Bool -> Int -> Bool # shiftR :: Bool -> Int -> Bool # unsafeShiftR :: Bool -> Int -> Bool # rotateL :: Bool -> Int -> Bool # | |
FiniteBits Bool | Since: base-4.7.0.0 |
Defined in GHC.Bits | |
Bounded Bool | Since: base-2.1 |
Enum Bool | Since: base-2.1 |
Generic Bool | |
SingKind Bool | Since: base-4.9.0.0 |
Defined in GHC.Generics type DemoteRep Bool | |
Read Bool | Since: base-2.1 |
Show Bool | Since: base-2.1 |
Eq Bool | |
Ord Bool | |
SingI 'False | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
SingI 'True | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
Lift Bool | |
type DemoteRep Bool | |
Defined in GHC.Generics | |
type Rep Bool | Since: base-4.6.0.0 |
data Sing (a :: Bool) | |
Case analysis for the Bool
type.
evaluates to bool
x y px
when p
is False
, and evaluates to y
when p
is True
.
This is equivalent to if p then y else x
; that is, one can
think of it as an if-then-else construct with its arguments
reordered.
Examples
Basic usage:
>>>
bool "foo" "bar" True
"bar">>>
bool "foo" "bar" False
"foo"
Confirm that
and bool
x y pif p then y else x
are
equivalent:
>>>
let p = True; x = "bar"; y = "foo"
>>>
bool x y p == if p then y else x
True>>>
let p = False
>>>
bool x y p == if p then y else x
True
Since: base-4.7.0.0
The character type Char
is an enumeration whose values represent
Unicode (or equivalently ISO/IEC 10646) code points (i.e. characters, see
http://www.unicode.org/ for details). This set extends the ISO 8859-1
(Latin-1) character set (the first 256 characters), which is itself an extension
of the ASCII character set (the first 128 characters). A character literal in
Haskell has type Char
.
To convert a Char
to or from the corresponding Int
value defined
by Unicode, use toEnum
and fromEnum
from the
Enum
class respectively (or equivalently ord
and
chr
).
Instances
Bounded Char | Since: base-2.1 |
Enum Char | Since: base-2.1 |
Read Char | Since: base-2.1 |
Show Char | Since: base-2.1 |
Eq Char | |
Ord Char | |
ToLText String Source # | |
ToString String Source # | |
ToText String Source # | |
ConvertUtf8 String ByteString Source # | |
Defined in Incipit.String.Conversion encodeUtf8 :: String -> ByteString Source # decodeUtf8 :: ByteString -> String Source # decodeUtf8Strict :: ByteString -> Either UnicodeException String Source # | |
ConvertUtf8 String ShortByteString Source # | Since: 0.6.0.0 |
Defined in Incipit.String.Conversion | |
ConvertUtf8 String LByteString Source # | Converting |
Defined in Incipit.String.Conversion | |
Lift Char | |
Generic1 (URec Char :: k -> Type) | |
Foldable (UChar :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Defined in Data.Foldable fold :: Monoid m => UChar m -> m # foldMap :: Monoid m => (a -> m) -> UChar a -> m # foldMap' :: Monoid m => (a -> m) -> UChar a -> m # foldr :: (a -> b -> b) -> b -> UChar a -> b # foldr' :: (a -> b -> b) -> b -> UChar a -> b # foldl :: (b -> a -> b) -> b -> UChar a -> b # foldl' :: (b -> a -> b) -> b -> UChar a -> b # foldr1 :: (a -> a -> a) -> UChar a -> a # foldl1 :: (a -> a -> a) -> UChar a -> a # elem :: Eq a => a -> UChar a -> Bool # maximum :: Ord a => UChar a -> a # minimum :: Ord a => UChar a -> a # | |
Traversable (UChar :: Type -> Type) | Since: base-4.9.0.0 |
Functor (URec Char :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Generic (URec Char p) | |
Show (URec Char p) | Since: base-4.9.0.0 |
Eq (URec Char p) | Since: base-4.9.0.0 |
Ord (URec Char p) | Since: base-4.9.0.0 |
data URec Char (p :: k) | Used for marking occurrences of Since: base-4.9.0.0 |
type Compare (a :: Char) (b :: Char) | |
Defined in Data.Type.Ord | |
type Rep1 (URec Char :: k -> Type) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
type Rep (URec Char p) | Since: base-4.9.0.0 |
Defined in GHC.Generics |
coerce :: forall {k :: RuntimeRep} (a :: TYPE k) (b :: TYPE k). Coercible a b => a -> b #
The function coerce
allows you to safely convert between values of
types that have the same representation with no run-time overhead. In the
simplest case you can use it instead of a newtype constructor, to go from
the newtype's concrete type to the abstract type. But it also works in
more complicated settings, e.g. converting a list of newtypes to a list of
concrete types.
This function is runtime-representation polymorphic, but the
RuntimeRep
type argument is marked as Inferred
, meaning
that it is not available for visible type application. This means
the typechecker will accept coerce @Int @Age 42
.
class a ~R# b => Coercible (a :: k) (b :: k) #
Coercible
is a two-parameter class that has instances for types a
and b
if
the compiler can infer that they have the same representation. This class
does not have regular instances; instead they are created on-the-fly during
type-checking. Trying to manually declare an instance of Coercible
is an error.
Nevertheless one can pretend that the following three kinds of instances exist. First, as a trivial base-case:
instance Coercible a a
Furthermore, for every type constructor there is
an instance that allows to coerce under the type constructor. For
example, let D
be a prototypical type constructor (data
or
newtype
) with three type arguments, which have roles nominal
,
representational
resp. phantom
. Then there is an instance of
the form
instance Coercible b b' => Coercible (D a b c) (D a b' c')
Note that the nominal
type arguments are equal, the
representational
type arguments can differ, but need to have a
Coercible
instance themself, and the phantom
type arguments can be
changed arbitrarily.
The third kind of instance exists for every newtype NT = MkNT T
and
comes in two variants, namely
instance Coercible a T => Coercible a NT
instance Coercible T b => Coercible NT b
This instance is only usable if the constructor MkNT
is in scope.
If, as a library author of a type constructor like Set a
, you
want to prevent a user of your module to write
coerce :: Set T -> Set NT
,
you need to set the role of Set
's type parameter to nominal
,
by writing
type role Set nominal
For more details about this feature, please refer to Safe Coercions by Joachim Breitner, Richard A. Eisenberg, Simon Peyton Jones and Stephanie Weirich.
Since: ghc-prim-4.7.0.0
module Data.Either
The Eq
class defines equality (==
) and inequality (/=
).
All the basic datatypes exported by the Prelude are instances of Eq
,
and Eq
may be derived for any datatype whose constituents are also
instances of Eq
.
The Haskell Report defines no laws for Eq
. However, instances are
encouraged to follow these properties:
Instances
Eq SomeTypeRep | |
Defined in Data.Typeable.Internal (==) :: SomeTypeRep -> SomeTypeRep -> Bool # (/=) :: SomeTypeRep -> SomeTypeRep -> Bool # | |
Eq Void | Since: base-4.8.0.0 |
Eq ArithException | Since: base-3.0 |
Defined in GHC.Exception.Type (==) :: ArithException -> ArithException -> Bool # (/=) :: ArithException -> ArithException -> Bool # | |
Eq SpecConstrAnnotation | Since: base-4.3.0.0 |
Defined in GHC.Exts (==) :: SpecConstrAnnotation -> SpecConstrAnnotation -> Bool # (/=) :: SpecConstrAnnotation -> SpecConstrAnnotation -> Bool # | |
Eq Associativity | Since: base-4.6.0.0 |
Defined in GHC.Generics (==) :: Associativity -> Associativity -> Bool # (/=) :: Associativity -> Associativity -> Bool # | |
Eq DecidedStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics (==) :: DecidedStrictness -> DecidedStrictness -> Bool # (/=) :: DecidedStrictness -> DecidedStrictness -> Bool # | |
Eq Fixity | Since: base-4.6.0.0 |
Eq SourceStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics (==) :: SourceStrictness -> SourceStrictness -> Bool # (/=) :: SourceStrictness -> SourceStrictness -> Bool # | |
Eq SourceUnpackedness | Since: base-4.9.0.0 |
Defined in GHC.Generics (==) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (/=) :: SourceUnpackedness -> SourceUnpackedness -> Bool # | |
Eq MaskingState | Since: base-4.3.0.0 |
Defined in GHC.IO (==) :: MaskingState -> MaskingState -> Bool # (/=) :: MaskingState -> MaskingState -> Bool # | |
Eq Int16 | Since: base-2.1 |
Eq Int32 | Since: base-2.1 |
Eq Int64 | Since: base-2.1 |
Eq Int8 | Since: base-2.1 |
Eq SrcLoc | Since: base-4.9.0.0 |
Eq SomeChar | |
Eq SomeSymbol | Since: base-4.7.0.0 |
Defined in GHC.TypeLits (==) :: SomeSymbol -> SomeSymbol -> Bool # (/=) :: SomeSymbol -> SomeSymbol -> Bool # | |
Eq SomeNat | Since: base-4.7.0.0 |
Eq Word16 | Since: base-2.1 |
Eq Word32 | Since: base-2.1 |
Eq Word64 | Since: base-2.1 |
Eq Word8 | Since: base-2.1 |
Eq ByteString | |
Defined in Data.ByteString.Internal (==) :: ByteString -> ByteString -> Bool # (/=) :: ByteString -> ByteString -> Bool # | |
Eq ByteString | |
Defined in Data.ByteString.Lazy.Internal (==) :: ByteString -> ByteString -> Bool # (/=) :: ByteString -> ByteString -> Bool # | |
Eq ShortByteString | |
Defined in Data.ByteString.Short.Internal (==) :: ShortByteString -> ShortByteString -> Bool # (/=) :: ShortByteString -> ShortByteString -> Bool # | |
Eq IntSet | |
Eq BigNat | |
Eq ForeignSrcLang | |
Defined in GHC.ForeignSrcLang.Type (==) :: ForeignSrcLang -> ForeignSrcLang -> Bool # (/=) :: ForeignSrcLang -> ForeignSrcLang -> Bool # | |
Eq Extension | |
Eq Module | |
Eq Ordering | |
Eq TrName | |
Eq TyCon | |
Eq AnnLookup | |
Eq AnnTarget | |
Eq Bang | |
Eq Body | |
Eq Bytes | |
Eq Callconv | |
Eq Clause | |
Eq Con | |
Eq Dec | |
Eq DecidedStrictness | |
Defined in Language.Haskell.TH.Syntax (==) :: DecidedStrictness -> DecidedStrictness -> Bool # (/=) :: DecidedStrictness -> DecidedStrictness -> Bool # | |
Eq DerivClause | |
Defined in Language.Haskell.TH.Syntax (==) :: DerivClause -> DerivClause -> Bool # (/=) :: DerivClause -> DerivClause -> Bool # | |
Eq DerivStrategy | |
Defined in Language.Haskell.TH.Syntax (==) :: DerivStrategy -> DerivStrategy -> Bool # (/=) :: DerivStrategy -> DerivStrategy -> Bool # | |
Eq DocLoc | |
Eq Exp | |
Eq FamilyResultSig | |
Defined in Language.Haskell.TH.Syntax (==) :: FamilyResultSig -> FamilyResultSig -> Bool # (/=) :: FamilyResultSig -> FamilyResultSig -> Bool # | |
Eq Fixity | |
Eq FixityDirection | |
Defined in Language.Haskell.TH.Syntax (==) :: FixityDirection -> FixityDirection -> Bool # (/=) :: FixityDirection -> FixityDirection -> Bool # | |
Eq Foreign | |
Eq FunDep | |
Eq Guard | |
Eq Info | |
Eq InjectivityAnn | |
Defined in Language.Haskell.TH.Syntax (==) :: InjectivityAnn -> InjectivityAnn -> Bool # (/=) :: InjectivityAnn -> InjectivityAnn -> Bool # | |
Eq Inline | |
Eq Lit | |
Eq Loc | |
Eq Match | |
Eq ModName | |
Eq Module | |
Eq ModuleInfo | |
Defined in Language.Haskell.TH.Syntax (==) :: ModuleInfo -> ModuleInfo -> Bool # (/=) :: ModuleInfo -> ModuleInfo -> Bool # | |
Eq Name | |
Eq NameFlavour | |
Defined in Language.Haskell.TH.Syntax (==) :: NameFlavour -> NameFlavour -> Bool # (/=) :: NameFlavour -> NameFlavour -> Bool # | |
Eq NameSpace | |
Eq OccName | |
Eq Overlap | |
Eq Pat | |
Eq PatSynArgs | |
Defined in Language.Haskell.TH.Syntax (==) :: PatSynArgs -> PatSynArgs -> Bool # (/=) :: PatSynArgs -> PatSynArgs -> Bool # | |
Eq PatSynDir | |
Eq Phases | |
Eq PkgName | |
Eq Pragma | |
Eq Range | |
Eq Role | |
Eq RuleBndr | |
Eq RuleMatch | |
Eq Safety | |
Eq SourceStrictness | |
Defined in Language.Haskell.TH.Syntax (==) :: SourceStrictness -> SourceStrictness -> Bool # (/=) :: SourceStrictness -> SourceStrictness -> Bool # | |
Eq SourceUnpackedness | |
Defined in Language.Haskell.TH.Syntax (==) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (/=) :: SourceUnpackedness -> SourceUnpackedness -> Bool # | |
Eq Specificity | |
Defined in Language.Haskell.TH.Syntax (==) :: Specificity -> Specificity -> Bool # (/=) :: Specificity -> Specificity -> Bool # | |
Eq Stmt | |
Eq TyLit | |
Eq TySynEqn | |
Eq Type | |
Eq TypeFamilyHead | |
Defined in Language.Haskell.TH.Syntax (==) :: TypeFamilyHead -> TypeFamilyHead -> Bool # (/=) :: TypeFamilyHead -> TypeFamilyHead -> Bool # | |
Eq CodePoint | |
Eq DecoderState | |
Eq UnicodeException | |
Defined in Data.Text.Encoding.Error (==) :: UnicodeException -> UnicodeException -> Bool # (/=) :: UnicodeException -> UnicodeException -> Bool # | |
Eq Integer | |
Eq Natural | |
Eq () | |
Eq Bool | |
Eq Char | |
Eq Double | Note that due to the presence of
Also note that
|
Eq Float | Note that due to the presence of
Also note that
|
Eq Int | |
Eq Word | |
Eq a => Eq (ZipList a) | Since: base-4.7.0.0 |
Eq a => Eq (And a) | Since: base-4.16 |
Eq a => Eq (Iff a) | Since: base-4.16 |
Eq a => Eq (Ior a) | Since: base-4.16 |
Eq a => Eq (Xor a) | Since: base-4.16 |
Eq a => Eq (Complex a) | Since: base-2.1 |
Eq a => Eq (Identity a) | Since: base-4.8.0.0 |
Eq a => Eq (First a) | Since: base-2.1 |
Eq a => Eq (Last a) | Since: base-2.1 |
Eq a => Eq (Down a) | Since: base-4.6.0.0 |
Eq a => Eq (First a) | Since: base-4.9.0.0 |
Eq a => Eq (Last a) | Since: base-4.9.0.0 |
Eq a => Eq (Max a) | Since: base-4.9.0.0 |
Eq a => Eq (Min a) | Since: base-4.9.0.0 |
Eq m => Eq (WrappedMonoid m) | Since: base-4.9.0.0 |
Defined in Data.Semigroup (==) :: WrappedMonoid m -> WrappedMonoid m -> Bool # (/=) :: WrappedMonoid m -> WrappedMonoid m -> Bool # | |
Eq p => Eq (Par1 p) | Since: base-4.7.0.0 |
Eq (MVar a) | Since: base-4.1.0.0 |
Eq a => Eq (Ratio a) | Since: base-2.1 |
Eq a => Eq (IntMap a) | |
Eq a => Eq (Seq a) | |
Eq a => Eq (ViewL a) | |
Eq a => Eq (ViewR a) | |
Eq a => Eq (Set a) | |
Eq a => Eq (DList a) | |
Eq flag => Eq (TyVarBndr flag) | |
Eq a => Eq (NonEmpty a) | Since: base-4.9.0.0 |
Eq a => Eq (Maybe a) | Since: base-2.1 |
Eq a => Eq (a) | |
Eq a => Eq [a] | |
(Eq a, Eq b) => Eq (Either a b) | Since: base-2.1 |
Eq (Fixed a) | Since: base-2.1 |
Eq (Proxy s) | Since: base-4.7.0.0 |
Eq a => Eq (Arg a b) | Since: base-4.9.0.0 |
Eq (TypeRep a) | Since: base-2.1 |
Eq (U1 p) | Since: base-4.9.0.0 |
Eq (V1 p) | Since: base-4.9.0.0 |
(Eq k, Eq a) => Eq (Map k a) | |
(Eq a, Eq b) => Eq (a, b) | |
Eq a => Eq (Const a b) | Since: base-4.9.0.0 |
Eq (f a) => Eq (Ap f a) | Since: base-4.12.0.0 |
Eq (a :~: b) | Since: base-4.7.0.0 |
Eq (OrderingI a b) | |
Eq (f p) => Eq (Rec1 f p) | Since: base-4.7.0.0 |
Eq (URec (Ptr ()) p) | Since: base-4.9.0.0 |
Eq (URec Char p) | Since: base-4.9.0.0 |
Eq (URec Double p) | Since: base-4.9.0.0 |
Eq (URec Float p) | |
Eq (URec Int p) | Since: base-4.9.0.0 |
Eq (URec Word p) | Since: base-4.9.0.0 |
(Eq a, Eq b, Eq c) => Eq (a, b, c) | |
(Eq1 f, Eq1 g, Eq a) => Eq (Product f g a) | Since: base-4.9.0.0 |
(Eq1 f, Eq1 g, Eq a) => Eq (Sum f g a) | Since: base-4.9.0.0 |
Eq (a :~~: b) | Since: base-4.10.0.0 |
(Eq (f p), Eq (g p)) => Eq ((f :*: g) p) | Since: base-4.7.0.0 |
(Eq (f p), Eq (g p)) => Eq ((f :+: g) p) | Since: base-4.7.0.0 |
Eq c => Eq (K1 i c p) | Since: base-4.7.0.0 |
(Eq a, Eq b, Eq c, Eq d) => Eq (a, b, c, d) | |
(Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) | Since: base-4.9.0.0 |
Eq (f (g p)) => Eq ((f :.: g) p) | Since: base-4.7.0.0 |
Eq (f p) => Eq (M1 i c f p) | Since: base-4.7.0.0 |
(Eq a, Eq b, Eq c, Eq d, Eq e) => Eq (a, b, c, d, e) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f) => Eq (a, b, c, d, e, f) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g) => Eq (a, b, c, d, e, f, g) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h) => Eq (a, b, c, d, e, f, g, h) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i) => Eq (a, b, c, d, e, f, g, h, i) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j) => Eq (a, b, c, d, e, f, g, h, i, j) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k) => Eq (a, b, c, d, e, f, g, h, i, j, k) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l) => Eq (a, b, c, d, e, f, g, h, i, j, k, l) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m, Eq n) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | |
(Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m, Eq n, Eq o) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | |
($) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b infixr 0 #
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
,
or map
($
0) xs
.zipWith
($
) fs xs
Note that (
is levity-polymorphic in its result type, so that
$
)foo
where $
Truefoo :: Bool -> Int#
is well-typed.
is the least fixed point of the function fix
ff
,
i.e. the least defined x
such that f x = x
.
For example, we can write the factorial function using direct recursion as
>>>
let fac n = if n <= 1 then 1 else n * fac (n-1) in fac 5
120
This uses the fact that Haskell’s let
introduces recursive bindings. We can
rewrite this definition using fix
,
>>>
fix (\rec n -> if n <= 1 then 1 else n * rec (n-1)) 5
120
Instead of making a recursive call, we introduce a dummy parameter rec
;
when used within fix
, this parameter then refers to fix
’s argument, hence
the recursion is reintroduced.
flip :: (a -> b -> c) -> b -> a -> c #
takes its (first) two arguments in the reverse order of flip
ff
.
