| Safe Haskell | Safe-Inferred |
|---|---|
| Language | GHC2021 |
Testlib.Prelude
Synopsis
- module Testlib.App
- module Testlib.Env
- module Testlib.Cannon
- module Testlib.Assertions
- module Testlib.Types
- module Testlib.ModService
- module Testlib.HTTP
- module Testlib.JSON
- module Testlib.PTest
- data One
- data Result a
- class FromJSON a where
- class ToJSON a where
- toJSON :: a -> Value
- toEncoding :: a -> Encoding
- toJSONList :: [a] -> Value
- toEncodingList :: [a] -> Encoding
- type Object = KeyMap Value
- type Array = Vector Value
- class FromJSON1 (f :: Type -> Type) where
- data Key
- data Zero
- data JSONKeyOptions
- data SumEncoding
- data Options
- newtype DotNetTime = DotNetTime {}
- data Value
- type JSONPath = [JSONPathElement]
- class FromJSON2 (f :: Type -> Type -> Type) where
- class (ConstructorNames f, SumFromString f) => GFromJSONKey (f :: Type -> Type)
- data FromJSONKeyFunction a where
- FromJSONKeyCoerce :: forall a. Coercible Text a => FromJSONKeyFunction a
- FromJSONKeyText :: forall a. !(Text -> a) -> FromJSONKeyFunction a
- FromJSONKeyTextParser :: forall a. !(Text -> Parser a) -> FromJSONKeyFunction a
- FromJSONKeyValue :: forall a. !(Value -> Parser a) -> FromJSONKeyFunction a
- class FromJSONKey a where
- data FromArgs arity a
- class GFromJSON arity (f :: Type -> Type)
- data Series
- type Encoding = Encoding' Value
- class ToJSON2 (f :: Type -> Type -> Type) where
- liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> f a b -> Value
- liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [f a b] -> Value
- liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> f a b -> Encoding
- liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [f a b] -> Encoding
- class ToJSON1 (f :: Type -> Type) where
- liftToJSON :: (a -> Value) -> ([a] -> Value) -> f a -> Value
- liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [f a] -> Value
- liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> f a -> Encoding
- liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [f a] -> Encoding
- class GetConName f => GToJSONKey (f :: k -> Type)
- data ToJSONKeyFunction a
- = ToJSONKeyText !(a -> Key) !(a -> Encoding' Key)
- | ToJSONKeyValue !(a -> Value) !(a -> Encoding)
- class ToJSONKey a where
- toJSONKey :: ToJSONKeyFunction a
- toJSONKeyList :: ToJSONKeyFunction [a]
- class KeyValue kv
- data ToArgs res arity a
- class GToJSON' enc arity (f :: Type -> Type)
- type GToEncoding = GToJSON' Encoding
- type GToJSON = GToJSON' Value
- newtype AesonException = AesonException String
- genericFromJSONKey :: (Generic a, GFromJSONKey (Rep a)) => JSONKeyOptions -> FromJSONKeyFunction a
- genericToJSONKey :: (Generic a, GToJSONKey (Rep a)) => JSONKeyOptions -> ToJSONKeyFunction a
- fromJSON :: FromJSON a => Value -> Result a
- genericToJSON :: (Generic a, GToJSON' Value Zero (Rep a)) => Options -> a -> Value
- object :: [Pair] -> Value
- (<?>) :: Parser a -> JSONPathElement -> Parser a
- defaultOptions :: Options
- defaultTaggedObject :: SumEncoding
- defaultJSONKeyOptions :: JSONKeyOptions
- camelTo2 :: Char -> String -> String
- json :: Parser Value
- json' :: Parser Value
- parseIndexedJSON :: (Value -> Parser a) -> Int -> Value -> Parser a
- genericParseJSON :: (Generic a, GFromJSON Zero (Rep a)) => Options -> Value -> Parser a
- genericLiftParseJSON :: (Generic1 f, GFromJSON One (Rep1 f)) => Options -> (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser (f a)
- parseJSON1 :: (FromJSON1 f, FromJSON a) => Value -> Parser (f a)
- parseJSON2 :: (FromJSON2 f, FromJSON a, FromJSON b) => Value -> Parser (f a b)
- withObject :: String -> (Object -> Parser a) -> Value -> Parser a
- withText :: String -> (Text -> Parser a) -> Value -> Parser a
- withArray :: String -> (Array -> Parser a) -> Value -> Parser a
- withScientific :: String -> (Scientific -> Parser a) -> Value -> Parser a
- withBool :: String -> (Bool -> Parser a) -> Value -> Parser a
- withEmbeddedJSON :: String -> (Value -> Parser a) -> Value -> Parser a
- (.:) :: FromJSON a => Object -> Key -> Parser a
- (.:?) :: FromJSON a => Object -> Key -> Parser (Maybe a)
- (.:!) :: FromJSON a => Object -> Key -> Parser (Maybe a)
- (.!=) :: Parser (Maybe a) -> a -> Parser a
- fromEncoding :: Encoding' tag -> Builder
- pairs :: Series -> Encoding
- genericLiftToJSON :: (Generic1 f, GToJSON' Value One (Rep1 f)) => Options -> (a -> Value) -> ([a] -> Value) -> f a -> Value
- genericToEncoding :: (Generic a, GToJSON' Encoding Zero (Rep a)) => Options -> a -> Encoding
- genericLiftToEncoding :: (Generic1 f, GToJSON' Encoding One (Rep1 f)) => Options -> (a -> Encoding) -> ([a] -> Encoding) -> f a -> Encoding
- toJSON1 :: (ToJSON1 f, ToJSON a) => f a -> Value
- toEncoding1 :: (ToJSON1 f, ToJSON a) => f a -> Encoding
- toJSON2 :: (ToJSON2 f, ToJSON a, ToJSON b) => f a b -> Value
- toEncoding2 :: (ToJSON2 f, ToJSON a, ToJSON b) => f a b -> Encoding
- foldable :: (Foldable t, ToJSON a) => t a -> Encoding
- encode :: ToJSON a => a -> ByteString
- encodeFile :: ToJSON a => FilePath -> a -> IO ()
- decode :: FromJSON a => ByteString -> Maybe a
- decodeStrict :: FromJSON a => ByteString -> Maybe a
- decodeFileStrict :: FromJSON a => FilePath -> IO (Maybe a)
- decode' :: FromJSON a => ByteString -> Maybe a
- decodeStrict' :: FromJSON a => ByteString -> Maybe a
- decodeFileStrict' :: FromJSON a => FilePath -> IO (Maybe a)
- eitherDecode :: FromJSON a => ByteString -> Either String a
- eitherDecodeStrict :: FromJSON a => ByteString -> Either String a
- eitherDecodeFileStrict :: FromJSON a => FilePath -> IO (Either String a)
- eitherDecode' :: FromJSON a => ByteString -> Either String a
- eitherDecodeStrict' :: FromJSON a => ByteString -> Either String a
- eitherDecodeFileStrict' :: FromJSON a => FilePath -> IO (Either String a)
- throwDecode :: (FromJSON a, MonadThrow m) => ByteString -> m a
- throwDecodeStrict :: (FromJSON a, MonadThrow m) => ByteString -> m a
- throwDecode' :: (FromJSON a, MonadThrow m) => ByteString -> m a
- throwDecodeStrict' :: (FromJSON a, MonadThrow m) => ByteString -> m a
- data Double
- data Float
- data Integer
- type ShowS = String -> String
- data IO a
- class Show a where
- class Bounded a where
- class Enum a where
- succ :: a -> a
- pred :: a -> a
- toEnum :: Int -> a
- fromEnum :: a -> Int
- enumFrom :: a -> [a]
- enumFromThen :: a -> a -> [a]
- enumFromTo :: a -> a -> [a]
- enumFromThenTo :: a -> a -> a -> [a]
- class (Real a, Fractional a) => RealFrac a where
- class (Real a, Enum a) => Integral a where
- class Read a where
- class Eq a => Ord a where
- type Rational = Ratio Integer
- class Num a => Fractional a where
- (/) :: a -> a -> a
- recip :: a -> a
- fromRational :: Rational -> a
- class (Num a, Ord a) => Real a where
- toRational :: a -> Rational
- class Eq a where
- class Fractional a => Floating a where
- class Num a where
- class (RealFrac a, Floating a) => RealFloat a where
- floatRadix :: a -> Integer
- floatDigits :: a -> Int
- floatRange :: a -> (Int, Int)
- decodeFloat :: a -> (Integer, Int)
- encodeFloat :: Integer -> Int -> a
- exponent :: a -> Int
- significand :: a -> a
- scaleFloat :: Int -> a -> a
- isNaN :: a -> Bool
- isInfinite :: a -> Bool
- isDenormalized :: a -> Bool
- isNegativeZero :: a -> Bool
- isIEEE :: a -> Bool
- atan2 :: a -> a -> a
- type ReadS a = String -> [(a, String)]
- type FilePath = String
- read :: Read a => String -> a
- realToFrac :: (Real a, Fractional b) => a -> b
- fromIntegral :: (Integral a, Num b) => a -> b
- seq :: forall {r :: RuntimeRep} a (b :: TYPE r). a -> b -> b
- error :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => [Char] -> a
- even :: Integral a => a -> Bool
- (^) :: (Num a, Integral b) => a -> b -> a
- undefined :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => a
- ($!) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b
- subtract :: Num a => a -> a -> a
- shows :: Show a => a -> ShowS
- showChar :: Char -> ShowS
- showString :: String -> ShowS
- showParen :: Bool -> ShowS -> ShowS
- odd :: Integral a => a -> Bool
- (^^) :: (Fractional a, Integral b) => a -> b -> a
- gcd :: Integral a => a -> a -> a
- lcm :: Integral a => a -> a -> a
- lex :: ReadS String
- readParen :: Bool -> ReadS a -> ReadS a
- reads :: Read a => ReadS a
- class Functor f => Applicative (f :: Type -> Type) where
- class Applicative f => Alternative (f :: Type -> Type) where
- (<|>) :: f a -> f a -> f a
- newtype Const a (b :: k) = Const {
- getConst :: a
- newtype ZipList a = ZipList {
- getZipList :: [a]
- newtype WrappedArrow (a :: Type -> Type -> Type) b c = WrapArrow {
- unwrapArrow :: a b c
- newtype WrappedMonad (m :: Type -> Type) a = WrapMonad {
- unwrapMonad :: m a
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- (<$) :: Functor f => a -> f b -> f a
- (<**>) :: Applicative f => f a -> f (a -> b) -> f b
- liftA :: Applicative f => (a -> b) -> f a -> f b
- liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
- asum :: (Foldable t, Alternative f) => t (f a) -> f a
- class Functor (f :: Type -> Type) where
- class Applicative m => Monad (m :: Type -> Type) where
- class Monad m => MonadFail (m :: Type -> Type) where
- class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where
- void :: Functor f => f a -> f ()
- join :: Monad m => m (m a) -> m a
- liftM :: Monad m => (a1 -> r) -> m a1 -> m r
- forever :: Applicative f => f a -> f b
- guard :: Alternative f => Bool -> f ()
- (=<<) :: Monad m => (a -> m b) -> m a -> m b
- when :: Applicative f => Bool -> f () -> f ()
- liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
- liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r
- liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r
- liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r
- ap :: Monad m => m (a -> b) -> m a -> m b
- filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a]
- (>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c
- (<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c
- mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c])
- zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c]
- zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m ()
- foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b
- foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m ()
- replicateM :: Applicative m => Int -> m a -> m [a]
- replicateM_ :: Applicative m => Int -> m a -> m ()
- unless :: Applicative f => Bool -> f () -> f ()
- (<$!>) :: Monad m => (a -> b) -> m a -> m b
- mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a
- module Data.Functor
- class (forall a. Functor (p a)) => Bifunctor (p :: Type -> Type -> Type) where
- bimap :: (a -> b) -> (c -> d) -> p a c -> p b d
- module Data.Function
- module Data.Functor.Identity
- module Data.Int
- module Data.Word
- module Data.Void
- module Data.Bool
- module Data.Char
- module Data.Ord
- newtype Any = Any {}
- class Semigroup a where
- newtype Sum a = Sum {
- getSum :: a
- newtype Product a = Product {
- getProduct :: a
- newtype Last a = Last {
- getLast :: a
- newtype First a = First {
- getFirst :: a
- newtype Min a = Min {
- getMin :: a
- newtype Max a = Max {
- getMax :: a
- newtype All = All {}
- newtype Endo a = Endo {
- appEndo :: a -> a
- newtype Dual a = Dual {
- getDual :: a
- newtype WrappedMonoid m = WrapMonoid {
- unwrapMonoid :: m
- type ArgMax a b = Max (Arg a b)
- type ArgMin a b = Min (Arg a b)
- data Arg a b = Arg a b
- stimesIdempotent :: Integral b => b -> a -> a
- stimesIdempotentMonoid :: (Integral b, Monoid a) => b -> a -> a
- stimesMonoid :: (Integral b, Monoid a) => b -> a -> a
- cycle1 :: Semigroup m => m -> m
- mtimesDefault :: (Integral b, Monoid a) => b -> a -> a
- newtype Any = Any {}
- class Semigroup a => Monoid a where
- newtype Sum a = Sum {
- getSum :: a
- newtype Product a = Product {
- getProduct :: a
- newtype Alt (f :: k -> Type) (a :: k) = Alt {
- getAlt :: f a
- newtype All = All {}
- newtype Endo a = Endo {
- appEndo :: a -> a
- newtype Dual a = Dual {
- getDual :: a
- newtype Ap (f :: k -> Type) (a :: k) = Ap {
- getAp :: f a
- (<>) :: Semigroup a => a -> a -> a
- module Data.Maybe
- module Data.Either
- module Data.Foldable
- module Data.Traversable
- module Data.Tuple
- module Data.String
- (++) :: [a] -> [a] -> [a]
- foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b
- null :: Foldable t => t a -> Bool
- foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b
- foldl' :: Foldable t => (b -> a -> b) -> b -> t a -> b
- length :: Foldable t => t a -> Int
- foldl1 :: Foldable t => (a -> a -> a) -> t a -> a
- sum :: (Foldable t, Num a) => t a -> a
- product :: (Foldable t, Num a) => t a -> a
- foldr1 :: Foldable t => (a -> a -> a) -> t a -> a
- maximum :: (Foldable t, Ord a) => t a -> a
- minimum :: (Foldable t, Ord a) => t a -> a
- elem :: (Foldable t, Eq a) => a -> t a -> Bool
- map :: (a -> b) -> [a] -> [b]
- sort :: Ord a => [a] -> [a]
- lookup :: Eq a => a -> [(a, b)] -> Maybe b
- union :: Eq a => [a] -> [a] -> [a]
- filter :: (a -> Bool) -> [a] -> [a]
- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
- sortBy :: (a -> a -> Ordering) -> [a] -> [a]
- genericLength :: Num i => [a] -> i
- maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
- minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
- genericReplicate :: Integral i => i -> a -> [a]
- genericTake :: Integral i => i -> [a] -> [a]
- genericDrop :: Integral i => i -> [a] -> [a]
- genericSplitAt :: Integral i => i -> [a] -> ([a], [a])
- genericIndex :: Integral i => [a] -> i -> a
- head :: HasCallStack => [a] -> a
- group :: Eq a => [a] -> [[a]]
- groupBy :: (a -> a -> Bool) -> [a] -> [[a]]
- unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
- transpose :: [[a]] -> [[a]]
- sortOn :: Ord b => (a -> b) -> [a] -> [a]
- cycle :: HasCallStack => [a] -> [a]
- concat :: Foldable t => t [a] -> [a]
- zip :: [a] -> [b] -> [(a, b)]
- uncons :: [a] -> Maybe (a, [a])
- tail :: HasCallStack => [a] -> [a]
- last :: HasCallStack => [a] -> a
- init :: HasCallStack => [a] -> [a]
- foldl1' :: HasCallStack => (a -> a -> a) -> [a] -> a
- scanl :: (b -> a -> b) -> b -> [a] -> [b]
- scanl1 :: (a -> a -> a) -> [a] -> [a]
- scanl' :: (b -> a -> b) -> b -> [a] -> [b]
- scanr :: (a -> b -> b) -> b -> [a] -> [b]
- scanr1 :: (a -> a -> a) -> [a] -> [a]
- iterate :: (a -> a) -> a -> [a]
- iterate' :: (a -> a) -> a -> [a]
- repeat :: a -> [a]
- replicate :: Int -> a -> [a]
- takeWhile :: (a -> Bool) -> [a] -> [a]
- dropWhile :: (a -> Bool) -> [a] -> [a]
- take :: Int -> [a] -> [a]
- drop :: Int -> [a] -> [a]
- splitAt :: Int -> [a] -> ([a], [a])
- span :: (a -> Bool) -> [a] -> ([a], [a])
- break :: (a -> Bool) -> [a] -> ([a], [a])
- reverse :: [a] -> [a]
- and :: Foldable t => t Bool -> Bool
- or :: Foldable t => t Bool -> Bool
- any :: Foldable t => (a -> Bool) -> t a -> Bool
- all :: Foldable t => (a -> Bool) -> t a -> Bool
- notElem :: (Foldable t, Eq a) => a -> t a -> Bool
- concatMap :: Foldable t => (a -> [b]) -> t a -> [b]
- (!!) :: HasCallStack => [a] -> Int -> a
- zip3 :: [a] -> [b] -> [c] -> [(a, b, c)]
- zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
- unzip :: [(a, b)] -> ([a], [b])
- unzip3 :: [(a, b, c)] -> ([a], [b], [c])
- find :: Foldable t => (a -> Bool) -> t a -> Maybe a
- dropWhileEnd :: (a -> Bool) -> [a] -> [a]
- stripPrefix :: Eq a => [a] -> [a] -> Maybe [a]
- elemIndex :: Eq a => a -> [a] -> Maybe Int
- elemIndices :: Eq a => a -> [a] -> [Int]
- findIndex :: (a -> Bool) -> [a] -> Maybe Int
- findIndices :: (a -> Bool) -> [a] -> [Int]
- isPrefixOf :: Eq a => [a] -> [a] -> Bool
- isSuffixOf :: Eq a => [a] -> [a] -> Bool
- isInfixOf :: Eq a => [a] -> [a] -> Bool
- nub :: Eq a => [a] -> [a]
- nubBy :: (a -> a -> Bool) -> [a] -> [a]
- deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
- (\\) :: Eq a => [a] -> [a] -> [a]
- unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- intersect :: Eq a => [a] -> [a] -> [a]
- intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- intersperse :: a -> [a] -> [a]
- intercalate :: [a] -> [[a]] -> [a]
- partition :: (a -> Bool) -> [a] -> ([a], [a])
- mapAccumL :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
- mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
- insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a]
- zip4 :: [a] -> [b] -> [c] -> [d] -> [(a, b, c, d)]
- zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a, b, c, d, e)]
- zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [(a, b, c, d, e, f)]
- zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [(a, b, c, d, e, f, g)]
- zipWith4 :: (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e]
- zipWith5 :: (a -> b -> c -> d -> e -> f) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f]
- zipWith6 :: (a -> b -> c -> d -> e -> f -> g) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g]
- zipWith7 :: (a -> b -> c -> d -> e -> f -> g -> h) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [h]
- unzip4 :: [(a, b, c, d)] -> ([a], [b], [c], [d])
- unzip5 :: [(a, b, c, d, e)] -> ([a], [b], [c], [d], [e])
- unzip6 :: [(a, b, c, d, e, f)] -> ([a], [b], [c], [d], [e], [f])
- unzip7 :: [(a, b, c, d, e, f, g)] -> ([a], [b], [c], [d], [e], [f], [g])
- deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- inits :: [a] -> [[a]]
- tails :: [a] -> [[a]]
- subsequences :: [a] -> [[a]]
- permutations :: [a] -> [[a]]
- lines :: String -> [String]
- unlines :: [String] -> String
- words :: String -> [String]
- unwords :: [String] -> String
- isSubsequenceOf :: Eq a => [a] -> [a] -> Bool
- class Default a where
- def :: a
- class Generic a
- class Typeable (a :: k)
- type HasCallStack = ?callStack :: CallStack
- data Map k a
- data Set a
- data ByteString
- class (Typeable e, Show e) => Exception e where
- toException :: e -> SomeException
- fromException :: SomeException -> Maybe e
- displayException :: e -> String
- data SomeException = Exception e => SomeException e
- data SomeAsyncException = Exception e => SomeAsyncException e
- data IOException
- putChar :: MonadIO m => Char -> m ()
- putStr :: MonadIO m => String -> m ()
- putStrLn :: MonadIO m => String -> m ()
- print :: (Show a, MonadIO m) => a -> m ()
- getChar :: MonadIO m => m Char
- getLine :: MonadIO m => m String
- getContents :: MonadIO m => m String
- interact :: MonadIO m => (String -> String) -> m ()
- readFile :: MonadIO m => FilePath -> m String
- writeFile :: MonadIO m => FilePath -> String -> m ()
- appendFile :: MonadIO m => FilePath -> String -> m ()
- readIO :: (Read a, MonadIO m) => String -> m a
- readLn :: (Read a, MonadIO m) => m a
- liftIO :: MonadIO m => IO a -> m a
- (<$$>) :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b)
- (<$$$>) :: (Functor f, Functor g, Functor h) => (a -> b) -> f (g (h a)) -> f (g (h b))
- allPreds :: Applicative f => [a -> f Bool] -> a -> f Bool
Documentation
module Testlib.App
module Testlib.Env
module Testlib.Cannon
module Testlib.Assertions
module Testlib.Types
module Testlib.ModService
module Testlib.HTTP
module Testlib.JSON
module Testlib.PTest
A type-level indicator that ToJSON1 or FromJSON1 is being derived generically.
