| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
RIO
- module RIO.Logger
- module UnliftIO
- mapLeft :: (a1 -> a2) -> Either a1 b -> Either a2 b
- withLazyFile :: MonadUnliftIO m => FilePath -> (ByteString -> m a) -> m a
- fromFirst :: a -> First a -> a
- mapMaybeA :: Applicative f => (a -> f (Maybe b)) -> [a] -> f [b]
- mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]
- forMaybeA :: Applicative f => [a] -> (a -> f (Maybe b)) -> f [b]
- forMaybeM :: Monad m => [a] -> (a -> m (Maybe b)) -> m [b]
- stripCR :: Text -> Text
- newtype RIO env a = RIO {}
- runRIO :: MonadIO m => env -> RIO env a -> m a
- liftRIO :: (MonadIO m, MonadReader env m) => RIO env a -> m a
- tshow :: Show a => a -> Text
- nubOrd :: Ord a => [a] -> [a]
- readFileBinary :: MonadIO m => FilePath -> m ByteString
- writeFileBinary :: MonadIO m => FilePath -> ByteString -> m ()
- data ReadFileUtf8Exception = ReadFileUtf8Exception !FilePath !UnicodeException
- readFileUtf8 :: MonadIO m => FilePath -> m Text
- writeFileUtf8 :: MonadIO m => FilePath -> Text -> m ()
- type LByteString = ByteString
- toStrictBytes :: LByteString -> ByteString
- fromStrictBytes :: ByteString -> LByteString
- decodeUtf8Lenient :: ByteString -> Text
- type LText = Text
- view :: MonadReader s m => Getting a s a -> m a
- type UVector = Vector
- type SVector = Vector
- type GVector = Vector
- newtype DisplayBuilder = DisplayBuilder {}
- class Display a where
- displayShow :: Show a => a -> DisplayBuilder
- displayBuilderToText :: DisplayBuilder -> Text
- displayBytesUtf8 :: ByteString -> DisplayBuilder
- writeFileDisplayBuilder :: MonadIO m => FilePath -> DisplayBuilder -> m ()
- hPutBuilder :: MonadIO m => Handle -> Builder -> m ()
- sappend :: Semigroup s => s -> s -> s
- class Applicative f => Alternative (f :: * -> *) where
- class Functor f => Applicative (f :: * -> *) where
- liftA :: Applicative f => (a -> b) -> f a -> f b
- liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
- many :: Alternative f => forall a. f a -> f [a]
- optional :: Alternative f => f a -> f (Maybe a)
- some :: Alternative f => forall a. f a -> f [a]
- (<|>) :: Alternative f => forall a. f a -> f a -> f a
- first :: Arrow a => forall b c d. a b c -> a (b, d) (c, d)
- second :: Arrow a => forall b c d. a b c -> a (d, b) (d, c)
- (&&&) :: Arrow a => forall b c c'. a b c -> a b c' -> a b (c, c')
- (***) :: Arrow a => forall b c b' c'. a b c -> a b' c' -> a (b, b') (c, c')
- class NFData a where
- force :: NFData a => a -> a
- ($!!) :: NFData a => (a -> b) -> a -> b
- class Applicative m => Monad (m :: * -> *) where
- class (Alternative m, Monad m) => MonadPlus (m :: * -> *) where
- filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a]
- foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b
- foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m ()
- forever :: Applicative f => f a -> f b
- guard :: Alternative f => Bool -> f ()
- join :: Monad m => m (m a) -> m a
- liftM :: Monad m => (a1 -> r) -> m a1 -> m r
- liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
- replicateM_ :: Applicative m => Int -> m a -> m ()
- unless :: Applicative f => Bool -> f () -> f ()
- when :: Applicative f => Bool -> f () -> f ()
- zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c]
- zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m ()
- (<$!>) :: Monad m => (a -> b) -> m a -> m b
- (<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c
- (=<<) :: Monad m => (a -> m b) -> m a -> m b
- (>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c
- class Monad m => MonadThrow (m :: * -> *) where
- class Monad m => MonadReader r (m :: * -> *) | m -> r where
- class MonadTrans (t :: (* -> *) -> * -> *) where
- newtype ReaderT k r (m :: k -> *) (a :: k) :: forall k. * -> (k -> *) -> k -> * = ReaderT {
- runReaderT :: r -> m a
- ask :: MonadReader r m => m r
- asks :: MonadReader r m => (r -> a) -> m a
- local :: MonadReader r m => forall a. (r -> r) -> m a -> m a
- data Bool :: *
- not :: Bool -> Bool
- otherwise :: Bool
- (&&) :: Bool -> Bool -> Bool
- (||) :: Bool -> Bool -> Bool
- data ByteString :: *
- data Builder :: *
- data ShortByteString :: *
- toShort :: ByteString -> ShortByteString
- fromShort :: ShortByteString -> ByteString
- data Char :: *
- class Typeable * a => Data a where
- data Either a b :: * -> * -> *
- either :: (a -> c) -> (b -> c) -> Either a b -> c
- isLeft :: Either a b -> Bool
- isRight :: Either a b -> Bool
- lefts :: [Either a b] -> [a]
- partitionEithers :: [Either a b] -> ([a], [b])
- rights :: [Either a b] -> [b]
- class Eq a where
- class Foldable (t :: * -> *) where
- all :: Foldable t => (a -> Bool) -> t a -> Bool
- and :: Foldable t => t Bool -> Bool
- any :: Foldable t => (a -> Bool) -> t a -> Bool
- asum :: (Foldable t, Alternative f) => t (f a) -> f a
- concat :: Foldable t => t [a] -> [a]
- concatMap :: Foldable t => (a -> [b]) -> t a -> [b]
- elem :: Foldable t => forall a. Eq a => a -> t a -> Bool
- fold :: Foldable t => forall m. Monoid m => t m -> m
- foldMap :: Foldable t => forall m a. Monoid m => (a -> m) -> t a -> m
- foldl' :: Foldable t => forall b a. (b -> a -> b) -> b -> t a -> b
- foldr :: Foldable t => forall a b. (a -> b -> b) -> b -> t a -> b
- forM_ :: (Foldable t, Monad m) => t a -> (a -> m b) -> m ()
- for_ :: (Foldable t, Applicative f) => t a -> (a -> f b) -> f ()
- length :: Foldable t => forall a. t a -> Int
- mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()
- msum :: (Foldable t, MonadPlus m) => t (m a) -> m a
- notElem :: (Foldable t, Eq a) => a -> t a -> Bool
- null :: Foldable t => forall a. t a -> Bool
- or :: Foldable t => t Bool -> Bool
- product :: Foldable t => forall a. Num a => t a -> a
- sequenceA_ :: (Foldable t, Applicative f) => t (f a) -> f ()
- sequence_ :: (Foldable t, Monad m) => t (m a) -> m ()
- sum :: Foldable t => forall a. Num a => t a -> a
- toList :: Foldable t => forall a. t a -> [a]
- traverse_ :: (Foldable t, Applicative f) => (a -> f b) -> t a -> f ()
- const :: a -> b -> a
- fix :: (a -> a) -> a
- flip :: (a -> b -> c) -> b -> a -> c
- id :: a -> a
- on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
- ($) :: (a -> b) -> a -> b
- (&) :: a -> (a -> b) -> b
- (.) :: (b -> c) -> (a -> b) -> a -> c
- class Functor (f :: * -> *) where
- void :: Functor f => f a -> f ()
- ($>) :: Functor f => f a -> b -> f b
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- class Hashable a
- data HashMap k v :: * -> * -> *
- data HashSet a :: * -> *
- data Int :: *
- data Int8 :: *
- data Int16 :: *
- data Int32 :: *
- data Int64 :: *
- data IntMap a :: * -> *
- data IntSet :: *
- break :: (a -> Bool) -> [a] -> ([a], [a])
- drop :: Int -> [a] -> [a]
- dropWhile :: (a -> Bool) -> [a] -> [a]
- filter :: (a -> Bool) -> [a] -> [a]
- lines :: String -> [String]
- lookup :: Eq a => a -> [(a, b)] -> Maybe b
- map :: (a -> b) -> [a] -> [b]
- replicate :: Int -> a -> [a]
- reverse :: [a] -> [a]
- span :: (a -> Bool) -> [a] -> ([a], [a])
- take :: Int -> [a] -> [a]
- takeWhile :: (a -> Bool) -> [a] -> [a]
- unlines :: [String] -> String
- unwords :: [String] -> String
- words :: String -> [String]
- zip :: [a] -> [b] -> [(a, b)]
- (++) :: [a] -> [a] -> [a]
- data Map k a :: * -> * -> *
- data Maybe a :: * -> *
- catMaybes :: [Maybe a] -> [a]
- fromMaybe :: a -> Maybe a -> a
- isJust :: Maybe a -> Bool
- isNothing :: Maybe a -> Bool
- listToMaybe :: [a] -> Maybe a
- mapMaybe :: (a -> Maybe b) -> [a] -> [b]
- maybe :: b -> (a -> b) -> Maybe a -> b
- maybeToList :: Maybe a -> [a]
- newtype All :: * = All {}
- newtype Any :: * = Any {}
- newtype Endo a :: * -> * = Endo {
- appEndo :: a -> a
- newtype First a :: * -> * = First {}
- newtype Last a :: * -> * = Last {}
- class Monoid a where
- newtype Product a :: * -> * = Product {
- getProduct :: a
- newtype Sum a :: * -> * = Sum {
- getSum :: a
- (<>) :: Monoid m => m -> m -> m
- class Eq a => Ord a where
- data Ordering :: *
- comparing :: Ord a => (b -> a) -> b -> b -> Ordering
- class Semigroup a
- data Set a :: * -> *
- class IsString a where
- data Text :: *
- decodeUtf8' :: ByteString -> Either UnicodeException Text
- decodeUtf8With :: OnDecodeError -> ByteString -> Text
- encodeUtf8 :: Text -> ByteString
- encodeUtf8Builder :: Text -> Builder
- data UnicodeException :: *
- = DecodeError String (Maybe Word8)
- | EncodeError String (Maybe Char)
- lenientDecode :: OnDecodeError
- class (Functor t, Foldable t) => Traversable (t :: * -> *) where
- for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b)
- forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)
- data Vector a :: * -> *
- data Void :: *
- absurd :: Void -> a
- data Word :: *
- data Word8 :: *
- data Word16 :: *
- data Word32 :: *
- data Word64 :: *
- byteSwap16 :: Word16 -> Word16
- byteSwap32 :: Word32 -> Word32
- byteSwap64 :: Word64 -> Word64
- class Storable a
- class Generic a
- type HasCallStack = ?callStack :: CallStack
- type ASetter s t a b = (a -> Identity b) -> s -> Identity t
- type ASetter' s a = ASetter s s a a
- type Getting r s a = (a -> Const * r a) -> s -> Const * r s
- type Lens s t a b = forall (f :: * -> *). Functor f => (a -> f b) -> s -> f t
- type Lens' s a = Lens s s a a
- type SimpleGetter s a = forall r. Getting r s a
- lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b
- over :: ASetter s t a b -> (a -> b) -> s -> t
- set :: ASetter s t a b -> b -> s -> t
- sets :: ((a -> b) -> s -> t) -> ASetter s t a b
- to :: (s -> a) -> SimpleGetter s a
- (^.) :: s -> Getting a s a -> a
- class Bounded a where
- data Double :: *
- class Enum a
- type FilePath = String
- data Float :: *
- class Fractional a => Floating a where
- class Num a => Fractional a where
- data IO a :: * -> *
- data Integer :: *
- class (Real a, Enum a) => Integral a where
- class Num a where
- type Rational = Ratio Integer
- class (Num a, Ord a) => Real a where
- class (RealFrac a, Floating a) => RealFloat a where
- class (Real a, Fractional a) => RealFrac a where
- class Show a where
- type String = [Char]
- asTypeOf :: a -> a -> a
- curry :: ((a, b) -> c) -> a -> b -> c
- error :: HasCallStack => [Char] -> a
- even :: Integral a => a -> Bool
- fromIntegral :: (Integral a, Num b) => a -> b
- fst :: (a, b) -> a
- gcd :: Integral a => a -> a -> a
- lcm :: Integral a => a -> a -> a
- odd :: Integral a => a -> Bool
- realToFrac :: (Real a, Fractional b) => a -> b
- seq :: a -> b -> b
- show :: Show a => a -> String
- snd :: (a, b) -> b
- subtract :: Num a => a -> a -> a
- uncurry :: (a -> b -> c) -> (a, b) -> c
- undefined :: HasCallStack => a
- ($!) :: (a -> b) -> a -> b
- (^) :: (Num a, Integral b) => a -> b -> a
- (^^) :: (Fractional a, Integral b) => a -> b -> a
- data ExitCode :: *
- class Read a
- readMaybe :: Read a => String -> Maybe a
Documentation
module RIO.Logger
module UnliftIO
withLazyFile :: MonadUnliftIO m => FilePath -> (ByteString -> m a) -> m a Source #
Lazily get the contents of a file. Unlike readFile, this
ensures that if an exception is thrown, the file handle is closed
immediately.
mapMaybeA :: Applicative f => (a -> f (Maybe b)) -> [a] -> f [b] Source #
Applicative mapMaybe.
forMaybeA :: Applicative f => [a] -> (a -> f (Maybe b)) -> f [b] Source #
The Reader+IO monad. This is different from a ReaderT because:
- It's not a transformer, it hardcodes IO for simpler usage and error messages.
- Instances of typeclasses like
MonadLoggerare implemented using classes defined on the environment, instead of using an underlying monad.
readFileBinary :: MonadIO m => FilePath -> m ByteString Source #
writeFileBinary :: MonadIO m => FilePath -> ByteString -> m () Source #
data ReadFileUtf8Exception Source #
Constructors
| ReadFileUtf8Exception !FilePath !UnicodeException |
readFileUtf8 :: MonadIO m => FilePath -> m Text Source #
Read a file in UTF8 encoding, throwing an exception on invalid character encoding.
type LByteString = ByteString Source #
decodeUtf8Lenient :: ByteString -> Text Source #
view :: MonadReader s m => Getting a s a -> m a Source #
newtype DisplayBuilder Source #
Constructors
| DisplayBuilder | |
Fields | |
class Display a where Source #
Minimal complete definition
Methods
display :: a -> DisplayBuilder Source #
displayShow :: Show a => a -> DisplayBuilder Source #
writeFileDisplayBuilder :: MonadIO m => FilePath -> DisplayBuilder -> m () Source #
class Applicative f => Alternative (f :: * -> *) where #
A monoid on applicative functors.
If defined, some and many should be the least solutions
of the equations:
Methods
(<|>) :: f a -> f a -> f a infixl 3 #
An associative binary operation
One or more.
Zero or more.
Instances
class Functor f => Applicative (f :: * -> *) 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 idliftA2 f x y = f <$> x <*> y
Further, any definition must satisfy the following:
- identity
pureid<*>v = v- composition
pure(.)<*>u<*>v<*>w = u<*>(v<*>w)- homomorphism
puref<*>purex =pure(f x)- interchange
u
<*>purey =pure($y)<*>u
The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:
As a consequence of these laws, the Functor instance for f will satisfy
It may be useful to note that supposing
forall x y. p (q x y) = f x . g y
it follows from the above that
liftA2p (liftA2q u v) =liftA2f u .liftA2g v
If f is also a Monad, it should satisfy
(which implies that pure and <*> satisfy the applicative functor laws).
Methods
Lift a value.
(<*>) :: f (a -> b) -> f a -> f b infixl 4 #
Sequential application.
A few functors support an implementation of <*> that is more
efficient than the default one.
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 <*>.
(*>) :: f a -> f b -> f b infixl 4 #
Sequence actions, discarding the value of the first argument.
(<*) :: f a -> f b -> f a infixl 4 #
Sequence actions, discarding the value of the second argument.