>>>
flip (++) "hello" "world"
"worldhello"
const x
is a unary function which evaluates to x
for all inputs.
>>>
const 42 "hello"
42
>>>
map (const 42) [0..3]
[42,42,42,42]
class Functor (f :: Type -> Type) where #
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.
fmap :: (a -> b) -> f a -> f b #
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
instance that allows
both the last and the penultimate parameters to be mapped over.Bifunctor
Examples
Convert from a
to a Maybe
IntMaybe String
using show
:
>>>
fmap show Nothing
Nothing>>>
fmap show (Just 3)
Just "3"
Convert from an
to 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 | Since: base-2.1 |
Functor Handler | Since: base-4.6.0.0 |
Functor Complex | Since: base-4.9.0.0 |
Functor Identity | Since: base-4.8.0.0 |
Functor First | Since: base-4.8.0.0 |
Functor Last | Since: base-4.8.0.0 |
Functor Down | Since: base-4.11.0.0 |
Functor First | Since: base-4.9.0.0 |
Functor Last | Since: base-4.9.0.0 |
Functor Max | Since: base-4.9.0.0 |
Functor Min | Since: base-4.9.0.0 |
Functor Par1 | Since: base-4.9.0.0 |
Functor P | Since: base-4.8.0.0 |
Defined in Text.ParserCombinators.ReadP | |
Functor ReadP | Since: base-2.1 |
Functor IntMap | |
Functor Digit | |
Functor Elem | |
Functor FingerTree | |
Defined in Data.Sequence.Internal fmap :: (a -> b) -> FingerTree a -> FingerTree b # (<$) :: a -> FingerTree b -> FingerTree a # | |
Functor Node | |
Functor Seq | |
Functor ViewL | |
Functor ViewR | |
Functor DList | |
Functor IO | Since: base-2.1 |
Functor Q | |
Functor TyVarBndr | |
Functor NonEmpty | Since: base-4.9.0.0 |
Functor Maybe | Since: base-2.1 |
Functor Solo | Since: base-4.15 |
Functor [] | Since: base-2.1 |
Monad m => Functor (WrappedMonad m) | Since: base-2.1 |
Defined in Control.Applicative fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b # (<$) :: a -> WrappedMonad m b -> WrappedMonad m a # | |
Arrow a => Functor (ArrowMonad a) | Since: base-4.6.0.0 |
Defined in Control.Arrow fmap :: (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b # (<$) :: a0 -> ArrowMonad a b -> ArrowMonad a a0 # | |
Functor (Either a) | Since: base-3.0 |
Functor (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
Functor (Arg a) | Since: base-4.9.0.0 |
Functor (U1 :: Type -> Type) | Since: base-4.9.0.0 |
Functor (V1 :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Functor (Map k) | |
Functor ((,) a) | Since: base-2.1 |
Arrow a => Functor (WrappedArrow a b) | Since: base-2.1 |
Defined in Control.Applicative fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 # (<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 # | |
Functor m => Functor (Kleisli m a) | Since: base-4.14.0.0 |
Functor (Const m :: Type -> Type) | Since: base-2.1 |
Functor f => Functor (Ap f) | Since: base-4.12.0.0 |
Functor f => Functor (Rec1 f) | Since: base-4.9.0.0 |
Functor (URec (Ptr ()) :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Functor (URec Char :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Functor (URec Double :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Functor (URec Float :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Functor (URec Int :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Functor (URec Word :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
(Applicative f, Monad f) => Functor (WhenMissing f x) | Since: containers-0.5.9 |
Defined in Data.IntMap.Internal fmap :: (a -> b) -> WhenMissing f x a -> WhenMissing f x b # (<$) :: a -> WhenMissing f x b -> WhenMissing f x a # | |
Functor ((,,) a b) | Since: base-4.14.0.0 |
(Functor f, Functor g) => Functor (Product f g) | Since: base-4.9.0.0 |
(Functor f, Functor g) => Functor (Sum f g) | Since: base-4.9.0.0 |
(Functor f, Functor g) => Functor (f :*: g) | Since: base-4.9.0.0 |
(Functor f, Functor g) => Functor (f :+: g) | Since: base-4.9.0.0 |
Functor (K1 i c :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Functor f => Functor (WhenMatched f x y) | Since: containers-0.5.9 |
Defined in Data.IntMap.Internal fmap :: (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b # (<$) :: a -> WhenMatched f x y b -> WhenMatched f x y a # | |
(Applicative f, Monad f) => Functor (WhenMissing f k x) | Since: containers-0.5.9 |
Defined in Data.Map.Internal fmap :: (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b # (<$) :: a -> WhenMissing f k x b -> WhenMissing f k x a # | |
Functor ((,,,) a b c) | Since: base-4.14.0.0 |
Functor ((->) r) | Since: base-2.1 |
(Functor f, Functor g) => Functor (Compose f g) | Since: base-4.9.0.0 |
(Functor f, Functor g) => Functor (f :.: g) | Since: base-4.9.0.0 |
Functor f => Functor (M1 i c f) | Since: base-4.9.0.0 |
Functor f => Functor (WhenMatched f k x y) | Since: containers-0.5.9 |
Defined in Data.Map.Internal fmap :: (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b # (<$) :: a -> WhenMatched f k x y b -> WhenMatched f k x y a # |
void :: Functor f => f a -> f () #
discards or ignores the result of evaluation, such
as the return value of an void
valueIO
action.
Examples
Replace the contents of a
with unit:Maybe
Int
>>>
void Nothing
Nothing>>>
void (Just 3)
Just ()
Replace the contents of an
with unit, resulting in an Either
Int
Int
:Either
Int
()
>>>
void (Left 8675309)
Left 8675309>>>
void (Right 8675309)
Right ()
Replace every element of a list with unit:
>>>
void [1,2,3]
[(),(),()]
Replace the second element of a pair with unit:
>>>
void (1,2)
(1,())
Discard the result of an IO
action:
>>>
mapM print [1,2]
1 2 [(),()]>>>
void $ mapM print [1,2]
1 2
(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 #
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, <$>
is function
application lifted over a Functor
.
Examples
Convert from a
to a Maybe
Int
using Maybe
String
show
:
>>>
show <$> Nothing
Nothing>>>
show <$> Just 3
Just "3"
Convert from an
to an
Either
Int
Int
Either
Int
String
using show
:
>>>
show <$> 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 => f a -> b -> f b infixl 4 #
Flipped version of <$
.
Examples
Replace the contents of a
with a constant
Maybe
Int
String
:
>>>
Nothing $> "foo"
Nothing>>>
Just 90210 $> "foo"
Just "foo"
Replace the contents of an
with a constant Either
Int
Int
String
, resulting in an
:Either
Int
String
>>>
Left 8675309 $> "foo"
Left 8675309>>>
Right 8675309 $> "foo"
Right "foo"
Replace each element of a list with a constant String
:
>>>
[1,2,3] $> "foo"
["foo","foo","foo"]
Replace the second element of a pair with a constant String
:
>>>
(1,2) $> "foo"
(1,"foo")
Since: base-4.7.0.0
newtype Compose (f :: k -> Type) (g :: k1 -> k) (a :: k1) infixr 9 #
Right-to-left composition of functors. The composition of applicative functors is always applicative, but the composition of monads is not always a monad.
Compose infixr 9 | |
|
Instances
TestEquality f => TestEquality (Compose f g :: k2 -> Type) | The deduction (via generativity) that if Since: base-4.14.0.0 |
Defined in Data.Functor.Compose | |
Functor f => Generic1 (Compose f g :: k -> Type) | |
(Foldable f, Foldable g) => Foldable (Compose f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose fold :: Monoid m => Compose f g m -> m # foldMap :: Monoid m => (a -> m) -> Compose f g a -> m # foldMap' :: Monoid m => (a -> m) -> Compose f g a -> m # foldr :: (a -> b -> b) -> b -> Compose f g a -> b # foldr' :: (a -> b -> b) -> b -> Compose f g a -> b # foldl :: (b -> a -> b) -> b -> Compose f g a -> b # foldl' :: (b -> a -> b) -> b -> Compose f g a -> b # foldr1 :: (a -> a -> a) -> Compose f g a -> a # foldl1 :: (a -> a -> a) -> Compose f g a -> a # toList :: Compose f g a -> [a] # null :: Compose f g a -> Bool # length :: Compose f g a -> Int # elem :: Eq a => a -> Compose f g a -> Bool # maximum :: Ord a => Compose f g a -> a # minimum :: Ord a => Compose f g a -> a # | |
(Eq1 f, Eq1 g) => Eq1 (Compose f g) | Since: base-4.9.0.0 |
(Ord1 f, Ord1 g) => Ord1 (Compose f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose | |
(Read1 f, Read1 g) => Read1 (Compose f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (Compose f g a) # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [Compose f g a] # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (Compose f g a) # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [Compose f g a] # | |
(Show1 f, Show1 g) => Show1 (Compose f g) | Since: base-4.9.0.0 |
(Functor f, Contravariant g) => Contravariant (Compose f g) | |
(Traversable f, Traversable g) => Traversable (Compose f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose | |
(Alternative f, Applicative g) => Alternative (Compose f g) | Since: base-4.9.0.0 |
(Applicative f, Applicative g) => Applicative (Compose f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose | |
(Functor f, Functor g) => Functor (Compose f g) | Since: base-4.9.0.0 |
(Typeable a, Typeable f, Typeable g, Typeable k1, Typeable k2, Data (f (g a))) => Data (Compose f g a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g0. g0 -> c g0) -> Compose f g a -> c (Compose f g a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Compose f g a) # toConstr :: Compose f g a -> Constr # dataTypeOf :: Compose f g a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Compose f g a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Compose f g a)) # gmapT :: (forall b. Data b => b -> b) -> Compose f g a -> Compose f g a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Compose f g a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Compose f g a -> r # gmapQ :: (forall d. Data d => d -> u) -> Compose f g a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Compose f g a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Compose f g a -> m (Compose f g a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Compose f g a -> m (Compose f g a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Compose f g a -> m (Compose f g a) # | |
Monoid (f (g a)) => Monoid (Compose f g a) | Since: base-4.16.0.0 |
Semigroup (f (g a)) => Semigroup (Compose f g a) | Since: base-4.16.0.0 |
Generic (Compose f g a) | |
(Read1 f, Read1 g, Read a) => Read (Compose f g a) | Since: base-4.9.0.0 |
(Show1 f, Show1 g, Show a) => Show (Compose f g a) | Since: base-4.9.0.0 |
(Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) | Since: base-4.9.0.0 |
(Ord1 f, Ord1 g, Ord a) => Ord (Compose f g a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose compare :: Compose f g a -> Compose f g a -> Ordering # (<) :: Compose f g a -> Compose f g a -> Bool # (<=) :: Compose f g a -> Compose f g a -> Bool # (>) :: Compose f g a -> Compose f g a -> Bool # (>=) :: Compose f g a -> Compose f g a -> Bool # | |
type Rep1 (Compose f g :: k -> Type) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose | |
type Rep (Compose f g a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose |
class Contravariant (f :: Type -> Type) where #
The class of contravariant functors.
Whereas in Haskell, one can think of a Functor
as containing or producing
values, a contravariant functor is a functor that can be thought of as
consuming values.
As an example, consider the type of predicate functions a -> Bool
. One
such predicate might be negative x = x < 0
, which
classifies integers as to whether they are negative. However, given this
predicate, we can re-use it in other situations, providing we have a way to
map values to integers. For instance, we can use the negative
predicate
on a person's bank balance to work out if they are currently overdrawn:
newtype Predicate a = Predicate { getPredicate :: a -> Bool } instance Contravariant Predicate where contramap :: (a' -> a) -> (Predicate a -> Predicate a') contramap f (Predicate p) = Predicate (p . f) | `- First, map the input... `----- then apply the predicate. overdrawn :: Predicate Person overdrawn = contramap personBankBalance negative
Any instance should be subject to the following laws:
Note, that the second law follows from the free theorem of the type of
contramap
and the first law, so you need only check that the former
condition holds.
Instances
(>$<) :: Contravariant f => (a -> b) -> f b -> f a infixl 4 #
This is an infix alias for contramap
.
Identity functor and monad. (a non-strict monad)
Since: base-4.8.0.0
Identity | |
|
Instances
A fixed-precision integer type with at least the range [-2^29 .. 2^29-1]
.
The exact range for a given implementation can be determined by using
minBound
and maxBound
from the Bounded
class.
Instances
Bits Int | Since: base-2.1 |
Defined in GHC.Bits | |
FiniteBits Int | Since: base-4.6.0.0 |
Defined in GHC.Bits | |
Bounded Int | Since: base-2.1 |
Enum Int | Since: base-2.1 |
Num Int | Since: base-2.1 |
Read Int | Since: base-2.1 |
Integral Int | Since: base-2.0.1 |
Real Int | Since: base-2.0.1 |
Defined in GHC.Real toRational :: Int -> Rational # | |
Show Int | Since: base-2.1 |
Default Int | |
Defined in Data.Default.Class | |
Eq Int | |
Ord Int | |
Lift Int | |
Generic1 (URec Int :: k -> Type) | |
Foldable (UInt :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Defined in Data.Foldable fold :: Monoid m => UInt m -> m # foldMap :: Monoid m => (a -> m) -> UInt a -> m # foldMap' :: Monoid m => (a -> m) -> UInt a -> m # foldr :: (a -> b -> b) -> b -> UInt a -> b # foldr' :: (a -> b -> b) -> b -> UInt a -> b # foldl :: (b -> a -> b) -> b -> UInt a -> b # foldl' :: (b -> a -> b) -> b -> UInt a -> b # foldr1 :: (a -> a -> a) -> UInt a -> a # foldl1 :: (a -> a -> a) -> UInt a -> a # elem :: Eq a => a -> UInt a -> Bool # maximum :: Ord a => UInt a -> a # | |
Traversable (UInt :: Type -> Type) | Since: base-4.9.0.0 |
Functor (URec Int :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Generic (URec Int p) | |
Show (URec Int p) | Since: base-4.9.0.0 |
Eq (URec Int p) | Since: base-4.9.0.0 |
Ord (URec Int p) | Since: base-4.9.0.0 |
data URec Int (p :: k) | Used for marking occurrences of Since: base-4.9.0.0 |
type Rep1 (URec Int :: k -> Type) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
type Rep (URec Int p) | Since: base-4.9.0.0 |
Defined in GHC.Generics |
8-bit signed integer type
Instances
Bits Int8 | Since: base-2.1 |
Defined in GHC.Int (.&.) :: Int8 -> Int8 -> Int8 # (.|.) :: Int8 -> Int8 -> Int8 # complement :: Int8 -> Int8 # shift :: Int8 -> Int -> Int8 # rotate :: Int8 -> Int -> Int8 # setBit :: Int8 -> Int -> Int8 # clearBit :: Int8 -> Int -> Int8 # complementBit :: Int8 -> Int -> Int8 # testBit :: Int8 -> Int -> Bool # bitSizeMaybe :: Int8 -> Maybe Int # shiftL :: Int8 -> Int -> Int8 # unsafeShiftL :: Int8 -> Int -> Int8 # shiftR :: Int8 -> Int -> Int8 # unsafeShiftR :: Int8 -> Int -> Int8 # rotateL :: Int8 -> Int -> Int8 # | |
FiniteBits Int8 | Since: base-4.6.0.0 |
Defined in GHC.Int | |
Bounded Int8 | Since: base-2.1 |
Enum Int8 | Since: base-2.1 |
Ix Int8 | Since: base-2.1 |
Num Int8 | Since: base-2.1 |
Read Int8 | Since: base-2.1 |
Integral Int8 | Since: base-2.1 |
Real Int8 | Since: base-2.1 |
Defined in GHC.Int toRational :: Int8 -> Rational # | |
Show Int8 | Since: base-2.1 |
Default Int8 | |
Defined in Data.Default.Class | |
Eq Int8 | Since: base-2.1 |
Ord Int8 | Since: base-2.1 |
Lift Int8 | |
16-bit signed integer type
Instances
32-bit signed integer type
Instances
64-bit signed integer type
Instances
data Constraint #
The kind of constraints, like Show a
(++) :: [a] -> [a] -> [a] infixr 5 #
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.
filter :: (a -> Bool) -> [a] -> [a] #
\(\mathcal{O}(n)\). filter
, applied to a predicate and a list, returns
the list of those elements that satisfy the predicate; i.e.,
filter p xs = [ x | x <- xs, p x]
>>>
filter odd [1, 2, 3]
[1,3]
zip :: [a] -> [b] -> [(a, b)] #
\(\mathcal{O}(\min(m,n))\). zip
takes two lists and returns a list of
corresponding pairs.
>>>
zip [1, 2] ['a', 'b']
[(1,'a'),(2,'b')]
If one input list is shorter than the other, excess elements of the longer list are discarded, even if one of the lists is infinite:
>>>
zip [1] ['a', 'b']
[(1,'a')]>>>
zip [1, 2] ['a']
[(1,'a')]>>>
zip [] [1..]
[]>>>
zip [1..] []
[]
zip
is right-lazy:
>>>
zip [] undefined
[]>>>
zip undefined []
*** Exception: Prelude.undefined ...
zip
is capable of list fusion, but it is restricted to its
first list argument and its resulting list.
map :: (a -> b) -> [a] -> [b] #
\(\mathcal{O}(n)\). 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]
unfoldr :: (b -> Maybe (a, b)) -> b -> [a] #
The unfoldr
function is a `dual' to foldr
: while foldr
reduces a list to a summary value, unfoldr
builds a list from
a seed value. The function takes the element and returns Nothing
if it is done producing the list or returns Just
(a,b)
, in which
case, a
is a prepended to the list and b
is used as the next
element in a recursive call. For example,
iterate f == unfoldr (\x -> Just (x, f x))
In some cases, unfoldr
can undo a foldr
operation:
unfoldr f' (foldr f z xs) == xs
if the following holds:
f' (f x y) = Just (x,y) f' z = Nothing
A simple use of unfoldr:
>>>
unfoldr (\b -> if b == 0 then Nothing else Just (b, b-1)) 10
[10,9,8,7,6,5,4,3,2,1]
The transpose
function transposes the rows and columns of its argument.
For example,
>>>
transpose [[1,2,3],[4,5,6]]
[[1,4],[2,5],[3,6]]
If some of the rows are shorter than the following rows, their elements are skipped:
>>>
transpose [[10,11],[20],[],[30,31,32]]
[[10,20,30],[11,31],[32]]
subsequences :: [a] -> [[a]] #
The subsequences
function returns the list of all subsequences of the argument.
>>>
subsequences "abc"
["","a","b","ab","c","ac","bc","abc"]
sortOn :: Ord b => (a -> b) -> [a] -> [a] #
Sort a list by comparing the results of a key function applied to each
element. sortOn f
is equivalent to sortBy (comparing f)
, but has the
performance advantage of only evaluating f
once for each element in the
input list. This is called the decorate-sort-undecorate paradigm, or
Schwartzian transform.
Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.
>>>
sortOn fst [(2, "world"), (4, "!"), (1, "Hello")]
[(1,"Hello"),(2,"world"),(4,"!")]
Since: base-4.8.0.0
permutations :: [a] -> [[a]] #
The permutations
function returns the list of all permutations of the argument.
>>>
permutations "abc"
["abc","bac","cba","bca","cab","acb"]
isPrefixOf :: Eq a => [a] -> [a] -> Bool #
\(\mathcal{O}(\min(m,n))\). The isPrefixOf
function takes two lists and
returns True
iff the first list is a prefix of the second.
>>>
"Hello" `isPrefixOf` "Hello World!"
True
>>>
"Hello" `isPrefixOf` "Wello Horld!"
False
intersperse :: a -> [a] -> [a] #
\(\mathcal{O}(n)\). The intersperse
function takes an element and a list
and `intersperses' that element between the elements of the list. For
example,
>>>
intersperse ',' "abcde"
"a,b,c,d,e"
intercalate :: [a] -> [[a]] -> [a] #
intercalate
xs xss
is equivalent to (
.
It inserts the list concat
(intersperse
xs xss))xs
in between the lists in xss
and concatenates the
result.