Instances
| GFromJSON One Par1 | |
Defined in Data.Aeson.Types.FromJSON | |
| GToJSON' enc One Par1 | |
| ToJSON1 f => GToJSON' Encoding One (Rec1 f) | |
| ToJSON1 f => GToJSON' Value One (Rec1 f) | |
| (ToJSON1 f, GToJSON' Encoding One g) => GToJSON' Encoding One (f :.: g) | |
| (ToJSON1 f, GToJSON' Value One g) => GToJSON' Value One (f :.: g) | |
| FromJSON1 f => GFromJSON One (Rec1 f) | |
Defined in Data.Aeson.Types.FromJSON | |
| (FromJSON1 f, GFromJSON One g) => GFromJSON One (f :.: g) | |
Defined in Data.Aeson.Types.FromJSON | |
The result of running a Parser.
Instances
| MonadFail Result | |
Defined in Data.Aeson.Types.Internal | |
| Foldable Result | |
Defined in Data.Aeson.Types.Internal Methods fold :: Monoid m => Result m -> m # foldMap :: Monoid m => (a -> m) -> Result a -> m # foldMap' :: Monoid m => (a -> m) -> Result a -> m # foldr :: (a -> b -> b) -> b -> Result a -> b # foldr' :: (a -> b -> b) -> b -> Result a -> b # foldl :: (b -> a -> b) -> b -> Result a -> b # foldl' :: (b -> a -> b) -> b -> Result a -> b # foldr1 :: (a -> a -> a) -> Result a -> a # foldl1 :: (a -> a -> a) -> Result a -> a # elem :: Eq a => a -> Result a -> Bool # maximum :: Ord a => Result a -> a # minimum :: Ord a => Result a -> a # | |
| Traversable Result | |
| Alternative Result | |
| Applicative Result | |
| Functor Result | |
| Monad Result | |
| MonadPlus Result | |
| Monoid (Result a) | |
| Semigroup (Result a) | |
| Show a => Show (Result a) | |
| NFData a => NFData (Result a) | |
Defined in Data.Aeson.Types.Internal | |
| Eq a => Eq (Result a) | |
class FromJSON a where Source #
A type that can be converted from JSON, with the possibility of failure.
In many cases, you can get the compiler to generate parsing code for you (see below). To begin, let's cover writing an instance by hand.
There are various reasons a conversion could fail. For example, an
Object could be missing a required key, an Array could be of
the wrong size, or a value could be of an incompatible type.
The basic ways to signal a failed conversion are as follows:
failyields a custom error message: it is the recommended way of reporting a failure;empty(ormzero) is uninformative: use it when the error is meant to be caught by some(;<|>)typeMismatchcan be used to report a failure when the encountered value is not of the expected JSON type;unexpectedis an appropriate alternative when more than one type may be expected, or to keep the expected type implicit.
prependFailure (or modifyFailure) add more information to a parser's
error messages.
An example type and instance using typeMismatch and prependFailure:
-- Allow ourselves to writeTextliterals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instanceFromJSONCoord whereparseJSON(Objectv) = Coord<$>v.:"x"<*>v.:"y" -- We do not expect a non-Objectvalue here. -- We could useemptyto fail, buttypeMismatch-- gives a much more informative error message.parseJSONinvalid =prependFailure"parsing Coord failed, " (typeMismatch"Object" invalid)
For this common case of only being concerned with a single
type of JSON value, the functions withObject, withScientific, etc.
are provided. Their use is to be preferred when possible, since
they are more terse. Using withObject, we can rewrite the above instance
(assuming the same language extension and data type) as:
instanceFromJSONCoord whereparseJSON=withObject"Coord" $ \v -> Coord<$>v.:"x"<*>v.:"y"
Instead of manually writing your FromJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
parseJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericFromJSON instance for your datatype without giving
a definition for parseJSON.
For example, the previous example can be simplified to just:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance FromJSON Coord
or using the DerivingVia extension
deriving viaGenericallyCoord instanceFromJSONCoord
The default implementation will be equivalent to
parseJSON = ; if you need different
options, you can customize the generic decoding by defining:genericParseJSON defaultOptions
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceFromJSONCoord whereparseJSON=genericParseJSONcustomOptions
Minimal complete definition
Nothing
Instances
A type that can be converted to JSON.
Instances in general must specify toJSON and should (but don't need
to) specify toEncoding.
An example type and instance:
-- Allow ourselves to writeTextliterals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instanceToJSONCoord wheretoJSON(Coord x y) =object["x".=x, "y".=y]toEncoding(Coord x y) =pairs("x".=x<>"y".=y)
Instead of manually writing your ToJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
toJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericToJSON instance. If you require nothing other than
defaultOptions, it is sufficient to write (and this is the only
alternative where the default toJSON implementation is sufficient):
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance ToJSON Coord where
toEncoding = genericToEncoding defaultOptions
or more conveniently using the DerivingVia extension
deriving viaGenericallyCoord instanceToJSONCoord
If on the other hand you wish to customize the generic decoding, you have to implement both methods:
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceToJSONCoord wheretoJSON=genericToJSONcustomOptionstoEncoding=genericToEncodingcustomOptions
Previous versions of this library only had the toJSON method. Adding
toEncoding had two reasons:
toEncodingis more efficient for the common case that the output oftoJSONis directly serialized to aByteString. Further, expressing either method in terms of the other would be non-optimal.- The choice of defaults allows a smooth transition for existing users:
Existing instances that do not define
toEncodingstill compile and have the correct semantics. This is ensured by making the default implementation oftoEncodingusetoJSON. This produces correct results, but since it performs an intermediate conversion to aValue, it will be less efficient than directly emitting anEncoding. (this also means that specifying nothing more thaninstance ToJSON Coordwould be sufficient as a generically decoding instance, but there probably exists no good reason to not specifytoEncodingin new instances.)
Minimal complete definition
Nothing
Methods
Convert a Haskell value to a JSON-friendly intermediate type.
toEncoding :: a -> Encoding Source #
Encode a Haskell value as JSON.
The default implementation of this method creates an
intermediate Value using toJSON. This provides
source-level compatibility for people upgrading from older
versions of this library, but obviously offers no performance
advantage.
To benefit from direct encoding, you must provide an
implementation for this method. The easiest way to do so is by
having your types implement Generic using the DeriveGeneric
extension, and then have GHC generate a method body as follows.
instanceToJSONCoord wheretoEncoding=genericToEncodingdefaultOptions
toJSONList :: [a] -> Value Source #
toEncodingList :: [a] -> Encoding Source #
Instances
class FromJSON1 (f :: Type -> Type) where Source #
Lifting of the FromJSON class to unary type constructors.
Instead of manually writing your FromJSON1 instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
liftParseJSON.
To use the second, simply add a deriving clause to your
datatype and declare a Generic1FromJSON1 instance for your datatype without giving
a definition for liftParseJSON.
For example:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Pair a b = Pair { pairFst :: a, pairSnd :: b } deriving Generic1
instance FromJSON a => FromJSON1 (Pair a)
or
deriving viaGenerically1(Pair a) instanceFromJSON1(Pair a)
If the default implementation doesn't give exactly the results you want,
you can customize the generic decoding with only a tiny amount of
effort, using genericLiftParseJSON with your preferred Options:
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceFromJSONa =>FromJSON1(Pair a) whereliftParseJSON=genericLiftParseJSONcustomOptions
Minimal complete definition
Nothing
Methods
liftParseJSON :: (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser (f a) Source #
liftParseJSONList :: (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser [f a] Source #
Instances
Instances
| Arbitrary Key | Since: aeson-2.0.3.0 |
| CoArbitrary Key | Since: aeson-2.0.3.0 |
Defined in Data.Aeson.Key | |
| Function Key | Since: aeson-2.0.3.0 |
| FromJSON Key | |
| FromJSONKey Key | |
Defined in Data.Aeson.Types.FromJSON Methods | |
| ToJSON Key | |
| ToJSONKey Key | |
Defined in Data.Aeson.Types.ToJSON | |
| Data Key | |
Defined in Data.Aeson.Key Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Key -> c Key # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Key # dataTypeOf :: Key -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Key) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Key) # gmapT :: (forall b. Data b => b -> b) -> Key -> Key # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Key -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Key -> r # gmapQ :: (forall d. Data d => d -> u) -> Key -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Key -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Key -> m Key # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Key -> m Key # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Key -> m Key # | |
| IsString Key | |
Defined in Data.Aeson.Key Methods fromString :: String -> Key # | |
| Monoid Key | |
| Semigroup Key | |
| Read Key | |
| Show Key | |
| NFData Key | |
Defined in Data.Aeson.Key | |
| Eq Key | |
| Ord Key | |
| Hashable Key | |
| IsKey Key | |
| FoldableWithIndex Key KeyMap | |
Defined in Data.Aeson.KeyMap Methods ifoldMap :: Monoid m => (Key -> a -> m) -> KeyMap a -> m Source # ifoldMap' :: Monoid m => (Key -> a -> m) -> KeyMap a -> m Source # ifoldr :: (Key -> a -> b -> b) -> b -> KeyMap a -> b Source # ifoldl :: (Key -> b -> a -> b) -> b -> KeyMap a -> b Source # ifoldr' :: (Key -> a -> b -> b) -> b -> KeyMap a -> b Source # ifoldl' :: (Key -> b -> a -> b) -> b -> KeyMap a -> b Source # | |
| FunctorWithIndex Key KeyMap | |
| TraversableWithIndex Key KeyMap | |
Defined in Data.Aeson.KeyMap | |
| SemialignWithIndex Key KeyMap | |
Defined in Data.Aeson.KeyMap | |
| ZipWithIndex Key KeyMap | |
| Lift Key | |
| FilterableWithIndex Key KeyMap | |
| WitherableWithIndex Key KeyMap | |
| FromPairs Value (DList Pair) | |
Defined in Data.Aeson.Types.ToJSON | |
| v ~ Value => KeyValuePair v (DList Pair) | |
Defined in Data.Aeson.Types.ToJSON | |
data JSONKeyOptions Source #
Options for encoding keys with genericFromJSONKey and
genericToJSONKey.
data SumEncoding Source #
Specifies how to encode constructors of a sum datatype.