Instances
| Applicative [] | Since: 2.1 |
| Applicative Maybe | Since: 2.1 |
| Applicative IO | Since: 2.1 |
| Applicative Par1 | Since: 4.9.0.0 |
| Applicative Q | |
| Applicative P | Since: 4.5.0.0 |
| Applicative Complex | Since: 4.9.0.0 |
| Applicative Min | Since: 4.9.0.0 |
| Applicative Max | Since: 4.9.0.0 |
| Applicative First | Since: 4.9.0.0 |
| Applicative Last | Since: 4.9.0.0 |
| Applicative Option | Since: 4.9.0.0 |
| Applicative NonEmpty | Since: 4.9.0.0 |
| Applicative ZipList | f '<$>' 'ZipList' xs1 '<*>' ... '<*>' 'ZipList' xsN
|
| Applicative Identity | Since: 4.8.0.0 |
| Applicative STM | Since: 4.8.0.0 |
| Applicative Dual | Since: 4.8.0.0 |
| Applicative Sum | Since: 4.8.0.0 |
| Applicative Product | Since: 4.8.0.0 |
| Applicative First | |
| Applicative Last | |
| Applicative ReadPrec | Since: 4.6.0.0 |
| Applicative ReadP | Since: 4.6.0.0 |
| Applicative Put | |
| Applicative Tree | |
| Applicative Seq | |
| Applicative Array | |
| Applicative Cleanup | |
| Applicative Vector | |
| Applicative Id | |
| Applicative Box | |
| Applicative (Either e) | Since: 3.0 |
| Applicative (U1 *) | Since: 4.9.0.0 |
| Monoid a => Applicative ((,) a) | For tuples, the ("hello ", (+15)) <*> ("world!", 2002)
("hello world!",2017)Since: 2.1 |
| Monad m => Applicative (WrappedMonad m) | Since: 2.1 |
| Arrow a => Applicative (ArrowMonad a) | Since: 4.6.0.0 |
| Applicative (Proxy *) | Since: 4.7.0.0 |
| Applicative (State s) | |
| Applicative m => Applicative (ListT m) | |
| (Functor m, Monad m) => Applicative (MaybeT m) | |
| Applicative (RIO env) # | |
| Applicative f => Applicative (Rec1 * f) | Since: 4.9.0.0 |
| Arrow a => Applicative (WrappedArrow a b) | Since: 2.1 |
| Monoid m => Applicative (Const * m) | Since: 2.0.1 |
| Applicative f => Applicative (Alt * f) | |
| (Applicative f, Monad f) => Applicative (WhenMissing f x) | Equivalent to |
| Applicative (Bazaar a b) | |
| (Functor m, Monad m) => Applicative (StateT s m) | |
| (Functor m, Monad m) => Applicative (ErrorT e m) | |
| (Functor m, Monad m) => Applicative (ExceptT e m) | |
| (Functor m, Monad m) => Applicative (StateT s m) | |
| (Functor m, Monad m) => Applicative (StateT s m) | |
| (Monoid w, Applicative m) => Applicative (WriterT w m) | |
| (Monoid w, Applicative m) => Applicative (WriterT w m) | |
| Applicative m => Applicative (IdentityT * m) | |
| Applicative ((->) LiftedRep LiftedRep a) | Since: 2.1 |
| (Applicative f, Applicative g) => Applicative ((:*:) * f g) | Since: 4.9.0.0 |
| (Applicative f, Applicative g) => Applicative (Product * f g) | Since: 4.9.0.0 |
| (Monad f, Applicative f) => Applicative (WhenMatched f x y) | Equivalent to |
| (Applicative f, Monad f) => Applicative (WhenMissing f k x) | Equivalent to |
| Applicative (ContT k r m) | |
| Applicative m => Applicative (ReaderT * r m) | |
| Applicative f => Applicative (M1 * i c f) | Since: 4.9.0.0 |
| (Applicative f, Applicative g) => Applicative ((:.:) * * f g) | Since: 4.9.0.0 |
| (Applicative f, Applicative g) => Applicative (Compose * * f g) | Since: 4.9.0.0 |
| (Monad f, Applicative f) => Applicative (WhenMatched f k x y) | Equivalent to |
| (Monoid w, Functor m, Monad m) => Applicative (RWST r w s m) | |
| (Monoid w, Functor m, Monad m) => Applicative (RWST r w s m) | |
liftA :: Applicative f => (a -> b) -> f a -> f b #
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d #
Lift a ternary function to actions.
many :: Alternative f => forall a. f a -> f [a] #
Zero or more.
optional :: Alternative f => f a -> f (Maybe a) #
One or none.
some :: Alternative f => forall a. f a -> f [a] #
One or more.
(<|>) :: Alternative f => forall a. f a -> f a -> f a infixl 3 #
An associative binary operation
first :: Arrow a => forall b c d. a b c -> a (b, d) (c, d) #
Send the first component of the input through the argument arrow, and copy the rest unchanged to the output.
second :: Arrow a => forall b c d. a b c -> a (d, b) (d, c) #
A mirror image of first.
The default definition may be overridden with a more efficient version if desired.
(&&&) :: Arrow a => forall b c c'. 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.
(***) :: Arrow a => forall b c b' c'. a b c -> a b' c' -> a (b, b') (c, c') infixr 3 #
Split the input between the two argument arrows and combine their output. Note that this is in general not a functor.
The default definition may be overridden with a more efficient version if desired.
A class of types that can be fully evaluated.
Since: 1.1.0.0
Methods
rnf should reduce its argument to normal form (that is, fully
evaluate all sub-components), and then return '()'.
Generic NFData deriving
Starting with GHC 7.2, you can automatically derive instances
for types possessing a Generic instance.
Note: Generic1 can be auto-derived starting with GHC 7.4
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics (Generic, Generic1)
import Control.DeepSeq
data Foo a = Foo a String
deriving (Eq, Generic, Generic1)
instance NFData a => NFData (Foo a)
instance NFData1 Foo
data Colour = Red | Green | Blue
deriving Generic
instance NFData ColourStarting with GHC 7.10, the example above can be written more
concisely by enabling the new DeriveAnyClass extension:
{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-}
import GHC.Generics (Generic)
import Control.DeepSeq
data Foo a = Foo a String
deriving (Eq, Generic, Generic1, NFData, NFData1)
data Colour = Red | Green | Blue
deriving (Generic, NFData)
Compatibility with previous deepseq versions
Prior to version 1.4.0.0, the default implementation of the rnf
method was defined as
rnfa =seqa ()
However, starting with deepseq-1.4.0.0, the default
implementation is based on DefaultSignatures allowing for
more accurate auto-derived NFData instances. If you need the
previously used exact default rnf method implementation
semantics, use
instance NFData Colour where rnf x = seq x ()
or alternatively
instance NFData Colour where rnf = rwhnf
or
{-# LANGUAGE BangPatterns #-}
instance NFData Colour where rnf !_ = ()Instances
| NFData Bool | |
| NFData Char | |
| NFData Double | |
| NFData Float | |
| NFData Int | |
| NFData Int8 | |
| NFData Int16 | |
| NFData Int32 | |
| NFData Int64 | |
| NFData Integer | |
| NFData Natural | Since: 1.4.0.0 |
| NFData Ordering | |
| NFData Word | |
| NFData Word8 | |
| NFData Word16 | |
| NFData Word32 | |
| NFData Word64 | |
| NFData CallStack | Since: 1.4.2.0 |
| NFData () | |
| NFData TyCon | NOTE: Only defined for Since: 1.4.0.0 |
| NFData ThreadId | Since: 1.4.0.0 |
| NFData Void | Since: 1.4.0.0 |
| NFData Unique | Since: 1.4.0.0 |
| NFData Version | Since: 1.3.0.0 |
| NFData ExitCode | Since: 1.4.2.0 |
| NFData TypeRep | NOTE: Only defined for Since: 1.4.0.0 |
| NFData All | Since: 1.4.0.0 |
| NFData Any | Since: 1.4.0.0 |
| NFData CChar | Since: 1.4.0.0 |
| NFData CSChar | Since: 1.4.0.0 |
| NFData CUChar | Since: 1.4.0.0 |
| NFData CShort | Since: 1.4.0.0 |
| NFData CUShort | Since: 1.4.0.0 |
| NFData CInt | Since: 1.4.0.0 |
| NFData CUInt | Since: 1.4.0.0 |
| NFData CLong | Since: 1.4.0.0 |
| NFData CULong | Since: 1.4.0.0 |
| NFData CLLong | Since: 1.4.0.0 |
| NFData CULLong | Since: 1.4.0.0 |
| NFData CBool | Since: 1.4.3.0 |
| NFData CFloat | Since: 1.4.0.0 |
| NFData CDouble | Since: 1.4.0.0 |
| NFData CPtrdiff | Since: 1.4.0.0 |
| NFData CSize | Since: 1.4.0.0 |
| NFData CWchar | Since: 1.4.0.0 |
| NFData CSigAtomic | Since: 1.4.0.0 |
| NFData CClock | Since: 1.4.0.0 |
| NFData CTime | Since: 1.4.0.0 |
| NFData CUSeconds | Since: 1.4.0.0 |
| NFData CSUSeconds | Since: 1.4.0.0 |
| NFData CFile | Since: 1.4.0.0 |
| NFData CFpos | Since: 1.4.0.0 |
| NFData CJmpBuf | Since: 1.4.0.0 |
| NFData CIntPtr | Since: 1.4.0.0 |
| NFData CUIntPtr | Since: 1.4.0.0 |
| NFData CIntMax | Since: 1.4.0.0 |
| NFData CUIntMax | Since: 1.4.0.0 |
| NFData Fingerprint | Since: 1.4.0.0 |
| NFData SrcLoc | Since: 1.4.2.0 |
| NFData ShortByteString | |
| NFData ByteString | |
| NFData ByteString | |
| NFData IntSet | |
| NFData UnicodeException | |
| NFData ZonedTime | |
| NFData LocalTime | |
| NFData TimeOfDay | |
| NFData TimeZone | |
| NFData UniversalTime | |
| NFData UTCTime | |
| NFData DiffTime | |
| NFData Day | |
| NFData a => NFData [a] | |
| NFData a => NFData (Maybe a) | |
| NFData a => NFData (Ratio a) | |
| NFData (Ptr a) | Since: 1.4.2.0 |
| NFData (FunPtr a) | Since: 1.4.2.0 |
| NFData a => NFData (Complex a) | |
| NFData (Fixed a) | Since: 1.3.0.0 |
| NFData a => NFData (Min a) | Since: 1.4.2.0 |
| NFData a => NFData (Max a) | Since: 1.4.2.0 |
| NFData a => NFData (First a) | Since: 1.4.2.0 |
| NFData a => NFData (Last a) | Since: 1.4.2.0 |
| NFData m => NFData (WrappedMonoid m) | Since: 1.4.2.0 |
| NFData a => NFData (Option a) | Since: 1.4.2.0 |
| NFData a => NFData (NonEmpty a) | Since: 1.4.2.0 |
| NFData (StableName a) | Since: 1.4.0.0 |
| NFData a => NFData (ZipList a) | Since: 1.4.0.0 |
| NFData a => NFData (Identity a) | Since: 1.4.0.0 |
| NFData (IORef a) | NOTE: Only strict in the reference and not the referenced value. Since: 1.4.2.0 |
| NFData a => NFData (Dual a) | Since: 1.4.0.0 |
| NFData a => NFData (Sum a) | Since: 1.4.0.0 |
| NFData a => NFData (Product a) | Since: 1.4.0.0 |
| NFData a => NFData (First a) | Since: 1.4.0.0 |
| NFData a => NFData (Last a) | Since: 1.4.0.0 |
| NFData a => NFData (Down a) | Since: 1.4.0.0 |
| NFData (MVar a) | NOTE: Only strict in the reference and not the referenced value. Since: 1.4.2.0 |
| NFData a => NFData (IntMap a) | |
| NFData a => NFData (Tree a) | |
| NFData a => NFData (Seq a) | |
| NFData a => NFData (FingerTree a) | |
| NFData a => NFData (Digit a) | |
| NFData a => NFData (Node a) | |
| NFData a => NFData (Elem a) | |
| NFData a => NFData (Set a) | |
| NFData a => NFData (Hashed a) | |
| NFData a => NFData (Array a) | |
| NFData a => NFData (HashSet a) | |
| NFData (Vector a) | |
| NFData (Vector a) | |
| NFData (Vector a) | |
| NFData a => NFData (Vector a) | |
| NFData (a -> b) | This instance is for convenience and consistency with Since: 1.3.0.0 |
| (NFData a, NFData b) => NFData (Either a b) | |
| (NFData a, NFData b) => NFData (a, b) | |
| (NFData a, NFData b) => NFData (Array a b) | |
| (NFData a, NFData b) => NFData (Arg a b) | Since: 1.4.2.0 |
| NFData (Proxy k a) | Since: 1.4.0.0 |
| NFData (STRef s a) | NOTE: Only strict in the reference and not the referenced value. Since: 1.4.2.0 |
| (NFData k, NFData a) => NFData (Map k a) | |
| (NFData k, NFData v) => NFData (Leaf k v) | |
| (NFData k, NFData v) => NFData (HashMap k v) | |
| NFData (MVector s a) | |
| NFData (MVector s a) | |
| NFData (MVector s a) | |
| (NFData a1, NFData a2, NFData a3) => NFData (a1, a2, a3) | |
| NFData a => NFData (Const k a b) | Since: 1.4.0.0 |
| NFData ((:~:) k a b) | Since: 1.4.3.0 |
| (NFData a1, NFData a2, NFData a3, NFData a4) => NFData (a1, a2, a3, a4) | |
| (NFData1 f, NFData1 g, NFData a) => NFData (Product * f g a) | Since: 1.4.3.0 |
| (NFData1 f, NFData1 g, NFData a) => NFData (Sum * f g a) | Since: 1.4.3.0 |
| NFData ((:~~:) k1 k2 a b) | Since: 1.4.3.0 |
| (NFData a1, NFData a2, NFData a3, NFData a4, NFData a5) => NFData (a1, a2, a3, a4, a5) | |
| (NFData1 f, NFData1 g, NFData a) => NFData (Compose * * f g a) | Since: 1.4.3.0 |
| (NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6) => NFData (a1, a2, a3, a4, a5, a6) | |
| (NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7) => NFData (a1, a2, a3, a4, a5, a6, a7) | |
| (NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8) => NFData (a1, a2, a3, a4, a5, a6, a7, a8) | |
| (NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8, NFData a9) => NFData (a1, a2, a3, a4, a5, a6, a7, a8, a9) | |
a variant of deepseq that is useful in some circumstances:
force x = x `deepseq` x
force x fully evaluates x, and then returns it. Note that
force x only performs evaluation when the value of force x
itself is demanded, so essentially it turns shallow evaluation into
deep evaluation.
force can be conveniently used in combination with ViewPatterns:
{-# LANGUAGE BangPatterns, ViewPatterns #-}
import Control.DeepSeq
someFun :: ComplexData -> SomeResult
someFun (force -> !arg) = {- 'arg' will be fully evaluated -}Another useful application is to combine force with
evaluate in order to force deep evaluation
relative to other IO operations:
import Control.Exception (evaluate)
import Control.DeepSeq
main = do
result <- evaluate $ force $ pureComputation
{- 'result' will be fully evaluated at this point -}
return ()Finally, here's an exception safe variant of the readFile' example:
readFile' :: FilePath -> IO String
readFile' fn = bracket (openFile fn ReadMode) hClose $ \h ->
evaluate . force =<< hGetContents hSince: 1.2.0.0
($!!) :: NFData a => (a -> b) -> a -> b infixr 0 #
the deep analogue of $!. In the expression f $!! x, x is
fully evaluated before the function f is applied to it.
Since: 1.2.0.0
class Applicative m => Monad (m :: * -> *) 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 laws:
Furthermore, the Monad and Applicative operations should relate as follows:
The above laws imply:
and that pure and (<*>) satisfy the applicative functor laws.
The instances of Monad for lists, Maybe and IO
defined in the Prelude satisfy these laws.
Minimal complete definition
Methods
(>>=) :: 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.
(>>) :: 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.
Inject a value into the monadic type.
Fail with a message. This operation is not part of the
mathematical definition of a monad, but is invoked on pattern-match
failure in a do expression.
As part of the MonadFail proposal (MFP), this function is moved
to its own class MonadFail (see Control.Monad.Fail for more
details). The definition here will be removed in a future
release.
Instances
| Monad [] | Since: 2.1 |
| Monad Maybe | Since: 2.1 |
| Monad IO | Since: 2.1 |
| Monad Par1 | Since: 4.9.0.0 |
| Monad Q | |
| Monad P | Since: 2.1 |
| Monad Complex | Since: 4.9.0.0 |
| Monad Min | Since: 4.9.0.0 |
| Monad Max | Since: 4.9.0.0 |
| Monad First | Since: 4.9.0.0 |
| Monad Last | Since: 4.9.0.0 |
| Monad Option | Since: 4.9.0.0 |
| Monad NonEmpty | Since: 4.9.0.0 |
| Monad Identity | Since: 4.8.0.0 |
| Monad STM | Since: 4.3.0.0 |
| Monad Dual | Since: 4.8.0.0 |
| Monad Sum | Since: 4.8.0.0 |
| Monad Product | Since: 4.8.0.0 |
| Monad First | |
| Monad Last | |
| Monad ReadPrec | Since: 2.1 |
| Monad ReadP | Since: 2.1 |
| Monad Put | |
| Monad Tree | |
| Monad Seq | |
| Monad Array | |
| Monad Vector | |
| Monad Id | |
| Monad Box | |
| Monad (Either e) | Since: 4.4.0.0 |
| Monad (U1 *) | Since: 4.9.0.0 |
| Monoid a => Monad ((,) a) | Since: 4.9.0.0 |
| Monad m => Monad (WrappedMonad m) | |
| ArrowApply a => Monad (ArrowMonad a) | Since: 2.1 |
| Monad (Proxy *) | Since: 4.7.0.0 |
| Monad (State s) | |
| Monad m => Monad (ListT m) | |
| Monad m => Monad (MaybeT m) | |
| Monad (RIO env) # | |
| Monad f => Monad (Rec1 * f) | Since: 4.9.0.0 |
| Monad f => Monad (Alt * f) | |
| (Applicative f, Monad f) => Monad (WhenMissing f x) | Equivalent to |
| Monad m => Monad (StateT s m) | |
| (Monad m, Error e) => Monad (ErrorT e m) | |
| Monad m => Monad (ExceptT e m) | |
| Monad m => Monad (StateT s m) | |
| Monad m => Monad (StateT s m) | |
| (Monoid w, Monad m) => Monad (WriterT w m) | |
| (Monoid w, Monad m) => Monad (WriterT w m) | |
| Monad m => Monad (IdentityT * m) | |
| Monad ((->) LiftedRep LiftedRep r) | Since: 2.1 |
| (Monad f, Monad g) => Monad ((:*:) * f g) | Since: 4.9.0.0 |
| (Monad f, Monad g) => Monad (Product * f g) | Since: 4.9.0.0 |
| (Monad f, Applicative f) => Monad (WhenMatched f x y) | Equivalent to |
| (Applicative f, Monad f) => Monad (WhenMissing f k x) | Equivalent to |
| Monad (ContT k r m) | |
| Monad m => Monad (ReaderT * r m) | |
| Monad f => Monad (M1 * i c f) | Since: 4.9.0.0 |
| (Monad f, Applicative f) => Monad (WhenMatched f k x y) | Equivalent to |
| (Monoid w, Monad m) => Monad (RWST r w s m) | |
| (Monoid w, Monad m) => Monad (RWST r w s m) | |
class (Alternative m, Monad m) => MonadPlus (m :: * -> *) where #
Monads that also support choice and failure.