>>>
intercalate ", " ["Lorem", "ipsum", "dolor"]
"Lorem, ipsum, dolor"
group :: Eq a => [a] -> [[a]] #
The group
function takes a list and returns a list of lists such
that the concatenation of the result is equal to the argument. Moreover,
each sublist in the result contains only equal elements. For example,
>>>
group "Mississippi"
["M","i","ss","i","ss","i","pp","i"]
It is a special case of groupBy
, which allows the programmer to supply
their own equality test.
genericTake :: Integral i => i -> [a] -> [a] #
The genericTake
function is an overloaded version of take
, which
accepts any Integral
value as the number of elements to take.
genericSplitAt :: Integral i => i -> [a] -> ([a], [a]) #
The genericSplitAt
function is an overloaded version of splitAt
, which
accepts any Integral
value as the position at which to split.
genericReplicate :: Integral i => i -> a -> [a] #
The genericReplicate
function is an overloaded version of replicate
,
which accepts any Integral
value as the number of repetitions to make.
genericLength :: Num i => [a] -> i #
\(\mathcal{O}(n)\). The genericLength
function is an overloaded version
of length
. In particular, instead of returning an Int
, it returns any
type which is an instance of Num
. It is, however, less efficient than
length
.
>>>
genericLength [1, 2, 3] :: Int
3>>>
genericLength [1, 2, 3] :: Float
3.0
genericDrop :: Integral i => i -> [a] -> [a] #
The genericDrop
function is an overloaded version of drop
, which
accepts any Integral
value as the number of elements to drop.
zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] #
\(\mathcal{O}(\min(m,n))\). zipWith
generalises zip
by zipping with the
function given as the first argument, instead of a tupling function.
zipWith (,) xs ys == zip xs ys zipWith f [x1,x2,x3..] [y1,y2,y3..] == [f x1 y1, f x2 y2, f x3 y3..]
For example,
is applied to two lists to produce the list of
corresponding sums:zipWith
(+)
>>>
zipWith (+) [1, 2, 3] [4, 5, 6]
[5,7,9]
zipWith
is right-lazy:
>>>
let f = undefined
>>>
zipWith f [] undefined
[]
zipWith
is capable of list fusion, but it is restricted to its
first list argument and its resulting list.
unzip :: [(a, b)] -> ([a], [b]) #
unzip
transforms a list of pairs into a list of first components
and a list of second components.
>>>
unzip []
([],[])>>>
unzip [(1, 'a'), (2, 'b')]
([1,2],"ab")
takeWhile :: (a -> Bool) -> [a] -> [a] #
takeWhile
, applied to a predicate p
and a list xs
, returns the
longest prefix (possibly empty) of xs
of elements that satisfy p
.
>>>
takeWhile (< 3) [1,2,3,4,1,2,3,4]
[1,2]>>>
takeWhile (< 9) [1,2,3]
[1,2,3]>>>
takeWhile (< 0) [1,2,3]
[]
take
n
, applied to a list xs
, returns the prefix of xs
of length n
, or xs
itself if n >=
.length
xs
>>>
take 5 "Hello World!"
"Hello">>>
take 3 [1,2,3,4,5]
[1,2,3]>>>
take 3 [1,2]
[1,2]>>>
take 3 []
[]>>>
take (-1) [1,2]
[]>>>
take 0 [1,2]
[]
It is an instance of the more general genericTake
,
in which n
may be of any integral type.
splitAt :: Int -> [a] -> ([a], [a]) #
splitAt
n xs
returns a tuple where first element is xs
prefix of
length n
and second element is the remainder of the list:
>>>
splitAt 6 "Hello World!"
("Hello ","World!")>>>
splitAt 3 [1,2,3,4,5]
([1,2,3],[4,5])>>>
splitAt 1 [1,2,3]
([1],[2,3])>>>
splitAt 3 [1,2,3]
([1,2,3],[])>>>
splitAt 4 [1,2,3]
([1,2,3],[])>>>
splitAt 0 [1,2,3]
([],[1,2,3])>>>
splitAt (-1) [1,2,3]
([],[1,2,3])
It is equivalent to (
when take
n xs, drop
n xs)n
is not _|_
(splitAt _|_ xs = _|_
).
splitAt
is an instance of the more general genericSplitAt
,
in which n
may be of any integral type.
span :: (a -> Bool) -> [a] -> ([a], [a]) #
span
, applied to a predicate p
and a list xs
, returns a tuple where
first element is longest prefix (possibly empty) of xs
of elements that
satisfy p
and second element is the remainder of the list:
>>>
span (< 3) [1,2,3,4,1,2,3,4]
([1,2],[3,4,1,2,3,4])>>>
span (< 9) [1,2,3]
([1,2,3],[])>>>
span (< 0) [1,2,3]
([],[1,2,3])
scanr1 :: (a -> a -> a) -> [a] -> [a] #
\(\mathcal{O}(n)\). scanr1
is a variant of scanr
that has no starting
value argument.
>>>
scanr1 (+) [1..4]
[10,9,7,4]>>>
scanr1 (+) []
[]>>>
scanr1 (-) [1..4]
[-2,3,-1,4]>>>
scanr1 (&&) [True, False, True, True]
[False,False,True,True]>>>
scanr1 (||) [True, True, False, False]
[True,True,False,False]>>>
force $ scanr1 (+) [1..]
*** Exception: stack overflow
scanr :: (a -> b -> b) -> b -> [a] -> [b] #
\(\mathcal{O}(n)\). scanr
is the right-to-left dual of scanl
. Note that the order of parameters on the accumulating function are reversed compared to scanl
.
Also note that
head (scanr f z xs) == foldr f z xs.
>>>
scanr (+) 0 [1..4]
[10,9,7,4,0]>>>
scanr (+) 42 []
[42]>>>
scanr (-) 100 [1..4]
[98,-97,99,-96,100]>>>
scanr (\nextChar reversedString -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']
["abcdfoo","bcdfoo","cdfoo","dfoo","foo"]>>>
force $ scanr (+) 0 [1..]
*** Exception: stack overflow
scanl1 :: (a -> a -> a) -> [a] -> [a] #
\(\mathcal{O}(n)\). scanl1
is a variant of scanl
that has no starting
value argument:
scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
>>>
scanl1 (+) [1..4]
[1,3,6,10]>>>
scanl1 (+) []
[]>>>
scanl1 (-) [1..4]
[1,-1,-4,-8]>>>
scanl1 (&&) [True, False, True, True]
[True,False,False,False]>>>
scanl1 (||) [False, False, True, True]
[False,False,True,True]>>>
scanl1 (+) [1..]
* Hangs forever *
scanl :: (b -> a -> b) -> b -> [a] -> [b] #
\(\mathcal{O}(n)\). scanl
is similar to foldl
, but returns a list of
successive reduced values from the left:
scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
Note that
last (scanl f z xs) == foldl f z xs
>>>
scanl (+) 0 [1..4]
[0,1,3,6,10]>>>
scanl (+) 42 []
[42]>>>
scanl (-) 100 [1..4]
[100,99,97,94,90]>>>
scanl (\reversedString nextChar -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']
["foo","afoo","bafoo","cbafoo","dcbafoo"]>>>
scanl (+) 0 [1..]
* Hangs forever *
reverse
xs
returns the elements of xs
in reverse order.
xs
must be finite.
>>>
reverse []
[]>>>
reverse [42]
[42]>>>
reverse [2,5,7]
[7,5,2]>>>
reverse [1..]
* Hangs forever *
replicate :: Int -> a -> [a] #
replicate
n x
is a list of length n
with x
the value of
every element.
It is an instance of the more general genericReplicate
,
in which n
may be of any integral type.
>>>
replicate 0 True
[]>>>
replicate (-1) True
[]>>>
replicate 4 True
[True,True,True,True]
repeat
x
is an infinite list, with x
the value of every element.
>>>
take 20 $ repeat 17
[17,17,17,17,17,17,17,17,17...
iterate :: (a -> a) -> a -> [a] #
iterate
f x
returns an infinite list of repeated applications
of f
to x
:
iterate f x == [x, f x, f (f x), ...]
Note that iterate
is lazy, potentially leading to thunk build-up if
the consumer doesn't force each iterate. See iterate'
for a strict
variant of this function.
>>>
take 10 $ iterate not True
[True,False,True,False...>>>
take 10 $ iterate (+3) 42
[42,45,48,51,54,57,60,63...
drop
n xs
returns the suffix of xs
after the first n
elements, or []
if n >=
.length
xs
>>>
drop 6 "Hello World!"
"World!">>>
drop 3 [1,2,3,4,5]
[4,5]>>>
drop 3 [1,2]
[]>>>
drop 3 []
[]>>>
drop (-1) [1,2]
[1,2]>>>
drop 0 [1,2]
[1,2]
It is an instance of the more general genericDrop
,
in which n
may be of any integral type.
break :: (a -> Bool) -> [a] -> ([a], [a]) #
break
, applied to a predicate p
and a list xs
, returns a tuple where
first element is longest prefix (possibly empty) of xs
of elements that
do not satisfy p
and second element is the remainder of the list:
>>>
break (> 3) [1,2,3,4,1,2,3,4]
([1,2,3],[4,1,2,3,4])>>>
break (< 9) [1,2,3]
([],[1,2,3])>>>
break (> 9) [1,2,3]
([1,2,3],[])
Non-empty (and non-strict) list type.
Since: base-4.9.0.0
a :| [a] infixr 5 |
Instances
Foldable NonEmpty | Since: base-4.9.0.0 |
Defined in Data.Foldable fold :: Monoid m => NonEmpty m -> m # foldMap :: Monoid m => (a -> m) -> NonEmpty a -> m # foldMap' :: Monoid m => (a -> m) -> NonEmpty a -> m # foldr :: (a -> b -> b) -> b -> NonEmpty a -> b # foldr' :: (a -> b -> b) -> b -> NonEmpty a -> b # foldl :: (b -> a -> b) -> b -> NonEmpty a -> b # foldl' :: (b -> a -> b) -> b -> NonEmpty a -> b # foldr1 :: (a -> a -> a) -> NonEmpty a -> a # foldl1 :: (a -> a -> a) -> NonEmpty a -> a # elem :: Eq a => a -> NonEmpty a -> Bool # maximum :: Ord a => NonEmpty a -> a # minimum :: Ord a => NonEmpty a -> a # | |
Traversable NonEmpty | Since: base-4.9.0.0 |
Applicative NonEmpty | Since: base-4.9.0.0 |
Functor NonEmpty | Since: base-4.9.0.0 |
Monad NonEmpty | Since: base-4.9.0.0 |
Generic1 NonEmpty | |
Lift a => Lift (NonEmpty a :: Type) | Since: template-haskell-2.15.0.0 |
Semigroup (NonEmpty a) | Since: base-4.9.0.0 |
IsList (NonEmpty a) | Since: base-4.9.0.0 |
Generic (NonEmpty a) | |
Read a => Read (NonEmpty a) | Since: base-4.11.0.0 |
Show a => Show (NonEmpty a) | Since: base-4.11.0.0 |
Eq a => Eq (NonEmpty a) | Since: base-4.9.0.0 |
Ord a => Ord (NonEmpty a) | Since: base-4.9.0.0 |
type Rep1 NonEmpty | Since: base-4.6.0.0 |
Defined in GHC.Generics type Rep1 NonEmpty = D1 ('MetaData "NonEmpty" "GHC.Base" "base" 'False) (C1 ('MetaCons ":|" ('InfixI 'LeftAssociative 9) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1 :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 []))) | |
type Item (NonEmpty a) | |
type Rep (NonEmpty a) | Since: base-4.6.0.0 |
Defined in GHC.Generics type Rep (NonEmpty a) = D1 ('MetaData "NonEmpty" "GHC.Base" "base" 'False) (C1 ('MetaCons ":|" ('InfixI 'LeftAssociative 9) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 [a]))) |
The Maybe
type encapsulates an optional value. A value of type
either contains a value of type Maybe
aa
(represented as
),
or it is empty (represented as Just
aNothing
). Using Maybe
is a good way to
deal with errors or exceptional cases without resorting to drastic
measures such as error
.
The Maybe
type is also a monad. It is a simple kind of error
monad, where all errors are represented by Nothing
. A richer
error monad can be built using the Either
type.
Instances
MonadFail Maybe | Since: base-4.9.0.0 |
Defined in Control.Monad.Fail | |
Foldable Maybe | Since: base-2.1 |
Defined in Data.Foldable fold :: Monoid m => Maybe m -> m # foldMap :: Monoid m => (a -> m) -> Maybe a -> m # foldMap' :: Monoid m => (a -> m) -> Maybe a -> m # foldr :: (a -> b -> b) -> b -> Maybe a -> b # foldr' :: (a -> b -> b) -> b -> Maybe a -> b # foldl :: (b -> a -> b) -> b -> Maybe a -> b # foldl' :: (b -> a -> b) -> b -> Maybe a -> b # foldr1 :: (a -> a -> a) -> Maybe a -> a # foldl1 :: (a -> a -> a) -> Maybe a -> a # elem :: Eq a => a -> Maybe a -> Bool # maximum :: Ord a => Maybe a -> a # minimum :: Ord a => Maybe a -> a # | |
Traversable Maybe | Since: base-2.1 |
Alternative Maybe | Since: base-2.1 |
Applicative Maybe | Since: base-2.1 |
Functor Maybe | Since: base-2.1 |
Monad Maybe | Since: base-2.1 |
MonadPlus Maybe | Since: base-2.1 |
Generic1 Maybe | |
Lift a => Lift (Maybe a :: Type) | |
Semigroup a => Monoid (Maybe a) | Lift a semigroup into Since 4.11.0: constraint on inner Since: base-2.1 |
Semigroup a => Semigroup (Maybe a) | Since: base-4.9.0.0 |
Generic (Maybe a) | |
SingKind a => SingKind (Maybe a) | Since: base-4.9.0.0 |
Defined in GHC.Generics type DemoteRep (Maybe a) | |
Read a => Read (Maybe a) | Since: base-2.1 |
Show a => Show (Maybe a) | Since: base-2.1 |
Default (Maybe a) | |
Defined in Data.Default.Class | |
Eq a => Eq (Maybe a) | Since: base-2.1 |
Ord a => Ord (Maybe a) | Since: base-2.1 |
SingI ('Nothing :: Maybe a) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
SingI a2 => SingI ('Just a2 :: Maybe a1) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
type Rep1 Maybe | Since: base-4.6.0.0 |
type DemoteRep (Maybe a) | |
Defined in GHC.Generics | |
type Rep (Maybe a) | Since: base-4.6.0.0 |
Defined in GHC.Generics | |
data Sing (b :: Maybe a) | |
maybeToList :: Maybe a -> [a] #
The maybeToList
function returns an empty list when given
Nothing
or a singleton list when given Just
.
Examples
Basic usage:
>>>
maybeToList (Just 7)
[7]
>>>
maybeToList Nothing
[]
One can use maybeToList
to avoid pattern matching when combined
with a function that (safely) works on lists:
>>>
import Text.Read ( readMaybe )
>>>
sum $ maybeToList (readMaybe "3")
3>>>
sum $ maybeToList (readMaybe "")
0
maybe :: b -> (a -> b) -> Maybe a -> b #
The maybe
function takes a default value, a function, and a Maybe
value. If the Maybe
value is Nothing
, the function returns the
default value. Otherwise, it applies the function to the value inside
the Just
and returns the result.
Examples
Basic usage:
>>>
maybe False odd (Just 3)
True
>>>
maybe False odd Nothing
False
Read an integer from a string using readMaybe
. If we succeed,
return twice the integer; that is, apply (*2)
to it. If instead
we fail to parse an integer, return 0
by default:
>>>
import Text.Read ( readMaybe )
>>>
maybe 0 (*2) (readMaybe "5")
10>>>
maybe 0 (*2) (readMaybe "")
0
Apply show
to a Maybe Int
. If we have Just n
, we want to show
the underlying Int
n
. But if we have Nothing
, we return the
empty string instead of (for example) "Nothing":
>>>
maybe "" show (Just 5)
"5">>>
maybe "" show Nothing
""
mapMaybe :: (a -> Maybe b) -> [a] -> [b] #
The mapMaybe
function is a version of map
which can throw
out elements. In particular, the functional argument returns
something of type
. If this is Maybe
bNothing
, no element
is added on to the result list. If it is
, then Just
bb
is
included in the result list.
Examples
Using
is a shortcut for mapMaybe
f x
in most cases:catMaybes
$ map
f x
>>>
import Text.Read ( readMaybe )
>>>
let readMaybeInt = readMaybe :: String -> Maybe Int
>>>
mapMaybe readMaybeInt ["1", "Foo", "3"]
[1,3]>>>
catMaybes $ map readMaybeInt ["1", "Foo", "3"]
[1,3]
If we map the Just
constructor, the entire list should be returned:
>>>
mapMaybe Just [1,2,3]
[1,2,3]
listToMaybe :: [a] -> Maybe a #
The listToMaybe
function returns Nothing
on an empty list
or
where Just
aa
is the first element of the list.
Examples
Basic usage:
>>>
listToMaybe []
Nothing
>>>
listToMaybe [9]
Just 9
>>>
listToMaybe [1,2,3]
Just 1
Composing maybeToList
with listToMaybe
should be the identity
on singleton/empty lists:
>>>
maybeToList $ listToMaybe [5]
[5]>>>
maybeToList $ listToMaybe []
[]
But not on lists with more than one element:
>>>
maybeToList $ listToMaybe [1,2,3]
[1]
fromMaybe :: a -> Maybe a -> a #
The fromMaybe
function takes a default value and a Maybe
value. If the Maybe
is Nothing
, it returns the default value;
otherwise, it returns the value contained in the Maybe
.
Examples
Basic usage:
>>>
fromMaybe "" (Just "Hello, World!")
"Hello, World!"
>>>
fromMaybe "" Nothing
""
Read an integer from a string using readMaybe
. If we fail to
parse an integer, we want to return 0
by default:
>>>
import Text.Read ( readMaybe )
>>>
fromMaybe 0 (readMaybe "5")
5>>>
fromMaybe 0 (readMaybe "")
0
catMaybes :: [Maybe a] -> [a] #
The catMaybes
function takes a list of Maybe
s and returns
a list of all the Just
values.
Examples
Basic usage:
>>>
catMaybes [Just 1, Nothing, Just 3]
[1,3]
When constructing a list of Maybe
values, catMaybes
can be used
to return all of the "success" results (if the list is the result
of a map
, then mapMaybe
would be more appropriate):
>>>
import Text.Read ( readMaybe )
>>>
[readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
[Just 1,Nothing,Just 3]>>>
catMaybes $ [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
[1,3]
class Semigroup a => Monoid a where #
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)<>
zSemigroup
law)- Concatenation
mconcat
=foldr
(<>
)mempty
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 newtype
s and make those instances
of Monoid
, e.g. Sum
and Product
.
NOTE: Semigroup
is a superclass of Monoid
since base-4.11.0.0.
Identity of mappend
>>>
"Hello world" <> mempty
"Hello world"
An associative operation
NOTE: This method is redundant and has the default
implementation
since base-4.11.0.0.