Constructors
| TaggedObject | A constructor will be encoded to an object with a field
|
Fields | |
| UntaggedValue | Constructor names won't be encoded. Instead only the contents of the constructor will be encoded as if the type had a single constructor. JSON encodings have to be disjoint for decoding to work properly. When decoding, constructors are tried in the order of definition. If some encodings overlap, the first one defined will succeed. Note: Nullary constructors are encoded as strings (using
Note: Only the last error is kept when decoding, so in the case of malformed JSON, only an error for the last constructor will be reported. |
| ObjectWithSingleField | A constructor will be encoded to an object with a single
field named after the constructor tag (modified by the
|
| TwoElemArray | A constructor will be encoded to a 2-element array where the
first element is the tag of the constructor (modified by the
|
Instances
| Show SumEncoding | |
Defined in Data.Aeson.Types.Internal Methods showsPrec :: Int -> SumEncoding -> ShowS # show :: SumEncoding -> String # showList :: [SumEncoding] -> ShowS # | |
| Eq SumEncoding | |
Defined in Data.Aeson.Types.Internal | |
Options that specify how to encode/decode your datatype to/from JSON.
Options can be set using record syntax on defaultOptions with the fields
below.
newtype DotNetTime Source #
A newtype wrapper for UTCTime that uses the same non-standard
serialization format as Microsoft .NET, whose
System.DateTime
type is by default serialized to JSON as in the following example:
/Date(1302547608878)/
The number represents milliseconds since the Unix epoch.
Constructors
| DotNetTime | |
Fields
| |
Instances
A JSON value represented as a Haskell value.
Instances
| Arbitrary Value | Since: aeson-2.0.3.0 |
| CoArbitrary Value | Since: aeson-2.0.3.0 |
Defined in Data.Aeson.Types.Internal | |
| Function Value | Since: aeson-2.0.3.0 |
| FromJSON Value | |
| FromString Encoding | |
Defined in Data.Aeson.Types.ToJSON Methods fromString :: String -> Encoding | |
| FromString Value | |
Defined in Data.Aeson.Types.ToJSON Methods fromString :: String -> Value | |
| ToJSON Value | |
| Data Value | |
Defined in Data.Aeson.Types.Internal Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Value -> c Value # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Value # dataTypeOf :: Value -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Value) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Value) # gmapT :: (forall b. Data b => b -> b) -> Value -> Value # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r # gmapQ :: (forall d. Data d => d -> u) -> Value -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Value -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Value -> m Value # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value # | |
| IsString Value | |
Defined in Data.Aeson.Types.Internal Methods fromString :: String -> Value # | |
| Generic Value | |
| Read Value | |
| Show Value | Since version 1.5.6.0 version object values are printed in lexicographic key order
|
| NFData Value | |
Defined in Data.Aeson.Types.Internal | |
| Eq Value | |
| Ord Value | The ordering is total, consistent with Since: aeson-1.5.2.0 |
| Hashable Value | |
| IsAssetToken Value Source # | |
Defined in Test.Cargohold.API.Util | |
| AsJSON Value | |
| AsNumber Value | |
| AsValue Value | |
| Lift Value | Since: aeson-0.11.0.0 |
| (GToJSON' Encoding arity a, ConsToJSON Encoding arity a, Constructor c) => SumToJSON' TwoElemArray Encoding arity (C1 c a) | |
Defined in Data.Aeson.Types.ToJSON | |
| (GToJSON' Value arity a, ConsToJSON Value arity a, Constructor c) => SumToJSON' TwoElemArray Value arity (C1 c a) | |
Defined in Data.Aeson.Types.ToJSON | |
| HasField "json" Response (App Value) Source # | |
| GToJSON' Encoding arity (U1 :: Type -> Type) | |
| GToJSON' Encoding arity (V1 :: Type -> Type) | |
| GToJSON' Value arity (U1 :: Type -> Type) | |
| GToJSON' Value arity (V1 :: Type -> Type) | |
| ToJSON1 f => GToJSON' Encoding One (Rec1 f) | |
| ToJSON1 f => GToJSON' Value One (Rec1 f) | |
| (EncodeProduct arity a, EncodeProduct arity b) => GToJSON' Encoding arity (a :*: b) | |
| ToJSON a => GToJSON' Encoding arity (K1 i a :: Type -> Type) | |
| (WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON' Value arity (a :*: b) | |
| ToJSON a => GToJSON' Value arity (K1 i a :: Type -> Type) | |
| (ToJSON1 f, GToJSON' Encoding One g) => GToJSON' Encoding One (f :.: g) | |
| (ToJSON1 f, GToJSON' Value One g) => GToJSON' Value One (f :.: g) | |
| FromPairs Value (DList Pair) | |
Defined in Data.Aeson.Types.ToJSON | |
| v ~ Value => KeyValuePair v (DList Pair) | |
Defined in Data.Aeson.Types.ToJSON | |
| type Rep Value | |
Defined in Data.Aeson.Types.Internal type Rep Value = D1 ('MetaData "Value" "Data.Aeson.Types.Internal" "aeson-2.1.2.1-B6SRSQXTctcEYV8oGyolai" 'False) ((C1 ('MetaCons "Object" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Object)) :+: (C1 ('MetaCons "Array" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Array)) :+: C1 ('MetaCons "String" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Text)))) :+: (C1 ('MetaCons "Number" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Scientific)) :+: (C1 ('MetaCons "Bool" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Bool)) :+: C1 ('MetaCons "Null" 'PrefixI 'False) (U1 :: Type -> Type)))) | |
| type Index Value | |
Defined in Data.Aeson.Lens | |
| type IxValue Value | |
Defined in Data.Aeson.Lens | |
type JSONPath = [JSONPathElement] Source #
class FromJSON2 (f :: Type -> Type -> Type) where Source #
Lifting of the FromJSON class to binary type constructors.
Instead of manually writing your FromJSON2 instance, Data.Aeson.TH
provides Template Haskell functions which will derive an instance at compile time.
Minimal complete definition
Methods
liftParseJSON2 :: (Value -> Parser a) -> (Value -> Parser [a]) -> (Value -> Parser b) -> (Value -> Parser [b]) -> Value -> Parser (f a b) Source #
liftParseJSONList2 :: (Value -> Parser a) -> (Value -> Parser [a]) -> (Value -> Parser b) -> (Value -> Parser [b]) -> Value -> Parser [f a b] Source #
Instances
class (ConstructorNames f, SumFromString f) => GFromJSONKey (f :: Type -> Type) Source #
Instances
| (ConstructorNames f, SumFromString f) => GFromJSONKey f | |
Defined in Data.Aeson.Types.FromJSON | |
data FromJSONKeyFunction a where Source #
This type is related to ToJSONKeyFunction. If FromJSONKeyValue is used in the
FromJSONKey instance, then ToJSONKeyValue should be used in the ToJSONKey
instance. The other three data constructors for this type all correspond to
ToJSONKeyText. Strictly speaking, FromJSONKeyTextParser is more powerful than
FromJSONKeyText, which is in turn more powerful than FromJSONKeyCoerce.
For performance reasons, these exist as three options instead of one.
Constructors
| FromJSONKeyCoerce | |
| FromJSONKeyText | |
Fields
| |
| FromJSONKeyTextParser | |
Fields
| |
| FromJSONKeyValue | |
Fields
| |
Instances
| Functor FromJSONKeyFunction | Only law abiding up to interpretation |
Defined in Data.Aeson.Types.FromJSON Methods fmap :: (a -> b) -> FromJSONKeyFunction a -> FromJSONKeyFunction b # (<$) :: a -> FromJSONKeyFunction b -> FromJSONKeyFunction a # | |
class FromJSONKey a where Source #
Read the docs for ToJSONKey first. This class is a conversion
in the opposite direction. If you have a newtype wrapper around Text,
the recommended way to define instances is with generalized newtype deriving:
newtype SomeId = SomeId { getSomeId :: Text }
deriving (Eq,Ord,Hashable,FromJSONKey)If you have a sum of nullary constructors, you may use the generic implementation:
data Color = Red | Green | Blue deriving Generic instanceFromJSONKeyColor wherefromJSONKey=genericFromJSONKeydefaultJSONKeyOptions
Minimal complete definition
Nothing
Methods
fromJSONKey :: FromJSONKeyFunction a Source #
Strategy for parsing the key of a map-like container.
Instances
class GFromJSON arity (f :: Type -> Type) Source #
Class of generic representation types that can be converted from JSON.
Minimal complete definition
gParseJSON
Instances
| GFromJSON One Par1 | |
Defined in Data.Aeson.Types.FromJSON | |
| GFromJSON arity (V1 :: Type -> Type) | |
Defined in Data.Aeson.Types.FromJSON | |
| FromJSON1 f => GFromJSON One (Rec1 f) | |
Defined in Data.Aeson.Types.FromJSON | |
| (GFromJSON' arity a, Datatype d) => GFromJSON arity (D1 d a) | |
Defined in Data.Aeson.Types.FromJSON | |
| FromJSON a => GFromJSON arity (K1 i a :: Type -> Type) | |
Defined in Data.Aeson.Types.FromJSON | |
| (FromJSON1 f, GFromJSON One g) => GFromJSON One (f :.: g) | |
Defined in Data.Aeson.Types.FromJSON | |
| GFromJSON arity a => GFromJSON arity (M1 i c a) | |
Defined in Data.Aeson.Types.FromJSON | |
A series of values that, when encoded, should be separated by
commas. Since 0.11.0.0, the .= operator is overloaded to create
either (Text, Value) or Series. You can use Series when
encoding directly to a bytestring builder as in the following
example:
toEncoding (Person name age) = pairs ("name" .= name <> "age" .= age)class ToJSON2 (f :: Type -> Type -> Type) where Source #
Lifting of the ToJSON class to binary type constructors.
Instead of manually writing your ToJSON2 instance, Data.Aeson.TH
provides Template Haskell functions which will derive an instance at compile time.
The compiler cannot provide a default generic implementation for liftToJSON2,
unlike toJSON and liftToJSON.