Methods
the identity of mplus. It should also satisfy the equations
mzero >>= f = mzero v >> mzero = mzero
an associative operation
Instances
filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] #
This generalizes the list-based filter function.
foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b #
The foldM function is analogous to foldl, except that its result is
encapsulated in a monad. Note that foldM works from left-to-right over
the list arguments. This could be an issue where ( and the `folded
function' are not commutative.>>)
foldM f a1 [x1, x2, ..., xm]
==
do
a2 <- f a1 x1
a3 <- f a2 x2
...
f am xmIf right-to-left evaluation is required, the input list should be reversed.
foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m () #
Like foldM, but discards the result.
forever :: Applicative f => f a -> f b #
forever act
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.
liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r #
Promote a function to a monad, scanning the monadic arguments from left to right. For example,
liftM2 (+) [0,1] [0,2] = [0,2,1,3] liftM2 (+) (Just 1) Nothing = Nothing
replicateM_ :: Applicative m => Int -> m a -> m () #
Like replicateM, but discards the result.
unless :: Applicative f => Bool -> f () -> f () #
The reverse of when.
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.
zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] #
zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () #
(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 #
Same as >>=, but with the arguments interchanged.
(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1 #
Left-to-right Kleisli composition of monads.
class Monad m => MonadThrow (m :: * -> *) where #
A class for monads in which exceptions may be thrown.
Instances should obey the following law:
throwM e >> x = throwM e
In other words, throwing an exception short-circuits the rest of the monadic computation.
Minimal complete definition
Methods
throwM :: Exception e => e -> m a #
Throw an exception. Note that this throws when this action is run in
the monad m, not when it is applied. It is a generalization of
Control.Exception's throwIO.
Should satisfy the law:
throwM e >> f = throwM e
Instances
| MonadThrow [] | |
| MonadThrow Maybe | |
| MonadThrow IO | |
| MonadThrow Q | |
| MonadThrow STM | |
| (~) * e SomeException => MonadThrow (Either e) | |
| MonadThrow m => MonadThrow (ListT m) | |
| MonadThrow m => MonadThrow (MaybeT m) | Throws exceptions into the base monad. |
| MonadThrow (RIO env) # | |
| (Error e, MonadThrow m) => MonadThrow (ErrorT e m) | Throws exceptions into the base monad. |
| MonadThrow m => MonadThrow (ExceptT e m) | Throws exceptions into the base monad. |
| MonadThrow m => MonadThrow (StateT s m) | |
| MonadThrow m => MonadThrow (StateT s m) | |
| (MonadThrow m, Monoid w) => MonadThrow (WriterT w m) | |
| (MonadThrow m, Monoid w) => MonadThrow (WriterT w m) | |
| MonadThrow m => MonadThrow (IdentityT * m) | |
| MonadThrow m => MonadThrow (ContT * r m) | |
| MonadThrow m => MonadThrow (ReaderT * r m) | |
| (MonadThrow m, Monoid w) => MonadThrow (RWST r w s m) | |
| (MonadThrow m, Monoid w) => MonadThrow (RWST r w s m) | |
class Monad m => MonadReader r (m :: * -> *) | m -> r where #
See examples in Control.Monad.Reader.
Note, the partially applied function type (->) r is a simple reader monad.
See the instance declaration below.
Methods
Retrieves the monad environment.
Arguments
| :: (r -> r) | The function to modify the environment. |
| -> m a |
|
| -> m a |
Executes a computation in a modified environment.
Instances
| MonadReader env (RIO env) # | |
| MonadReader r m => MonadReader r (MaybeT m) | |
| MonadReader r m => MonadReader r (ListT m) | |
| (Monoid w, MonadReader r m) => MonadReader r (WriterT w m) | |
| (Monoid w, MonadReader r m) => MonadReader r (WriterT w m) | |
| MonadReader r m => MonadReader r (StateT s m) | |
| MonadReader r m => MonadReader r (StateT s m) | |
| MonadReader r m => MonadReader r (IdentityT * m) | |
| MonadReader r m => MonadReader r (ExceptT e m) | |
| (Error e, MonadReader r m) => MonadReader r (ErrorT e m) | |
| Monad m => MonadReader r (ReaderT * r m) | |
| MonadReader r ((->) LiftedRep LiftedRep r) | |
| MonadReader r' m => MonadReader r' (ContT * r m) | |
| (Monad m, Monoid w) => MonadReader r (RWST r w s m) | |
| (Monad m, Monoid w) => MonadReader r (RWST r w s m) | |
class MonadTrans (t :: (* -> *) -> * -> *) where #
The class of monad transformers. Instances should satisfy the
following laws, which state that lift is a monad transformation:
Minimal complete definition
Methods
lift :: Monad m => m a -> t m a #
Lift a computation from the argument monad to the constructed monad.
Instances
| MonadTrans ListT | |
| MonadTrans MaybeT | |
| MonadTrans (ErrorT e) | |
| MonadTrans (ExceptT e) | |
| MonadTrans (StateT s) | |
| MonadTrans (StateT s) | |
| Monoid w => MonadTrans (WriterT w) | |
| Monoid w => MonadTrans (WriterT w) | |
| MonadTrans (IdentityT *) | |
| MonadTrans (ContT * r) | |
| MonadTrans (ReaderT * r) | |
| Monoid w => MonadTrans (RWST r w s) | |
| Monoid w => MonadTrans (RWST r w s) | |
newtype ReaderT k r (m :: k -> *) (a :: k) :: forall k. * -> (k -> *) -> k -> * #
The reader monad transformer, which adds a read-only environment to the given monad.
The return function ignores the environment, while >>= passes
the inherited environment to both subcomputations.
Constructors
| ReaderT | |
Fields
| |
Instances
| Monad m => MonadReader r (ReaderT * r m) | |
| MonadTrans (ReaderT * r) | |
| Monad m => Monad (ReaderT * r m) | |
| Functor m => Functor (ReaderT * r m) | |
| MonadFix m => MonadFix (ReaderT * r m) | |
| MonadFail m => MonadFail (ReaderT * r m) | |
| Applicative m => Applicative (ReaderT * r m) | |
| MonadZip m => MonadZip (ReaderT * r m) | |
| MonadIO m => MonadIO (ReaderT * r m) | |
| Alternative m => Alternative (ReaderT * r m) | |
| MonadPlus m => MonadPlus (ReaderT * r m) | |
| MonadThrow m => MonadThrow (ReaderT * r m) | |
| MonadCatch m => MonadCatch (ReaderT * r m) | |
| MonadMask m => MonadMask (ReaderT * r m) | |
| PrimMonad m => PrimMonad (ReaderT * r m) | |
| MonadUnliftIO m => MonadUnliftIO (ReaderT * r m) | |
| type PrimState (ReaderT * r m) | |
ask :: MonadReader r m => m r #
Retrieves the monad environment.
Arguments
| :: MonadReader r m | |
| => (r -> a) | The selector function to apply to the environment. |
| -> m a |
Retrieves a function of the current environment.
Arguments
| :: MonadReader r m | |
| => (r -> r) | The function to modify the environment. |
| -> m a |
|
| -> m a |
Executes a computation in a modified environment.
Instances
| Bounded Bool | Since: 2.1 |
| Enum Bool | Since: 2.1 |
| Eq Bool | |
| Data Bool | Since: 4.0.0.0 |
| Ord Bool | |
| Read Bool | Since: 2.1 |
| Show Bool | |
| Generic Bool | |
| Lift Bool | |
| SingKind Bool | Since: 4.9.0.0 |
| Storable Bool | Since: 2.1 |
| NFData Bool | |
| Hashable Bool | |
| Unbox Bool | |
| SingI Bool False | Since: 4.9.0.0 |
| SingI Bool True | Since: 4.9.0.0 |
| Vector Vector Bool | |
| MVector MVector Bool | |
| type Rep Bool | |
| data Sing Bool | |
| type DemoteRep Bool | |
| data Vector Bool | |
| data MVector s Bool | |
| type (==) Bool a b | |
data ByteString :: * #
A space-efficient representation of a Word8 vector, supporting many
efficient operations.
A ByteString contains 8-bit bytes, or by using the operations from
Data.ByteString.Char8 it can be interpreted as containing 8-bit
characters.
data ShortByteString :: * #
A compact representation of a Word8 vector.
It has a lower memory overhead than a ByteString and and does not
contribute to heap fragmentation. It can be converted to or from a
ByteString (at the cost of copying the string data). It supports very few
other operations.
It is suitable for use as an internal representation for code that needs
to keep many short strings in memory, but it should not be used as an
interchange type. That is, it should not generally be used in public APIs.
The ByteString type is usually more suitable for use in interfaces; it is
more flexible and it supports a wide range of operations.
toShort :: ByteString -> ShortByteString #
O(n). Convert a ByteString into a ShortByteString.
This makes a copy, so does not retain the input string.
fromShort :: ShortByteString -> ByteString #
O(n). Convert a ShortByteString into a ByteString.
The character type Char is an enumeration whose values represent
Unicode (or equivalently ISO/IEC 10646) 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: 2.1 |
| Enum Char | Since: 2.1 |
| Eq Char | |
| Data Char | Since: 4.0.0.0 |
| Ord Char | |
| Read Char | Since: 2.1 |
| Show Char | Since: 2.1 |
| Lift Char | |
| Storable Char | Since: 2.1 |
| NFData Char | |
| Hashable Char | |
| Prim Char | |
| ErrorList Char | |
| Unbox Char | |
| Vector Vector Char | |
| MVector MVector Char | |
| Generic1 k (URec k Char) | |
| IsString (Seq Char) | |
| Functor (URec * Char) | |
| Foldable (URec * Char) | |
| Traversable (URec * Char) | |
| Eq (URec k Char p) | |
| Ord (URec k Char p) | |
| Show (URec k Char p) | |
| Generic (URec k Char p) | |
| data Vector Char | |
| data URec k Char | Used for marking occurrences of Since: 4.9.0.0 |
| data MVector s Char | |
| type Rep1 k (URec k Char) | |
| type Rep (URec k Char p) | |
class Typeable * a => Data a where #
The Data class comprehends a fundamental primitive gfoldl for
folding over constructor applications, say terms. This primitive can
be instantiated in several ways to map over the immediate subterms
of a term; see the gmap combinators later in this class. Indeed, a
generic programmer does not necessarily need to use the ingenious gfoldl
primitive but rather the intuitive gmap combinators. The gfoldl
primitive is completed by means to query top-level constructors, to
turn constructor representations into proper terms, and to list all
possible datatype constructors. This completion allows us to serve
generic programming scenarios like read, show, equality, term generation.
The combinators gmapT, gmapQ, gmapM, etc are all provided with
default definitions in terms of gfoldl, leaving open the opportunity
to provide datatype-specific definitions.
(The inclusion of the gmap combinators as members of class Data
allows the programmer or the compiler to derive specialised, and maybe
more efficient code per datatype. Note: gfoldl is more higher-order
than the gmap combinators. This is subject to ongoing benchmarking
experiments. It might turn out that the gmap combinators will be
moved out of the class Data.)
Conceptually, the definition of the gmap combinators in terms of the
primitive gfoldl requires the identification of the gfoldl function
arguments. Technically, we also need to identify the type constructor
c for the construction of the result type from the folded term type.
In the definition of gmapQx combinators, we use phantom type
constructors for the c in the type of gfoldl because the result type
of a query does not involve the (polymorphic) type of the term argument.
In the definition of gmapQl we simply use the plain constant type
constructor because gfoldl is left-associative anyway and so it is
readily suited to fold a left-associative binary operation over the
immediate subterms. In the definition of gmapQr, extra effort is
needed. We use a higher-order accumulation trick to mediate between
left-associative constructor application vs. right-associative binary
operation (e.g., (:)). When the query is meant to compute a value
of type r, then the result type withing generic folding is r -> r.
So the result of folding is a function to which we finally pass the
right unit.
With the -XDeriveDataTypeable option, GHC can generate instances of the
Data class automatically. For example, given the declaration
data T a b = C1 a b | C2 deriving (Typeable, Data)
GHC will generate an instance that is equivalent to
instance (Data a, Data b) => Data (T a b) where
gfoldl k z (C1 a b) = z C1 `k` a `k` b
gfoldl k z C2 = z C2
gunfold k z c = case constrIndex c of
1 -> k (k (z C1))
2 -> z C2
toConstr (C1 _ _) = con_C1
toConstr C2 = con_C2
dataTypeOf _ = ty_T
con_C1 = mkConstr ty_T "C1" [] Prefix
con_C2 = mkConstr ty_T "C2" [] Prefix
ty_T = mkDataType "Module.T" [con_C1, con_C2]This is suitable for datatypes that are exported transparently.
Minimal complete definition
Methods
Arguments
| :: (forall d b. Data d => c (d -> b) -> d -> c b) | defines how nonempty constructor applications are folded. It takes the folded tail of the constructor application and its head, i.e., an immediate subterm, and combines them in some way. |
| -> (forall g. g -> c g) | defines how the empty constructor application is folded, like the neutral / start element for list folding. |
| -> a | structure to be folded. |
| -> c a | result, with a type defined in terms of |
Left-associative fold operation for constructor applications.
The type of gfoldl is a headache, but operationally it is a simple
generalisation of a list fold.
The default definition for gfoldl is const id
gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c a #
Unfolding constructor applications
Obtaining the constructor from a given datum. For proper terms, this is meant to be the top-level constructor. Primitive datatypes are here viewed as potentially infinite sets of values (i.e., constructors).
dataTypeOf :: a -> DataType #
The outer type constructor of the type
dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c a) #
Mediate types and unary type constructors.
In Data instances of the form T a, dataCast1 should be defined
as gcast1.
The default definition is const Nothing
dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a) #
Mediate types and binary type constructors.
In Data instances of the form T a b, dataCast2 should be
defined as gcast2.
The default definition is const Nothing
gmapT :: (forall b. Data b => b -> b) -> a -> a #
A generic transformation that maps over the immediate subterms
The default definition instantiates the type constructor c in the
type of gfoldl to an identity datatype constructor, using the
isomorphism pair as injection and projection.
gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r #
A generic query with a left-associative binary operator
gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r #
A generic query with a right-associative binary operator
gmapQ :: (forall d. Data d => d -> u) -> a -> [u] #
A generic query that processes the immediate subterms and returns a list of results. The list is given in the same order as originally specified in the declaration of the data constructors.
gmapQi :: Int -> (forall d. Data d => d -> u) -> a -> u #
A generic query that processes one child by index (zero-based)
gmapM :: Monad m => (forall d. Data d => d -> m d) -> a -> m a #
A generic monadic transformation that maps over the immediate subterms
The default definition instantiates the type constructor c in
the type of gfoldl to the monad datatype constructor, defining
injection and projection using return and >>=.
gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a #
Transformation of at least one immediate subterm does not fail
gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a #
Transformation of one immediate subterm with success
Instances
| Data Bool | Since: 4.0.0.0 |
| Data Char | Since: 4.0.0.0 |
| Data Double | Since: 4.0.0.0 |
| Data Float | Since: 4.0.0.0 |
| Data Int | Since: 4.0.0.0 |
| Data Int8 | Since: 4.0.0.0 |
| Data Int16 | Since: 4.0.0.0 |
| Data Int32 | Since: 4.0.0.0 |
| Data Int64 | Since: 4.0.0.0 |
| Data Integer | Since: 4.0.0.0 |
| Data Natural | Since: 4.8.0.0 |
| Data Ordering | Since: 4.0.0.0 |
| Data Word | Since: 4.0.0.0 |
| Data Word8 | Since: 4.0.0.0 |
| Data Word16 | Since: 4.0.0.0 |
| Data Word32 | Since: 4.0.0.0 |
| Data Word64 | Since: 4.0.0.0 |
| Data Exp | |
| Data Match | |
| Data Clause | |
| Data Pat | |
| Data Type | |
| Data Dec | |
| Data Name | |
| Data FunDep | |
| Data TyVarBndr | |
| Data InjectivityAnn | |
| Data Overlap | |
| Data DerivStrategy | |
| Data () | Since: 4.0.0.0 |
| Data Void | |
| Data SpecConstrAnnotation | |
| Data Version | Since: 4.7.0.0 |
| Data All | Since: 4.8.0.0 |
| Data Any | Since: 4.8.0.0 |
| Data Fixity | Since: 4.9.0.0 |
| Data Associativity | Since: 4.9.0.0 |
| Data SourceUnpackedness | Since: 4.9.0.0 |
| Data SourceStrictness | Since: 4.9.0.0 |
| Data DecidedStrictness | Since: 4.9.0.0 |
| Data ShortByteString | |
| Data ByteString | |
| Data ByteString | |
| Data IntSet | |
| Data Addr | |
| Data ModName | |
| Data PkgName | |
| Data Module | |
| Data OccName | |
| Data NameFlavour | |
| Data NameSpace | |
| Data Loc | |
| Data Info | |
| Data ModuleInfo | |
| Data Fixity | |
| Data FixityDirection | |
| Data Lit | |
| Data Body | |
| Data Guard | |
| Data Stmt | |
| Data Range | |
| Data DerivClause | |
| Data TypeFamilyHead | |
| Data TySynEqn | |
| Data FamFlavour | |
| Data Foreign | |
| Data Callconv | |
| Data Safety | |
| Data Pragma | |
| Data Inline | |
| Data RuleMatch | |
| Data Phases | |
| Data RuleBndr | |
| Data AnnTarget | |
| Data SourceUnpackedness | |
| Data SourceStrictness | |
| Data DecidedStrictness | |
| Data Con | |
| Data Bang | |
| Data PatSynDir | |
| Data PatSynArgs | |
| Data FamilyResultSig | |
| Data TyLit | |
| Data Role | |
| Data AnnLookup | |
| Data ZonedTime | |
| Data LocalTime | |
| Data TimeOfDay | |
| Data TimeZone | |
| Data UniversalTime | |
| Data UTCTime | |
| Data DiffTime | |
| Data Day | |
| Data a => Data [a] | Since: 4.0.0.0 |
| Data a => Data (Maybe a) | Since: 4.0.0.0 |
| (Data a, Integral a) => Data (Ratio a) | Since: 4.0.0.0 |
| Data a => Data (Ptr a) | Since: 4.8.0.0 |
| Data p => Data (Par1 p) | Since: 4.9.0.0 |
| Data a => Data (ForeignPtr a) | Since: 4.8.0.0 |
| Data a => Data (Complex a) | |
| Data a => Data (Min a) | |
| Data a => Data (Max a) | |
| Data a => Data (First a) | |
| Data a => Data (Last a) | |
| Data m => Data (WrappedMonoid m) | |
| Data a => Data (Option a) | |
| Data a => Data (NonEmpty a) | |
| Data a => Data (Identity a) | Since: 4.9.0.0 |
| Data a => Data (Dual a) | Since: 4.8.0.0 |
| Data a => Data (Sum a) | Since: 4.8.0.0 |
| Data a => Data (Product a) | Since: 4.8.0.0 |
| Data a => Data (First a) | Since: 4.8.0.0 |
| Data a => Data (Last a) | Since: 4.8.0.0 |
| Data a => Data (IntMap a) | |
| Data a => Data (Tree a) | |
| Data a => Data (Seq a) | |
| Data a => Data (ViewL a) | |
| Data a => Data (ViewR a) | |
| (Data a, Ord a) => Data (Set a) | |
| Data a => Data (Array a) | |
| (Data a, Eq a, Hashable a) => Data (HashSet a) | |
| (Data a, Unbox a) => Data (Vector a) | |
| (Data a, Storable a) => Data (Vector a) | |
| (Data a, Prim a) => Data (Vector a) | |
| Data a => Data (Vector a) | |
| (Data a, Data b) => Data (Either a b) | Since: 4.0.0.0 |
| Data p => Data (V1 * p) | Since: 4.9.0.0 |
| Data p => Data (U1 * p) | Since: 4.9.0.0 |
| (Data a, Data b) => Data (a, b) | Since: 4.0.0.0 |
| (Data a, Data b, Ix a) => Data (Array a b) | Since: 4.8.0.0 |
| (Data b, Data a) => Data (Arg a b) | |
| Data t => Data (Proxy * t) | Since: 4.7.0.0 |
| (Data k, Data a, Ord k) => Data (Map k a) | |
| (Typeable * s, Typeable * a) => Data (MutableArray s a) | |
| (Data k, Data v, Eq k, Hashable k) => Data (HashMap k v) | |
| (Data (f p), Typeable (* -> *) f, Data p) => Data (Rec1 * f p) | Since: 4.9.0.0 |
| (Data a, Data b, Data c) => Data (a, b, c) | Since: 4.0.0.0 |
| (Typeable * k3, Data a, Typeable k3 b) => Data (Const k3 a b) | Since: 4.10.0.0 |
| (Data (f a), Data a, Typeable (* -> *) f) => Data (Alt * f a) | Since: 4.8.0.0 |
| (Coercible * a b, Data a, Data b) => Data (Coercion * a b) | Since: 4.7.0.0 |
| ((~) * a b, Data a) => Data ((:~:) * a b) | Since: 4.7.0.0 |
| (Typeable * i, Data p, Data c) => Data (K1 * i c p) | Since: 4.9.0.0 |
| (Typeable (* -> *) f, Typeable (* -> *) g, Data p, Data (f p), Data (g p)) => Data ((:+:) * f g p) | Since: 4.9.0.0 |
| (Typeable (* -> *) f, Typeable (* -> *) g, Data p, Data (f p), Data (g p)) => Data ((:*:) * f g p) | Since: 4.9.0.0 |
| (Data a, Data b, Data c, Data d) => Data (a, b, c, d) | Since: 4.0.0.0 |
| (Data (g a), Data (f a), Typeable * k, Typeable (k -> *) g, Typeable (k -> *) f, Typeable k a) => Data (Product k f g a) | |
| (Data (g a), Data (f a), Typeable * k, Typeable (k -> *) g, Typeable (k -> *) f, Typeable k a) => Data (Sum k f g a) | |
| (Typeable * i2, Typeable * j2, Typeable i2 a, Typeable j2 b, (~~) i2 j2 a b) => Data ((:~~:) i2 j2 a b) | Since: 4.10.0.0 |
| (Data p, Data (f p), Typeable Meta c, Typeable * i, Typeable (* -> *) f) => Data (M1 * i c f p) | Since: 4.9.0.0 |
| (Typeable (* -> *) f, Typeable (* -> *) g, Data p, Data (f (g p))) => Data ((:.:) * * f g p) | Since: 4.9.0.0 |
| (Data a, Data b, Data c, Data d, Data e) => Data (a, b, c, d, e) | Since: 4.0.0.0 |
| (Data (f (g a)), Typeable * k2, Typeable * k1, Typeable (k2 -> k1) g, Typeable (k1 -> *) f, Typeable k2 a) => Data (Compose k1 k2 f g a) | |
| (Data a, Data b, Data c, Data d, Data e, Data f) => Data (a, b, c, d, e, f) | Since: 4.0.0.0 |
| (Data a, Data b, Data c, Data d, Data e, Data f, Data g) => Data (a, b, c, d, e, f, g) | Since: 4.0.0.0 |
data Either a b :: * -> * -> * #
The Either type represents values with two possibilities: a value of
type Either a bLeft aRight b
The Either type is sometimes used to represent a value which is
either correct or an error; by convention, the Left constructor is
used to hold an error value and the Right constructor is used to
hold a correct value (mnemonic: "right" also means "correct").
Examples
The type Either String IntString or an Int. The Left constructor can be used only on
Strings, and the Right constructor can be used only on Ints:
>>>let s = Left "foo" :: Either String Int>>>sLeft "foo">>>let n = Right 3 :: Either String Int>>>nRight 3>>>:type ss :: Either String Int>>>:type nn :: Either String Int
The fmap from our Functor instance will ignore Left values, but
will apply the supplied function to values contained in a Right:
>>>let s = Left "foo" :: Either String Int>>>let n = Right 3 :: Either String Int>>>fmap (*2) sLeft "foo">>>fmap (*2) nRight 6
The Monad instance for Either allows us to chain together multiple
actions which may fail, and fail overall if any of the individual
steps failed. First we'll write a function that can either parse an
Int from a Char, or fail.
>>>import Data.Char ( digitToInt, isDigit )>>>:{let parseEither :: Char -> Either String Int parseEither c | isDigit c = Right (digitToInt c) | otherwise = Left "parse error">>>:}
The following should work, since both '1' and '2' can be
parsed as Ints.
>>>:{let parseMultiple :: Either String Int parseMultiple = do x <- parseEither '1' y <- parseEither '2' return (x + y)>>>:}
>>>parseMultipleRight 3
But the following should fail overall, since the first operation where
we attempt to parse 'm' as an Int will fail:
>>>:{let parseMultiple :: Either String Int parseMultiple = do x <- parseEither 'm' y <- parseEither '2' return (x + y)>>>:}
>>>parseMultipleLeft "parse error"
Instances
| Eq2 Either | Since: 4.9.0.0 |
| Ord2 Either | Since: 4.9.0.0 |
| Read2 Either | Since: 4.9.0.0 |
| Show2 Either | Since: 4.9.0.0 |
| NFData2 Either | Since: 1.4.3.0 |
| Hashable2 Either | |
| Monad (Either e) | Since: 4.4.0.0 |
| Functor (Either a) | Since: 3.0 |
| Applicative (Either e) | Since: 3.0 |
| Foldable (Either a) | Since: 4.7.0.0 |
| Traversable (Either a) | Since: 4.7.0.0 |
| Eq a => Eq1 (Either a) | Since: 4.9.0.0 |
| Ord a => Ord1 (Either a) | Since: 4.9.0.0 |
| Read a => Read1 (Either a) | Since: 4.9.0.0 |
| Show a => Show1 (Either a) | Since: 4.9.0.0 |
| NFData a => NFData1 (Either a) | Since: 1.4.3.0 |
| (~) * e SomeException => MonadThrow (Either e) | |
| (~) * e SomeException => MonadCatch (Either e) | Since: 0.8.3 |
| (~) * e SomeException => MonadMask (Either e) | Since: 0.8.3 |
| Hashable a => Hashable1 (Either a) | |
| Generic1 * (Either a) | |
| (Eq b, Eq a) => Eq (Either a b) | |
| (Data a, Data b) => Data (Either a b) | Since: 4.0.0.0 |
| (Ord b, Ord a) => Ord (Either a b) | |
| (Read b, Read a) => Read (Either a b) | |
| (Show b, Show a) => Show (Either a b) | |
| Generic (Either a b) | |
| Semigroup (Either a b) | Since: 4.9.0.0 |
| (Lift a, Lift b) => Lift (Either a b) | |
| (NFData a, NFData b) => NFData (Either a b) | |
| (Hashable a, Hashable b) => Hashable (Either a b) | |
| type Rep1 * (Either a) | |
| type Rep (Either a b) | |
| type (==) (Either k1 k2) a b | |
either :: (a -> c) -> (b -> c) -> Either a b -> c #
Case analysis for the Either type.
If the value is Left aa;
if it is Right bb.
Examples
We create two values of type Either String IntLeft constructor and another using the Right constructor. Then
we apply "either" the length function (if we have a String)
or the "times-two" function (if we have an Int):
>>>let s = Left "foo" :: Either String Int>>>let n = Right 3 :: Either String Int>>>either length (*2) s3>>>either length (*2) n6
isLeft :: Either a b -> Bool #
Return True if the given value is a Left-value, False otherwise.
Examples
Basic usage:
>>>isLeft (Left "foo")True>>>isLeft (Right 3)False
Assuming a Left value signifies some sort of error, we can use
isLeft to write a very simple error-reporting function that does
absolutely nothing in the case of success, and outputs "ERROR" if
any error occurred.
This example shows how isLeft might be used to avoid pattern
matching when one does not care about the value contained in the
constructor:
>>>import Control.Monad ( when )>>>let report e = when (isLeft e) $ putStrLn "ERROR">>>report (Right 1)>>>report (Left "parse error")ERROR
Since: 4.7.0.0
isRight :: Either a b -> Bool #
Return True if the given value is a Right-value, False otherwise.
Examples
Basic usage:
>>>isRight (Left "foo")False>>>isRight (Right 3)True
Assuming a Left value signifies some sort of error, we can use
isRight to write a very simple reporting function that only
outputs "SUCCESS" when a computation has succeeded.
This example shows how isRight might be used to avoid pattern
matching when one does not care about the value contained in the
constructor:
>>>import Control.Monad ( when )>>>let report e = when (isRight e) $ putStrLn "SUCCESS">>>report (Left "parse error")>>>report (Right 1)SUCCESS
Since: 4.7.0.0
partitionEithers :: [Either a b] -> ([a], [b]) #
Partitions a list of Either into two lists.
All the Left elements are extracted, in order, to the first
component of the output. Similarly the Right elements are extracted
to the second component of the output.
Examples
Basic usage:
>>>let list = [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]>>>partitionEithers list(["foo","bar","baz"],[3,7])
The pair returned by partitionEithers x(:lefts x, rights x)
>>>let list = [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]>>>partitionEithers list == (lefts list, rights list)True
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.
Instances
| Eq Bool | |
| Eq Char | |
| Eq Double | |
| Eq Float | |
| Eq Int | |
| Eq Int8 | Since: 2.1 |
| Eq Int16 | Since: 2.1 |
| Eq Int32 | Since: 2.1 |
| Eq Int64 | Since: 2.1 |
| Eq Integer | |
| Eq Ordering | |
| Eq Word | |
| Eq Word8 | Since: 2.1 |
| Eq Word16 | Since: 2.1 |
| Eq Word32 | Since: 2.1 |
| Eq Word64 | Since: 2.1 |
| Eq SomeTypeRep | |
| Eq Exp | |
| Eq Match | |
| Eq Clause | |
| Eq Pat | |
| Eq Type | |
| Eq Dec | |
| Eq Name | |
| Eq FunDep | |
| Eq TyVarBndr | |
| Eq InjectivityAnn | |
| Eq Overlap | |
| Eq DerivStrategy | |
| Eq () | |
| Eq TyCon | |
| Eq Module | |
| Eq TrName | |
| Eq Handle | Since: 4.1.0.0 |
| Eq ThreadId | Since: 4.2.0.0 |
| Eq EventLifetime | |
| Eq BigNat | |
| Eq Void | Since: 4.8.0.0 |
| Eq SpecConstrAnnotation | |
| Eq Constr | Equality of constructors Since: 4.0.0.0 |
| Eq DataRep | |
| Eq ConstrRep | |
| Eq Fixity | |
| Eq BlockReason | |
| Eq ThreadStatus | |
| Eq Event | |
| Eq Lifetime | |
| Eq AsyncException | |
| Eq ArrayException | |
| Eq ExitCode | |
| Eq IOErrorType | Since: 4.1.0.0 |
| Eq BufferMode | |
| Eq Newline | |
| Eq NewlineMode | |
| Eq CodingProgress | |
| Eq MaskingState | |
| Eq IOException | Since: 4.1.0.0 |
| Eq ErrorCall | |
| Eq ArithException | |
| Eq All | |
| Eq Any | |
| Eq Fixity | |
| Eq Associativity | |
| Eq SourceUnpackedness | |
| Eq SourceStrictness | |
| Eq DecidedStrictness | |
| Eq CChar | |
| Eq CSChar | |
| Eq CUChar | |
| Eq CShort | |
| Eq CUShort | |
| Eq CInt | |
| Eq CUInt | |
| Eq CLong | |
| Eq CULong | |
| Eq CLLong | |
| Eq CULLong | |
| Eq CBool | |
| Eq CFloat | |
| Eq CDouble | |
| Eq CPtrdiff | |
| Eq CSize | |
| Eq CWchar | |
| Eq CSigAtomic | |
| Eq CClock | |
| Eq CTime | |
| Eq CUSeconds | |
| Eq CSUSeconds | |
| Eq CIntPtr | |
| Eq CUIntPtr | |
| Eq CIntMax | |
| Eq CUIntMax | |
| Eq IOMode | |
| Eq Lexeme | |
| Eq Number | |
| Eq SrcLoc | |
| Eq ShortByteString | |
| Eq ByteString | |
| Eq ByteString | |
| Eq IntSet | |
| Eq DirectoryType | |
| Eq Permissions | |
| Eq XdgDirectory | |
| Eq Extension | |
| Eq ForeignSrcLang | |
| Eq Addr | |
| Eq ModName | |
| Eq PkgName | |
| Eq Module | |
| Eq OccName | |
| Eq NameFlavour | |
| Eq NameSpace | |
| Eq Loc | |
| Eq Info | |
| Eq ModuleInfo | |
| Eq Fixity | |
| Eq FixityDirection | |
| Eq Lit | |
| Eq Body | |
| Eq Guard | |
| Eq Stmt | |
| Eq Range | |
| Eq DerivClause | |
| Eq TypeFamilyHead | |
| Eq TySynEqn | |
| Eq FamFlavour | |
| Eq Foreign | |
| Eq Callconv | |
| Eq Safety | |
| Eq Pragma | |
| Eq Inline | |
| Eq RuleMatch | |
| Eq Phases | |
| Eq RuleBndr | |
| Eq AnnTarget | |
| Eq SourceUnpackedness | |
| Eq SourceStrictness | |
| Eq DecidedStrictness | |
| Eq Con | |
| Eq Bang | |
| Eq PatSynDir | |
| Eq PatSynArgs | |
| Eq FamilyResultSig | |
| Eq TyLit | |
| Eq Role | |
| Eq AnnLookup | |
| Eq CodePoint | |
| Eq DecoderState | |
| Eq UnicodeException | |
| Eq TimeLocale | |
| Eq LocalTime | |
| Eq TimeOfDay | |
| Eq TimeZone | |
| Eq UniversalTime | |
| Eq UTCTime | |
| Eq DiffTime | |
| Eq Day | |
| Eq LogLevel # | |
| Eq a => Eq [a] | |
| Eq a => Eq (Maybe a) | |
| Eq a => Eq (Ratio a) | |
| Eq (Ptr a) | |
| Eq (FunPtr a) | |
| Eq p => Eq (Par1 p) | |
| Eq (ForeignPtr a) | Since: 2.1 |
| Eq a => Eq (Complex a) | |
| Eq a => Eq (Min a) | |
| Eq a => Eq (Max a) | |
| Eq a => Eq (First a) | |
| Eq a => Eq (Last a) | |
| Eq m => Eq (WrappedMonoid m) | |
| Eq a => Eq (Option a) | |
| Eq a => Eq (NonEmpty a) | |
| Eq a => Eq (ZipList a) | |
| Eq a => Eq (Identity a) | |
| Eq (TVar a) | Since: 4.8.0.0 |
| Eq (IORef a) | Since: 4.1.0.0 |
| Eq a => Eq (Dual a) | |
| Eq a => Eq (Sum a) | |
| Eq a => Eq (Product a) | |
| Eq a => Eq (First a) | |
| Eq a => Eq (Last a) | |
| Eq a => Eq (Down a) | |
| Eq (MVar a) | Since: 4.1.0.0 |
| Eq a => Eq (IntMap a) | |
| Eq a => Eq (Tree a) | |
| Eq a => Eq (Seq a) | |
| Eq a => Eq (ViewL a) | |
| Eq a => Eq (ViewR a) | |
| Eq a => Eq (Set a) | |
| Eq a => Eq (Hashed a) | Uses precomputed hash to detect inequality faster |
| Eq a => Eq (Array a) | |
| Eq a => Eq (HashSet a) | |
| (Storable a, Eq a) => Eq (Vector a) | |
| (Prim a, Eq a) => Eq (Vector a) | |
| Eq a => Eq (Vector a) | |
| (Eq b, Eq a) => Eq (Either a b) | |
| Eq (V1 k p) | |
| Eq (U1 k p) | Since: 4.9.0.0 |
| Eq (TypeRep k a) | Since: 2.1 |
| (Eq a, Eq b) => Eq (a, b) | |
| Eq a => Eq (Arg a b) | Since: 4.9.0.0 |
| Eq (Proxy k s) | Since: 4.7.0.0 |
| (Eq k, Eq a) => Eq (Map k a) | |
| (Eq1 m, Eq a) => Eq (ListT m a) | |
| Eq (MutableArray s a) | |
| (Eq1 m, Eq a) => Eq (MaybeT m a) | |
| (Eq v, Eq k) => Eq (Leaf k v) | |
| (Eq k, Eq v) => Eq (HashMap k v) | |
| Eq (f p) => Eq (Rec1 k f p) | |
| Eq (URec k (Ptr ()) p) | |
| Eq (URec k Char p) | |
| Eq (URec k Double p) | |
| Eq (URec k Float p) | |
| Eq (URec k Int p) | |
| Eq (URec k Word p) | |
| (Eq a, Eq b, Eq c) => Eq (a, b, c) | |
| Eq a => Eq (Const k a b) | |
| Eq (f a) => Eq (Alt k f a) | |
| Eq ((:~:) k a b) | |
| (Eq e, Eq1 m, Eq a) => Eq (ErrorT e m a) | |
| (Eq e, Eq1 m, Eq a) => Eq (ExceptT e m a) | |
| (Eq w, Eq1 m, Eq a) => Eq (WriterT w m a) | |
| (Eq w, Eq1 m, Eq a) => Eq (WriterT w m a) | |
| (Eq1 f, Eq a) => Eq (IdentityT * f a) | |
| Eq c => Eq (K1 k i c p) | |
| (Eq (g p), Eq (f p)) => Eq ((:+:) k f g p) | |
| (Eq (g p), Eq (f p)) => Eq ((:*:) k f g p) | |
| (Eq a, Eq b, Eq c, Eq d) => Eq (a, b, c, d) | |
| (Eq1 f, Eq1 g, Eq a) => Eq (Product * f g a) | Since: 4.9.0.0 |
| (Eq1 f, Eq1 g, Eq a) => Eq (Sum * f g a) | Since: 4.9.0.0 |
| Eq ((:~~:) k1 k2 a b) | Since: 4.10.0.0 |
| Eq (f p) => Eq (M1 k i c f p) | |
| Eq (f (g p)) => Eq ((:.:) k2 k1 f g p) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e) => Eq (a, b, c, d, e) | |
| (Eq1 f, Eq1 g, Eq a) => Eq (Compose * * f g a) | Since: 4.9.0.0 |
| (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) | |
class Foldable (t :: * -> *) where #
Data structures that can be folded.