Should it be implemented manually, since 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 ByteString | |
Defined in Data.ByteString.Internal mempty :: ByteString # mappend :: ByteString -> ByteString -> ByteString # mconcat :: [ByteString] -> ByteString # | |
Monoid ByteString | |
Defined in Data.ByteString.Lazy.Internal mempty :: ByteString # mappend :: ByteString -> ByteString -> ByteString # mconcat :: [ByteString] -> ByteString # | |
Monoid ShortByteString | |
Defined in Data.ByteString.Short.Internal mappend :: ShortByteString -> ShortByteString -> ShortByteString # mconcat :: [ShortByteString] -> ShortByteString # | |
Monoid IntSet | |
Monoid Ordering | Since: base-2.1 |
Monoid () | Since: base-2.1 |
FiniteBits a => Monoid (And a) | This constraint is arguably too strong. However,
as some types (such as Since: base-4.16 |
FiniteBits a => Monoid (Iff a) | This constraint is arguably
too strong. However, as some types (such as Since: base-4.16 |
Bits a => Monoid (Ior a) | Since: base-4.16 |
Bits a => Monoid (Xor a) | Since: base-4.16 |
Monoid (Comparison a) |
mempty :: Comparison a mempty = Comparison _ _ -> EQ |
Defined in Data.Functor.Contravariant mempty :: Comparison a # mappend :: Comparison a -> Comparison a -> Comparison a # mconcat :: [Comparison a] -> Comparison a # | |
Monoid (Equivalence a) |
mempty :: Equivalence a mempty = Equivalence _ _ -> True |
Defined in Data.Functor.Contravariant mempty :: Equivalence a # mappend :: Equivalence a -> Equivalence a -> Equivalence a # mconcat :: [Equivalence a] -> Equivalence a # | |
Monoid (Predicate a) |
mempty :: Predicate a mempty = _ -> True |
Monoid a => Monoid (Identity a) | Since: base-4.9.0.0 |
Monoid (First a) | Since: base-2.1 |
Monoid (Last a) | Since: base-2.1 |
Monoid a => Monoid (Down a) | Since: base-4.11.0.0 |
(Ord a, Bounded a) => Monoid (Max a) | Since: base-4.9.0.0 |
(Ord a, Bounded a) => Monoid (Min a) | Since: base-4.9.0.0 |
Monoid m => Monoid (WrappedMonoid m) | Since: base-4.9.0.0 |
Defined in Data.Semigroup mempty :: WrappedMonoid m # mappend :: WrappedMonoid m -> WrappedMonoid m -> WrappedMonoid m # mconcat :: [WrappedMonoid m] -> WrappedMonoid m # | |
Monoid p => Monoid (Par1 p) | Since: base-4.12.0.0 |
Monoid (IntMap a) | |
Monoid (Seq a) | |
Monoid (MergeSet a) | |
Ord a => Monoid (Set a) | |
Monoid (DList a) | |
Monoid a => Monoid (IO a) | Since: base-4.9.0.0 |
Monoid a => Monoid (Q a) | Since: template-haskell-2.17.0.0 |
Semigroup a => Monoid (Maybe a) | Lift a semigroup into Since 4.11.0: constraint on inner Since: base-2.1 |
Monoid a => Monoid (a) | Since: base-4.15 |
Monoid [a] | Since: base-2.1 |
Monoid a => Monoid (Op a b) |
mempty :: Op a b mempty = Op _ -> mempty |
Monoid (Proxy s) | Since: base-4.7.0.0 |
Monoid (U1 p) | Since: base-4.12.0.0 |
Ord k => Monoid (Map k v) | |
Monoid b => Monoid (a -> b) | Since: base-2.1 |
(Monoid a, Monoid b) => Monoid (a, b) | Since: base-2.1 |
Monoid a => Monoid (Const a b) | Since: base-4.9.0.0 |
(Applicative f, Monoid a) => Monoid (Ap f a) | Since: base-4.12.0.0 |
Monoid (f p) => Monoid (Rec1 f p) | Since: base-4.12.0.0 |
(Monoid a, Monoid b, Monoid c) => Monoid (a, b, c) | Since: base-2.1 |
(Monoid (f a), Monoid (g a)) => Monoid (Product f g a) | Since: base-4.16.0.0 |
(Monoid (f p), Monoid (g p)) => Monoid ((f :*: g) p) | Since: base-4.12.0.0 |
Monoid c => Monoid (K1 i c p) | Since: base-4.12.0.0 |
(Monoid a, Monoid b, Monoid c, Monoid d) => Monoid (a, b, c, d) | Since: base-2.1 |
Monoid (f (g a)) => Monoid (Compose f g a) | Since: base-4.16.0.0 |
Monoid (f (g p)) => Monoid ((f :.: g) p) | Since: base-4.12.0.0 |
Monoid (f p) => Monoid (M1 i c f p) | Since: base-4.12.0.0 |
(Monoid a, Monoid b, Monoid c, Monoid d, Monoid e) => Monoid (a, b, c, d, e) | Since: base-2.1 |
The Ord
class is used for totally ordered datatypes.
Instances of Ord
can be derived for any user-defined datatype whose
constituent types are in Ord
. The declared order of the constructors in
the data declaration determines the ordering in derived Ord
instances. The
Ordering
datatype allows a single comparison to determine the precise
ordering of two objects.
Ord
, as defined by the Haskell report, implements a total order and has the
following properties:
- Comparability
x <= y || y <= x
=True
- Transitivity
- if
x <= y && y <= z
=True
, thenx <= z
=True
- Reflexivity
x <= x
=True
- Antisymmetry
- if
x <= y && y <= x
=True
, thenx == y
=True
The following operator interactions are expected to hold:
x >= y
=y <= x
x < y
=x <= y && x /= y
x > y
=y < x
x < y
=compare x y == LT
x > y
=compare x y == GT
x == y
=compare x y == EQ
min x y == if x <= y then x else y
=True
max x y == if x >= y then x else y
=True
Note that (7.) and (8.) do not require min
and max
to return either of
their arguments. The result is merely required to equal one of the
arguments in terms of (==)
.
Minimal complete definition: either compare
or <=
.
Using compare
can be more efficient for complex types.
compare :: a -> a -> Ordering #
(<) :: a -> a -> Bool infix 4 #
(<=) :: a -> a -> Bool infix 4 #
(>) :: a -> a -> Bool infix 4 #
Instances
Ord SomeTypeRep | |
Defined in Data.Typeable.Internal compare :: SomeTypeRep -> SomeTypeRep -> Ordering # (<) :: SomeTypeRep -> SomeTypeRep -> Bool # (<=) :: SomeTypeRep -> SomeTypeRep -> Bool # (>) :: SomeTypeRep -> SomeTypeRep -> Bool # (>=) :: SomeTypeRep -> SomeTypeRep -> Bool # max :: SomeTypeRep -> SomeTypeRep -> SomeTypeRep # min :: SomeTypeRep -> SomeTypeRep -> SomeTypeRep # | |
Ord Void | Since: base-4.8.0.0 |
Ord ArithException | Since: base-3.0 |
Defined in GHC.Exception.Type compare :: ArithException -> ArithException -> Ordering # (<) :: ArithException -> ArithException -> Bool # (<=) :: ArithException -> ArithException -> Bool # (>) :: ArithException -> ArithException -> Bool # (>=) :: ArithException -> ArithException -> Bool # max :: ArithException -> ArithException -> ArithException # min :: ArithException -> ArithException -> ArithException # | |
Ord Associativity | Since: base-4.6.0.0 |
Defined in GHC.Generics compare :: Associativity -> Associativity -> Ordering # (<) :: Associativity -> Associativity -> Bool # (<=) :: Associativity -> Associativity -> Bool # (>) :: Associativity -> Associativity -> Bool # (>=) :: Associativity -> Associativity -> Bool # max :: Associativity -> Associativity -> Associativity # min :: Associativity -> Associativity -> Associativity # | |
Ord DecidedStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics compare :: DecidedStrictness -> DecidedStrictness -> Ordering # (<) :: DecidedStrictness -> DecidedStrictness -> Bool # (<=) :: DecidedStrictness -> DecidedStrictness -> Bool # (>) :: DecidedStrictness -> DecidedStrictness -> Bool # (>=) :: DecidedStrictness -> DecidedStrictness -> Bool # max :: DecidedStrictness -> DecidedStrictness -> DecidedStrictness # min :: DecidedStrictness -> DecidedStrictness -> DecidedStrictness # | |
Ord Fixity | Since: base-4.6.0.0 |
Ord SourceStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics compare :: SourceStrictness -> SourceStrictness -> Ordering # (<) :: SourceStrictness -> SourceStrictness -> Bool # (<=) :: SourceStrictness -> SourceStrictness -> Bool # (>) :: SourceStrictness -> SourceStrictness -> Bool # (>=) :: SourceStrictness -> SourceStrictness -> Bool # max :: SourceStrictness -> SourceStrictness -> SourceStrictness # min :: SourceStrictness -> SourceStrictness -> SourceStrictness # | |
Ord SourceUnpackedness | Since: base-4.9.0.0 |
Defined in GHC.Generics compare :: SourceUnpackedness -> SourceUnpackedness -> Ordering # (<) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (<=) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (>) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (>=) :: SourceUnpackedness -> SourceUnpackedness -> Bool # max :: SourceUnpackedness -> SourceUnpackedness -> SourceUnpackedness # min :: SourceUnpackedness -> SourceUnpackedness -> SourceUnpackedness # | |
Ord Int16 | Since: base-2.1 |
Ord Int32 | Since: base-2.1 |
Ord Int64 | Since: base-2.1 |
Ord Int8 | Since: base-2.1 |
Ord SomeChar | |
Defined in GHC.TypeLits | |
Ord SomeSymbol | Since: base-4.7.0.0 |
Defined in GHC.TypeLits compare :: SomeSymbol -> SomeSymbol -> Ordering # (<) :: SomeSymbol -> SomeSymbol -> Bool # (<=) :: SomeSymbol -> SomeSymbol -> Bool # (>) :: SomeSymbol -> SomeSymbol -> Bool # (>=) :: SomeSymbol -> SomeSymbol -> Bool # max :: SomeSymbol -> SomeSymbol -> SomeSymbol # min :: SomeSymbol -> SomeSymbol -> SomeSymbol # | |
Ord SomeNat | Since: base-4.7.0.0 |
Ord Word16 | Since: base-2.1 |
Ord Word32 | Since: base-2.1 |
Ord Word64 | Since: base-2.1 |
Ord Word8 | Since: base-2.1 |
Ord ByteString | |
Defined in Data.ByteString.Internal compare :: ByteString -> ByteString -> Ordering # (<) :: ByteString -> ByteString -> Bool # (<=) :: ByteString -> ByteString -> Bool # (>) :: ByteString -> ByteString -> Bool # (>=) :: ByteString -> ByteString -> Bool # max :: ByteString -> ByteString -> ByteString # min :: ByteString -> ByteString -> ByteString # | |
Ord ByteString | |
Defined in Data.ByteString.Lazy.Internal compare :: ByteString -> ByteString -> Ordering # (<) :: ByteString -> ByteString -> Bool # (<=) :: ByteString -> ByteString -> Bool # (>) :: ByteString -> ByteString -> Bool # (>=) :: ByteString -> ByteString -> Bool # max :: ByteString -> ByteString -> ByteString # min :: ByteString -> ByteString -> ByteString # | |
Ord ShortByteString | |
Defined in Data.ByteString.Short.Internal compare :: ShortByteString -> ShortByteString -> Ordering # (<) :: ShortByteString -> ShortByteString -> Bool # (<=) :: ShortByteString -> ShortByteString -> Bool # (>) :: ShortByteString -> ShortByteString -> Bool # (>=) :: ShortByteString -> ShortByteString -> Bool # max :: ShortByteString -> ShortByteString -> ShortByteString # min :: ShortByteString -> ShortByteString -> ShortByteString # | |
Ord IntSet | |
Ord BigNat | |
Ord Extension | |
Defined in GHC.LanguageExtensions.Type | |
Ord Ordering | |
Defined in GHC.Classes | |
Ord TyCon | |
Ord AnnLookup | |
Defined in Language.Haskell.TH.Syntax | |
Ord AnnTarget | |
Defined in Language.Haskell.TH.Syntax | |
Ord Bang | |
Ord Body | |
Ord Bytes | |
Ord Callconv | |
Defined in Language.Haskell.TH.Syntax | |
Ord Clause | |
Ord Con | |
Ord Dec | |
Ord DecidedStrictness | |
Defined in Language.Haskell.TH.Syntax compare :: DecidedStrictness -> DecidedStrictness -> Ordering # (<) :: DecidedStrictness -> DecidedStrictness -> Bool # (<=) :: DecidedStrictness -> DecidedStrictness -> Bool # (>) :: DecidedStrictness -> DecidedStrictness -> Bool # (>=) :: DecidedStrictness -> DecidedStrictness -> Bool # max :: DecidedStrictness -> DecidedStrictness -> DecidedStrictness # min :: DecidedStrictness -> DecidedStrictness -> DecidedStrictness # | |
Ord DerivClause | |
Defined in Language.Haskell.TH.Syntax compare :: DerivClause -> DerivClause -> Ordering # (<) :: DerivClause -> DerivClause -> Bool # (<=) :: DerivClause -> DerivClause -> Bool # (>) :: DerivClause -> DerivClause -> Bool # (>=) :: DerivClause -> DerivClause -> Bool # max :: DerivClause -> DerivClause -> DerivClause # min :: DerivClause -> DerivClause -> DerivClause # | |
Ord DerivStrategy | |
Defined in Language.Haskell.TH.Syntax compare :: DerivStrategy -> DerivStrategy -> Ordering # (<) :: DerivStrategy -> DerivStrategy -> Bool # (<=) :: DerivStrategy -> DerivStrategy -> Bool # (>) :: DerivStrategy -> DerivStrategy -> Bool # (>=) :: DerivStrategy -> DerivStrategy -> Bool # max :: DerivStrategy -> DerivStrategy -> DerivStrategy # min :: DerivStrategy -> DerivStrategy -> DerivStrategy # | |
Ord DocLoc | |
Ord Exp | |
Ord FamilyResultSig | |
Defined in Language.Haskell.TH.Syntax compare :: FamilyResultSig -> FamilyResultSig -> Ordering # (<) :: FamilyResultSig -> FamilyResultSig -> Bool # (<=) :: FamilyResultSig -> FamilyResultSig -> Bool # (>) :: FamilyResultSig -> FamilyResultSig -> Bool # (>=) :: FamilyResultSig -> FamilyResultSig -> Bool # max :: FamilyResultSig -> FamilyResultSig -> FamilyResultSig # min :: FamilyResultSig -> FamilyResultSig -> FamilyResultSig # | |
Ord Fixity | |
Ord FixityDirection | |
Defined in Language.Haskell.TH.Syntax compare :: FixityDirection -> FixityDirection -> Ordering # (<) :: FixityDirection -> FixityDirection -> Bool # (<=) :: FixityDirection -> FixityDirection -> Bool # (>) :: FixityDirection -> FixityDirection -> Bool # (>=) :: FixityDirection -> FixityDirection -> Bool # max :: FixityDirection -> FixityDirection -> FixityDirection # min :: FixityDirection -> FixityDirection -> FixityDirection # | |
Ord Foreign | |
Ord FunDep | |
Ord Guard | |
Ord Info | |
Ord InjectivityAnn | |
Defined in Language.Haskell.TH.Syntax compare :: InjectivityAnn -> InjectivityAnn -> Ordering # (<) :: InjectivityAnn -> InjectivityAnn -> Bool # (<=) :: InjectivityAnn -> InjectivityAnn -> Bool # (>) :: InjectivityAnn -> InjectivityAnn -> Bool # (>=) :: InjectivityAnn -> InjectivityAnn -> Bool # max :: InjectivityAnn -> InjectivityAnn -> InjectivityAnn # min :: InjectivityAnn -> InjectivityAnn -> InjectivityAnn # | |
Ord Inline | |
Ord Lit | |
Ord Loc | |
Ord Match | |
Ord ModName | |
Ord Module | |
Ord ModuleInfo | |
Defined in Language.Haskell.TH.Syntax compare :: ModuleInfo -> ModuleInfo -> Ordering # (<) :: ModuleInfo -> ModuleInfo -> Bool # (<=) :: ModuleInfo -> ModuleInfo -> Bool # (>) :: ModuleInfo -> ModuleInfo -> Bool # (>=) :: ModuleInfo -> ModuleInfo -> Bool # max :: ModuleInfo -> ModuleInfo -> ModuleInfo # min :: ModuleInfo -> ModuleInfo -> ModuleInfo # | |
Ord Name | |
Ord NameFlavour | |
Defined in Language.Haskell.TH.Syntax compare :: NameFlavour -> NameFlavour -> Ordering # (<) :: NameFlavour -> NameFlavour -> Bool # (<=) :: NameFlavour -> NameFlavour -> Bool # (>) :: NameFlavour -> NameFlavour -> Bool # (>=) :: NameFlavour -> NameFlavour -> Bool # max :: NameFlavour -> NameFlavour -> NameFlavour # min :: NameFlavour -> NameFlavour -> NameFlavour # | |
Ord NameSpace | |
Defined in Language.Haskell.TH.Syntax | |
Ord OccName | |
Ord Overlap | |
Ord Pat | |
Ord PatSynArgs | |
Defined in Language.Haskell.TH.Syntax compare :: PatSynArgs -> PatSynArgs -> Ordering # (<) :: PatSynArgs -> PatSynArgs -> Bool # (<=) :: PatSynArgs -> PatSynArgs -> Bool # (>) :: PatSynArgs -> PatSynArgs -> Bool # (>=) :: PatSynArgs -> PatSynArgs -> Bool # max :: PatSynArgs -> PatSynArgs -> PatSynArgs # min :: PatSynArgs -> PatSynArgs -> PatSynArgs # | |
Ord PatSynDir | |
Defined in Language.Haskell.TH.Syntax | |
Ord Phases | |
Ord PkgName | |
Ord Pragma | |
Ord Range | |
Ord Role | |
Ord RuleBndr | |
Defined in Language.Haskell.TH.Syntax | |
Ord RuleMatch | |
Defined in Language.Haskell.TH.Syntax | |
Ord Safety | |
Ord SourceStrictness | |
Defined in Language.Haskell.TH.Syntax compare :: SourceStrictness -> SourceStrictness -> Ordering # (<) :: SourceStrictness -> SourceStrictness -> Bool # (<=) :: SourceStrictness -> SourceStrictness -> Bool # (>) :: SourceStrictness -> SourceStrictness -> Bool # (>=) :: SourceStrictness -> SourceStrictness -> Bool # max :: SourceStrictness -> SourceStrictness -> SourceStrictness # min :: SourceStrictness -> SourceStrictness -> SourceStrictness # | |
Ord SourceUnpackedness | |
Defined in Language.Haskell.TH.Syntax compare :: SourceUnpackedness -> SourceUnpackedness -> Ordering # (<) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (<=) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (>) :: SourceUnpackedness -> SourceUnpackedness -> Bool # (>=) :: SourceUnpackedness -> SourceUnpackedness -> Bool # max :: SourceUnpackedness -> SourceUnpackedness -> SourceUnpackedness # min :: SourceUnpackedness -> SourceUnpackedness -> SourceUnpackedness # | |
Ord Specificity | |
Defined in Language.Haskell.TH.Syntax compare :: Specificity -> Specificity -> Ordering # (<) :: Specificity -> Specificity -> Bool # (<=) :: Specificity -> Specificity -> Bool # (>) :: Specificity -> Specificity -> Bool # (>=) :: Specificity -> Specificity -> Bool # max :: Specificity -> Specificity -> Specificity # min :: Specificity -> Specificity -> Specificity # | |
Ord Stmt | |
Ord TyLit | |
Ord TySynEqn | |
Defined in Language.Haskell.TH.Syntax | |
Ord Type | |
Ord TypeFamilyHead | |
Defined in Language.Haskell.TH.Syntax compare :: TypeFamilyHead -> TypeFamilyHead -> Ordering # (<) :: TypeFamilyHead -> TypeFamilyHead -> Bool # (<=) :: TypeFamilyHead -> TypeFamilyHead -> Bool # (>) :: TypeFamilyHead -> TypeFamilyHead -> Bool # (>=) :: TypeFamilyHead -> TypeFamilyHead -> Bool # max :: TypeFamilyHead -> TypeFamilyHead -> TypeFamilyHead # min :: TypeFamilyHead -> TypeFamilyHead -> TypeFamilyHead # | |
Ord Integer | |
Ord Natural | |
Ord () | |
Ord Bool | |
Ord Char | |
Ord Double | Note that due to the presence of
Also note that, due to the same,
|
Ord Float | Note that due to the presence of
Also note that, due to the same,
|
Ord Int | |
Ord Word | |
Ord a => Ord (ZipList a) | Since: base-4.7.0.0 |
Defined in Control.Applicative | |
Ord a => Ord (Identity a) | Since: base-4.8.0.0 |
Ord a => Ord (First a) | Since: base-2.1 |
Ord a => Ord (Last a) | Since: base-2.1 |
Ord a => Ord (Down a) | Since: base-4.6.0.0 |
Ord a => Ord (First a) | Since: base-4.9.0.0 |
Ord a => Ord (Last a) | Since: base-4.9.0.0 |
Ord a => Ord (Max a) | Since: base-4.9.0.0 |
Ord a => Ord (Min a) | Since: base-4.9.0.0 |