Minimal complete definition
Methods
liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> f a b -> Value Source #
liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [f a b] -> Value Source #
liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> f a b -> Encoding Source #
liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [f a b] -> Encoding Source #
Instances
| ToJSON2 Either | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> Either a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [Either a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> Either a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [Either a b] -> Encoding Source # | |
| ToJSON2 Either | Since: aeson-1.5.3.0 |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> Either a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [Either a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> Either a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [Either a b] -> Encoding Source # | |
| ToJSON2 These | Since: aeson-1.5.3.0 |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> These a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [These a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> These a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [These a b] -> Encoding Source # | |
| ToJSON2 Pair | Since: aeson-1.5.3.0 |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> Pair a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [Pair a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> Pair a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [Pair a b] -> Encoding Source # | |
| ToJSON2 These | Since: aeson-1.5.1.0 |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> These a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [These a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> These a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [These a b] -> Encoding Source # | |
| ToJSON2 (,) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> (a, b) -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [(a, b)] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> (a, b) -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [(a, b)] -> Encoding Source # | |
| ToJSON2 (Const :: Type -> Type -> Type) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> Const a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [Const a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> Const a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [Const a b] -> Encoding Source # | |
| ToJSON2 (Tagged :: Type -> Type -> Type) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> Tagged a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [Tagged a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> Tagged a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [Tagged a b] -> Encoding Source # | |
| ToJSON a => ToJSON2 ((,,) a) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b -> Value) -> ([b] -> Value) -> (a, a0, b) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b -> Value) -> ([b] -> Value) -> [(a, a0, b)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> (a, a0, b) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [(a, a0, b)] -> Encoding Source # | |
| (ToJSON a, ToJSON b) => ToJSON2 ((,,,) a b) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c) => ToJSON2 ((,,,,) a b c) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d) => ToJSON2 ((,,,,,) a b c d) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e) => ToJSON2 ((,,,,,,) a b c d e) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f) => ToJSON2 ((,,,,,,,) a b c d e f) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g) => ToJSON2 ((,,,,,,,,) a b c d e f g) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, g, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, g, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, g, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, g, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h) => ToJSON2 ((,,,,,,,,,) a b c d e f g h) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, g, h, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, g, h, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, g, h, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, g, h, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i) => ToJSON2 ((,,,,,,,,,,) a b c d e f g h i) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, g, h, i, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, g, h, i, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, g, h, i, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, g, h, i, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i, ToJSON j) => ToJSON2 ((,,,,,,,,,,,) a b c d e f g h i j) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, g, h, i, j, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, g, h, i, j, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, g, h, i, j, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, g, h, i, j, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i, ToJSON j, ToJSON k) => ToJSON2 ((,,,,,,,,,,,,) a b c d e f g h i j k) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, g, h, i, j, k, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, g, h, i, j, k, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, g, h, i, j, k, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, g, h, i, j, k, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i, ToJSON j, ToJSON k, ToJSON l) => ToJSON2 ((,,,,,,,,,,,,,) a b c d e f g h i j k l) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, g, h, i, j, k, l, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, g, h, i, j, k, l, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, g, h, i, j, k, l, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, g, h, i, j, k, l, a0, b0)] -> Encoding Source # | |
| (ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i, ToJSON j, ToJSON k, ToJSON l, ToJSON m) => ToJSON2 ((,,,,,,,,,,,,,,) a b c d e f g h i j k l m) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, a0, b0) -> Value Source # liftToJSONList2 :: (a0 -> Value) -> ([a0] -> Value) -> (b0 -> Value) -> ([b0] -> Value) -> [(a, b, c, d, e, f, g, h, i, j, k, l, m, a0, b0)] -> Value Source # liftToEncoding2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> (a, b, c, d, e, f, g, h, i, j, k, l, m, a0, b0) -> Encoding Source # liftToEncodingList2 :: (a0 -> Encoding) -> ([a0] -> Encoding) -> (b0 -> Encoding) -> ([b0] -> Encoding) -> [(a, b, c, d, e, f, g, h, i, j, k, l, m, a0, b0)] -> Encoding Source # | |
class ToJSON1 (f :: Type -> Type) where Source #
Lifting of the ToJSON class to unary type constructors.
Instead of manually writing your ToJSON1 instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
toJSON1.
To use the second, simply add a deriving clause to your
datatype and declare a Generic1ToJSON1 instance for your datatype without giving
definitions for liftToJSON or liftToEncoding.
For example:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Pair a b = Pair { pairFst :: a, pairSnd :: b } deriving Generic1
instance ToJSON a => ToJSON1 (Pair a)
If the default implementation doesn't give exactly the results you want,
you can customize the generic encoding with only a tiny amount of
effort, using genericLiftToJSON and genericLiftToEncoding with
your preferred Options:
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceToJSONa =>ToJSON1(Pair a) whereliftToJSON=genericLiftToJSONcustomOptionsliftToEncoding=genericLiftToEncodingcustomOptions
See also ToJSON.
Minimal complete definition
Nothing
Methods
liftToJSON :: (a -> Value) -> ([a] -> Value) -> f a -> Value Source #
liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [f a] -> Value Source #
liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> f a -> Encoding Source #
liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [f a] -> Encoding Source #
Instances
class GetConName f => GToJSONKey (f :: k -> Type) Source #
Instances
| GetConName f => GToJSONKey (f :: k -> Type) | |
Defined in Data.Aeson.Types.ToJSON | |
data ToJSONKeyFunction a Source #
Constructors
| ToJSONKeyText !(a -> Key) !(a -> Encoding' Key) | key is encoded to string, produces object |
| ToJSONKeyValue !(a -> Value) !(a -> Encoding) | key is encoded to value, produces array |
Instances
| Contravariant ToJSONKeyFunction | |
Defined in Data.Aeson.Types.ToJSON Methods contramap :: (a' -> a) -> ToJSONKeyFunction a -> ToJSONKeyFunction a' # (>$) :: b -> ToJSONKeyFunction b -> ToJSONKeyFunction a # | |
class ToJSONKey a where Source #
Typeclass for types that can be used as the key of a map-like container
(like Map or HashMap). For example, since Text has a ToJSONKey
instance and Char has a ToJSON instance, we can encode a value of
type Map Text Char:
>>>LBC8.putStrLn $ encode $ Map.fromList [("foo" :: Text, 'a')]{"foo":"a"}
Since Int also has a ToJSONKey instance, we can similarly write:
>>>LBC8.putStrLn $ encode $ Map.fromList [(5 :: Int, 'a')]{"5":"a"}
JSON documents only accept strings as object keys. For any type
from base that has a natural textual representation, it can be
expected that its ToJSONKey instance will choose that representation.
For data types that lack a natural textual representation, an alternative is provided. The map-like container is represented as a JSON array instead of a JSON object. Each value in the array is an array with exactly two values. The first is the key and the second is the value.
For example, values of type '[Text]' cannot be encoded to a
string, so a Map with keys of type '[Text]' is encoded as follows:
>>>LBC8.putStrLn $ encode $ Map.fromList [(["foo","bar","baz" :: Text], 'a')][[["foo","bar","baz"],"a"]]
The default implementation of ToJSONKey chooses this method of
encoding a key, using the ToJSON instance of the type.
To use your own data type as the key in a map, all that is needed
is to write a ToJSONKey (and possibly a FromJSONKey) instance
for it. If the type cannot be trivially converted to and from Text,
it is recommended that ToJSONKeyValue is used. Since the default
implementations of the typeclass methods can build this from a
ToJSON instance, there is nothing that needs to be written:
data Foo = Foo { fooAge :: Int, fooName :: Text }
deriving (Eq,Ord,Generic)
instance ToJSON Foo
instance ToJSONKey FooThat's it. We can now write:
>>>let m = Map.fromList [(Foo 4 "bar",'a'),(Foo 6 "arg",'b')]>>>LBC8.putStrLn $ encode m[[{"fooName":"bar","fooAge":4},"a"],[{"fooName":"arg","fooAge":6},"b"]]
The next case to consider is if we have a type that is a
newtype wrapper around Text. The recommended approach is to use
generalized newtype deriving:
newtype RecordId = RecordId { getRecordId :: Text }
deriving (Eq,Ord,ToJSONKey)Then we may write:
>>>LBC8.putStrLn $ encode $ Map.fromList [(RecordId "abc",'a')]{"abc":"a"}
Simple sum types are a final case worth considering. Suppose we have:
data Color = Red | Green | Blue deriving (Show,Read,Eq,Ord)
It is possible to get the ToJSONKey instance for free as we did
with Foo. However, in this case, we have a natural way to go to
and from Text that does not require any escape sequences. So
ToJSONKeyText can be used instead of ToJSONKeyValue to encode maps
as objects instead of arrays of pairs. This instance may be
implemented using generics as follows:
instanceToJSONKeyColor wheretoJSONKey=genericToJSONKeydefaultJSONKeyOptions
Low-level implementations
The Show instance can be used to help write ToJSONKey:
instance ToJSONKey Color where
toJSONKey = ToJSONKeyText f g
where f = Text.pack . show
g = text . Text.pack . show
-- text function is from Data.Aeson.EncodingThe situation of needing to turning function a -> Text into
a ToJSONKeyFunction is common enough that a special combinator
is provided for it. The above instance can be rewritten as:
instance ToJSONKey Color where toJSONKey = toJSONKeyText (Text.pack . show)
The performance of the above instance can be improved by
not using Value as an intermediate step when converting to
Text. One option for improving performance would be to use
template haskell machinery from the text-show package. However,
even with the approach, the Encoding (a wrapper around a bytestring
builder) is generated by encoding the Text to a ByteString,
an intermediate step that could be avoided. The fastest possible
implementation would be:
-- Assuming that OverloadedStrings is enabled
instance ToJSONKey Color where
toJSONKey = ToJSONKeyText f g
where f x = case x of {Red -> "Red";Green ->"Green";Blue -> "Blue"}
g x = case x of {Red -> text "Red";Green -> text "Green";Blue -> text "Blue"}
-- text function is from Data.Aeson.EncodingThis works because GHC can lift the encoded values out of the case statements, which means that they are only evaluated once. This approach should only be used when there is a serious need to maximize performance.
Minimal complete definition
Nothing
Methods
toJSONKey :: ToJSONKeyFunction a Source #
Strategy for rendering the key for a map-like container.
toJSONKeyList :: ToJSONKeyFunction [a] Source #
Instances
A key-value pair for encoding a JSON object.
Minimal complete definition
class GToJSON' enc arity (f :: Type -> Type) Source #
Class of generic representation types that can be converted to JSON.