For example, given a data type
data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
a suitable instance would be
instance Foldable Tree where foldMap f Empty = mempty foldMap f (Leaf x) = f x foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r
This is suitable even for abstract types, as the monoid is assumed
to satisfy the monoid laws. Alternatively, one could define foldr:
instance Foldable Tree where foldr f z Empty = z foldr f z (Leaf x) = f x z foldr f z (Node l k r) = foldr f (f k (foldr f z r)) l
Foldable instances are expected to satisfy the following laws:
foldr f z t = appEndo (foldMap (Endo . f) t ) z
foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z
fold = foldMap id
sum, product, maximum, and minimum should all be essentially
equivalent to foldMap forms, such as
sum = getSum . foldMap Sum
but may be less defined.
If the type is also a Functor instance, it should satisfy
foldMap f = fold . fmap f
which implies that
foldMap f . fmap g = foldMap (f . g)
Methods
fold :: Monoid m => t m -> m #
Combine the elements of a structure using a monoid.
foldMap :: Monoid m => (a -> m) -> t a -> m #
Map each element of the structure to a monoid, and combine the results.
foldr :: (a -> b -> b) -> b -> t a -> b #
Right-associative fold of a structure.
In the case of lists, foldr, when applied to a binary operator, a
starting value (typically the right-identity of the operator), and a
list, reduces the list using the binary operator, from right to left:
foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
Note that, since the head of the resulting expression is produced by
an application of the operator to the first element of the list,
foldr can produce a terminating expression from an infinite list.
For a general Foldable structure this should be semantically identical
to,
foldr f z =foldrf z .toList
foldl' :: (b -> a -> b) -> b -> t a -> b #
Left-associative fold of a structure but with strict application of the operator.
This ensures that each step of the fold is forced to weak head normal
form before being applied, avoiding the collection of thunks that would
otherwise occur. This is often what you want to strictly reduce a finite
list to a single, monolithic result (e.g. length).
For a general Foldable structure this should be semantically identical
to,
foldl f z =foldl'f z .toList
List of elements of a structure, from left to right.
Test whether the structure is empty. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
Returns the size/length of a finite structure as an Int. The
default implementation is optimized for structures that are similar to
cons-lists, because there is no general way to do better.
elem :: Eq a => a -> t a -> Bool infix 4 #
Does the element occur in the structure?
The sum function computes the sum of the numbers of a structure.
product :: Num a => t a -> a #
The product function computes the product of the numbers of a
structure.
Instances
all :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether all elements of the structure satisfy the predicate.
any :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether any element of the structure satisfies the predicate.
asum :: (Foldable t, Alternative f) => t (f a) -> f a #
The sum of a collection of actions, generalizing concat.
concat :: Foldable t => t [a] -> [a] #
The concatenation of all the elements of a container of lists.
concatMap :: Foldable t => (a -> [b]) -> t a -> [b] #
Map a function over all the elements of a container and concatenate the resulting lists.
elem :: Foldable t => forall a. Eq a => a -> t a -> Bool infix 4 #
Does the element occur in the structure?
fold :: Foldable t => forall m. Monoid m => t m -> m #
Combine the elements of a structure using a monoid.
foldMap :: Foldable t => forall m a. Monoid m => (a -> m) -> t a -> m #
Map each element of the structure to a monoid, and combine the results.
foldl' :: Foldable t => forall b a. (b -> a -> b) -> b -> t a -> b #
Left-associative fold of a structure but with strict application of the operator.
This ensures that each step of the fold is forced to weak head normal
form before being applied, avoiding the collection of thunks that would
otherwise occur. This is often what you want to strictly reduce a finite
list to a single, monolithic result (e.g. length).
For a general Foldable structure this should be semantically identical
to,
foldl f z =foldl'f z .toList
foldr :: Foldable t => forall a b. (a -> b -> b) -> b -> t a -> b #
Right-associative fold of a structure.
In the case of lists, foldr, when applied to a binary operator, a
starting value (typically the right-identity of the operator), and a
list, reduces the list using the binary operator, from right to left:
foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
Note that, since the head of the resulting expression is produced by
an application of the operator to the first element of the list,
foldr can produce a terminating expression from an infinite list.
For a general Foldable structure this should be semantically identical
to,
foldr f z =foldrf z .toList
for_ :: (Foldable t, Applicative f) => t a -> (a -> f b) -> f () #
length :: Foldable t => forall a. t a -> Int #
Returns the size/length of a finite structure as an Int. The
default implementation is optimized for structures that are similar to
cons-lists, because there is no general way to do better.
null :: Foldable t => forall a. t a -> Bool #
Test whether the structure is empty. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
product :: Foldable t => forall a. Num a => t a -> a #
The product function computes the product of the numbers of a
structure.
sequenceA_ :: (Foldable t, Applicative f) => t (f a) -> f () #
Evaluate each action in the structure from left to right, and
ignore the results. For a version that doesn't ignore the results
see sequenceA.
sequence_ :: (Foldable t, Monad m) => t (m a) -> m () #
Evaluate each monadic action in the structure from left to right,
and ignore the results. For a version that doesn't ignore the
results see sequence.
As of base 4.8.0.0, sequence_ is just sequenceA_, specialized
to Monad.
sum :: Foldable t => forall a. Num a => t a -> a #
The sum function computes the sum of the numbers of a structure.
traverse_ :: (Foldable t, Applicative f) => (a -> f b) -> t a -> f () #
Map each element of a structure to an action, evaluate these
actions from left to right, and ignore the results. For a version
that doesn't ignore the results see traverse.
const x is a unary function which evaluates to x for all inputs.
For instance,
>>>map (const 42) [0..3][42,42,42,42]
fix ff,
i.e. the least defined x such that f x = x.
flip :: (a -> b -> c) -> b -> a -> c #
flip ff.
($) :: (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 map ($ 0) xszipWith ($) fs xs
class Functor (f :: * -> *) where #
The Functor class is used for types that can be mapped over.
Instances of Functor should satisfy the following laws:
fmap id == id fmap (f . g) == fmap f . fmap g
The instances of Functor for lists, Maybe and IO
satisfy these laws.
Minimal complete definition
Instances
void :: Functor f => f a -> f () #
void valueIO action.
Examples
Replace the contents of a Maybe Int
>>>void NothingNothing>>>void (Just 3)Just ()
Replace the contents of an Either Int IntEither 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
($>) :: Functor f => f a -> b -> f b infixl 4 #
Flipped version of <$.
Examples
Replace the contents of a Maybe IntString:
>>>Nothing $> "foo"Nothing>>>Just 90210 $> "foo"Just "foo"
Replace the contents of an Either Int IntString, 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) $> "foo"(1,"foo")
Since: 4.7.0.0
(<$>) :: 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, <$> is function
application lifted over a Functor.
Examples
Convert from a Maybe IntMaybe Stringshow:
>>>show <$> NothingNothing>>>show <$> Just 3Just "3"
Convert from an Either Int IntEither IntString using show:
>>>show <$> Left 17Left 17>>>show <$> Right 17Right "17"
Double each element of a list:
>>>(*2) <$> [1,2,3][2,4,6]
Apply even to the second element of a pair:
>>>even <$> (2,2)(2,True)
The class of types that can be converted to a hash value.
Minimal implementation: hashWithSalt.
Instances
data HashMap k v :: * -> * -> * #
A map from keys to values. A map cannot contain duplicate keys; each key can map to at most one value.
Instances
| Eq2 HashMap | |
| Show2 HashMap | |
| Hashable2 HashMap | |
| Functor (HashMap k) | |
| Foldable (HashMap k) | |
| Traversable (HashMap k) | |
| Eq k => Eq1 (HashMap k) | |
| (Eq k, Hashable k, Read k) => Read1 (HashMap k) | |
| Show k => Show1 (HashMap k) | |
| Hashable k => Hashable1 (HashMap k) | |
| (Eq k, Hashable k) => IsList (HashMap k v) | |
| (Eq k, Eq v) => Eq (HashMap k v) | |
| (Data k, Data v, Eq k, Hashable k) => Data (HashMap k v) | |
| (Eq k, Hashable k, Read k, Read e) => Read (HashMap k e) | |
| (Show k, Show v) => Show (HashMap k v) | |
| (Eq k, Hashable k) => Semigroup (HashMap k v) | |
| (Eq k, Hashable k) => Monoid (HashMap k v) | |
| (NFData k, NFData v) => NFData (HashMap k v) | |
| (Hashable k, Hashable v) => Hashable (HashMap k v) | |
| type Item (HashMap k v) | |
A set of values. A set cannot contain duplicate values.
Instances
| Foldable HashSet | |
| Eq1 HashSet | |
| Show1 HashSet | |
| Hashable1 HashSet | |
| (Eq a, Hashable a) => IsList (HashSet a) | |
| Eq a => Eq (HashSet a) | |
| (Data a, Eq a, Hashable a) => Data (HashSet a) | |
| (Eq a, Hashable a, Read a) => Read (HashSet a) | |
| Show a => Show (HashSet a) | |
| (Hashable a, Eq a) => Semigroup (HashSet a) | |
| (Hashable a, Eq a) => Monoid (HashSet a) | |
| NFData a => NFData (HashSet a) | |
| Hashable a => Hashable (HashSet a) | |
| type Item (HashSet a) | |
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
| Bounded Int | Since: 2.1 |
| Enum Int | Since: 2.1 |
| Eq Int | |
| Integral Int | Since: 2.0.1 |
| Data Int | Since: 4.0.0.0 |
| Num Int | Since: 2.1 |
| Ord Int | |
| Read Int | Since: 2.1 |
| Real Int | Since: 2.0.1 |
| Show Int | Since: 2.1 |
| Lift Int | |
| Storable Int | Since: 2.1 |
| NFData Int | |
| Hashable Int | |
| Prim Int | |
| Unbox Int | |
| Display Int Source # | |
| Vector Vector Int | |
| MVector MVector Int | |
| Generic1 k (URec k Int) | |
| Functor (URec * Int) | |
| Foldable (URec * Int) | |
| Traversable (URec * Int) | |
| Eq (URec k Int p) | |
| Ord (URec k Int p) | |
| Show (URec k Int p) | |
| Generic (URec k Int p) | |
| data Vector Int | |
| data URec k Int | Used for marking occurrences of Since: 4.9.0.0 |
| data MVector s Int | |
| type Rep1 k (URec k Int) | |
| type Rep (URec k Int p) | |
8-bit signed integer type
Instances
| Bounded Int8 | Since: 2.1 |
| Enum Int8 | Since: 2.1 |
| Eq Int8 | Since: 2.1 |
| Integral Int8 | Since: 2.1 |
| Data Int8 | Since: 4.0.0.0 |
| Num Int8 | Since: 2.1 |
| Ord Int8 | Since: 2.1 |
| Read Int8 | Since: 2.1 |
| Real Int8 | Since: 2.1 |
| Show Int8 | Since: 2.1 |
| Ix Int8 | Since: 2.1 |
| Lift Int8 | |
| Storable Int8 | Since: 2.1 |
| Bits Int8 | Since: 2.1 |
| FiniteBits Int8 | Since: 4.6.0.0 |
| NFData Int8 | |
| Hashable Int8 | |
| Prim Int8 | |
| Unbox Int8 | |
| Vector Vector Int8 | |
| MVector MVector Int8 | |
| data Vector Int8 | |
| data MVector s Int8 | |
16-bit signed integer type
Instances
| Bounded Int16 | Since: 2.1 |
| Enum Int16 | Since: 2.1 |
| Eq Int16 | Since: 2.1 |
| Integral Int16 | Since: 2.1 |
| Data Int16 | Since: 4.0.0.0 |
| Num Int16 | Since: 2.1 |
| Ord Int16 | Since: 2.1 |
| Read Int16 | Since: 2.1 |
| Real Int16 | Since: 2.1 |
| Show Int16 | Since: 2.1 |
| Ix Int16 | Since: 2.1 |
| Lift Int16 | |
| Storable Int16 | Since: 2.1 |
| Bits Int16 | Since: 2.1 |
| FiniteBits Int16 | Since: 4.6.0.0 |
| NFData Int16 | |
| Hashable Int16 | |
| Prim Int16 | |
| Unbox Int16 | |
| Vector Vector Int16 | |
| MVector MVector Int16 | |
| data Vector Int16 | |
| data MVector s Int16 | |
32-bit signed integer type
Instances
| Bounded Int32 | Since: 2.1 |
| Enum Int32 | Since: 2.1 |
| Eq Int32 | Since: 2.1 |
| Integral Int32 | Since: 2.1 |
| Data Int32 | Since: 4.0.0.0 |
| Num Int32 | Since: 2.1 |
| Ord Int32 | Since: 2.1 |
| Read Int32 | Since: 2.1 |
| Real Int32 | Since: 2.1 |
| Show Int32 | Since: 2.1 |
| Ix Int32 | Since: 2.1 |
| Lift Int32 | |
| Storable Int32 | Since: 2.1 |
| Bits Int32 | Since: 2.1 |
| FiniteBits Int32 | Since: 4.6.0.0 |
| NFData Int32 | |
| Hashable Int32 | |
| Prim Int32 | |
| Unbox Int32 | |
| Vector Vector Int32 | |
| MVector MVector Int32 | |
| data Vector Int32 | |
| data MVector s Int32 | |
64-bit signed integer type
Instances
| Bounded Int64 | Since: 2.1 |
| Enum Int64 | Since: 2.1 |
| Eq Int64 | Since: 2.1 |
| Integral Int64 | Since: 2.1 |
| Data Int64 | Since: 4.0.0.0 |
| Num Int64 | Since: 2.1 |
| Ord Int64 | Since: 2.1 |
| Read Int64 | Since: 2.1 |
| Real Int64 | Since: 2.1 |
| Show Int64 | Since: 2.1 |
| Ix Int64 | Since: 2.1 |
| Lift Int64 | |
| Storable Int64 | Since: 2.1 |
| Bits Int64 | Since: 2.1 |
| FiniteBits Int64 | Since: 4.6.0.0 |
| NFData Int64 | |
| Hashable Int64 | |
| Prim Int64 | |
| Unbox Int64 | |
| Vector Vector Int64 | |
| MVector MVector Int64 | |
| data Vector Int64 | |
| data MVector s Int64 | |
A map of integers to values a.
Instances
| Functor IntMap | |
| Foldable IntMap | |
| Traversable IntMap | |
| Eq1 IntMap | |
| Ord1 IntMap | |
| Read1 IntMap | |
| Show1 IntMap | |
| IsList (IntMap a) | |
| Eq a => Eq (IntMap a) | |
| Data a => Data (IntMap a) | |
| Ord a => Ord (IntMap a) | |
| Read e => Read (IntMap e) | |
| Show a => Show (IntMap a) | |
| Semigroup (IntMap a) | |
| Monoid (IntMap a) | |
| NFData a => NFData (IntMap a) | |
| type Item (IntMap a) | |
A set of integers.
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],[])
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.
filter :: (a -> Bool) -> [a] -> [a] #
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]
lines breaks a string up into a list of strings at newline
characters. The resulting strings do not contain newlines.
Note that after splitting the string at newline characters, the last part of the string is considered a line even if it doesn't end with a newline. For example,
lines "" == [] lines "\n" == [""] lines "one" == ["one"] lines "one\n" == ["one"] lines "one\n\n" == ["one",""] lines "one\ntwo" == ["one","two"] lines "one\ntwo\n" == ["one","two"]
Thus lines ss.
lookup :: Eq a => a -> [(a, b)] -> Maybe b #
lookup key assocs looks up a key in an association list.
map :: (a -> b) -> [a] -> [b] #
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, ...]
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.
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])
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.
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] == []
words breaks a string up into a list of words, which were delimited
by white space.
(++) :: [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.
A Map from keys k to values a.