Ord m => Ord (WrappedMonoid m) | Since: base-4.9.0.0 |
Defined in Data.Semigroup compare :: WrappedMonoid m -> WrappedMonoid m -> Ordering # (<) :: WrappedMonoid m -> WrappedMonoid m -> Bool # (<=) :: WrappedMonoid m -> WrappedMonoid m -> Bool # (>) :: WrappedMonoid m -> WrappedMonoid m -> Bool # (>=) :: WrappedMonoid m -> WrappedMonoid m -> Bool # max :: WrappedMonoid m -> WrappedMonoid m -> WrappedMonoid m # min :: WrappedMonoid m -> WrappedMonoid m -> WrappedMonoid m # | |
Ord p => Ord (Par1 p) | Since: base-4.7.0.0 |
Integral a => Ord (Ratio a) | Since: base-2.0.1 |
Ord a => Ord (IntMap a) | |
Defined in Data.IntMap.Internal | |
Ord a => Ord (Seq a) | |
Ord a => Ord (ViewL a) | |
Ord a => Ord (ViewR a) | |
Ord a => Ord (Set a) | |
Ord a => Ord (DList a) | |
Ord flag => Ord (TyVarBndr flag) | |
Defined in Language.Haskell.TH.Syntax compare :: TyVarBndr flag -> TyVarBndr flag -> Ordering # (<) :: TyVarBndr flag -> TyVarBndr flag -> Bool # (<=) :: TyVarBndr flag -> TyVarBndr flag -> Bool # (>) :: TyVarBndr flag -> TyVarBndr flag -> Bool # (>=) :: TyVarBndr flag -> TyVarBndr flag -> Bool # | |
Ord a => Ord (NonEmpty a) | Since: base-4.9.0.0 |
Ord a => Ord (Maybe a) | Since: base-2.1 |
Ord a => Ord (a) | |
Ord a => Ord [a] | |
(Ord a, Ord b) => Ord (Either a b) | Since: base-2.1 |
Ord (Fixed a) | Since: base-2.1 |
Ord (Proxy s) | Since: base-4.7.0.0 |
Ord a => Ord (Arg a b) | Since: base-4.9.0.0 |
Ord (TypeRep a) | Since: base-4.4.0.0 |
Defined in Data.Typeable.Internal | |
Ord (U1 p) | Since: base-4.7.0.0 |
Ord (V1 p) | Since: base-4.9.0.0 |
(Ord k, Ord v) => Ord (Map k v) | |
(Ord a, Ord b) => Ord (a, b) | |
Ord a => Ord (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
Ord (f a) => Ord (Ap f a) | Since: base-4.12.0.0 |
Ord (a :~: b) | Since: base-4.7.0.0 |
Defined in Data.Type.Equality | |
Ord (f p) => Ord (Rec1 f p) | Since: base-4.7.0.0 |
Defined in GHC.Generics | |
Ord (URec (Ptr ()) p) | Since: base-4.9.0.0 |
Defined in GHC.Generics compare :: URec (Ptr ()) p -> URec (Ptr ()) p -> Ordering # (<) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # (<=) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # (>) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # (>=) :: URec (Ptr ()) p -> URec (Ptr ()) p -> Bool # max :: URec (Ptr ()) p -> URec (Ptr ()) p -> URec (Ptr ()) p # min :: URec (Ptr ()) p -> URec (Ptr ()) p -> URec (Ptr ()) p # | |
Ord (URec Char p) | Since: base-4.9.0.0 |
Ord (URec Double p) | Since: base-4.9.0.0 |
Defined in GHC.Generics compare :: URec Double p -> URec Double p -> Ordering # (<) :: URec Double p -> URec Double p -> Bool # (<=) :: URec Double p -> URec Double p -> Bool # (>) :: URec Double p -> URec Double p -> Bool # (>=) :: URec Double p -> URec Double p -> Bool # | |
Ord (URec Float p) | |
Defined in GHC.Generics | |
Ord (URec Int p) | Since: base-4.9.0.0 |
Ord (URec Word p) | Since: base-4.9.0.0 |
(Ord a, Ord b, Ord c) => Ord (a, b, c) | |
Defined in GHC.Classes | |
(Ord1 f, Ord1 g, Ord a) => Ord (Product f g a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Product compare :: Product f g a -> Product f g a -> Ordering # (<) :: Product f g a -> Product f g a -> Bool # (<=) :: Product f g a -> Product f g a -> Bool # (>) :: Product f g a -> Product f g a -> Bool # (>=) :: Product f g a -> Product f g a -> Bool # | |
(Ord1 f, Ord1 g, Ord a) => Ord (Sum f g a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Sum | |
Ord (a :~~: b) | Since: base-4.10.0.0 |
(Ord (f p), Ord (g p)) => Ord ((f :*: g) p) | Since: base-4.7.0.0 |
(Ord (f p), Ord (g p)) => Ord ((f :+: g) p) | Since: base-4.7.0.0 |
Ord c => Ord (K1 i c p) | Since: base-4.7.0.0 |
Defined in GHC.Generics | |
(Ord a, Ord b, Ord c, Ord d) => Ord (a, b, c, d) | |
Defined in GHC.Classes | |
(Ord1 f, Ord1 g, Ord a) => Ord (Compose f g a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose compare :: Compose f g a -> Compose f g a -> Ordering # (<) :: Compose f g a -> Compose f g a -> Bool # (<=) :: Compose f g a -> Compose f g a -> Bool # (>) :: Compose f g a -> Compose f g a -> Bool # (>=) :: Compose f g a -> Compose f g a -> Bool # | |
Ord (f (g p)) => Ord ((f :.: g) p) | Since: base-4.7.0.0 |
Ord (f p) => Ord (M1 i c f p) | Since: base-4.7.0.0 |
(Ord a, Ord b, Ord c, Ord d, Ord e) => Ord (a, b, c, d, e) | |
Defined in GHC.Classes compare :: (a, b, c, d, e) -> (a, b, c, d, e) -> Ordering # (<) :: (a, b, c, d, e) -> (a, b, c, d, e) -> Bool # (<=) :: (a, b, c, d, e) -> (a, b, c, d, e) -> Bool # (>) :: (a, b, c, d, e) -> (a, b, c, d, e) -> Bool # (>=) :: (a, b, c, d, e) -> (a, b, c, d, e) -> Bool # max :: (a, b, c, d, e) -> (a, b, c, d, e) -> (a, b, c, d, e) # min :: (a, b, c, d, e) -> (a, b, c, d, e) -> (a, b, c, d, e) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f) => Ord (a, b, c, d, e, f) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f) -> (a, b, c, d, e, f) -> Ordering # (<) :: (a, b, c, d, e, f) -> (a, b, c, d, e, f) -> Bool # (<=) :: (a, b, c, d, e, f) -> (a, b, c, d, e, f) -> Bool # (>) :: (a, b, c, d, e, f) -> (a, b, c, d, e, f) -> Bool # (>=) :: (a, b, c, d, e, f) -> (a, b, c, d, e, f) -> Bool # max :: (a, b, c, d, e, f) -> (a, b, c, d, e, f) -> (a, b, c, d, e, f) # min :: (a, b, c, d, e, f) -> (a, b, c, d, e, f) -> (a, b, c, d, e, f) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g) => Ord (a, b, c, d, e, f, g) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) -> Ordering # (<) :: (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) -> Bool # (<=) :: (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) -> Bool # (>) :: (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) -> Bool # (>=) :: (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) -> Bool # max :: (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) # min :: (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) -> (a, b, c, d, e, f, g) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h) => Ord (a, b, c, d, e, f, g, h) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) -> Ordering # (<) :: (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) -> Bool # (<=) :: (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) -> Bool # (>) :: (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) -> Bool # (>=) :: (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) -> Bool # max :: (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) # min :: (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) -> (a, b, c, d, e, f, g, h) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i) => Ord (a, b, c, d, e, f, g, h, i) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) -> Ordering # (<) :: (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) -> Bool # (<=) :: (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) -> Bool # (>) :: (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) -> Bool # (>=) :: (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) -> Bool # max :: (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) # min :: (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) -> (a, b, c, d, e, f, g, h, i) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j) => Ord (a, b, c, d, e, f, g, h, i, j) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) -> Ordering # (<) :: (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) -> Bool # (<=) :: (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) -> Bool # (>) :: (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) -> Bool # (>=) :: (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) -> Bool # max :: (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) # min :: (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) -> (a, b, c, d, e, f, g, h, i, j) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k) => Ord (a, b, c, d, e, f, g, h, i, j, k) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) -> Ordering # (<) :: (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) -> Bool # (<=) :: (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) -> Bool # (>) :: (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) -> Bool # (>=) :: (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) -> Bool # max :: (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) # min :: (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) -> (a, b, c, d, e, f, g, h, i, j, k) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l) => Ord (a, b, c, d, e, f, g, h, i, j, k, l) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) -> Ordering # (<) :: (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) -> Bool # (<=) :: (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) -> Bool # (>) :: (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) -> Bool # (>=) :: (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) -> Bool # max :: (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) # min :: (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) -> (a, b, c, d, e, f, g, h, i, j, k, l) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Ordering # (<) :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Bool # (<=) :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Bool # (>) :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Bool # (>=) :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Bool # max :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) # min :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> (a, b, c, d, e, f, g, h, i, j, k, l, m) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m, Ord n) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Ordering # (<) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Bool # (<=) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Bool # (>) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Bool # (>=) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Bool # max :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) # min :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) # | |
(Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m, Ord n, Ord o) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | |
Defined in GHC.Classes compare :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Ordering # (<) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Bool # (<=) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Bool # (>) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Bool # (>=) :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Bool # max :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) # min :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) # |
Instances
Monoid Ordering | Since: base-2.1 |
Semigroup Ordering | Since: base-4.9.0.0 |
Bounded Ordering | Since: base-2.1 |
Enum Ordering | Since: base-2.1 |
Generic Ordering | |
Read Ordering | Since: base-2.1 |
Show Ordering | Since: base-2.1 |
Default Ordering | |
Defined in Data.Default.Class | |
Eq Ordering | |
Ord Ordering | |
Defined in GHC.Classes | |
type Rep Ordering | Since: base-4.6.0.0 |
The Down
type allows you to reverse sort order conveniently. A value of type
contains a value of type Down
aa
(represented as
).Down
a
If a
has an
instance associated with it then comparing two
values thus wrapped will give you the opposite of their normal sort order.
This is particularly useful when sorting in generalised list comprehensions,
as in: Ord
then sortWith by
.Down
x
>>>
compare True False
GT
>>>
compare (Down True) (Down False)
LT
If a
has a
instance then the wrapped instance also respects
the reversed ordering by exchanging the values of Bounded
and
minBound
.maxBound
>>>
minBound :: Int
-9223372036854775808
>>>
minBound :: Down Int
Down 9223372036854775807
All other instances of
behave as they do for Down
aa
.
Since: base-4.6.0.0
Instances
Foldable Down | Since: base-4.12.0.0 |
Defined in Data.Foldable fold :: Monoid m => Down m -> m # foldMap :: Monoid m => (a -> m) -> Down a -> m # foldMap' :: Monoid m => (a -> m) -> Down a -> m # foldr :: (a -> b -> b) -> b -> Down a -> b # foldr' :: (a -> b -> b) -> b -> Down a -> b # foldl :: (b -> a -> b) -> b -> Down a -> b # foldl' :: (b -> a -> b) -> b -> Down a -> b # foldr1 :: (a -> a -> a) -> Down a -> a # foldl1 :: (a -> a -> a) -> Down a -> a # elem :: Eq a => a -> Down a -> Bool # maximum :: Ord a => Down a -> a # | |
Traversable Down | Since: base-4.12.0.0 |
Applicative Down | Since: base-4.11.0.0 |
Functor Down | Since: base-4.11.0.0 |
Monad Down | Since: base-4.11.0.0 |
Generic1 Down | |
Storable a => Storable (Down a) | Since: base-4.14.0.0 |
Monoid a => Monoid (Down a) | Since: base-4.11.0.0 |
Semigroup a => Semigroup (Down a) | Since: base-4.11.0.0 |
Bits a => Bits (Down a) | Since: base-4.14.0.0 |
Defined in Data.Ord (.&.) :: Down a -> Down a -> Down a # (.|.) :: Down a -> Down a -> Down a # xor :: Down a -> Down a -> Down a # complement :: Down a -> Down a # shift :: Down a -> Int -> Down a # rotate :: Down a -> Int -> Down a # setBit :: Down a -> Int -> Down a # clearBit :: Down a -> Int -> Down a # complementBit :: Down a -> Int -> Down a # testBit :: Down a -> Int -> Bool # bitSizeMaybe :: Down a -> Maybe Int # shiftL :: Down a -> Int -> Down a # unsafeShiftL :: Down a -> Int -> Down a # shiftR :: Down a -> Int -> Down a # unsafeShiftR :: Down a -> Int -> Down a # rotateL :: Down a -> Int -> Down a # | |
FiniteBits a => FiniteBits (Down a) | Since: base-4.14.0.0 |
Defined in Data.Ord finiteBitSize :: Down a -> Int # countLeadingZeros :: Down a -> Int # countTrailingZeros :: Down a -> Int # | |
Bounded a => Bounded (Down a) | Swaps Since: base-4.14.0.0 |
Floating a => Floating (Down a) | Since: base-4.14.0.0 |
RealFloat a => RealFloat (Down a) | Since: base-4.14.0.0 |
Defined in Data.Ord floatRadix :: Down a -> Integer # floatDigits :: Down a -> Int # floatRange :: Down a -> (Int, Int) # decodeFloat :: Down a -> (Integer, Int) # encodeFloat :: Integer -> Int -> Down a # significand :: Down a -> Down a # scaleFloat :: Int -> Down a -> Down a # isInfinite :: Down a -> Bool # isDenormalized :: Down a -> Bool # isNegativeZero :: Down a -> Bool # | |
Generic (Down a) | |
Ix a => Ix (Down a) | Since: base-4.14.0.0 |
Num a => Num (Down a) | Since: base-4.11.0.0 |
Read a => Read (Down a) | This instance would be equivalent to the derived instances of the
Since: base-4.7.0.0 |
Fractional a => Fractional (Down a) | Since: base-4.14.0.0 |
Real a => Real (Down a) | Since: base-4.14.0.0 |
Defined in Data.Ord toRational :: Down a -> Rational # | |
RealFrac a => RealFrac (Down a) | Since: base-4.14.0.0 |
Show a => Show (Down a) | This instance would be equivalent to the derived instances of the
Since: base-4.7.0.0 |
Eq a => Eq (Down a) | Since: base-4.6.0.0 |
Ord a => Ord (Down a) | Since: base-4.6.0.0 |
type Rep1 Down | Since: base-4.12.0.0 |
Defined in GHC.Generics | |
type Rep (Down a) | Since: base-4.12.0.0 |
Defined in GHC.Generics |
comparing :: Ord a => (b -> a) -> b -> b -> Ordering #
comparing p x y = compare (p x) (p y)
Useful combinator for use in conjunction with the xxxBy
family
of functions from Data.List, for example:
... sortBy (comparing fst) ...
Proxy
is a type that holds no data, but has a phantom parameter of
arbitrary type (or even kind). Its use is to provide type information, even
though there is no value available of that type (or it may be too costly to
create one).
Historically,
is a safer alternative to the
Proxy
:: Proxy
a
idiom.undefined
:: a
>>>
Proxy :: Proxy (Void, Int -> Int)
Proxy
Proxy can even hold types of higher kinds,
>>>
Proxy :: Proxy Either
Proxy
>>>
Proxy :: Proxy Functor
Proxy
>>>
Proxy :: Proxy complicatedStructure
Proxy
Instances
Generic1 (Proxy :: k -> Type) | |
Foldable (Proxy :: TYPE LiftedRep -> Type) | Since: base-4.7.0.0 |
Defined in Data.Foldable fold :: Monoid m => Proxy m -> m # foldMap :: Monoid m => (a -> m) -> Proxy a -> m # foldMap' :: Monoid m => (a -> m) -> Proxy a -> m # foldr :: (a -> b -> b) -> b -> Proxy a -> b # foldr' :: (a -> b -> b) -> b -> Proxy a -> b # foldl :: (b -> a -> b) -> b -> Proxy a -> b # foldl' :: (b -> a -> b) -> b -> Proxy a -> b # foldr1 :: (a -> a -> a) -> Proxy a -> a # foldl1 :: (a -> a -> a) -> Proxy a -> a # elem :: Eq a => a -> Proxy a -> Bool # maximum :: Ord a => Proxy a -> a # minimum :: Ord a => Proxy a -> a # | |
Contravariant (Proxy :: Type -> Type) | |
Traversable (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
Alternative (Proxy :: Type -> Type) | Since: base-4.9.0.0 |
Applicative (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
Functor (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
Monad (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
MonadPlus (Proxy :: Type -> Type) | Since: base-4.9.0.0 |
Monoid (Proxy s) | Since: base-4.7.0.0 |
Semigroup (Proxy s) | Since: base-4.9.0.0 |
Bounded (Proxy t) | Since: base-4.7.0.0 |
Enum (Proxy s) | Since: base-4.7.0.0 |
Generic (Proxy t) | |
Ix (Proxy s) | Since: base-4.7.0.0 |
Defined in Data.Proxy | |
Read (Proxy t) | Since: base-4.7.0.0 |
Show (Proxy s) | Since: base-4.7.0.0 |
Eq (Proxy s) | Since: base-4.7.0.0 |
Ord (Proxy s) | Since: base-4.7.0.0 |
type Rep1 (Proxy :: k -> Type) | Since: base-4.6.0.0 |
type Rep (Proxy t) | Since: base-4.6.0.0 |
The class of semigroups (types with an associative binary operation).
Instances should satisfy the following:
Since: base-4.9.0.0
(<>) :: a -> a -> a infixr 6 #
An associative operation.