Minimal complete definition
gToJSON
Instances
| GToJSON' enc One Par1 | |
| GToJSON' Encoding arity (U1 :: Type -> Type) | |
| GToJSON' Encoding arity (V1 :: Type -> Type) | |
| GToJSON' Value arity (U1 :: Type -> Type) | |
| GToJSON' Value arity (V1 :: Type -> Type) | |
| ToJSON1 f => GToJSON' Encoding One (Rec1 f) | |
| ToJSON1 f => GToJSON' Value One (Rec1 f) | |
| (EncodeProduct arity a, EncodeProduct arity b) => GToJSON' Encoding arity (a :*: b) | |
| ToJSON a => GToJSON' Encoding arity (K1 i a :: Type -> Type) | |
| (WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON' Value arity (a :*: b) | |
| ToJSON a => GToJSON' Value arity (K1 i a :: Type -> Type) | |
| (AllNullary (a :+: b) allNullary, SumToJSON enc arity (a :+: b) allNullary) => GToJSON' enc arity (a :+: b) | |
Defined in Data.Aeson.Types.ToJSON | |
| ConsToJSON enc arity a => GToJSON' enc arity (C1 c a) | |
Defined in Data.Aeson.Types.ToJSON | |
| (ConsToJSON enc arity a, AllNullary (C1 c a) allNullary, SumToJSON enc arity (C1 c a) allNullary) => GToJSON' enc arity (D1 d (C1 c a)) | |
| (ToJSON1 f, GToJSON' Encoding One g) => GToJSON' Encoding One (f :.: g) | |
| (ToJSON1 f, GToJSON' Value One g) => GToJSON' Value One (f :.: g) | |
| GToJSON' enc arity a => GToJSON' enc arity (M1 i c a) | |
Defined in Data.Aeson.Types.ToJSON | |
type GToEncoding = GToJSON' Encoding Source #
newtype AesonException Source #
Exception thrown by throwDecode and variants.
Since: aeson-2.1.2.0
Constructors
| AesonException String |
Instances
| Exception AesonException | |
Defined in Data.Aeson Methods toException :: AesonException -> SomeException # | |
| Show AesonException | |
Defined in Data.Aeson Methods showsPrec :: Int -> AesonException -> ShowS # show :: AesonException -> String # showList :: [AesonException] -> ShowS # | |
genericFromJSONKey :: (Generic a, GFromJSONKey (Rep a)) => JSONKeyOptions -> FromJSONKeyFunction a Source #
fromJSONKey for Generic types.
These types must be sums of nullary constructors, whose names will be used
as keys for JSON objects.
See also genericToJSONKey.
Example
data Color = Red | Green | Blue derivingGenericinstanceFromJSONKeyColor wherefromJSONKey=genericFromJSONKeydefaultJSONKeyOptions
genericToJSONKey :: (Generic a, GToJSONKey (Rep a)) => JSONKeyOptions -> ToJSONKeyFunction a Source #
fromJSON :: FromJSON a => Value -> Result a Source #
Convert a value from JSON, failing if the types do not match.
genericToJSON :: (Generic a, GToJSON' Value Zero (Rep a)) => Options -> a -> Value Source #
A configurable generic JSON creator. This function applied to
defaultOptions is used as the default for toJSON when the type
is an instance of Generic.
(<?>) :: Parser a -> JSONPathElement -> Parser a Source #
Add JSON Path context to a parser
When parsing a complex structure, it helps to annotate (sub)parsers with context, so that if an error occurs, you can find its location.
withObject "Person" $ \o ->
Person
<$> o .: "name" <?> Key "name"
<*> o .: "age" <?> Key "age"(Standard methods like (.:) already do this.)
With such annotations, if an error occurs, you will get a JSON Path location of that error.
Since 0.10
defaultOptions :: Options Source #
Default encoding Options:
Options{fieldLabelModifier= id ,constructorTagModifier= id ,allNullaryToStringTag= True ,omitNothingFields= False ,sumEncoding=defaultTaggedObject,unwrapUnaryRecords= False ,tagSingleConstructors= False ,rejectUnknownFields= False }
defaultTaggedObject :: SumEncoding Source #
Default TaggedObject SumEncoding options:
defaultTaggedObject =TaggedObject{tagFieldName= "tag" ,contentsFieldName= "contents" }
defaultJSONKeyOptions :: JSONKeyOptions Source #
Default JSONKeyOptions:
defaultJSONKeyOptions =JSONKeyOptions{keyModifier=id}
camelTo2 :: Char -> String -> String Source #
Better version of camelTo. Example where it works better:
camelTo '_' "CamelAPICase" == "camel_apicase" camelTo2 '_' "CamelAPICase" == "camel_api_case"
Parse any JSON value.
The conversion of a parsed value to a Haskell value is deferred until the Haskell value is needed. This may improve performance if only a subset of the results of conversions are needed, but at a cost in thunk allocation.
This function is an alias for value. In aeson 0.8 and earlier, it
parsed only object or array types, in conformance with the
now-obsolete RFC 4627.
Warning
If an object contains duplicate keys, only the first one will be kept.
For a more flexible alternative, see jsonWith.
json' :: Parser Value Source #
Parse any JSON value.
This is a strict version of json which avoids building up thunks
during parsing; it performs all conversions immediately. Prefer
this version if most of the JSON data needs to be accessed.
This function is an alias for value'. In aeson 0.8 and earlier, it
parsed only object or array types, in conformance with the
now-obsolete RFC 4627.
Warning
If an object contains duplicate keys, only the first one will be kept.
For a more flexible alternative, see jsonWith'.
genericParseJSON :: (Generic a, GFromJSON Zero (Rep a)) => Options -> Value -> Parser a Source #
A configurable generic JSON decoder. This function applied to
defaultOptions is used as the default for parseJSON when the
type is an instance of Generic.
genericLiftParseJSON :: (Generic1 f, GFromJSON One (Rep1 f)) => Options -> (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser (f a) Source #
A configurable generic JSON decoder. This function applied to
defaultOptions is used as the default for liftParseJSON when the
type is an instance of Generic1.
parseJSON1 :: (FromJSON1 f, FromJSON a) => Value -> Parser (f a) Source #
Lift the standard parseJSON function through the type constructor.
parseJSON2 :: (FromJSON2 f, FromJSON a, FromJSON b) => Value -> Parser (f a b) Source #
Lift the standard parseJSON function through the type constructor.
withObject :: String -> (Object -> Parser a) -> Value -> Parser a Source #
withObject name f valuef to the Object when value
is an Object and fails otherwise.
Error message example
withObject "MyType" f (String "oops") -- Error: "parsing MyType failed, expected Object, but encountered String"
withScientific :: String -> (Scientific -> Parser a) -> Value -> Parser a Source #
withScientific name f valuef to the Scientific number
when value is a Number and fails using typeMismatch
otherwise.
Warning: If you are converting from a scientific to an unbounded
type such as Integer you may want to add a restriction on the
size of the exponent (see withBoundedScientific) to prevent
malicious input from filling up the memory of the target system.
Error message example
withScientific "MyType" f (String "oops") -- Error: "parsing MyType failed, expected Number, but encountered String"
withEmbeddedJSON :: String -> (Value -> Parser a) -> Value -> Parser a Source #
Decode a nested JSON-encoded string.
(.:) :: FromJSON a => Object -> Key -> Parser a Source #
Retrieve the value associated with the given key of an Object.
The result is empty if the key is not present or the value cannot
be converted to the desired type.
This accessor is appropriate if the key and value must be present
in an object for it to be valid. If the key and value are
optional, use .:? instead.
(.:?) :: FromJSON a => Object -> Key -> Parser (Maybe a) Source #
Retrieve the value associated with the given key of an Object. The
result is Nothing if the key is not present or if its value is Null,
or empty if the value cannot be converted to the desired type.
This accessor is most useful if the key and value can be absent
from an object without affecting its validity. If the key and
value are mandatory, use .: instead.
(.!=) :: Parser (Maybe a) -> a -> Parser a Source #
Helper for use in combination with .:? to provide default
values for optional JSON object fields.
This combinator is most useful if the key and value can be absent
from an object without affecting its validity and we know a default
value to assign in that case. If the key and value are mandatory,
use .: instead.
Example usage:
v1 <- o.:?"opt_field_with_dfl" .!= "default_val" v2 <- o.:"mandatory_field" v3 <- o.:?"opt_field2"
fromEncoding :: Encoding' tag -> Builder Source #
Acquire the underlying bytestring builder.
genericLiftToJSON :: (Generic1 f, GToJSON' Value One (Rep1 f)) => Options -> (a -> Value) -> ([a] -> Value) -> f a -> Value Source #
A configurable generic JSON creator. This function applied to
defaultOptions is used as the default for liftToJSON when the type
is an instance of Generic1.
genericToEncoding :: (Generic a, GToJSON' Encoding Zero (Rep a)) => Options -> a -> Encoding Source #
A configurable generic JSON encoder. This function applied to
defaultOptions is used as the default for toEncoding when the type
is an instance of Generic.
genericLiftToEncoding :: (Generic1 f, GToJSON' Encoding One (Rep1 f)) => Options -> (a -> Encoding) -> ([a] -> Encoding) -> f a -> Encoding Source #
A configurable generic JSON encoder. This function applied to
defaultOptions is used as the default for liftToEncoding when the type
is an instance of Generic1.
toJSON1 :: (ToJSON1 f, ToJSON a) => f a -> Value Source #
Lift the standard toJSON function through the type constructor.
toEncoding1 :: (ToJSON1 f, ToJSON a) => f a -> Encoding Source #
Lift the standard toEncoding function through the type constructor.
toJSON2 :: (ToJSON2 f, ToJSON a, ToJSON b) => f a b -> Value Source #
Lift the standard toJSON function through the type constructor.
toEncoding2 :: (ToJSON2 f, ToJSON a, ToJSON b) => f a b -> Encoding Source #
Lift the standard toEncoding function through the type constructor.
encode :: ToJSON a => a -> ByteString Source #
Efficiently serialize a JSON value as a lazy ByteString.
This is implemented in terms of the ToJSON class's toEncoding method.
encodeFile :: ToJSON a => FilePath -> a -> IO () Source #
Efficiently serialize a JSON value as a lazy ByteString and write it to a file.
decode :: FromJSON a => ByteString -> Maybe a Source #
Efficiently deserialize a JSON value from a lazy ByteString.
If this fails due to incomplete or invalid input, Nothing is
returned.
The input must consist solely of a JSON document, with no trailing data except for whitespace.
This function parses immediately, but defers conversion. See
json for details.
decodeStrict :: FromJSON a => ByteString -> Maybe a Source #
Efficiently deserialize a JSON value from a strict ByteString.
If this fails due to incomplete or invalid input, Nothing is
returned.
The input must consist solely of a JSON document, with no trailing data except for whitespace.
This function parses immediately, but defers conversion. See
json for details.
decodeFileStrict :: FromJSON a => FilePath -> IO (Maybe a) Source #
Efficiently deserialize a JSON value from a file.
If this fails due to incomplete or invalid input, Nothing is
returned.
The input file's content must consist solely of a JSON document, with no trailing data except for whitespace.
This function parses immediately, but defers conversion. See
json for details.
decode' :: FromJSON a => ByteString -> Maybe a Source #
Efficiently deserialize a JSON value from a lazy ByteString.