Instances
| Eq2 Map | |
| Ord2 Map | |
| Show2 Map | |
| Functor (Map k) | |
| Foldable (Map k) | |
| Traversable (Map k) | |
| Eq k => Eq1 (Map k) | |
| Ord k => Ord1 (Map k) | |
| (Ord k, Read k) => Read1 (Map k) | |
| Show k => Show1 (Map k) | |
| Ord k => IsList (Map k v) | |
| (Eq k, Eq a) => Eq (Map k a) | |
| (Data k, Data a, Ord k) => Data (Map k a) | |
| (Ord k, Ord v) => Ord (Map k v) | |
| (Ord k, Read k, Read e) => Read (Map k e) | |
| (Show k, Show a) => Show (Map k a) | |
| Ord k => Semigroup (Map k v) | |
| Ord k => Monoid (Map k v) | |
| (NFData k, NFData a) => NFData (Map k a) | |
| type Item (Map k v) | |
The Maybe type encapsulates an optional value. A value of type
Maybe aa (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
| Monad Maybe | Since: 2.1 |
| Functor Maybe | Since: 2.1 |
| Applicative Maybe | Since: 2.1 |
| Foldable Maybe | Since: 2.1 |
| Traversable Maybe | Since: 2.1 |
| Eq1 Maybe | Since: 4.9.0.0 |
| Ord1 Maybe | Since: 4.9.0.0 |
| Read1 Maybe | Since: 4.9.0.0 |
| Show1 Maybe | Since: 4.9.0.0 |
| Alternative Maybe | Since: 2.1 |
| MonadPlus Maybe | Since: 2.1 |
| NFData1 Maybe | Since: 1.4.3.0 |
| MonadThrow Maybe | |
| Hashable1 Maybe | |
| Eq a => Eq (Maybe a) | |
| Data a => Data (Maybe a) | Since: 4.0.0.0 |
| Ord a => Ord (Maybe a) | |
| Read a => Read (Maybe a) | Since: 2.1 |
| Show a => Show (Maybe a) | |
| Generic (Maybe a) | |
| Semigroup a => Semigroup (Maybe a) | Since: 4.9.0.0 |
| Monoid a => Monoid (Maybe a) | Lift a semigroup into Since: 2.1 |
| Lift a => Lift (Maybe a) | |
| SingKind a => SingKind (Maybe a) | Since: 4.9.0.0 |
| NFData a => NFData (Maybe a) | |
| Hashable a => Hashable (Maybe a) | |
| Generic1 * Maybe | |
| SingI (Maybe a) (Nothing a) | Since: 4.9.0.0 |
| Each (Maybe a) (Maybe b) a b | |
| SingI a1 a2 => SingI (Maybe a1) (Just a1 a2) | Since: 4.9.0.0 |
| type Rep (Maybe a) | |
| data Sing (Maybe a) | |
| type DemoteRep (Maybe a) | |
| type Rep1 * Maybe | |
| type (==) (Maybe k) a b | |
catMaybes :: [Maybe a] -> [a] #
The catMaybes function takes a list of Maybes 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]
fromMaybe :: a -> Maybe a -> a #
The fromMaybe function takes a default value and and Maybe
value. If the Maybe is Nothing, it returns the default values;
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
listToMaybe :: [a] -> Maybe a #
The listToMaybe function returns Nothing on an empty list
or 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]
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 Maybe bNothing, no element
is added on to the result list. If it is Just bb is
included in the result list.
Examples
Using mapMaybe f xcatMaybes $ 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]
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 NothingFalse
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""
maybeToList :: Maybe a -> [a] #
The maybeToList function returns an empty list when given
Nothing or a singleton list when not given Nothing.
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
Boolean monoid under conjunction (&&).
Boolean monoid under disjunction (||).
The monoid of endomorphisms under composition.
Maybe monoid returning the leftmost non-Nothing value.
First aAlt Maybe a
Instances
| Monad First | |
| Functor First | |
| Applicative First | |
| Foldable First | Since: 4.8.0.0 |
| Traversable First | Since: 4.8.0.0 |
| NFData1 First | Since: 1.4.3.0 |
| Eq a => Eq (First a) | |
| Data a => Data (First a) | Since: 4.8.0.0 |
| Ord a => Ord (First a) | |
| Read a => Read (First a) | |
| Show a => Show (First a) | |
| Generic (First a) | |
| Semigroup (First a) | Since: 4.9.0.0 |
| Monoid (First a) | Since: 2.1 |
| NFData a => NFData (First a) | Since: 1.4.0.0 |
| Generic1 * First | |
| type Rep (First a) | |
| type Rep1 * First | |
Maybe monoid returning the rightmost non-Nothing value.
Last aDual (First a)Dual (Alt Maybe a)
Instances
| Monad Last | |
| Functor Last | |
| Applicative Last | |
| Foldable Last | Since: 4.8.0.0 |
| Traversable Last | Since: 4.8.0.0 |
| NFData1 Last | Since: 1.4.3.0 |
| Eq a => Eq (Last a) | |
| Data a => Data (Last a) | Since: 4.8.0.0 |
| Ord a => Ord (Last a) | |
| Read a => Read (Last a) | |
| Show a => Show (Last a) | |
| Generic (Last a) | |
| Semigroup (Last a) | Since: 4.9.0.0 |
| Monoid (Last a) | Since: 2.1 |
| NFData a => NFData (Last a) | Since: 1.4.0.0 |
| Generic1 * Last | |
| type Rep (Last a) | |
| type Rep1 * Last | |
The class of monoids (types with an associative binary operation that has an identity). Instances should satisfy the following laws:
mappend mempty x = x
mappend x mempty = x
mappend x (mappend y z) = mappend (mappend x y) z
mconcat =
foldrmappend 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 newtypes and make those instances
of Monoid, e.g. Sum and Product.
Methods
Identity of mappend
An associative operation
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.
Instances
| Monoid Ordering | Since: 2.1 |
| Monoid () | Since: 2.1 |
| Monoid EventLifetime | Since: 4.8.0.0 |
| Monoid Event | Since: 4.3.1.0 |
| Monoid Lifetime |
Since: 4.8.0.0 |
| Monoid All | Since: 2.1 |
| Monoid Any | Since: 2.1 |
| Monoid ShortByteString | |
| Monoid ByteString | |
| Monoid ByteString | |
| Monoid Builder | |
| Monoid IntSet | |
| Monoid DisplayBuilder # | |
| Monoid [a] | Since: 2.1 |
| Monoid a => Monoid (Maybe a) | Lift a semigroup into Since: 2.1 |
| Monoid a => Monoid (IO a) | Since: 4.9.0.0 |
| (Ord a, Bounded a) => Monoid (Min a) | Since: 4.9.0.0 |
| (Ord a, Bounded a) => Monoid (Max a) | Since: 4.9.0.0 |
| Monoid m => Monoid (WrappedMonoid m) | Since: 4.9.0.0 |
| Semigroup a => Monoid (Option a) | Since: 4.9.0.0 |
| Monoid a => Monoid (Identity a) | |
| Monoid a => Monoid (Dual a) | Since: 2.1 |
| Monoid (Endo a) | Since: 2.1 |
| Num a => Monoid (Sum a) | Since: 2.1 |
| Num a => Monoid (Product a) | Since: 2.1 |
| Monoid (First a) | Since: 2.1 |
| Monoid (Last a) | Since: 2.1 |
| Monoid (IntMap a) | |
| Monoid (Seq a) | |
| Ord a => Monoid (Set a) | |
| Monoid (Array a) | |
| (Hashable a, Eq a) => Monoid (HashSet a) | |
| Storable a => Monoid (Vector a) | |
| Prim a => Monoid (Vector a) | |
| Monoid (Vector a) | |
| Monoid b => Monoid (a -> b) | Since: 2.1 |
| (Monoid a, Monoid b) => Monoid (a, b) | Since: 2.1 |
| Monoid (Proxy k s) | Since: 4.7.0.0 |
| Ord k => Monoid (Map k v) | |
| Applicative f => Monoid (Traversed a f) | |
| (Eq k, Hashable k) => Monoid (HashMap k v) | |
| (Monoid a, Monoid b, Monoid c) => Monoid (a, b, c) | Since: 2.1 |
| Monoid a => Monoid (Const k a b) | |
| Alternative f => Monoid (Alt * f a) | Since: 4.8.0.0 |
| (Monoid a, Monoid b, Monoid c, Monoid d) => Monoid (a, b, c, d) | Since: 2.1 |
| (Monoid a, Monoid b, Monoid c, Monoid d, Monoid e) => Monoid (a, b, c, d, e) | Since: 2.1 |
Monoid under multiplication.
Constructors
| Product | |
Fields
| |
Instances
| Monad Product | Since: 4.8.0.0 |
| Functor Product | Since: 4.8.0.0 |
| Applicative Product | Since: 4.8.0.0 |
| Foldable Product | Since: 4.8.0.0 |
| Traversable Product | Since: 4.8.0.0 |
| NFData1 Product | Since: 1.4.3.0 |
| Bounded a => Bounded (Product a) | |
| Eq a => Eq (Product a) | |
| Data a => Data (Product a) | Since: 4.8.0.0 |
| Num a => Num (Product a) | |
| Ord a => Ord (Product a) | |
| Read a => Read (Product a) | |
| Show a => Show (Product a) | |
| Generic (Product a) | |
| Num a => Semigroup (Product a) | Since: 4.9.0.0 |
| Num a => Monoid (Product a) | Since: 2.1 |
| NFData a => NFData (Product a) | Since: 1.4.0.0 |
| Generic1 * Product | |
| type Rep (Product a) | |
| type Rep1 * Product | |
Monoid under addition.
Instances
| Monad Sum | Since: 4.8.0.0 |
| Functor Sum | Since: 4.8.0.0 |
| Applicative Sum | Since: 4.8.0.0 |
| Foldable Sum | Since: 4.8.0.0 |
| Traversable Sum | Since: 4.8.0.0 |
| NFData1 Sum | Since: 1.4.3.0 |
| Bounded a => Bounded (Sum a) | |
| Eq a => Eq (Sum a) | |
| Data a => Data (Sum a) | Since: 4.8.0.0 |
| Num a => Num (Sum a) | |
| Ord a => Ord (Sum a) | |
| Read a => Read (Sum a) | |
| Show a => Show (Sum a) | |
| Generic (Sum a) | |
| Num a => Semigroup (Sum a) | Since: 4.9.0.0 |
| Num a => Monoid (Sum a) | Since: 2.1 |
| NFData a => NFData (Sum a) | Since: 1.4.0.0 |
| Generic1 * Sum | |
| type Rep (Sum a) | |
| type Rep1 * Sum | |
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.
Minimal complete definition: either compare or <=.
Using compare can be more efficient for complex types.
Methods
compare :: a -> a -> Ordering #
(<) :: a -> a -> Bool infix 4 #
(<=) :: a -> a -> Bool infix 4 #
(>) :: a -> a -> Bool infix 4 #
Instances
Instances
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) ...
The class of semigroups (types with an associative binary operation).
Since: 4.9.0.0
Instances
| Semigroup Ordering | Since: 4.9.0.0 |
| Semigroup () | Since: 4.9.0.0 |
| Semigroup Void | Since: 4.9.0.0 |
| Semigroup Event | Since: 4.10.0.0 |
| Semigroup Lifetime | Since: 4.10.0.0 |
| Semigroup All | Since: 4.9.0.0 |
| Semigroup Any | Since: 4.9.0.0 |
| Semigroup ShortByteString | |
| Semigroup ByteString | |
| Semigroup ByteString | |
| Semigroup Builder | |
| Semigroup IntSet | |
| Semigroup DisplayBuilder # | |
| Semigroup [a] | Since: 4.9.0.0 |
| Semigroup a => Semigroup (Maybe a) | Since: 4.9.0.0 |
| Semigroup a => Semigroup (IO a) | Since: 4.10.0.0 |
| Ord a => Semigroup (Min a) | Since: 4.9.0.0 |
| Ord a => Semigroup (Max a) | Since: 4.9.0.0 |
| Semigroup (First a) | Since: 4.9.0.0 |
| Semigroup (Last a) | Since: 4.9.0.0 |
| Monoid m => Semigroup (WrappedMonoid m) | Since: 4.9.0.0 |
| Semigroup a => Semigroup (Option a) | Since: 4.9.0.0 |
| Semigroup (NonEmpty a) | Since: 4.9.0.0 |
| Semigroup a => Semigroup (Identity a) | Since: 4.9.0.0 |
| Semigroup a => Semigroup (Dual a) | Since: 4.9.0.0 |
| Semigroup (Endo a) | Since: 4.9.0.0 |
| Num a => Semigroup (Sum a) | Since: 4.9.0.0 |
| Num a => Semigroup (Product a) | Since: 4.9.0.0 |
| Semigroup (First a) | Since: 4.9.0.0 |
| Semigroup (Last a) | Since: 4.9.0.0 |
| Semigroup (IntMap a) | |
| Semigroup (Seq a) | |
| Ord a => Semigroup (Set a) | |
| (Hashable a, Eq a) => Semigroup (HashSet a) | |
| Storable a => Semigroup (Vector a) | |
| Prim a => Semigroup (Vector a) | |
| Semigroup (Vector a) | |
| Semigroup b => Semigroup (a -> b) | Since: 4.9.0.0 |
| Semigroup (Either a b) | Since: 4.9.0.0 |
| (Semigroup a, Semigroup b) => Semigroup (a, b) | Since: 4.9.0.0 |
| Semigroup (Proxy k s) | Since: 4.9.0.0 |
| Ord k => Semigroup (Map k v) | |
| (Eq k, Hashable k) => Semigroup (HashMap k v) | |
| (Semigroup a, Semigroup b, Semigroup c) => Semigroup (a, b, c) | Since: 4.9.0.0 |
| Semigroup a => Semigroup (Const k a b) | Since: 4.9.0.0 |
| Alternative f => Semigroup (Alt * f a) | Since: 4.9.0.0 |
| (Semigroup a, Semigroup b, Semigroup c, Semigroup d) => Semigroup (a, b, c, d) | Since: 4.9.0.0 |
| (Semigroup a, Semigroup b, Semigroup c, Semigroup d, Semigroup e) => Semigroup (a, b, c, d, e) | Since: 4.9.0.0 |
A set of values a.
Class for string-like datastructures; used by the overloaded string extension (-XOverloadedStrings in GHC).
Minimal complete definition
Methods
fromString :: String -> a #
Instances
| IsString ShortByteString | |
| IsString ByteString | |
| IsString ByteString | |
| IsString DisplayBuilder # | |
| (~) * a Char => IsString [a] |
Since: 2.1 |
| IsString a => IsString (Identity a) | |
| IsString (Seq Char) | |
| (IsString a, Hashable a) => IsString (Hashed a) | |
| ((~) StreamType streamType STInput, (~) * res ()) => IsString (StreamSpec streamType res) | This instance uses Since: 0.1.0.0 |
| IsString a => IsString (Const * a b) | Since: 4.9.0.0 |
| ((~) * stdin (), (~) * stdout (), (~) * stderr ()) => IsString (ProcessConfig stdin stdout stderr) | |
A space efficient, packed, unboxed Unicode text type.
decodeUtf8' :: ByteString -> Either UnicodeException Text #
Decode a ByteString containing UTF-8 encoded text.
If the input contains any invalid UTF-8 data, the relevant exception will be returned, otherwise the decoded text.
decodeUtf8With :: OnDecodeError -> ByteString -> Text #
Decode a ByteString containing UTF-8 encoded text.
encodeUtf8 :: Text -> ByteString #
Encode text using UTF-8 encoding.
encodeUtf8Builder :: Text -> Builder #
Encode text to a ByteString Builder using UTF-8 encoding.
data UnicodeException :: * #
An exception type for representing Unicode encoding errors.
Constructors
| DecodeError String (Maybe Word8) | Could not decode a byte sequence because it was invalid under the given encoding, or ran out of input in mid-decode. |
| EncodeError String (Maybe Char) | Tried to encode a character that could not be represented under the given encoding, or ran out of input in mid-encode. |
lenientDecode :: OnDecodeError #
Replace an invalid input byte with the Unicode replacement character U+FFFD.
class (Functor t, Foldable t) => Traversable (t :: * -> *) where #
Functors representing data structures that can be traversed from left to right.
A definition of traverse must satisfy the following laws:
- naturality
t .for every applicative transformationtraversef =traverse(t . f)t- identity
traverseIdentity = Identity- composition
traverse(Compose .fmapg . f) = Compose .fmap(traverseg) .traversef
A definition of sequenceA must satisfy the following laws:
- naturality
t .for every applicative transformationsequenceA=sequenceA.fmaptt- identity
sequenceA.fmapIdentity = Identity- composition
sequenceA.fmapCompose = Compose .fmapsequenceA.sequenceA
where an applicative transformation is a function
t :: (Applicative f, Applicative g) => f a -> g a
preserving the Applicative operations, i.e.
and the identity functor Identity and composition of functors Compose
are defined as
newtype Identity a = Identity a
instance Functor Identity where
fmap f (Identity x) = Identity (f x)
instance Applicative Identity where
pure x = Identity x
Identity f <*> Identity x = Identity (f x)
newtype Compose f g a = Compose (f (g a))
instance (Functor f, Functor g) => Functor (Compose f g) where
fmap f (Compose x) = Compose (fmap (fmap f) x)
instance (Applicative f, Applicative g) => Applicative (Compose f g) where
pure x = Compose (pure (pure x))
Compose f <*> Compose x = Compose ((<*>) <$> f <*> x)(The naturality law is implied by parametricity.)
Instances are similar to Functor, e.g. given a data type
data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
a suitable instance would be
instance Traversable Tree where traverse f Empty = pure Empty traverse f (Leaf x) = Leaf <$> f x traverse f (Node l k r) = Node <$> traverse f l <*> f k <*> traverse f r
This is suitable even for abstract types, as the laws for <*>
imply a form of associativity.
The superclass instances should satisfy the following:
- In the
Functorinstance,fmapshould be equivalent to traversal with the identity applicative functor (fmapDefault). - In the
Foldableinstance,foldMapshould be equivalent to traversal with a constant applicative functor (foldMapDefault).
Methods
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_.
sequenceA :: Applicative f => t (f a) -> f (t a) #
Evaluate each action in the structure from left to right, and
and collect the results. For a version that ignores the results
see sequenceA_.
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_.
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_.