>>>
[1,2,3] <> [4,5,6]
[1,2,3,4,5,6]
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 #
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 stimesIdempotent
stimes =
respectively.stimesIdempotentMonoid
>>>
stimes 4 [1]
[1,1,1,1]
Instances
Semigroup Void | Since: base-4.9.0.0 |
Semigroup ByteString | |
Defined in Data.ByteString.Internal (<>) :: ByteString -> ByteString -> ByteString # sconcat :: NonEmpty ByteString -> ByteString # stimes :: Integral b => b -> ByteString -> ByteString # | |
Semigroup ByteString | |
Defined in Data.ByteString.Lazy.Internal (<>) :: ByteString -> ByteString -> ByteString # sconcat :: NonEmpty ByteString -> ByteString # stimes :: Integral b => b -> ByteString -> ByteString # | |
Semigroup ShortByteString | |
Defined in Data.ByteString.Short.Internal (<>) :: ShortByteString -> ShortByteString -> ShortByteString # sconcat :: NonEmpty ShortByteString -> ShortByteString # stimes :: Integral b => b -> ShortByteString -> ShortByteString # | |
Semigroup IntSet | Since: containers-0.5.7 |
Semigroup Ordering | Since: base-4.9.0.0 |
Semigroup () | Since: base-4.9.0.0 |
Bits a => Semigroup (And a) | Since: base-4.16 |
FiniteBits a => Semigroup (Iff a) | This constraint is arguably
too strong. However, as some types (such as Since: base-4.16 |
Bits a => Semigroup (Ior a) | Since: base-4.16 |
Bits a => Semigroup (Xor a) | Since: base-4.16 |
Semigroup (Comparison a) |
(<>) :: Comparison a -> Comparison a -> Comparison a Comparison cmp <> Comparison cmp' = Comparison a a' -> cmp a a' <> cmp a a' |
Defined in Data.Functor.Contravariant (<>) :: Comparison a -> Comparison a -> Comparison a # sconcat :: NonEmpty (Comparison a) -> Comparison a # stimes :: Integral b => b -> Comparison a -> Comparison a # | |
Semigroup (Equivalence a) |
(<>) :: Equivalence a -> Equivalence a -> Equivalence a Equivalence equiv <> Equivalence equiv' = Equivalence a b -> equiv a b && equiv a b |
Defined in Data.Functor.Contravariant (<>) :: Equivalence a -> Equivalence a -> Equivalence a # sconcat :: NonEmpty (Equivalence a) -> Equivalence a # stimes :: Integral b => b -> Equivalence a -> Equivalence a # | |
Semigroup (Predicate a) |
(<>) :: Predicate a -> Predicate a -> Predicate a Predicate pred <> Predicate pred' = Predicate a -> pred a && pred' a |
Semigroup a => Semigroup (Identity a) | Since: base-4.9.0.0 |
Semigroup (First a) | Since: base-4.9.0.0 |
Semigroup (Last a) | Since: base-4.9.0.0 |
Semigroup a => Semigroup (Down a) | Since: base-4.11.0.0 |
Semigroup (First a) | Since: base-4.9.0.0 |
Semigroup (Last a) | Since: base-4.9.0.0 |
Ord a => Semigroup (Max a) | Since: base-4.9.0.0 |
Ord a => Semigroup (Min a) | Since: base-4.9.0.0 |
Monoid m => Semigroup (WrappedMonoid m) | Since: base-4.9.0.0 |
Defined in Data.Semigroup (<>) :: WrappedMonoid m -> WrappedMonoid m -> WrappedMonoid m # sconcat :: NonEmpty (WrappedMonoid m) -> WrappedMonoid m # stimes :: Integral b => b -> WrappedMonoid m -> WrappedMonoid m # | |
Semigroup p => Semigroup (Par1 p) | Since: base-4.12.0.0 |
Semigroup (IntMap a) | Since: containers-0.5.7 |
Semigroup (Seq a) | Since: containers-0.5.7 |
Semigroup (MergeSet a) | |
Ord a => Semigroup (Set a) | Since: containers-0.5.7 |
Semigroup (DList a) | |
Semigroup a => Semigroup (IO a) | Since: base-4.10.0.0 |
Semigroup a => Semigroup (Q a) | Since: template-haskell-2.17.0.0 |
Semigroup (NonEmpty a) | Since: base-4.9.0.0 |
Semigroup a => Semigroup (Maybe a) | Since: base-4.9.0.0 |
Semigroup a => Semigroup (a) | Since: base-4.15 |
Semigroup [a] | Since: base-4.9.0.0 |
Semigroup (Either a b) | Since: base-4.9.0.0 |
Semigroup a => Semigroup (Op a b) |
(<>) :: Op a b -> Op a b -> Op a b Op f <> Op g = Op a -> f a <> g a |
Semigroup (Proxy s) | Since: base-4.9.0.0 |
Semigroup (U1 p) | Since: base-4.12.0.0 |
Semigroup (V1 p) | Since: base-4.12.0.0 |
Ord k => Semigroup (Map k v) | |
Semigroup b => Semigroup (a -> b) | Since: base-4.9.0.0 |
(Semigroup a, Semigroup b) => Semigroup (a, b) | Since: base-4.9.0.0 |
Semigroup a => Semigroup (Const a b) | Since: base-4.9.0.0 |
(Applicative f, Semigroup a) => Semigroup (Ap f a) | Since: base-4.12.0.0 |
Semigroup (f p) => Semigroup (Rec1 f p) | Since: base-4.12.0.0 |
(Semigroup a, Semigroup b, Semigroup c) => Semigroup (a, b, c) | Since: base-4.9.0.0 |
(Semigroup (f a), Semigroup (g a)) => Semigroup (Product f g a) | Since: base-4.16.0.0 |
(Semigroup (f p), Semigroup (g p)) => Semigroup ((f :*: g) p) | Since: base-4.12.0.0 |
Semigroup c => Semigroup (K1 i c p) | Since: base-4.12.0.0 |
(Semigroup a, Semigroup b, Semigroup c, Semigroup d) => Semigroup (a, b, c, d) | Since: base-4.9.0.0 |
Semigroup (f (g a)) => Semigroup (Compose f g a) | Since: base-4.16.0.0 |
Semigroup (f (g p)) => Semigroup ((f :.: g) p) | Since: base-4.12.0.0 |
Semigroup (f p) => Semigroup (M1 i c f p) | Since: base-4.12.0.0 |
(Semigroup a, Semigroup b, Semigroup c, Semigroup d, Semigroup e) => Semigroup (a, b, c, d, e) | Since: base-4.9.0.0 |
class (Functor t, Foldable t) => Traversable (t :: Type -> Type) where #
Functors representing data structures that can be transformed to
structures of the same shape by performing an Applicative
(or,
therefore, Monad
) action on each element from left to right.
A more detailed description of what same shape means, the various methods, how traversals are constructed, and example advanced use-cases can be found in the Overview section of Data.Traversable.
For the class laws see the Laws section of Data.Traversable.
traverse :: Applicative f => (a -> f b) -> t a -> f (t b) #
Map each element of a structure to an action, evaluate these actions
from left to right, and collect the results. For a version that ignores
the results see traverse_
.
Examples
Basic usage:
In the first two examples we show each evaluated action mapping to the output structure.
>>>
traverse Just [1,2,3,4]
Just [1,2,3,4]
>>>
traverse id [Right 1, Right 2, Right 3, Right 4]
Right [1,2,3,4]
In the next examples, we show that Nothing
and Left
values short
circuit the created structure.
>>>
traverse (const Nothing) [1,2,3,4]
Nothing
>>>
traverse (\x -> if odd x then Just x else Nothing) [1,2,3,4]
Nothing
>>>
traverse id [Right 1, Right 2, Right 3, Right 4, Left 0]
Left 0
sequenceA :: Applicative f => t (f a) -> f (t a) #
Evaluate each action in the structure from left to right, and
collect the results. For a version that ignores the results
see sequenceA_
.
Examples
Basic usage:
For the first two examples we show sequenceA fully evaluating a a structure and collecting the results.
>>>
sequenceA [Just 1, Just 2, Just 3]
Just [1,2,3]
>>>
sequenceA [Right 1, Right 2, Right 3]
Right [1,2,3]
The next two example show Nothing
and Just
will short circuit
the resulting structure if present in the input. For more context,
check the Traversable
instances for Either
and Maybe
.
>>>
sequenceA [Just 1, Just 2, Just 3, Nothing]
Nothing
>>>
sequenceA [Right 1, Right 2, Right 3, Left 4]
Left 4
mapM :: Monad m => (a -> m b) -> t a -> m (t b) #
Map each element of a structure to a monadic action, evaluate
these actions from left to right, and collect the results. For
a version that ignores the results see mapM_
.
Examples
sequence :: Monad m => t (m a) -> m (t a) #
Evaluate each monadic action in the structure from left to
right, and collect the results. For a version that ignores the
results see sequence_
.
Examples
Basic usage:
The first two examples are instances where the input and
and output of sequence
are isomorphic.
>>>
sequence $ Right [1,2,3,4]
[Right 1,Right 2,Right 3,Right 4]
>>>
sequence $ [Right 1,Right 2,Right 3,Right 4]
Right [1,2,3,4]
The following examples demonstrate short circuit behavior
for sequence
.
>>>
sequence $ Left [1,2,3,4]
Left [1,2,3,4]
>>>
sequence $ [Left 0, Right 1,Right 2,Right 3,Right 4]
Left 0
Instances
Traversable ZipList | Since: base-4.9.0.0 |
Traversable Complex | Since: base-4.9.0.0 |
Traversable Identity | Since: base-4.9.0.0 |
Traversable First | Since: base-4.8.0.0 |
Traversable Last | Since: base-4.8.0.0 |
Traversable Down | Since: base-4.12.0.0 |
Traversable First | Since: base-4.9.0.0 |
Traversable Last | Since: base-4.9.0.0 |
Traversable Max | Since: base-4.9.0.0 |
Traversable Min | Since: base-4.9.0.0 |
Traversable Dual | Since: base-4.8.0.0 |
Traversable Product | Since: base-4.8.0.0 |
Traversable Sum | Since: base-4.8.0.0 |
Traversable Par1 | Since: base-4.9.0.0 |
Traversable IntMap | Traverses in order of increasing key. |
Traversable Digit | |
Traversable Elem | |
Traversable FingerTree | |
Defined in Data.Sequence.Internal traverse :: Applicative f => (a -> f b) -> FingerTree a -> f (FingerTree b) # sequenceA :: Applicative f => FingerTree (f a) -> f (FingerTree a) # mapM :: Monad m => (a -> m b) -> FingerTree a -> m (FingerTree b) # sequence :: Monad m => FingerTree (m a) -> m (FingerTree a) # | |
Traversable Node | |
Traversable Seq | |
Traversable ViewL | |
Traversable ViewR | |
Traversable DList | |
Traversable NonEmpty | Since: base-4.9.0.0 |
Traversable Maybe | Since: base-2.1 |
Traversable Solo | Since: base-4.15 |
Traversable [] | Since: base-2.1 |
Defined in Data.Traversable | |
Traversable (Either a) | Since: base-4.7.0.0 |
Traversable (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
Traversable (Arg a) | Since: base-4.9.0.0 |
Ix i => Traversable (Array i) | Since: base-2.1 |
Traversable (U1 :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (UAddr :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (UChar :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (UDouble :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (UFloat :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (UInt :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (UWord :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (V1 :: Type -> Type) | Since: base-4.9.0.0 |
Traversable (Map k) | Traverses in order of increasing key. |
Traversable ((,) a) | Since: base-4.7.0.0 |
Defined in Data.Traversable | |
Traversable (Const m :: Type -> Type) | Since: base-4.7.0.0 |
Traversable f => Traversable (Ap f) | Since: base-4.12.0.0 |
Traversable f => Traversable (Alt f) | Since: base-4.12.0.0 |
Traversable f => Traversable (Rec1 f) | Since: base-4.9.0.0 |
(Traversable f, Traversable g) => Traversable (Product f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Product | |
(Traversable f, Traversable g) => Traversable (Sum f g) | Since: base-4.9.0.0 |
(Traversable f, Traversable g) => Traversable (f :*: g) | Since: base-4.9.0.0 |
(Traversable f, Traversable g) => Traversable (f :+: g) | Since: base-4.9.0.0 |
Traversable (K1 i c :: Type -> Type) | Since: base-4.9.0.0 |
(Traversable f, Traversable g) => Traversable (Compose f g) | Since: base-4.9.0.0 |
Defined in Data.Functor.Compose | |
(Traversable f, Traversable g) => Traversable (f :.: g) | Since: base-4.9.0.0 |
Traversable f => Traversable (M1 i c f) | Since: base-4.9.0.0 |
mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b) #
The mapAccumR
function behaves like a combination of fmap
and foldr
; it applies a function to each element of a structure,
passing an accumulating parameter from right to left, and returning
a final value of this accumulator together with the new structure.
Examples
Basic usage:
>>>
mapAccumR (\a b -> (a + b, a)) 0 [1..10]
(55,[54,52,49,45,40,34,27,19,10,0])
>>>
mapAccumR (\a b -> (a <> show b, a)) "0" [1..5]
("054321",["05432","0543","054","05","0"])
mapAccumL :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b) #
The mapAccumL
function behaves like a combination of fmap
and foldl
; it applies a function to each element of a structure,
passing an accumulating parameter from left to right, and returning
a final value of this accumulator together with the new structure.
Examples
Basic usage:
>>>
mapAccumL (\a b -> (a + b, a)) 0 [1..10]
(55,[0,1,3,6,10,15,21,28,36,45])
>>>
mapAccumL (\a b -> (a <> show b, a)) "0" [1..5]
("012345",["0","01","012","0123","01234"])
forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b) #
for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b) #
uncurry :: (a -> b -> c) -> (a, b) -> c #
uncurry
converts a curried function to a function on pairs.
Examples
>>>
uncurry (+) (1,2)
3
>>>
uncurry ($) (show, 1)
"1"
>>>
map (uncurry max) [(1,2), (3,4), (6,8)]
[2,4,8]
The class Typeable
allows a concrete representation of a type to
be calculated.
typeRep#
Uninhabited data type
Since: base-4.8.0.0
Instances
Data Void | Since: base-4.8.0.0 |
Defined in Data.Void gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Void -> c Void # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Void # dataTypeOf :: Void -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Void) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Void) # gmapT :: (forall b. Data b => b -> b) -> Void -> Void # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Void -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Void -> r # gmapQ :: (forall d. Data d => d -> u) -> Void -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Void -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Void -> m Void # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Void -> m Void # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Void -> m Void # | |
Semigroup Void | Since: base-4.9.0.0 |
Exception Void | Since: base-4.8.0.0 |
Defined in Data.Void toException :: Void -> SomeException # fromException :: SomeException -> Maybe Void # displayException :: Void -> String # | |
Generic Void | |
Ix Void | Since: base-4.8.0.0 |
Read Void | Reading a Since: base-4.8.0.0 |
Show Void | Since: base-4.8.0.0 |
Eq Void | Since: base-4.8.0.0 |
Ord Void | Since: base-4.8.0.0 |
Lift Void | Since: template-haskell-2.15.0.0 |
type Rep Void | Since: base-4.8.0.0 |
Instances
Bits Word | Since: base-2.1 |
Defined in GHC.Bits (.&.) :: Word -> Word -> Word # (.|.) :: Word -> Word -> Word # complement :: Word -> Word # shift :: Word -> Int -> Word # rotate :: Word -> Int -> Word # setBit :: Word -> Int -> Word # clearBit :: Word -> Int -> Word # complementBit :: Word -> Int -> Word # testBit :: Word -> Int -> Bool # bitSizeMaybe :: Word -> Maybe Int # shiftL :: Word -> Int -> Word # unsafeShiftL :: Word -> Int -> Word # shiftR :: Word -> Int -> Word # unsafeShiftR :: Word -> Int -> Word # rotateL :: Word -> Int -> Word # | |
FiniteBits Word | Since: base-4.6.0.0 |
Defined in GHC.Bits | |
Bounded Word | Since: base-2.1 |
Enum Word | Since: base-2.1 |
Num Word | Since: base-2.1 |
Read Word | Since: base-4.5.0.0 |
Integral Word | Since: base-2.1 |
Real Word | Since: base-2.1 |
Defined in GHC.Real toRational :: Word -> Rational # | |
Show Word | Since: base-2.1 |
Default Word | |
Defined in Data.Default.Class | |
Eq Word | |
Ord Word | |
Lift Word | |
Generic1 (URec Word :: k -> Type) | |
Foldable (UWord :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Defined in Data.Foldable fold :: Monoid m => UWord m -> m # foldMap :: Monoid m => (a -> m) -> UWord a -> m # foldMap' :: Monoid m => (a -> m) -> UWord a -> m # foldr :: (a -> b -> b) -> b -> UWord a -> b # foldr' :: (a -> b -> b) -> b -> UWord a -> b # foldl :: (b -> a -> b) -> b -> UWord a -> b # foldl' :: (b -> a -> b) -> b -> UWord a -> b # foldr1 :: (a -> a -> a) -> UWord a -> a # foldl1 :: (a -> a -> a) -> UWord a -> a # elem :: Eq a => a -> UWord a -> Bool # maximum :: Ord a => UWord a -> a # minimum :: Ord a => UWord a -> a # | |
Traversable (UWord :: Type -> Type) | Since: base-4.9.0.0 |
Functor (URec Word :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Generic (URec Word p) | |
Show (URec Word p) | Since: base-4.9.0.0 |
Eq (URec Word p) | Since: base-4.9.0.0 |
Ord (URec Word p) | Since: base-4.9.0.0 |
data URec Word (p :: k) | Used for marking occurrences of Since: base-4.9.0.0 |
type Rep1 (URec Word :: k -> Type) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
type Rep (URec Word p) | Since: base-4.9.0.0 |
Defined in GHC.Generics |
8-bit unsigned integer type
Instances
16-bit unsigned integer type
Instances
32-bit unsigned integer type
Instances
64-bit unsigned integer type
Instances
seq :: forall {r :: RuntimeRep} a (b :: TYPE r). a -> b -> b infixr 0 #
The value of seq a b
is bottom if a
is bottom, and
otherwise equal to b
. In other words, it evaluates the first
argument a
to weak head normal form (WHNF). seq
is usually
introduced to improve performance by avoiding unneeded laziness.
A note on evaluation order: the expression seq a b
does
not guarantee that a
will be evaluated before b
.
The only guarantee given by seq
is that the both a
and b
will be evaluated before seq
returns a value.
In particular, this means that b
may be evaluated before
a
. If you need to guarantee a specific order of evaluation,
you must use the function pseq
from the "parallel" package.
($!) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b infixr 0 #
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.
The Bounded
class is used to name the upper and lower limits of a
type. Ord
is not a superclass of Bounded
since types that are not
totally ordered may also have upper and lower bounds.
The Bounded
class may be derived for any enumeration type;
minBound
is the first constructor listed in the data
declaration
and maxBound
is the last.
Bounded
may also be derived for single-constructor datatypes whose
constituent types are in Bounded
.
Instances
Bounded Associativity | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
Bounded DecidedStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
Bounded SourceStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
Bounded SourceUnpackedness | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
Bounded Int16 | Since: base-2.1 |
Bounded Int32 | Since: base-2.1 |
Bounded Int64 | Since: base-2.1 |
Bounded Int8 | Since: base-2.1 |
Bounded Word16 | Since: base-2.1 |
Bounded Word32 | Since: base-2.1 |
Bounded Word64 | Since: base-2.1 |
Bounded Word8 | Since: base-2.1 |
Bounded Extension | |
Bounded Ordering | Since: base-2.1 |
Bounded () | Since: base-2.1 |
Bounded Bool | Since: base-2.1 |
Bounded Char | Since: base-2.1 |
Bounded Int | Since: base-2.1 |
Bounded Levity | Since: base-4.16.0.0 |
Bounded VecCount | Since: base-4.10.0.0 |
Bounded VecElem | Since: base-4.10.0.0 |
Bounded Word | Since: base-2.1 |
Bounded a => Bounded (And a) | Since: base-4.16 |
Bounded a => Bounded (Iff a) | Since: base-4.16 |
Bounded a => Bounded (Ior a) | Since: base-4.16 |
Bounded a => Bounded (Xor a) | Since: base-4.16 |
Bounded a => Bounded (Identity a) | Since: base-4.9.0.0 |
Bounded a => Bounded (Down a) | Swaps Since: base-4.14.0.0 |
Bounded a => Bounded (First a) | Since: base-4.9.0.0 |
Bounded a => Bounded (Last a) | Since: base-4.9.0.0 |
Bounded a => Bounded (Max a) | Since: base-4.9.0.0 |
Bounded a => Bounded (Min a) | Since: base-4.9.0.0 |
Bounded m => Bounded (WrappedMonoid m) | Since: base-4.9.0.0 |
Defined in Data.Semigroup minBound :: WrappedMonoid m # maxBound :: WrappedMonoid m # | |
Bounded a => Bounded (a) | |
Bounded (Proxy t) | Since: base-4.7.0.0 |
(Bounded a, Bounded b) => Bounded (a, b) | Since: base-2.1 |
Bounded a => Bounded (Const a b) | Since: base-4.9.0.0 |
(Applicative f, Bounded a) => Bounded (Ap f a) | Since: base-4.12.0.0 |
a ~ b => Bounded (a :~: b) | Since: base-4.7.0.0 |
(Bounded a, Bounded b, Bounded c) => Bounded (a, b, c) | Since: base-2.1 |
a ~~ b => Bounded (a :~~: b) | Since: base-4.10.0.0 |
(Bounded a, Bounded b, Bounded c, Bounded d) => Bounded (a, b, c, d) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e) => Bounded (a, b, c, d, e) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f) => Bounded (a, b, c, d, e, f) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g) => Bounded (a, b, c, d, e, f, g) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h) => Bounded (a, b, c, d, e, f, g, h) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h, Bounded i) => Bounded (a, b, c, d, e, f, g, h, i) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h, Bounded i, Bounded j) => Bounded (a, b, c, d, e, f, g, h, i, j) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h, Bounded i, Bounded j, Bounded k) => Bounded (a, b, c, d, e, f, g, h, i, j, k) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h, Bounded i, Bounded j, Bounded k, Bounded l) => Bounded (a, b, c, d, e, f, g, h, i, j, k, l) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h, Bounded i, Bounded j, Bounded k, Bounded l, Bounded m) => Bounded (a, b, c, d, e, f, g, h, i, j, k, l, m) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h, Bounded i, Bounded j, Bounded k, Bounded l, Bounded m, Bounded n) => Bounded (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | Since: base-2.1 |
(Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g, Bounded h, Bounded i, Bounded j, Bounded k, Bounded l, Bounded m, Bounded n, Bounded o) => Bounded (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | Since: base-2.1 |
Class Enum
defines operations on sequentially ordered types.