If this fails due to incomplete or invalid input, Nothing is
returned.
The input must consist solely of a JSON document, with no trailing data except for whitespace.
This function parses and performs conversion immediately. See
json' for details.
decodeStrict' :: FromJSON a => ByteString -> Maybe a Source #
Efficiently deserialize a JSON value from a strict ByteString.
If this fails due to incomplete or invalid input, Nothing is
returned.
The input must consist solely of a JSON document, with no trailing data except for whitespace.
This function parses and performs conversion immediately. See
json' for details.
decodeFileStrict' :: FromJSON a => FilePath -> IO (Maybe a) Source #
Efficiently deserialize a JSON value from a file.
If this fails due to incomplete or invalid input, Nothing is
returned.
The input file's content must consist solely of a JSON document, with no trailing data except for whitespace.
This function parses and performs conversion immediately. See
json' for details.
eitherDecode :: FromJSON a => ByteString -> Either String a Source #
Like decode but returns an error message when decoding fails.
eitherDecodeStrict :: FromJSON a => ByteString -> Either String a Source #
Like decodeStrict but returns an error message when decoding fails.
eitherDecodeFileStrict :: FromJSON a => FilePath -> IO (Either String a) Source #
Like decodeFileStrict but returns an error message when decoding fails.
eitherDecode' :: FromJSON a => ByteString -> Either String a Source #
Like decode' but returns an error message when decoding fails.
eitherDecodeStrict' :: FromJSON a => ByteString -> Either String a Source #
Like decodeStrict' but returns an error message when decoding fails.
eitherDecodeFileStrict' :: FromJSON a => FilePath -> IO (Either String a) Source #
Like decodeFileStrict' but returns an error message when decoding fails.
throwDecode :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like decode but throws an AesonException when decoding fails.
>>>throwDecode "42" :: Maybe IntJust 42
>>>throwDecode "42" :: IO Int42
>>>throwDecode "true" :: IO Int...Exception: AesonException...
Since: aeson-2.1.2.0
throwDecodeStrict :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like decodeStrict but throws an AesonException when decoding fails.
Since: aeson-2.1.2.0
throwDecode' :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like decode' but throws an AesonException when decoding fails.
Since: aeson-2.1.2.0
throwDecodeStrict' :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like decodeStrict' but throws an AesonException when decoding fails.
Since: aeson-2.1.2.0
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
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
Arbitrary precision integers. In contrast with fixed-size integral types
such as Int, the Integer type represents the entire infinite range of
integers.
Integers are stored in a kind of sign-magnitude form, hence do not expect two's complement form when using bit operations.
If the value is small (fit into an Int), IS constructor is used.
Otherwise Integer and IN constructors are used to store a BigNat
representing respectively the positive or the negative value magnitude.
Invariant: Integer and IN are used iff value doesn't fit in IS
Instances
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
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
Arguments
| :: Int | the operator precedence of the enclosing
context (a number from |
| -> a | the value to be converted to a |
| -> ShowS |
Convert a value to a readable String.
showsPrec should satisfy the law
showsPrec d x r ++ s == showsPrec d x (r ++ s)
Derived instances of Read and Show satisfy the following:
That is, readsPrec parses the string produced by
showsPrec, and delivers the value that showsPrec started with.
Instances
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
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 = minBoundMethods
the successor of a value. For numeric types, succ adds 1.
the predecessor of a value. For numeric types, pred subtracts 1.
Convert from an Int.
Convert to an Int.
It is implementation-dependent what fromEnum returns when
applied to a value that is too large to fit in an Int.
Used in Haskell's translation of [n..] with [n..] = enumFrom n,
a possible implementation being enumFrom n = n : enumFrom (succ n).
For example:
enumFrom 4 :: [Integer] = [4,5,6,7,...]
enumFrom 6 :: [Int] = [6,7,8,9,...,maxBound :: Int]
enumFromThen :: a -> a -> [a] #
Used in Haskell's translation of [n,n'..]
with [n,n'..] = enumFromThen n n', a possible implementation being
enumFromThen n n' = n : n' : worker (f x) (f x n'),
worker s v = v : worker s (s v), x = fromEnum n' - fromEnum n and
f n y
| n > 0 = f (n - 1) (succ y)
| n < 0 = f (n + 1) (pred y)
| otherwise = y
For example:
enumFromThen 4 6 :: [Integer] = [4,6,8,10...]
enumFromThen 6 2 :: [Int] = [6,2,-2,-6,...,minBound :: Int]
enumFromTo :: a -> a -> [a] #
Used in Haskell's translation of [n..m] with
[n..m] = enumFromTo n m, a possible implementation being
enumFromTo n m
| n <= m = n : enumFromTo (succ n) m
| otherwise = [].
For example:
enumFromTo 6 10 :: [Int] = [6,7,8,9,10]
enumFromTo 42 1 :: [Integer] = []
enumFromThenTo :: a -> a -> a -> [a] #
Used in Haskell's translation of [n,n'..m] with
[n,n'..m] = enumFromThenTo n n' m, a possible implementation
being enumFromThenTo n n' m = worker (f x) (c x) n m,
x = fromEnum n' - fromEnum n, c x = bool (>=) ((x 0)
f n y
| n > 0 = f (n - 1) (succ y)
| n < 0 = f (n + 1) (pred y)
| otherwise = y and
worker s c v m
| c v m = v : worker s c (s v) m
| otherwise = []
For example:
enumFromThenTo 4 2 -6 :: [Integer] = [4,2,0,-2,-4,-6]
enumFromThenTo 6 8 2 :: [Int] = []
Instances
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
Instances
| RealFrac Number | |
| RealFrac CDouble | |
| RealFrac CFloat | |
| RealFrac Half | |
| RealFrac Scientific | WARNING: the methods of the |
Defined in Data.Scientific Methods properFraction :: Integral b => Scientific -> (b, Scientific) # truncate :: Integral b => Scientific -> b # round :: Integral b => Scientific -> b # ceiling :: Integral b => Scientific -> b # floor :: Integral b => Scientific -> b # | |
| RealFrac DiffTime | |
| RealFrac NominalDiffTime | |
Defined in Data.Time.Clock.Internal.NominalDiffTime Methods properFraction :: Integral b => NominalDiffTime -> (b, NominalDiffTime) # truncate :: Integral b => NominalDiffTime -> b # round :: Integral b => NominalDiffTime -> b # ceiling :: Integral b => NominalDiffTime -> b # floor :: Integral b => NominalDiffTime -> b # | |
| RealFrac a => RealFrac (Identity a) | Since: base-4.9.0.0 |
| RealFrac a => RealFrac (Down a) | Since: base-4.14.0.0 |
| Integral a => RealFrac (Ratio a) | Since: base-2.0.1 |
| HasResolution a => RealFrac (Fixed a) | Since: base-2.1 |
| RealFrac a => RealFrac (Const a b) | Since: base-4.9.0.0 |
| RealFrac a => RealFrac (Tagged s a) | |
class (Real a, Enum a) => Integral a where #
Integral numbers, supporting integer division.
The Haskell Report defines no laws for Integral. However, Integral
instances are customarily expected to define a Euclidean domain and have the
following properties for the div/mod and quot/rem pairs, given
suitable Euclidean functions f and g:
x=y * quot x y + rem x ywithrem x y=fromInteger 0org (rem x y)<g yx=y * div x y + mod x ywithmod x y=fromInteger 0orf (mod x y)<f y
An example of a suitable Euclidean function, for Integer's instance, is
abs.
In addition, toInteger should be total, and fromInteger should be a left
inverse for it, i.e. fromInteger (toInteger i) = i.
Methods
quot :: a -> a -> a infixl 7 #
integer division truncated toward zero
WARNING: This function is partial (because it throws when 0 is passed as
the divisor) for all the integer types in base.
integer remainder, satisfying
(x `quot` y)*y + (x `rem` y) == x
WARNING: This function is partial (because it throws when 0 is passed as
the divisor) for all the integer types in base.
integer division truncated toward negative infinity
WARNING: This function is partial (because it throws when 0 is passed as
the divisor) for all the integer types in base.
integer modulus, satisfying
(x `div` y)*y + (x `mod` y) == x
WARNING: This function is partial (because it throws when 0 is passed as
the divisor) for all the integer types in base.
WARNING: This function is partial (because it throws when 0 is passed as
the divisor) for all the integer types in base.
WARNING: This function is partial (because it throws when 0 is passed as
the divisor) for all the integer types in base.
conversion to Integer
Instances
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
Methods
Arguments
| :: Int | the operator precedence of the enclosing
context (a number from |
| -> ReadS a |
attempts to parse a value from the front of the string, returning a list of (parsed value, remaining string) pairs. If there is no successful parse, the returned list is empty.
Derived instances of Read and Show satisfy the following:
That is, readsPrec parses the string produced by
showsPrec, and delivers the value that
showsPrec started with.
Instances
The Ord class is used for totally ordered datatypes.
Instances of Ord can be derived for any user-defined datatype whose
constituent types are in Ord. The declared order of the constructors in
the data declaration determines the ordering in derived Ord instances. The
Ordering datatype allows a single comparison to determine the precise
ordering of two objects.
Ord, as defined by the Haskell report, implements a total order and has the
following properties:
- Comparability
x <= y || y <= x=True- Transitivity
- if
x <= y && y <= z=True, thenx <= z=True - Reflexivity
x <= x=True- Antisymmetry
- if
x <= y && y <= x=True, thenx == y=True
The following operator interactions are expected to hold:
x >= y=y <= xx < y=x <= y && x /= yx > y=y < xx < y=compare x y == LTx > y=compare x y == GTx == y=compare x y == EQmin x y == if x <= y then x else y=Truemax x y == if x >= y then x else y=True
Note that (7.) and (8.) do not require min and max to return either of
their arguments. The result is merely required to equal one of the
arguments in terms of (==).
Minimal complete definition: either compare or <=.
Using compare can be more efficient for complex types.
Methods
compare :: a -> a -> Ordering #
(<) :: a -> a -> Bool infix 4 #
(<=) :: a -> a -> Bool infix 4 #
(>) :: a -> a -> Bool infix 4 #
Instances
class Num a => Fractional a where #
Fractional numbers, supporting real division.
The Haskell Report defines no laws for Fractional. However, ( and
+)( are customarily expected to define a division ring and have the
following properties:*)
recipgives the multiplicative inversex * recip x=recip x * x=fromInteger 1- Totality of
toRational toRationalis total- Coherence with
toRational - if the type also implements
Real, thenfromRationalis a left inverse fortoRational, i.e.fromRational (toRational i) = i
Note that it isn't customarily expected that a type instance of
Fractional implement a field. However, all instances in base do.