Instances
for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b) #
forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b) #
Boxed vectors, supporting efficient slicing.
Instances
| Monad Vector | |
| Functor Vector | |
| Applicative Vector | |
| Foldable Vector | |
| Traversable Vector | |
| Eq1 Vector | |
| Ord1 Vector | |
| Read1 Vector | |
| Show1 Vector | |
| MonadZip Vector | |
| Alternative Vector | |
| MonadPlus Vector | |
| Vector Vector a | |
| IsList (Vector a) | |
| Eq a => Eq (Vector a) | |
| Data a => Data (Vector a) | |
| Ord a => Ord (Vector a) | |
| Read a => Read (Vector a) | |
| Show a => Show (Vector a) | |
| Semigroup (Vector a) | |
| Monoid (Vector a) | |
| NFData a => NFData (Vector a) | |
| type Mutable Vector | |
| type Item (Vector a) | |
Uninhabited data type
Since: 4.8.0.0
Instances
| Eq Void | Since: 4.8.0.0 |
| Data Void | |
| Ord Void | Since: 4.8.0.0 |
| Read Void | Reading a |
| Show Void | Since: 4.8.0.0 |
| Ix Void | Since: 4.8.0.0 |
| Generic Void | |
| Semigroup Void | Since: 4.9.0.0 |
| Exception Void | Since: 4.8.0.0 |
| NFData Void | Since: 1.4.0.0 |
| Hashable Void | |
| type Rep Void | |
Since Void values logically don't exist, this witnesses the
logical reasoning tool of "ex falso quodlibet".
Since: 4.8.0.0
Instances
| Bounded Word | Since: 2.1 |
| Enum Word | Since: 2.1 |
| Eq Word | |
| Integral Word | Since: 2.1 |
| Data Word | Since: 4.0.0.0 |
| Num Word | Since: 2.1 |
| Ord Word | |
| Read Word | Since: 4.5.0.0 |
| Real Word | Since: 2.1 |
| Show Word | Since: 2.1 |
| Lift Word | |
| Storable Word | Since: 2.1 |
| NFData Word | |
| Hashable Word | |
| Prim Word | |
| Unbox Word | |
| Vector Vector Word | |
| MVector MVector Word | |
| Generic1 k (URec k Word) | |
| Functor (URec * Word) | |
| Foldable (URec * Word) | |
| Traversable (URec * Word) | |
| Eq (URec k Word p) | |
| Ord (URec k Word p) | |
| Show (URec k Word p) | |
| Generic (URec k Word p) | |
| data Vector Word | |
| data URec k Word | Used for marking occurrences of Since: 4.9.0.0 |
| data MVector s Word | |
| type Rep1 k (URec k Word) | |
| type Rep (URec k Word p) | |
8-bit unsigned integer type
Instances
| Bounded Word8 | Since: 2.1 |
| Enum Word8 | Since: 2.1 |
| Eq Word8 | Since: 2.1 |
| Integral Word8 | Since: 2.1 |
| Data Word8 | Since: 4.0.0.0 |
| Num Word8 | Since: 2.1 |
| Ord Word8 | Since: 2.1 |
| Read Word8 | Since: 2.1 |
| Real Word8 | Since: 2.1 |
| Show Word8 | Since: 2.1 |
| Ix Word8 | Since: 2.1 |
| Lift Word8 | |
| Storable Word8 | Since: 2.1 |
| Bits Word8 | Since: 2.1 |
| FiniteBits Word8 | Since: 4.6.0.0 |
| NFData Word8 | |
| Hashable Word8 | |
| Prim Word8 | |
| Unbox Word8 | |
| Vector Vector Word8 | |
| MVector MVector Word8 | |
| data Vector Word8 | |
| data MVector s Word8 | |
16-bit unsigned integer type
Instances
| Bounded Word16 | Since: 2.1 |
| Enum Word16 | Since: 2.1 |
| Eq Word16 | Since: 2.1 |
| Integral Word16 | Since: 2.1 |
| Data Word16 | Since: 4.0.0.0 |
| Num Word16 | Since: 2.1 |
| Ord Word16 | Since: 2.1 |
| Read Word16 | Since: 2.1 |
| Real Word16 | Since: 2.1 |
| Show Word16 | Since: 2.1 |
| Ix Word16 | Since: 2.1 |
| Lift Word16 | |
| Storable Word16 | Since: 2.1 |
| Bits Word16 | Since: 2.1 |
| FiniteBits Word16 | Since: 4.6.0.0 |
| NFData Word16 | |
| Hashable Word16 | |
| Prim Word16 | |
| Unbox Word16 | |
| Vector Vector Word16 | |
| MVector MVector Word16 | |
| data Vector Word16 | |
| data MVector s Word16 | |
32-bit unsigned integer type
Instances
| Bounded Word32 | Since: 2.1 |
| Enum Word32 | Since: 2.1 |
| Eq Word32 | Since: 2.1 |
| Integral Word32 | Since: 2.1 |
| Data Word32 | Since: 4.0.0.0 |
| Num Word32 | Since: 2.1 |
| Ord Word32 | Since: 2.1 |
| Read Word32 | Since: 2.1 |
| Real Word32 | Since: 2.1 |
| Show Word32 | Since: 2.1 |
| Ix Word32 | Since: 2.1 |
| Lift Word32 | |
| Storable Word32 | Since: 2.1 |
| Bits Word32 | Since: 2.1 |
| FiniteBits Word32 | Since: 4.6.0.0 |
| NFData Word32 | |
| Hashable Word32 | |
| Prim Word32 | |
| Unbox Word32 | |
| Vector Vector Word32 | |
| MVector MVector Word32 | |
| data Vector Word32 | |
| data MVector s Word32 | |
64-bit unsigned integer type
Instances
| Bounded Word64 | Since: 2.1 |
| Enum Word64 | Since: 2.1 |
| Eq Word64 | Since: 2.1 |
| Integral Word64 | Since: 2.1 |
| Data Word64 | Since: 4.0.0.0 |
| Num Word64 | Since: 2.1 |
| Ord Word64 | Since: 2.1 |
| Read Word64 | Since: 2.1 |
| Real Word64 | Since: 2.1 |
| Show Word64 | Since: 2.1 |
| Ix Word64 | Since: 2.1 |
| Lift Word64 | |
| Storable Word64 | Since: 2.1 |
| Bits Word64 | Since: 2.1 |
| FiniteBits Word64 | Since: 4.6.0.0 |
| NFData Word64 | |
| Hashable Word64 | |
| Prim Word64 | |
| Unbox Word64 | |
| Vector Vector Word64 | |
| MVector MVector Word64 | |
| data Vector Word64 | |
| data MVector s Word64 | |
byteSwap16 :: Word16 -> Word16 #
Swap bytes in Word16.
Since: 4.7.0.0
byteSwap32 :: Word32 -> Word32 #
Reverse order of bytes in Word32.
Since: 4.7.0.0
byteSwap64 :: Word64 -> Word64 #
Reverse order of bytes in Word64.
Since: 4.7.0.0
The member functions of this class facilitate writing values of primitive types to raw memory (which may have been allocated with the above mentioned routines) and reading values from blocks of raw memory. The class, furthermore, includes support for computing the storage requirements and alignment restrictions of storable types.
Memory addresses are represented as values of type Ptr aa which is an instance of class Storable. The type argument to
Ptr helps provide some valuable type safety in FFI code (you can't
mix pointers of different types without an explicit cast), while
helping the Haskell type system figure out which marshalling method is
needed for a given pointer.
All marshalling between Haskell and a foreign language ultimately
boils down to translating Haskell data structures into the binary
representation of a corresponding data structure of the foreign
language and vice versa. To code this marshalling in Haskell, it is
necessary to manipulate primitive data types stored in unstructured
memory blocks. The class Storable facilitates this manipulation on
all types for which it is instantiated, which are the standard basic
types of Haskell, the fixed size Int types (Int8, Int16,
Int32, Int64), the fixed size Word types (Word8, Word16,
Word32, Word64), StablePtr, all types from Foreign.C.Types,
as well as Ptr.
Minimal complete definition
sizeOf, alignment, (peek | peekElemOff | peekByteOff), (poke | pokeElemOff | pokeByteOff)
Instances
Representable types of kind *. This class is derivable in GHC with the DeriveGeneric flag on.
Instances
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: 4.9.0.0
type ASetter s t a b = (a -> Identity b) -> s -> Identity t #
ASetter s t a b is something that turns a function modifying a value into a function modifying a structure. If you ignore Identity (as Identity a is the same thing as a), the type is:
type ASetter s t a b = (a -> b) -> s -> t
The reason Identity is used here is for ASetter to be composable with other types, such as Lens.
Technically, if you're writing a library, you shouldn't use this type for setters you are exporting from your library; the right type to use is Setter, but it is not provided by this package (because then it'd have to depend on distributive). It's completely alright, however, to export functions which take an ASetter as an argument.
type Getting r s a = (a -> Const * r a) -> s -> Const * r s #
Functions that operate on getters and folds – such as (^.), (^..), (^?) – use Getter r s a (with different values of r) to describe what kind of result they need. For instance, (^.) needs the getter to be able to return a single value, and so it accepts a getter of type Getting a s a. (^..) wants the getter to gather values together, so it uses Getting (Endo [a]) s a (it could've used Getting [a] s a instead, but it's faster with Endo). The choice of r depends on what you want to do with elements you're extracting from s.
type Lens s t a b = forall (f :: * -> *). Functor f => (a -> f b) -> s -> f t #
Lens s t a b is the lowest common denominator of a setter and a getter, something that has the power of both; it has a Functor constraint, and since both Const and Identity are functors, it can be used whenever a getter or a setter is needed.
ais the type of the value inside of structurebis the type of the replaced valuesis the type of the whole structuretis the type of the structure after replacingain it withb
type Lens' s a = Lens s s a a #
This is a type alias for monomorphic lenses which don't change the type of the container (or of the value inside).
type SimpleGetter s a = forall r. Getting r s a #
A SimpleGetter s a extracts a from s; so, it's the same thing as (s -> a), but you can use it in lens chains because its type looks like this:
type SimpleGetter s a = forall r. (a -> Const r a) -> s -> Const r s
Since Const r is a functor, SimpleGetter has the same shape as other lens types and can be composed with them. To get (s -> a) out of a SimpleGetter, choose r ~ a and feed Const :: a -> Const a a to the getter:
-- the actual signature is more permissive: --view::Gettinga s a -> s -> aview::SimpleGetters a -> s -> aviewgetter =getConst. getterConst
The actual Getter from lens is more general:
type Getter s a = forall f. (Contravariant f, Functor f) => (a -> f a) -> s -> f s
I'm not currently aware of any functions that take lens's Getter but won't accept SimpleGetter, but you should try to avoid exporting SimpleGetters anyway to minimise confusion. Alternatively, look at microlens-contra, which provides a fully lens-compatible Getter.
Lens users: you can convert a SimpleGetter to Getter by applying to . view to it.
lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b #
lens creates a Lens from a getter and a setter. The resulting lens isn't the most effective one (because of having to traverse the structure twice when modifying), but it shouldn't matter much.
A (partial) lens for list indexing:
ix :: Int ->Lens'[a] a ix i =lens(!!i) -- getter (\s b -> take i s ++ b : drop (i+1) s) -- setter
Usage:
>>> [1..9]^.ix 3 4 >>> [1..9] & ix 3%~negate [1,2,3,-4,5,6,7,8,9]
When getting, the setter is completely unused; when setting, the getter is unused. Both are used only when the value is being modified. For instance, here we define a lens for the 1st element of a list, but instead of a legitimate getter we use undefined. Then we use the resulting lens for setting and it works, which proves that the getter wasn't used:
>>>[1,2,3] & lens undefined (\s b -> b : tail s) .~ 10[10,2,3]
over :: ASetter s t a b -> (a -> b) -> s -> t #
Getting fmap in a roundabout way:
overmapped::Functorf => (a -> b) -> f a -> f bovermapped=fmap
Applying a function to both components of a pair:
overboth:: (a -> b) -> (a, a) -> (b, b)overboth= \f t -> (f (fst t), f (snd t))
Using over _2second:
>>>over _2 show (10,20)(10,"20")
to :: (s -> a) -> SimpleGetter s a #
to creates a getter from any function:
a^.tof = f a
It's most useful in chains, because it lets you mix lenses and ordinary functions. Suppose you have a record which comes from some third-party library and doesn't have any lens accessors. You want to do something like this:
value ^. _1 . field . at 2
However, field isn't a getter, and you have to do this instead:
field (value ^. _1) ^. at 2
but now value is in the middle and it's hard to read the resulting code. A variant with to is prettier and more readable:
value ^. _1 . to field . at 2
(^.) :: s -> Getting a s a -> a infixl 8 #
(^.) applies a getter to a value; in other words, it gets a value out of a structure using a getter (which can be a lens, traversal, fold, etc.).
Getting 1st field of a tuple:
(^._1) :: (a, b) -> a (^._1) =fst
When (^.) is used with a traversal, it combines all results using the Monoid instance for the resulting type. For instance, for lists it would be simple concatenation:
>>>("str","ing") ^. each"string"
The reason for this is that traversals use Applicative, and the Applicative instance for Const uses monoid concatenation to combine “effects” of Const.
A non-operator version of (^.) is called view, and it's a bit more general than (^.) (it works in MonadReader). If you need the general version, you can get it from microlens-mtl; otherwise there's view available in Lens.Micro.Extras.
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
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
| Eq Double | |
| Floating Double | Since: 2.1 |
| Data Double | Since: 4.0.0.0 |
| Ord Double | |
| Read Double | Since: 2.1 |
| RealFloat Double | Since: 2.1 |
| Lift Double | |
| Storable Double | Since: 2.1 |
| NFData Double | |
| Hashable Double | |
| Prim Double | |
| Unbox Double | |
| Vector Vector Double | |
| MVector MVector Double | |
| Generic1 k (URec k Double) | |
| Functor (URec * Double) | |
| Foldable (URec * Double) | |
| Traversable (URec * Double) | |
| Eq (URec k Double p) | |
| Ord (URec k Double p) | |
| Show (URec k Double p) | |
| Generic (URec k Double p) | |
| data Vector Double | |
| data URec k Double | Used for marking occurrences of Since: 4.9.0.0 |
| data MVector s Double | |
| type Rep1 k (URec k Double) | |
| type Rep (URec k Double p) | |
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
succmaxBoundpredminBound fromEnumandtoEnumshould give a runtime error if the result value is not representable in the result type. For example,toEnum7 ::BoolenumFromandenumFromThenshould 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 = minBoundInstances
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.
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
| Eq Float | |
| Floating Float | Since: 2.1 |
| Data Float | Since: 4.0.0.0 |
| Ord Float | |
| Read Float | Since: 2.1 |
| RealFloat Float | Since: 2.1 |
| Lift Float | |
| Storable Float | Since: 2.1 |
| NFData Float | |
| Hashable Float | |
| Prim Float | |
| Unbox Float | |
| Vector Vector Float | |
| MVector MVector Float | |
| Generic1 k (URec k Float) | |
| Functor (URec * Float) | |
| Foldable (URec * Float) | |
| Traversable (URec * Float) | |
| Eq (URec k Float p) | |
| Ord (URec k Float p) | |
| Show (URec k Float p) | |
| Generic (URec k Float p) | |
| data Vector Float | |
| data URec k Float | Used for marking occurrences of Since: 4.9.0.0 |
| data MVector s Float | |
| type Rep1 k (URec k Float) | |
| type Rep (URec k Float p) | |
class Fractional a => Floating a where #
Trigonometric and hyperbolic functions and related functions.
Minimal complete definition
pi, exp, log, sin, cos, asin, acos, atan, sinh, cosh, asinh, acosh, atanh
class Num a => Fractional a where #
Fractional numbers, supporting real division.
Minimal complete definition
fromRational, (recip | (/))
Methods
fractional division
reciprocal fraction
fromRational :: Rational -> a #
Conversion from a Rational (that is Ratio IntegerfromRational
to a value of type Rational, so such literals have type
(.Fractional a) => a
Instances
| Fractional CFloat | |
| Fractional CDouble | |
| Fractional DiffTime | |
| Integral a => Fractional (Ratio a) | Since: 2.0.1 |
| RealFloat a => Fractional (Complex a) | Since: 2.1 |
| Fractional a => Fractional (Identity a) | |
| Fractional a => Fractional (Const k a b) | |
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
| Monad IO | Since: 2.1 |
| Functor IO | Since: 2.1 |
| Applicative IO | Since: 2.1 |
| MonadIO IO | Since: 4.9.0.0 |
| Alternative IO | Since: 4.9.0.0 |
| MonadPlus IO | Since: 4.9.0.0 |
| MonadThrow IO | |
| MonadCatch IO | |
| MonadMask IO | |
| PrimMonad IO | |
| PrimBase IO | |
| Quasi IO | |
| MonadUnliftIO IO | |
| Semigroup a => Semigroup (IO a) | Since: 4.10.0.0 |
| Monoid a => Monoid (IO a) | Since: 4.9.0.0 |
| type PrimState IO | |
class (Real a, Enum a) => Integral a where #
Integral numbers, supporting integer division.
Methods
quot :: a -> a -> a infixl 7 #
integer division truncated toward zero
integer remainder, satisfying
(x `quot` y)*y + (x `rem` y) == x
integer division truncated toward negative infinity
integer modulus, satisfying
(x `div` y)*y + (x `mod` y) == x
conversion to Integer
Instances
| Integral Int | Since: 2.0.1 |
| Integral Int8 | Since: 2.1 |
| Integral Int16 | Since: 2.1 |
| Integral Int32 | Since: 2.1 |
| Integral Int64 | Since: 2.1 |
| Integral Integer | Since: 2.0.1 |
| Integral Word | Since: 2.1 |
| Integral Word8 | Since: 2.1 |
| Integral Word16 | Since: 2.1 |
| Integral Word32 | Since: 2.1 |
| Integral Word64 | Since: 2.1 |
| Integral CChar | |
| Integral CSChar | |
| Integral CUChar | |
| Integral CShort | |
| Integral CUShort | |
| Integral CInt | |
| Integral CUInt | |
| Integral CLong | |
| Integral CULong | |
| Integral CLLong | |
| Integral CULLong | |
| Integral CBool | |
| Integral CPtrdiff | |
| Integral CSize | |
| Integral CWchar | |
| Integral CSigAtomic | |
| Integral CIntPtr | |
| Integral CUIntPtr | |
| Integral CIntMax | |
| Integral CUIntMax | |
| Integral a => Integral (Identity a) | |
| Integral a => Integral (Const k a b) | |
Basic numeric class.