The enumFrom
... methods are used in Haskell's translation of
arithmetic sequences.
Instances of Enum
may be derived for any enumeration type (types
whose constructors have no fields). The nullary constructors are
assumed to be numbered left-to-right by fromEnum
from 0
through n-1
.
See Chapter 10 of the Haskell Report for more details.
For any type that is an instance of class Bounded
as well as Enum
,
the following should hold:
- The calls
andsucc
maxBound
should result in a runtime error.pred
minBound
fromEnum
andtoEnum
should give a runtime error if the result value is not representable in the result type. For example,
is an error.toEnum
7 ::Bool
enumFrom
andenumFromThen
should be defined with an implicit bound, thus:
enumFrom x = enumFromTo x maxBound enumFromThen x y = enumFromThenTo x y bound where bound | fromEnum y >= fromEnum x = maxBound | otherwise = minBound
the successor of a value. For numeric types, succ
adds 1.
the predecessor of a value. For numeric types, pred
subtracts 1.
Convert from an Int
.
Convert to an Int
.
It is implementation-dependent what fromEnum
returns when
applied to a value that is too large to fit in an Int
.
Used in Haskell's translation of [n..]
with [n..] = enumFrom n
,
a possible implementation being enumFrom n = n : enumFrom (succ n)
.
For example:
enumFrom 4 :: [Integer] = [4,5,6,7,...]
enumFrom 6 :: [Int] = [6,7,8,9,...,maxBound :: Int]
enumFromThen :: a -> a -> [a] #
Used in Haskell's translation of [n,n'..]
with [n,n'..] = enumFromThen n n'
, a possible implementation being
enumFromThen n n' = n : n' : worker (f x) (f x n')
,
worker s v = v : worker s (s v)
, x = fromEnum n' - fromEnum n
and
f n y
| n > 0 = f (n - 1) (succ y)
| n < 0 = f (n + 1) (pred y)
| otherwise = y
For example:
enumFromThen 4 6 :: [Integer] = [4,6,8,10...]
enumFromThen 6 2 :: [Int] = [6,2,-2,-6,...,minBound :: Int]
enumFromTo :: a -> a -> [a] #
Used in Haskell's translation of [n..m]
with
[n..m] = enumFromTo n m
, a possible implementation being
enumFromTo n m
| n <= m = n : enumFromTo (succ n) m
| otherwise = []
.
For example:
enumFromTo 6 10 :: [Int] = [6,7,8,9,10]
enumFromTo 42 1 :: [Integer] = []
enumFromThenTo :: a -> a -> a -> [a] #
Used in Haskell's translation of [n,n'..m]
with
[n,n'..m] = enumFromThenTo n n' m
, a possible implementation
being enumFromThenTo n n' m = worker (f x) (c x) n m
,
x = fromEnum n' - fromEnum n
, c x = bool (>=) ((x 0)
f n y
| n > 0 = f (n - 1) (succ y)
| n < 0 = f (n + 1) (pred y)
| otherwise = y
and
worker s c v m
| c v m = v : worker s c (s v) m
| otherwise = []
For example:
enumFromThenTo 4 2 -6 :: [Integer] = [4,2,0,-2,-4,-6]
enumFromThenTo 6 8 2 :: [Int] = []
Instances
Enum Associativity | Since: base-4.9.0.0 |
Defined in GHC.Generics succ :: Associativity -> Associativity # pred :: Associativity -> Associativity # toEnum :: Int -> Associativity # fromEnum :: Associativity -> Int # enumFrom :: Associativity -> [Associativity] # enumFromThen :: Associativity -> Associativity -> [Associativity] # enumFromTo :: Associativity -> Associativity -> [Associativity] # enumFromThenTo :: Associativity -> Associativity -> Associativity -> [Associativity] # | |
Enum DecidedStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics succ :: DecidedStrictness -> DecidedStrictness # pred :: DecidedStrictness -> DecidedStrictness # toEnum :: Int -> DecidedStrictness # fromEnum :: DecidedStrictness -> Int # enumFrom :: DecidedStrictness -> [DecidedStrictness] # enumFromThen :: DecidedStrictness -> DecidedStrictness -> [DecidedStrictness] # enumFromTo :: DecidedStrictness -> DecidedStrictness -> [DecidedStrictness] # enumFromThenTo :: DecidedStrictness -> DecidedStrictness -> DecidedStrictness -> [DecidedStrictness] # | |
Enum SourceStrictness | Since: base-4.9.0.0 |
Defined in GHC.Generics succ :: SourceStrictness -> SourceStrictness # pred :: SourceStrictness -> SourceStrictness # toEnum :: Int -> SourceStrictness # fromEnum :: SourceStrictness -> Int # enumFrom :: SourceStrictness -> [SourceStrictness] # enumFromThen :: SourceStrictness -> SourceStrictness -> [SourceStrictness] # enumFromTo :: SourceStrictness -> SourceStrictness -> [SourceStrictness] # enumFromThenTo :: SourceStrictness -> SourceStrictness -> SourceStrictness -> [SourceStrictness] # | |
Enum SourceUnpackedness | Since: base-4.9.0.0 |
Defined in GHC.Generics succ :: SourceUnpackedness -> SourceUnpackedness # pred :: SourceUnpackedness -> SourceUnpackedness # toEnum :: Int -> SourceUnpackedness # fromEnum :: SourceUnpackedness -> Int # enumFrom :: SourceUnpackedness -> [SourceUnpackedness] # enumFromThen :: SourceUnpackedness -> SourceUnpackedness -> [SourceUnpackedness] # enumFromTo :: SourceUnpackedness -> SourceUnpackedness -> [SourceUnpackedness] # enumFromThenTo :: SourceUnpackedness -> SourceUnpackedness -> SourceUnpackedness -> [SourceUnpackedness] # | |
Enum Int16 | Since: base-2.1 |
Enum Int32 | Since: base-2.1 |
Enum Int64 | Since: base-2.1 |
Enum Int8 | Since: base-2.1 |
Enum Word16 | Since: base-2.1 |
Defined in GHC.Word | |
Enum Word32 | Since: base-2.1 |
Defined in GHC.Word | |
Enum Word64 | Since: base-2.1 |
Defined in GHC.Word | |
Enum Word8 | Since: base-2.1 |
Enum Extension | |
Defined in GHC.LanguageExtensions.Type succ :: Extension -> Extension # pred :: Extension -> Extension # fromEnum :: Extension -> Int # enumFrom :: Extension -> [Extension] # enumFromThen :: Extension -> Extension -> [Extension] # enumFromTo :: Extension -> Extension -> [Extension] # enumFromThenTo :: Extension -> Extension -> Extension -> [Extension] # | |
Enum Ordering | Since: base-2.1 |
Enum Integer | Since: base-2.1 |
Enum Natural | Since: base-4.8.0.0 |
Enum () | Since: base-2.1 |
Enum Bool | Since: base-2.1 |
Enum Char | Since: base-2.1 |
Enum Int | Since: base-2.1 |
Enum Levity | Since: base-4.16.0.0 |
Defined in GHC.Enum | |
Enum VecCount | Since: base-4.10.0.0 |
Enum VecElem | Since: base-4.10.0.0 |
Enum Word | Since: base-2.1 |
Enum a => Enum (And a) | Since: base-4.16 |
Enum a => Enum (Iff a) | Since: base-4.16 |
Enum a => Enum (Ior a) | Since: base-4.16 |
Enum a => Enum (Xor a) | Since: base-4.16 |
Enum a => Enum (Identity a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Identity succ :: Identity a -> Identity a # pred :: Identity a -> Identity a # fromEnum :: Identity a -> Int # enumFrom :: Identity a -> [Identity a] # enumFromThen :: Identity a -> Identity a -> [Identity a] # enumFromTo :: Identity a -> Identity a -> [Identity a] # enumFromThenTo :: Identity a -> Identity a -> Identity a -> [Identity a] # | |
Enum a => Enum (First a) | Since: base-4.9.0.0 |
Enum a => Enum (Last a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
Enum a => Enum (Max a) | Since: base-4.9.0.0 |
Enum a => Enum (Min a) | Since: base-4.9.0.0 |
Enum a => Enum (WrappedMonoid a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup succ :: WrappedMonoid a -> WrappedMonoid a # pred :: WrappedMonoid a -> WrappedMonoid a # toEnum :: Int -> WrappedMonoid a # fromEnum :: WrappedMonoid a -> Int # enumFrom :: WrappedMonoid a -> [WrappedMonoid a] # enumFromThen :: WrappedMonoid a -> WrappedMonoid a -> [WrappedMonoid a] # enumFromTo :: WrappedMonoid a -> WrappedMonoid a -> [WrappedMonoid a] # enumFromThenTo :: WrappedMonoid a -> WrappedMonoid a -> WrappedMonoid a -> [WrappedMonoid a] # | |
Integral a => Enum (Ratio a) | Since: base-2.0.1 |
Enum a => Enum (a) | |
Enum (Fixed a) | Recall that, for numeric types, succ (0.000 :: Milli) == 1.001 and likewise pred (0.000 :: Milli) == -0.001 In other words, succ (0.000000000000 :: Pico) == 0.000000000001 and similarly pred (0.000000000000 :: Pico) == -0.000000000001 This is worth bearing in mind when defining [1..10] :: [Pico] evaluates to However, this is not true. On the contrary, similarly to the above
implementations of [1.000000000000, 1.00000000001, 1.00000000002, ..., 10.000000000000] and contains Since: base-2.1 |
Enum (Proxy s) | Since: base-4.7.0.0 |
Enum a => Enum (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const succ :: Const a b -> Const a b # pred :: Const a b -> Const a b # fromEnum :: Const a b -> Int # enumFrom :: Const a b -> [Const a b] # enumFromThen :: Const a b -> Const a b -> [Const a b] # enumFromTo :: Const a b -> Const a b -> [Const a b] # enumFromThenTo :: Const a b -> Const a b -> Const a b -> [Const a b] # | |
Enum (f a) => Enum (Ap f a) | Since: base-4.12.0.0 |
Defined in Data.Monoid | |
a ~ b => Enum (a :~: b) | Since: base-4.7.0.0 |
Defined in Data.Type.Equality | |
a ~~ b => Enum (a :~~: b) | Since: base-4.10.0.0 |
Defined in Data.Type.Equality succ :: (a :~~: b) -> a :~~: b # pred :: (a :~~: b) -> a :~~: b # fromEnum :: (a :~~: b) -> Int # enumFrom :: (a :~~: b) -> [a :~~: b] # enumFromThen :: (a :~~: b) -> (a :~~: b) -> [a :~~: b] # enumFromTo :: (a :~~: b) -> (a :~~: b) -> [a :~~: b] # enumFromThenTo :: (a :~~: b) -> (a :~~: b) -> (a :~~: b) -> [a :~~: b] # |
undefined :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => a #
error :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => [Char] -> a #
error
stops execution and displays an error message.
Double-precision floating point numbers. It is desirable that this type be at least equal in range and precision to the IEEE double-precision type.
Instances
Floating Double | Since: base-2.1 |
RealFloat Double | Since: base-2.1 |
Defined in GHC.Float floatRadix :: Double -> Integer # floatDigits :: Double -> Int # floatRange :: Double -> (Int, Int) # decodeFloat :: Double -> (Integer, Int) # encodeFloat :: Integer -> Int -> Double # significand :: Double -> Double # scaleFloat :: Int -> Double -> Double # isInfinite :: Double -> Bool # isDenormalized :: Double -> Bool # isNegativeZero :: Double -> Bool # | |
Read Double | Since: base-2.1 |
Default Double | |
Defined in Data.Default.Class | |
Eq Double | Note that due to the presence of
Also note that
|
Ord Double | Note that due to the presence of
Also note that, due to the same,
|
Lift Double | |
Generic1 (URec Double :: k -> Type) | |
Foldable (UDouble :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Defined in Data.Foldable fold :: Monoid m => UDouble m -> m # foldMap :: Monoid m => (a -> m) -> UDouble a -> m # foldMap' :: Monoid m => (a -> m) -> UDouble a -> m # foldr :: (a -> b -> b) -> b -> UDouble a -> b # foldr' :: (a -> b -> b) -> b -> UDouble a -> b # foldl :: (b -> a -> b) -> b -> UDouble a -> b # foldl' :: (b -> a -> b) -> b -> UDouble a -> b # foldr1 :: (a -> a -> a) -> UDouble a -> a # foldl1 :: (a -> a -> a) -> UDouble a -> a # elem :: Eq a => a -> UDouble a -> Bool # maximum :: Ord a => UDouble a -> a # minimum :: Ord a => UDouble a -> a # | |
Traversable (UDouble :: Type -> Type) | Since: base-4.9.0.0 |
Functor (URec Double :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Generic (URec Double p) | |
Show (URec Double p) | Since: base-4.9.0.0 |
Eq (URec Double p) | Since: base-4.9.0.0 |
Ord (URec Double p) | Since: base-4.9.0.0 |
Defined in GHC.Generics compare :: URec Double p -> URec Double p -> Ordering # (<) :: URec Double p -> URec Double p -> Bool # (<=) :: URec Double p -> URec Double p -> Bool # (>) :: URec Double p -> URec Double p -> Bool # (>=) :: URec Double p -> URec Double p -> Bool # | |
data URec Double (p :: k) | Used for marking occurrences of Since: base-4.9.0.0 |
type Rep1 (URec Double :: k -> Type) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
type Rep (URec Double p) | Since: base-4.9.0.0 |
Defined in GHC.Generics |
Single-precision floating point numbers. It is desirable that this type be at least equal in range and precision to the IEEE single-precision type.
Instances
Floating Float | Since: base-2.1 |
RealFloat Float | Since: base-2.1 |
Defined in GHC.Float floatRadix :: Float -> Integer # floatDigits :: Float -> Int # floatRange :: Float -> (Int, Int) # decodeFloat :: Float -> (Integer, Int) # encodeFloat :: Integer -> Int -> Float # significand :: Float -> Float # scaleFloat :: Int -> Float -> Float # isInfinite :: Float -> Bool # isDenormalized :: Float -> Bool # isNegativeZero :: Float -> Bool # | |
Read Float | Since: base-2.1 |
Default Float | |
Defined in Data.Default.Class | |
Eq Float | Note that due to the presence of
Also note that
|
Ord Float | Note that due to the presence of
Also note that, due to the same,
|
Lift Float | |
Generic1 (URec Float :: k -> Type) | |
Foldable (UFloat :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Defined in Data.Foldable fold :: Monoid m => UFloat m -> m # foldMap :: Monoid m => (a -> m) -> UFloat a -> m # foldMap' :: Monoid m => (a -> m) -> UFloat a -> m # foldr :: (a -> b -> b) -> b -> UFloat a -> b # foldr' :: (a -> b -> b) -> b -> UFloat a -> b # foldl :: (b -> a -> b) -> b -> UFloat a -> b # foldl' :: (b -> a -> b) -> b -> UFloat a -> b # foldr1 :: (a -> a -> a) -> UFloat a -> a # foldl1 :: (a -> a -> a) -> UFloat a -> a # elem :: Eq a => a -> UFloat a -> Bool # maximum :: Ord a => UFloat a -> a # minimum :: Ord a => UFloat a -> a # | |
Traversable (UFloat :: Type -> Type) | Since: base-4.9.0.0 |
Functor (URec Float :: TYPE LiftedRep -> Type) | Since: base-4.9.0.0 |
Generic (URec Float p) | |
Show (URec Float p) | |
Eq (URec Float p) | |
Ord (URec Float p) | |
Defined in GHC.Generics | |
data URec Float (p :: k) | Used for marking occurrences of Since: base-4.9.0.0 |
type Rep1 (URec Float :: k -> Type) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
type Rep (URec Float p) | |
Defined in GHC.Generics |
Representable types of kind *
.
This class is derivable in GHC with the DeriveGeneric
flag on.
A Generic
instance must satisfy the following laws:
from
.to
≡id
to
.from
≡id
Instances
Basic numeric class.
The Haskell Report defines no laws for Num
. However, (
and +
)(
are
customarily expected to define a ring and have the following properties:*
)
- Associativity of
(
+
) (x + y) + z
=x + (y + z)
- Commutativity of
(
+
) x + y
=y + x
is the additive identityfromInteger
0x + fromInteger 0
=x
negate
gives the additive inversex + negate x
=fromInteger 0
- Associativity of
(
*
) (x * y) * z
=x * (y * z)
is the multiplicative identityfromInteger
1x * fromInteger 1
=x
andfromInteger 1 * x
=x
- Distributivity of
(
with respect to*
)(
+
) a * (b + c)
=(a * b) + (a * c)
and(b + c) * a
=(b * a) + (c * a)
Note that it isn't customarily expected that a type instance of both Num
and Ord
implement an ordered ring. Indeed, in base
only Integer
and
Rational
do.
Unary negation.
Absolute value.
Sign of a number.
The functions abs
and signum
should satisfy the law:
abs x * signum x == x
For real numbers, the signum
is either -1
(negative), 0
(zero)
or 1
(positive).
fromInteger :: Integer -> a #
Conversion from an Integer
.
An integer literal represents the application of the function
fromInteger
to the appropriate value of type Integer
,
so such literals have type (
.Num
a) => a
Instances
Num Int16 | Since: base-2.1 |
Num Int32 | Since: base-2.1 |
Num Int64 | Since: base-2.1 |
Num Int8 | Since: base-2.1 |
Num Word16 | Since: base-2.1 |
Num Word32 | Since: base-2.1 |
Num Word64 | Since: base-2.1 |
Num Word8 | Since: base-2.1 |
Num CodePoint | |
Num DecoderState | |
Defined in Data.Text.Encoding (+) :: DecoderState -> DecoderState -> DecoderState # (-) :: DecoderState -> DecoderState -> DecoderState # (*) :: DecoderState -> DecoderState -> DecoderState # negate :: DecoderState -> DecoderState # abs :: DecoderState -> DecoderState # signum :: DecoderState -> DecoderState # fromInteger :: Integer -> DecoderState # | |
Num Integer | Since: base-2.1 |
Num Natural | Note that Since: base-4.8.0.0 |
Num Int | Since: base-2.1 |
Num Word | Since: base-2.1 |
RealFloat a => Num (Complex a) | Since: base-2.1 |
Num a => Num (Identity a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Identity | |
Num a => Num (Down a) | Since: base-4.11.0.0 |
Num a => Num (Max a) | Since: base-4.9.0.0 |
Num a => Num (Min a) | Since: base-4.9.0.0 |
Integral a => Num (Ratio a) | Since: base-2.0.1 |
HasResolution a => Num (Fixed a) | Since: base-2.1 |
Num a => Num (Op a b) | |
Num a => Num (Const a b) | Since: base-4.9.0.0 |
(Applicative f, Num a) => Num (Ap f a) | Note that even if the underlying Commutativity:
Additive inverse:
Distributivity:
Since: base-4.12.0.0 |
Arbitrary precision integers. In contrast with fixed-size integral types
such as Int
, the Integer
type represents the entire infinite range of
integers.
Integers are stored in a kind of sign-magnitude form, hence do not expect two's complement form when using bit operations.
If the value is small (fit into an Int
), IS
constructor is used.
Otherwise Integer
and IN
constructors are used to store a BigNat
representing respectively the positive or the negative value magnitude.