Methods
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 Int | Since: 2.1 |
| Num Int8 | Since: 2.1 |
| Num Int16 | Since: 2.1 |
| Num Int32 | Since: 2.1 |
| Num Int64 | Since: 2.1 |
| Num Integer | Since: 2.1 |
| Num Word | Since: 2.1 |
| Num Word8 | Since: 2.1 |
| Num Word16 | Since: 2.1 |
| Num Word32 | Since: 2.1 |
| Num Word64 | Since: 2.1 |
| Num CChar | |
| Num CSChar | |
| Num CUChar | |
| Num CShort | |
| Num CUShort | |
| Num CInt | |
| Num CUInt | |
| Num CLong | |
| Num CULong | |
| Num CLLong | |
| Num CULLong | |
| Num CBool | |
| Num CFloat | |
| Num CDouble | |
| Num CPtrdiff | |
| Num CSize | |
| Num CWchar | |
| Num CSigAtomic | |
| Num CClock | |
| Num CTime | |
| Num CUSeconds | |
| Num CSUSeconds | |
| Num CIntPtr | |
| Num CUIntPtr | |
| Num CIntMax | |
| Num CUIntMax | |
| Num CodePoint | |
| Num DecoderState | |
| Num DiffTime | |
| Integral a => Num (Ratio a) | Since: 2.0.1 |
| RealFloat a => Num (Complex a) | Since: 2.1 |
| Num a => Num (Min a) | Since: 4.9.0.0 |
| Num a => Num (Max a) | Since: 4.9.0.0 |
| Num a => Num (Identity a) | |
| Num a => Num (Sum a) | |
| Num a => Num (Product a) | |
| Num a => Num (Const k a b) | |
| Num (f a) => Num (Alt k f a) | |
class (Num a, Ord a) => Real a where #
Minimal complete definition
Methods
toRational :: a -> Rational #
the rational equivalent of its real argument with full precision
Instances
| Real Int | Since: 2.0.1 |
| Real Int8 | Since: 2.1 |
| Real Int16 | Since: 2.1 |
| Real Int32 | Since: 2.1 |
| Real Int64 | Since: 2.1 |
| Real Integer | Since: 2.0.1 |
| Real Word | Since: 2.1 |
| Real Word8 | Since: 2.1 |
| Real Word16 | Since: 2.1 |
| Real Word32 | Since: 2.1 |
| Real Word64 | Since: 2.1 |
| Real CChar | |
| Real CSChar | |
| Real CUChar | |
| Real CShort | |
| Real CUShort | |
| Real CInt | |
| Real CUInt | |
| Real CLong | |
| Real CULong | |
| Real CLLong | |
| Real CULLong | |
| Real CBool | |
| Real CFloat | |
| Real CDouble | |
| Real CPtrdiff | |
| Real CSize | |
| Real CWchar | |
| Real CSigAtomic | |
| Real CClock | |
| Real CTime | |
| Real CUSeconds | |
| Real CSUSeconds | |
| Real CIntPtr | |
| Real CUIntPtr | |
| Real CIntMax | |
| Real CUIntMax | |
| Real DiffTime | |
| Integral a => Real (Ratio a) | Since: 2.0.1 |
| Real a => Real (Identity a) | |
| Real a => Real (Const k a b) | |
class (RealFrac a, Floating a) => RealFloat a where #
Efficient, machine-independent access to the components of a floating-point number.
Minimal complete definition
floatRadix, floatDigits, floatRange, decodeFloat, encodeFloat, isNaN, isInfinite, isDenormalized, isNegativeZero, isIEEE
Methods
floatRadix :: a -> Integer #
a constant function, returning the radix of the representation
(often 2)
floatDigits :: a -> Int #
a constant function, returning the number of digits of
floatRadix in the significand
floatRange :: a -> (Int, Int) #
a constant function, returning the lowest and highest values the exponent may assume
decodeFloat :: a -> (Integer, Int) #
The function decodeFloat applied to a real floating-point
number returns the significand expressed as an Integer and an
appropriately scaled exponent (an Int). If decodeFloat x(m,n), then x is equal in value to m*b^^n, where b
is the floating-point radix, and furthermore, either m and n
are both zero or else b^(d-1) <= , where abs m < b^dd is
the value of floatDigits xdecodeFloat 0 = (0,0)decodeFloat (-0.0) = (0,0)decodeFloat xisNaN xisInfinite xTrue.
encodeFloat :: Integer -> Int -> a #
encodeFloat performs the inverse of decodeFloat in the
sense that for finite x with the exception of -0.0,
uncurry encodeFloat (decodeFloat x) = xencodeFloat m nm*b^^n (or ±Infinity if overflow
occurs); usually the closer, but if m contains too many bits,
the result may be rounded in the wrong direction.
exponent corresponds to the second component of decodeFloat.
exponent 0 = 0x,
exponent x = snd (decodeFloat x) + floatDigits xx is a finite floating-point number, it is equal in value to
significand x * b ^^ exponent xb is the
floating-point radix.
The behaviour is unspecified on infinite or NaN values.
significand :: a -> a #
The first component of decodeFloat, scaled to lie in the open
interval (-1,1), either 0.0 or of absolute value >= 1/b,
where b is the floating-point radix.
The behaviour is unspecified on infinite or NaN values.
scaleFloat :: Int -> a -> a #
multiplies a floating-point number by an integer power of the radix
True if the argument is an IEEE "not-a-number" (NaN) value
isInfinite :: a -> Bool #
True if the argument is an IEEE infinity or negative infinity
isDenormalized :: a -> Bool #
True if the argument is too small to be represented in
normalized format
isNegativeZero :: a -> Bool #
True if the argument is an IEEE negative zero
True if the argument is an IEEE floating point number
a version of arctangent taking two real floating-point arguments.
For real floating x and y, atan2 y x(x,y). atan2 y x-pi,
pi]. It follows the Common Lisp semantics for the origin when
signed zeroes are supported. atan2 y 1y in a type
that is RealFloat, should return the same value as atan yatan2 is provided, but implementors
can provide a more accurate implementation.
class (Real a, Fractional a) => RealFrac a where #
Extracting components of fractions.
Minimal complete definition
Methods
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:
nis an integral number with the same sign asx; andfis 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 #
truncate xx between zero and x
round :: Integral b => a -> b #
round xx;
the even integer if x is equidistant between two integers
ceiling :: Integral b => a -> b #
ceiling xx
floor :: Integral b => a -> b #
floor xx
Conversion of values to readable Strings.
Derived instances of Show have the following properties, which
are compatible with derived instances of Read:
- The result of
showis 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
showsPrecwill produce infix applications of the constructor. - the representation will be enclosed in parentheses if the
precedence of the top-level constructor in
xis less thand(associativity is ignored). Thus, ifdis0then the result is never surrounded in parentheses; ifdis11it is always surrounded in parentheses, unless it is an atomic expression. - If the constructor is defined using record syntax, then
showwill 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 = 5Note that right-associativity of :^: is ignored. For example,
show(Leaf 1 :^: Leaf 2 :^: Leaf 3)"Leaf 1 :^: (Leaf 2 :^: Leaf 3)".
Methods
Instances
error :: HasCallStack => [Char] -> a #
error stops execution and displays an error message.
fromIntegral :: (Integral a, Num b) => a -> b #
general coercion from integral types
gcd :: Integral a => a -> a -> a #
gcd x yx and y of which
every common factor of x and y is also a factor; for example
gcd 4 2 = 2gcd (-4) 6 = 2gcd 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, abs minBound < 0minBound0 or minBound
lcm :: Integral a => a -> a -> a #
lcm x yx and y divide.
realToFrac :: (Real a, Fractional b) => a -> b #
general coercion to fractional types
The value of seq a b is bottom if a is bottom, and
otherwise equal to b. 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.
uncurry :: (a -> b -> c) -> (a, b) -> c #
uncurry converts a curried function to a function on pairs.
undefined :: HasCallStack => a #
($!) :: (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.
(^^) :: (Fractional a, Integral b) => a -> b -> a infixr 8 #
raise a number to an integral power
Defines the exit codes that a program can return.
Constructors
| ExitSuccess | indicates successful termination; |
| ExitFailure Int | indicates program failure with an exit code. The exact interpretation of the code is operating-system dependent. In particular, some values may be prohibited (e.g. 0 on a POSIX-compliant system). |
Parsing of Strings, producing values.
Derived instances of Read make the following assumptions, which
derived instances of Show obey:
- If the constructor is defined to be an infix operator, then the
derived
Readinstance will parse only infix applications of the constructor (not the prefix form). - Associativity is not used to reduce the occurrence of parentheses, although precedence may be.
- If the constructor is defined using record syntax, the derived
Readwill parse only the record-syntax form, and furthermore, the fields must be given in the same order as the original declaration. - The derived
Readinstance allows arbitrary Haskell whitespace between tokens of the input string. Extra parentheses are also allowed.
For example, given the declarations
infixr 5 :^: data Tree a = Leaf a | Tree a :^: Tree a
the derived instance of Read in Haskell 2010 is equivalent to
instance (Read a) => Read (Tree a) where
readsPrec d r = readParen (d > app_prec)
(\r -> [(Leaf m,t) |
("Leaf",s) <- lex r,
(m,t) <- readsPrec (app_prec+1) s]) r
++ readParen (d > up_prec)
(\r -> [(u:^:v,w) |
(u,s) <- readsPrec (up_prec+1) r,
(":^:",t) <- lex s,
(v,w) <- readsPrec (up_prec+1) t]) r
where app_prec = 10
up_prec = 5Note that right-associativity of :^: is unused.
The derived instance in GHC is equivalent to
instance (Read a) => Read (Tree a) where
readPrec = parens $ (prec app_prec $ do
Ident "Leaf" <- lexP
m <- step readPrec
return (Leaf m))
+++ (prec up_prec $ do
u <- step readPrec
Symbol ":^:" <- lexP
v <- step readPrec
return (u :^: v))
where app_prec = 10
up_prec = 5
readListPrec = readListPrecDefaultWhy do both readsPrec and readPrec exist, and why does GHC opt to
implement readPrec in derived Read instances instead of readsPrec?
The reason is that readsPrec is based on the ReadS type, and although
ReadS is mentioned in the Haskell 2010 Report, it is not a very efficient
parser data structure.
readPrec, on the other hand, is based on a much more efficient ReadPrec
datatype (a.k.a "new-style parsers"), but its definition relies on the use
of the RankNTypes language extension. Therefore, readPrec (and its
cousin, readListPrec) are marked as GHC-only. Nevertheless, it is
recommended to use readPrec instead of readsPrec whenever possible
for the efficiency improvements it brings.
As mentioned above, derived Read instances in GHC will implement
readPrec instead of readsPrec. The default implementations of
readsPrec (and its cousin, readList) will simply use readPrec under
the hood. If you are writing a Read instance by hand, it is recommended
to write it like so:
instanceReadT wherereadPrec= ...readListPrec=readListPrecDefault
Instances
| Read Bool | Since: 2.1 |
| Read Char | Since: 2.1 |
| Read Double | Since: 2.1 |
| Read Float | Since: 2.1 |
| Read Int | Since: 2.1 |
| Read Int8 | Since: 2.1 |
| Read Int16 | Since: 2.1 |
| Read Int32 | Since: 2.1 |
| Read Int64 | Since: 2.1 |
| Read Integer | Since: 2.1 |
| Read Ordering | Since: 2.1 |
| Read Word | Since: 4.5.0.0 |
| Read Word8 | Since: 2.1 |
| Read Word16 | Since: 2.1 |
| Read Word32 | Since: 2.1 |
| Read Word64 | Since: 2.1 |
| Read () | Since: 2.1 |
| Read Void | Reading a |
| Read ExitCode | |
| Read BufferMode | |
| Read Newline | |
| Read NewlineMode | |
| Read All | |
| Read Any | |
| Read Fixity | |
| Read Associativity | |
| Read SourceUnpackedness | |
| Read SourceStrictness | |
| Read DecidedStrictness | |
| Read CChar | |
| Read CSChar | |
| Read CUChar | |
| Read CShort | |
| Read CUShort | |
| Read CInt | |
| Read CUInt | |
| Read CLong | |
| Read CULong | |
| Read CLLong | |
| Read CULLong | |
| Read CBool | |
| Read CFloat | |
| Read CDouble | |
| Read CPtrdiff | |
| Read CSize | |
| Read CWchar | |
| Read CSigAtomic | |
| Read CClock | |
| Read CTime | |
| Read CUSeconds | |
| Read CSUSeconds | |
| Read CIntPtr | |
| Read CUIntPtr | |
| Read CIntMax | |
| Read CUIntMax | |
| Read IOMode | |
| Read Lexeme | Since: 2.1 |
| Read GeneralCategory | |
| Read ShortByteString | |
| Read ByteString | |
| Read ByteString | |
| Read IntSet | |
| Read DirectoryType | |
| Read Permissions | |
| Read XdgDirectory | |
| Read LogLevel # | |
| Read a => Read [a] | Since: 2.1 |
| Read a => Read (Maybe a) | Since: 2.1 |
| (Integral a, Read a) => Read (Ratio a) | Since: 2.1 |
| Read p => Read (Par1 p) | |
| Read a => Read (Complex a) | |
| Read a => Read (Min a) | |
| Read a => Read (Max a) | |
| Read a => Read (First a) | |
| Read a => Read (Last a) | |
| Read m => Read (WrappedMonoid m) | |
| Read a => Read (Option a) | |
| Read a => Read (NonEmpty a) | |
| Read a => Read (ZipList a) | |
| Read a => Read (Identity a) | This instance would be equivalent to the derived instances of the
Since: 4.8.0.0 |
| Read a => Read (Dual a) | |
| Read a => Read (Sum a) | |
| Read a => Read (Product a) | |
| Read a => Read (First a) | |
| Read a => Read (Last a) | |
| Read a => Read (Down a) | |
| Read e => Read (IntMap e) | |
| Read a => Read (Tree a) | |
| Read a => Read (Seq a) | |
| Read a => Read (ViewL a) | |
| Read a => Read (ViewR a) | |
| (Read a, Ord a) => Read (Set a) | |
| Read a => Read (Array a) | |
| (Eq a, Hashable a, Read a) => Read (HashSet a) | |
| (Read a, Storable a) => Read (Vector a) | |
| (Read a, Prim a) => Read (Vector a) | |
| Read a => Read (Vector a) | |
| (Read b, Read a) => Read (Either a b) | |
| Read (V1 k p) | |
| Read (U1 k p) | Since: 4.9.0.0 |
| (Read a, Read b) => Read (a, b) | Since: 2.1 |
| (Ix a, Read a, Read b) => Read (Array a b) | Since: 2.1 |
| (Read b, Read a) => Read (Arg a b) | |
| Read (Proxy k s) | Since: 4.7.0.0 |
| (Ord k, Read k, Read e) => Read (Map k e) | |
| (Read1 m, Read a) => Read (ListT m a) | |
| (Read1 m, Read a) => Read (MaybeT m a) | |
| (Eq k, Hashable k, Read k, Read e) => Read (HashMap k e) | |
| Read (f p) => Read (Rec1 k f p) | |
| (Read a, Read b, Read c) => Read (a, b, c) | Since: 2.1 |
| Read a => Read (Const k a b) | This instance would be equivalent to the derived instances of the
Since: 4.8.0.0 |
| Read (f a) => Read (Alt k f a) | |
| (~) k a b => Read ((:~:) k a b) | Since: 4.7.0.0 |
| (Read e, Read1 m, Read a) => Read (ErrorT e m a) | |
| (Read e, Read1 m, Read a) => Read (ExceptT e m a) | |
| (Read w, Read1 m, Read a) => Read (WriterT w m a) | |
| (Read w, Read1 m, Read a) => Read (WriterT w m a) | |
| (Read1 f, Read a) => Read (IdentityT * f a) | |
| Read c => Read (K1 k i c p) | |
| (Read (g p), Read (f p)) => Read ((:+:) k f g p) | |
| (Read (g p), Read (f p)) => Read ((:*:) k f g p) | |
| (Read a, Read b, Read c, Read d) => Read (a, b, c, d) | Since: 2.1 |
| (Read1 f, Read1 g, Read a) => Read (Product * f g a) | Since: 4.9.0.0 |
| (Read1 f, Read1 g, Read a) => Read (Sum * f g a) | Since: 4.9.0.0 |
| (~~) k1 k2 a b => Read ((:~~:) k1 k2 a b) | Since: 4.10.0.0 |
| Read (f p) => Read (M1 k i c f p) | |
| Read (f (g p)) => Read ((:.:) k2 k1 f g p) | |
| (Read a, Read b, Read c, Read d, Read e) => Read (a, b, c, d, e) | Since: 2.1 |
| (Read1 f, Read1 g, Read a) => Read (Compose * * f g a) | Since: 4.9.0.0 |
| (Read a, Read b, Read c, Read d, Read e, Read f) => Read (a, b, c, d, e, f) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g) => Read (a, b, c, d, e, f, g) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h) => Read (a, b, c, d, e, f, g, h) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i) => Read (a, b, c, d, e, f, g, h, i) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j) => Read (a, b, c, d, e, f, g, h, i, j) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k) => Read (a, b, c, d, e, f, g, h, i, j, k) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l) => Read (a, b, c, d, e, f, g, h, i, j, k, l) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l, Read m) => Read (a, b, c, d, e, f, g, h, i, j, k, l, m) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l, Read m, Read n) => Read (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l, Read m, Read n, Read o) => Read (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | Since: 2.1 |