Invariant: Integer
and IN
are used iff value doesn't fit in IS
Instances
Bits Integer | Since: base-2.1 |
Defined in GHC.Bits (.&.) :: Integer -> Integer -> Integer # (.|.) :: Integer -> Integer -> Integer # xor :: Integer -> Integer -> Integer # complement :: Integer -> Integer # shift :: Integer -> Int -> Integer # rotate :: Integer -> Int -> Integer # setBit :: Integer -> Int -> Integer # clearBit :: Integer -> Int -> Integer # complementBit :: Integer -> Int -> Integer # testBit :: Integer -> Int -> Bool # bitSizeMaybe :: Integer -> Maybe Int # shiftL :: Integer -> Int -> Integer # unsafeShiftL :: Integer -> Int -> Integer # shiftR :: Integer -> Int -> Integer # unsafeShiftR :: Integer -> Int -> Integer # rotateL :: Integer -> Int -> Integer # | |
Enum Integer | Since: base-2.1 |
Num Integer | Since: base-2.1 |
Read Integer | Since: base-2.1 |
Integral Integer | Since: base-2.0.1 |
Defined in GHC.Real | |
Real Integer | Since: base-2.0.1 |
Defined in GHC.Real toRational :: Integer -> Rational # | |
Show Integer | Since: base-2.1 |
Default Integer | |
Defined in Data.Default.Class | |
Eq Integer | |
Ord Integer | |
Lift Integer | |
fromIntegral :: (Integral a, Num b) => a -> b #
general coercion from integral types
realToFrac :: (Real a, Fractional b) => a -> b #
general coercion to fractional types
class Num a => Fractional a where #
Fractional numbers, supporting real division.
The Haskell Report defines no laws for Fractional
. However, (
and
+
)(
are customarily expected to define a division ring and have the
following properties:*
)
recip
gives the multiplicative inversex * recip x
=recip x * x
=fromInteger 1
Note that it isn't customarily expected that a type instance of
Fractional
implement a field. However, all instances in base
do.
fromRational :: Rational -> a #
Conversion from a Rational
(that is
).
A floating literal stands for an application of Ratio
Integer
fromRational
to a value of type Rational
, so such literals have type
(
.Fractional
a) => a
Instances
RealFloat a => Fractional (Complex a) | Since: base-2.1 |
Fractional a => Fractional (Identity a) | Since: base-4.9.0.0 |
Fractional a => Fractional (Down a) | Since: base-4.14.0.0 |
Integral a => Fractional (Ratio a) | Since: base-2.0.1 |
HasResolution a => Fractional (Fixed a) | Since: base-2.1 |
Fractional a => Fractional (Op a b) | |
Fractional a => Fractional (Const a b) | Since: base-4.9.0.0 |
class (Real a, Enum a) => Integral a where #
Integral numbers, supporting integer division.
The Haskell Report defines no laws for Integral
. However, Integral
instances are customarily expected to define a Euclidean domain and have the
following properties for the div
/mod
and quot
/rem
pairs, given
suitable Euclidean functions f
and g
:
x
=y * quot x y + rem x y
withrem x y
=fromInteger 0
org (rem x y)
<g y
x
=y * div x y + mod x y
withmod x y
=fromInteger 0
orf (mod x y)
<f y
An example of a suitable Euclidean function, for Integer
's instance, is
abs
.
Instances
Integral Int16 | Since: base-2.1 |
Integral Int32 | Since: base-2.1 |
Integral Int64 | Since: base-2.1 |
Integral Int8 | Since: base-2.1 |
Integral Word16 | Since: base-2.1 |
Integral Word32 | Since: base-2.1 |
Integral Word64 | Since: base-2.1 |
Integral Word8 | Since: base-2.1 |
Integral Integer | Since: base-2.0.1 |
Defined in GHC.Real | |
Integral Natural | Since: base-4.8.0.0 |
Defined in GHC.Real | |
Integral Int | Since: base-2.0.1 |
Integral Word | Since: base-2.1 |
Integral a => Integral (Identity a) | Since: base-4.9.0.0 |
Defined in Data.Functor.Identity quot :: Identity a -> Identity a -> Identity a # rem :: Identity a -> Identity a -> Identity a # div :: Identity a -> Identity a -> Identity a # mod :: Identity a -> Identity a -> Identity a # quotRem :: Identity a -> Identity a -> (Identity a, Identity a) # divMod :: Identity a -> Identity a -> (Identity a, Identity a) # | |
Integral a => Integral (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const |
class (Num a, Ord a) => Real a where #
toRational :: a -> Rational #
the rational equivalent of its real argument with full precision
Instances
class (Real a, Fractional a) => RealFrac a where #
Extracting components of fractions.
properFraction :: Integral b => a -> (b, a) #
The function properFraction
takes a real fractional number x
and returns a pair (n,f)
such that x = n+f
, and:
n
is an integral number with the same sign asx
; andf
is a fraction with the same type and sign asx
, and with absolute value less than1
.
The default definitions of the ceiling
, floor
, truncate
and round
functions are in terms of properFraction
.
truncate :: Integral b => a -> b #
returns the integer nearest truncate
xx
between zero and x
round :: Integral b => a -> b #
returns the nearest integer to round
xx
;
the even integer if x
is equidistant between two integers
ceiling :: Integral b => a -> b #
returns the least integer not less than ceiling
xx
floor :: Integral b => a -> b #
returns the greatest integer not greater than floor
xx
Rational numbers, with numerator and denominator of some Integral
type.
Note that Ratio
's instances inherit the deficiencies from the type
parameter's. For example, Ratio Natural
's Num
instance has similar
problems to Natural
's.
Instances
Integral a => Lift (Ratio a :: Type) | |
Integral a => Enum (Ratio a) | Since: base-2.0.1 |
Integral a => Num (Ratio a) | Since: base-2.0.1 |
(Integral a, Read a) => Read (Ratio a) | Since: base-2.1 |
Integral a => Fractional (Ratio a) | Since: base-2.0.1 |
Integral a => Real (Ratio a) | Since: base-2.0.1 |
Defined in GHC.Real toRational :: Ratio a -> Rational # | |
Integral a => RealFrac (Ratio a) | Since: base-2.0.1 |
Show a => Show (Ratio a) | Since: base-2.0.1 |
Integral a => Default (Ratio a) | |
Defined in Data.Default.Class | |
Eq a => Eq (Ratio a) | Since: base-2.1 |
Integral a => Ord (Ratio a) | Since: base-2.0.1 |
Extract the numerator of the ratio in reduced form: the numerator and denominator have no common factor and the denominator is positive.
lcm :: Integral a => a -> a -> a #
is the smallest positive integer that both lcm
x yx
and y
divide.
gcd :: Integral a => a -> a -> a #
is the non-negative factor of both gcd
x yx
and y
of which
every common factor of x
and y
is also a factor; for example
, gcd
4 2 = 2
, gcd
(-4) 6 = 2
= gcd
0 44
.
= gcd
0 00
.
(That is, the common divisor that is "greatest" in the divisibility
preordering.)
Note: Since for signed fixed-width integer types,
,
the result may be negative if one of the arguments is abs
minBound
< 0
(and
necessarily is if the other is minBound
0
or
) for such types.minBound
denominator :: Ratio a -> a #
Extract the denominator of the ratio in reduced form: the numerator and denominator have no common factor and the denominator is positive.
(^^) :: (Fractional a, Integral b) => a -> b -> a infixr 8 #
raise a number to an integral power
Conversion of values to readable String
s.
Derived instances of Show
have the following properties, which
are compatible with derived instances of Read
:
- The result of
show
is a syntactically correct Haskell expression containing only constants, given the fixity declarations in force at the point where the type is declared. It contains only the constructor names defined in the data type, parentheses, and spaces. When labelled constructor fields are used, braces, commas, field names, and equal signs are also used. - If the constructor is defined to be an infix operator, then
showsPrec
will produce infix applications of the constructor. - the representation will be enclosed in parentheses if the
precedence of the top-level constructor in
x
is less thand
(associativity is ignored). Thus, ifd
is0
then the result is never surrounded in parentheses; ifd
is11
it is always surrounded in parentheses, unless it is an atomic expression. - If the constructor is defined using record syntax, then
show
will produce the record-syntax form, with the fields given in the same order as the original declaration.
For example, given the declarations
infixr 5 :^: data Tree a = Leaf a | Tree a :^: Tree a
the derived instance of Show
is equivalent to
instance (Show a) => Show (Tree a) where showsPrec d (Leaf m) = showParen (d > app_prec) $ showString "Leaf " . showsPrec (app_prec+1) m where app_prec = 10 showsPrec d (u :^: v) = showParen (d > up_prec) $ showsPrec (up_prec+1) u . showString " :^: " . showsPrec (up_prec+1) v where up_prec = 5
Note that right-associativity of :^:
is ignored. For example,
produces the stringshow
(Leaf 1 :^: Leaf 2 :^: Leaf 3)"Leaf 1 :^: (Leaf 2 :^: Leaf 3)"
.
Instances
withFrozenCallStack :: HasCallStack => (HasCallStack => a) -> a #
Perform some computation without adding new entries to the CallStack
.
Since: base-4.9.0.0
type HasCallStack = ?callStack :: CallStack #
Request a CallStack.
NOTE: The implicit parameter ?callStack :: CallStack
is an
implementation detail and should not be considered part of the
CallStack
API, we may decide to change the implementation in the
future.
Since: base-4.9.0.0
This class gives the integer associated with a type-level natural. There are instances of the class for every concrete literal: 0, 1, 2, etc.
Since: base-4.7.0.0
natSing
class KnownSymbol (n :: Symbol) #
This class gives the string associated with a type-level symbol. There are instances of the class for every concrete literal: "hello", etc.
Since: base-4.7.0.0
symbolSing
Natural number
Invariant: numbers <= 0xffffffffffffffff use the NS
constructor
Instances
type family TypeError (a :: ErrorMessage) :: b where ... #
The type-level equivalent of error
.
The polymorphic kind of this type allows it to be used in several settings. For instance, it can be used as a constraint, e.g. to provide a better error message for a non-existent instance,
-- in a context
instance TypeError (Text "Cannot Show
functions." :$$:
Text "Perhaps there is a missing argument?")
=> Show (a -> b) where
showsPrec = error "unreachable"
It can also be placed on the right-hand side of a type-level function to provide an error for an invalid case,
type family ByteSize x where ByteSize Word16 = 2 ByteSize Word8 = 1 ByteSize a = TypeError (Text "The type " :<>: ShowType a :<>: Text " is not exportable.")
Since: base-4.9.0.0
type family AppendSymbol (a :: Symbol) (b :: Symbol) :: Symbol where ... #
Concatenation of type-level symbols.
Since: base-4.10.0.0
(Kind) This is the kind of type-level symbols. Declared here because class IP needs it
Instances
SingKind Symbol | Since: base-4.9.0.0 |
Defined in GHC.Generics type DemoteRep Symbol | |
KnownSymbol a => SingI (a :: Symbol) | Since: base-4.9.0.0 |
Defined in GHC.Generics sing :: Sing a | |
type DemoteRep Symbol | |
Defined in GHC.Generics | |
data Sing (s :: Symbol) | |
Defined in GHC.Generics | |
type Compare (a :: Symbol) (b :: Symbol) | |
Defined in Data.Type.Ord |
type family (a :: Natural) + (b :: Natural) :: Natural where ... infixl 6 #
Addition of type-level naturals.
Since: base-4.7.0.0
type family (a :: Natural) * (b :: Natural) :: Natural where ... infixl 7 #
Multiplication of type-level naturals.
Since: base-4.7.0.0
type family (a :: Natural) ^ (b :: Natural) :: Natural where ... infixr 8 #
Exponentiation of type-level naturals.
Since: base-4.7.0.0
type family (a :: Natural) - (b :: Natural) :: Natural where ... infixl 6 #
Subtraction of type-level naturals.
Since: base-4.7.0.0
type family CmpSymbol (a :: Symbol) (b :: Symbol) :: Ordering where ... #
Comparison of type-level symbols, as a function.
Since: base-4.7.0.0
type family CmpNat (a :: Natural) (b :: Natural) :: Ordering where ... #
Comparison of type-level naturals, as a function.
Since: base-4.7.0.0
type family CmpChar (a :: Char) (b :: Char) :: Ordering where ... #
Comparison of type-level characters.
Since: base-4.16.0.0
type family Div (a :: Natural) (b :: Natural) :: Natural where ... infixl 7 #
Division (round down) of natural numbers.
Div x 0
is undefined (i.e., it cannot be reduced).
Since: base-4.11.0.0
type family Mod (a :: Natural) (b :: Natural) :: Natural where ... infixl 7 #
Modulus of natural numbers.
Mod x 0
is undefined (i.e., it cannot be reduced).
Since: base-4.11.0.0
type family Log2 (a :: Natural) :: Natural where ... #
Log base 2 (round down) of natural numbers.
Log 0
is undefined (i.e., it cannot be reduced).
Since: base-4.11.0.0
type family ConsSymbol (a :: Char) (b :: Symbol) :: Symbol where ... #
Extending a type-level symbol with a type-level character
Since: base-4.16.0.0
type family CharToNat (a :: Char) :: Natural where ... #
Convert a character to its Unicode code point (cf. ord
)
Since: base-4.16.0.0
type family NatToChar (a :: Natural) :: Char where ... #
Convert a Unicode code point to a character (cf. chr
)
Since: base-4.16.0.0
data SomeSymbol #
This type represents unknown type-level symbols.
KnownSymbol n => SomeSymbol (Proxy n) | Since: base-4.7.0.0 |
Instances
Read SomeSymbol | Since: base-4.7.0.0 |
Defined in GHC.TypeLits readsPrec :: Int -> ReadS SomeSymbol # readList :: ReadS [SomeSymbol] # readPrec :: ReadPrec SomeSymbol # readListPrec :: ReadPrec [SomeSymbol] # | |
Show SomeSymbol | Since: base-4.7.0.0 |
Defined in GHC.TypeLits showsPrec :: Int -> SomeSymbol -> ShowS # show :: SomeSymbol -> String # showList :: [SomeSymbol] -> ShowS # | |
Eq SomeSymbol | Since: base-4.7.0.0 |
Defined in GHC.TypeLits (==) :: SomeSymbol -> SomeSymbol -> Bool # (/=) :: SomeSymbol -> SomeSymbol -> Bool # | |
Ord SomeSymbol | Since: base-4.7.0.0 |
Defined in GHC.TypeLits compare :: SomeSymbol -> SomeSymbol -> Ordering # (<) :: SomeSymbol -> SomeSymbol -> Bool # (<=) :: SomeSymbol -> SomeSymbol -> Bool # (>) :: SomeSymbol -> SomeSymbol -> Bool # (>=) :: SomeSymbol -> SomeSymbol -> Bool # max :: SomeSymbol -> SomeSymbol -> SomeSymbol # min :: SomeSymbol -> SomeSymbol -> SomeSymbol # |
pattern ShowType :: t -> ErrorMessage #
Pretty print the type.
ShowType :: k -> ErrorMessage
pattern (:<>:) :: ErrorMessage -> ErrorMessage -> ErrorMessage infixl 6 #
Put two pieces of error message next to each other.
pattern (:$$:) :: ErrorMessage -> ErrorMessage -> ErrorMessage infixl 5 #
Stack two pieces of error message on top of each other.
symbolVal' :: forall (n :: Symbol). KnownSymbol n => Proxy# n -> String #
Since: base-4.8.0.0
symbolVal :: forall (n :: Symbol) proxy. KnownSymbol n => proxy n -> String #
Since: base-4.7.0.0
someSymbolVal :: String -> SomeSymbol #
Convert a string into an unknown type-level symbol.
Since: base-4.7.0.0
someNatVal :: Integer -> Maybe SomeNat #
Convert an integer into an unknown type-level natural.
Since: base-4.7.0.0
someCharVal :: Char -> SomeChar #
Convert a character into an unknown type-level char.
Since: base-4.16.0.0
sameSymbol :: forall (a :: Symbol) (b :: Symbol) proxy1 proxy2. (KnownSymbol a, KnownSymbol b) => proxy1 a -> proxy2 b -> Maybe (a :~: b) #
We either get evidence that this function was instantiated with the
same type-level symbols, or Nothing
.
Since: base-4.7.0.0
sameChar :: forall (a :: Char) (b :: Char) proxy1 proxy2. (KnownChar a, KnownChar b) => proxy1 a -> proxy2 b -> Maybe (a :~: b) #
We either get evidence that this function was instantiated with the
same type-level characters, or Nothing
.
Since: base-4.16.0.0
cmpSymbol :: forall (a :: Symbol) (b :: Symbol) proxy1 proxy2. (KnownSymbol a, KnownSymbol b) => proxy1 a -> proxy2 b -> OrderingI a b #
Like sameSymbol
, but if the symbols aren't equal, this additionally
provides proof of LT or GT.
Since: base-4.16.0.0
cmpChar :: forall (a :: Char) (b :: Char) proxy1 proxy2. (KnownChar a, KnownChar b) => proxy1 a -> proxy2 b -> OrderingI a b #
Like sameChar
, but if the Chars aren't equal, this additionally
provides proof of LT or GT.
Since: base-4.16.0.0
This type represents unknown type-level natural numbers.
Since: base-4.10.0.0
A type synonym for Natural
.
Prevously, this was an opaque data type, but it was changed to a type synonym.
Since: base-4.16.0.0
sameNat :: forall (a :: Nat) (b :: Nat) proxy1 proxy2. (KnownNat a, KnownNat b) => proxy1 a -> proxy2 b -> Maybe (a :~: b) #
We either get evidence that this function was instantiated with the
same type-level numbers, or Nothing
.
Since: base-4.7.0.0
cmpNat :: forall (a :: Nat) (b :: Nat) proxy1 proxy2. (KnownNat a, KnownNat b) => proxy1 a -> proxy2 b -> OrderingI a b #
Like sameNat
, but if the numbers aren't equal, this additionally
provides proof of LT or GT.
Since: base-4.16.0.0
data OrderingI (a :: k) (b :: k) where #
Ordering data type for type literals that provides proof of their ordering.
Since: base-4.16.0.0
LTI :: forall {k} (a :: k) (b :: k). Compare a b ~ 'LT => OrderingI a b | |
EQI :: forall {k} (a :: k). Compare a a ~ 'EQ => OrderingI a a | |
GTI :: forall {k} (a :: k) (b :: k). Compare a b ~ 'GT => OrderingI a b |
type (<=?) (m :: k) (n :: k) = OrdCond (Compare m n) 'True 'True 'False infix 4 #
Comparison (<=) of comparable types, as a function.
Since: base-4.16.0.0
type (<=) (x :: k) (y :: k) = (x <=? y) ~ 'True infix 4 #
Comparison (<=) of comparable types, as a constraint.
Since: base-4.16.0.0
module Incipit.Fixed
module Incipit.Foldable
module Incipit.Fractional
rem :: Integral a => a -> a -> Maybe a Source #
integer remainder, satisfying
(x `quot` y)*y + (x `rem` y) == x
mod :: Integral a => a -> a -> Maybe a Source #
integer modulus, satisfying
(x `div` y)*y + (x `mod` y) == x
Natural number
Invariant: numbers <= 0xffffffffffffffff use the NS
constructor
Instances
print :: Show a => a -> IO () #
The print
function outputs a value of any printable type to the
standard output device.
Printable types are those that are instances of class Show
; print
converts values to strings for output using the show
operation and
adds a newline.
For example, a program to print the first 20 integers and their powers of 2 could be written as:
main = print ([(n, 2^n) | n <- [0..19]])
A value of type
is a computation which, when performed,
does some I/O before returning a value of type IO
aa
.
There is really only one way to "perform" an I/O action: bind it to
Main.main
in your program. When your program is run, the I/O will
be performed. It isn't possible to perform I/O from an arbitrary
function, unless that function is itself in the IO
monad and called
at some point, directly or indirectly, from Main.main
.
IO
is a monad, so IO
actions can be combined using either the do-notation
or the >>
and >>=
operations from the Monad
class.
Instances
File and directory names are values of type String
, whose precise
meaning is operating system dependent. Files can be opened, yielding a
handle which can then be used to operate on the contents of that file.
:: Show a | |
=> Int | the operator precedence of the enclosing
context (a number from |
-> a | the value to be converted to a |
-> ShowS |
showString :: String -> ShowS #
utility function converting a String
to a show function that
simply prepends the string unchanged.