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 Number | |
Defined in Data.Attoparsec.Number | |
| Fractional CDouble | |
| Fractional CFloat | |
| Fractional Half | |
| Fractional Scientific | WARNING: These methods also compute
|
Defined in Data.Scientific Methods (/) :: Scientific -> Scientific -> Scientific # recip :: Scientific -> Scientific # fromRational :: Rational -> Scientific # | |
| Fractional DiffTime | |
| Fractional NominalDiffTime | |
Defined in Data.Time.Clock.Internal.NominalDiffTime Methods (/) :: NominalDiffTime -> NominalDiffTime -> NominalDiffTime # recip :: NominalDiffTime -> NominalDiffTime # fromRational :: Rational -> NominalDiffTime # | |
| RealFloat a => Fractional (Complex a) | Since: base-2.1 |
| Fractional a => Fractional (Identity a) | Since: base-4.9.0.0 |
| Fractional a => Fractional (Down a) | Since: base-4.14.0.0 |
| Integral a => Fractional (Ratio a) | Since: base-2.0.1 |
| HasResolution a => Fractional (Fixed a) | Since: base-2.1 |
| Fractional a => Fractional (Op a b) | |
| Fractional a => Fractional (Const a b) | Since: base-4.9.0.0 |
| Fractional a => Fractional (Tagged s a) | |
class (Num a, Ord a) => Real a where #
Real numbers.
The Haskell report defines no laws for Real, however Real instances
are customarily expected to adhere to the following law:
- Coherence with
fromRational - if the type also implements
Fractional, thenfromRationalis a left inverse fortoRational, i.e.fromRational (toRational i) = i
Methods
toRational :: a -> Rational #
the rational equivalent of its real argument with full precision
Instances
The Eq class defines equality (==) and inequality (/=).
All the basic datatypes exported by the Prelude are instances of Eq,
and Eq may be derived for any datatype whose constituents are also
instances of Eq.
The Haskell Report defines no laws for Eq. However, instances are
encouraged to follow these properties:
Instances
class Fractional a => Floating a where #
Trigonometric and hyperbolic functions and related functions.
The Haskell Report defines no laws for Floating. However, (, +)(
and *)exp are customarily expected to define an exponential field and have
the following properties:
exp (a + b)=exp a * exp bexp (fromInteger 0)=fromInteger 1
Minimal complete definition
pi, exp, log, sin, cos, asin, acos, atan, sinh, cosh, asinh, acosh, atanh
Instances
Basic numeric class.
The Haskell Report defines no laws for Num. However, ( and +)( are
customarily expected to define a ring and have the following properties:*)
- Associativity of
(+) (x + y) + z=x + (y + z)- Commutativity of
(+) x + y=y + xfromInteger0x + fromInteger 0=xnegategives the additive inversex + negate x=fromInteger 0- Associativity of
(*) (x * y) * z=x * (y * z)fromInteger1x * fromInteger 1=xandfromInteger 1 * x=x- Distributivity of
(with respect to*)(+) a * (b + c)=(a * b) + (a * c)and(b + c) * a=(b * a) + (c * a)- Coherence with
toInteger - if the type also implements
Integral, thenfromIntegeris a left inverse fortoInteger, i.e.fromInteger (toInteger i) == i
Note that it isn't customarily expected that a type instance of both Num
and Ord implement an ordered ring. Indeed, in base only Integer and
Rational do.
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
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.
Instances
File and directory names are values of type String, whose precise
meaning is operating system dependent. Files can be opened, yielding a
handle which can then be used to operate on the contents of that file.
read :: Read a => String -> a #
The read function reads input from a string, which must be
completely consumed by the input process. read fails with an error if the
parse is unsuccessful, and it is therefore discouraged from being used in
real applications. Use readMaybe or readEither for safe alternatives.
>>>read "123" :: Int123
>>>read "hello" :: Int*** Exception: Prelude.read: no parse
realToFrac :: (Real a, Fractional b) => a -> b #
General coercion to Fractional types.
WARNING: This function goes through the Rational type, which does not have values for NaN for example.
This means it does not round-trip.
For Double it also behaves differently with or without -O0:
Prelude> realToFrac nan -- With -O0 -Infinity Prelude> realToFrac nan NaN
fromIntegral :: (Integral a, Num b) => a -> b #
General coercion from Integral types.
WARNING: This function performs silent truncation if the result type is not at least as big as the argument's type.
seq :: forall {r :: RuntimeRep} a (b :: TYPE r). a -> b -> b infixr 0 #
The value of seq a ba is bottom, and
otherwise equal to b. In other words, it evaluates the first
argument a to weak head normal form (WHNF). seq is usually
introduced to improve performance by avoiding unneeded laziness.
A note on evaluation order: the expression seq a ba 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.
error :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => [Char] -> a #
error stops execution and displays an error message.
undefined :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => a #
($!) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b infixr 0 #
Strict (call-by-value) application operator. It takes a function and an argument, evaluates the argument to weak head normal form (WHNF), then calls the function with that value.
utility function converting a Char to a show function that
simply prepends the character unchanged.
showString :: String -> ShowS #
utility function converting a String to a show function that
simply prepends the string unchanged.
(^^) :: (Fractional a, Integral b) => a -> b -> a infixr 8 #
raise a number to an integral power
gcd :: Integral a => a -> a -> a #
gcd x yx and y of which
every common factor of x and y is also a factor; for example
gcd 4 2 = 2gcd (-4) 6 = 2gcd 0 44. gcd 0 00.
(That is, the common divisor that is "greatest" in the divisibility
preordering.)
Note: Since for signed fixed-width integer types, abs minBound < 0minBound0 or minBound
lcm :: Integral a => a -> a -> a #
lcm x yx and y divide.
The lex function reads a single lexeme from the input, discarding
initial white space, and returning the characters that constitute the
lexeme. If the input string contains only white space, lex returns a
single successful `lexeme' consisting of the empty string. (Thus
lex "" = [("","")]lex fails (i.e. returns []).
This lexer is not completely faithful to the Haskell lexical syntax in the following respects:
- Qualified names are not handled properly
- Octal and hexadecimal numerics are not recognized as a single token
- Comments are not treated properly
class Functor f => Applicative (f :: Type -> Type) where #
A functor with application, providing operations to
A minimal complete definition must include implementations of pure
and of either <*> or liftA2. If it defines both, then they must behave
the same as their default definitions:
(<*>) =liftA2id
liftA2f x y = f<$>x<*>y
Further, any definition must satisfy the following:
- Identity
pureid<*>v = v- Composition
pure(.)<*>u<*>v<*>w = u<*>(v<*>w)- Homomorphism
puref<*>purex =pure(f x)- Interchange
u
<*>purey =pure($y)<*>u
The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:
As a consequence of these laws, the Functor instance for f will satisfy
It may be useful to note that supposing
forall x y. p (q x y) = f x . g y
it follows from the above that
liftA2p (liftA2q u v) =liftA2f u .liftA2g v
If f is also a Monad, it should satisfy
(which implies that pure and <*> satisfy the applicative functor laws).
Methods
Lift a value.
(<*>) :: f (a -> b) -> f a -> f b infixl 4 #
Sequential application.
A few functors support an implementation of <*> that is more
efficient than the default one.
Example
Used in combination with (, <$>)( can be used to build a record.<*>)
>>>data MyState = MyState {arg1 :: Foo, arg2 :: Bar, arg3 :: Baz}
>>>produceFoo :: Applicative f => f Foo
>>>produceBar :: Applicative f => f Bar>>>produceBaz :: Applicative f => f Baz
>>>mkState :: Applicative f => f MyState>>>mkState = MyState <$> produceFoo <*> produceBar <*> produceBaz
liftA2 :: (a -> b -> c) -> f a -> f b -> f c #
Lift a binary function to actions.
Some functors support an implementation of liftA2 that is more
efficient than the default one. In particular, if fmap is an
expensive operation, it is likely better to use liftA2 than to
fmap over the structure and then use <*>.
This became a typeclass method in 4.10.0.0. Prior to that, it was
a function defined in terms of <*> and fmap.
Example
>>>liftA2 (,) (Just 3) (Just 5)Just (3,5)
(*>) :: f a -> f b -> f b infixl 4 #
Sequence actions, discarding the value of the first argument.
Examples
If used in conjunction with the Applicative instance for Maybe,
you can chain Maybe computations, with a possible "early return"
in case of Nothing.
>>>Just 2 *> Just 3Just 3
>>>Nothing *> Just 3Nothing
Of course a more interesting use case would be to have effectful computations instead of just returning pure values.
>>>import Data.Char>>>import Text.ParserCombinators.ReadP>>>let p = string "my name is " *> munch1 isAlpha <* eof>>>readP_to_S p "my name is Simon"[("Simon","")]
(<*) :: f a -> f b -> f a infixl 4 #
Sequence actions, discarding the value of the second argument.
Instances
class Applicative f => Alternative (f :: Type -> Type) where #
A monoid on applicative functors.
If defined, some and many should be the least solutions
of the equations:
Instances
The Const functor.
Instances
| Generic1 (Const a :: k -> Type) | |
| FoldableWithIndex Void (Const e :: Type -> Type) | |
Defined in WithIndex Methods ifoldMap :: Monoid m => (Void -> a -> m) -> Const e a -> m Source # ifoldMap' :: Monoid m => (Void -> a -> m) -> Const e a -> m Source # ifoldr :: (Void -> a -> b -> b) -> b -> Const e a -> b Source # ifoldl :: (Void -> b -> a -> b) -> b -> Const e a -> b Source # ifoldr' :: (Void -> a -> b -> b) -> b -> Const e a -> b Source # ifoldl' :: (Void -> b -> a -> b) -> b -> Const e a -> b Source # | |
| FunctorWithIndex Void (Const e :: Type -> Type) | |
| TraversableWithIndex Void (Const e :: Type -> Type) | |
| Unbox a => Vector Vector (Const a b) | |
Defined in Data.Vector.Unboxed.Base Methods basicUnsafeFreeze :: Mutable Vector s (Const a b) -> ST s (Vector (Const a b)) Source # basicUnsafeThaw :: Vector (Const a b) -> ST s (Mutable Vector s (Const a b)) Source # basicLength :: Vector (Const a b) -> Int Source # basicUnsafeSlice :: Int -> Int -> Vector (Const a b) -> Vector (Const a b) Source # basicUnsafeIndexM :: Vector (Const a b) -> Int -> Box (Const a b) Source # basicUnsafeCopy :: Mutable Vector s (Const a b) -> Vector (Const a b) -> ST s () Source # elemseq :: Vector (Const a b) -> Const a b -> b0 -> b0 Source # | |
| Unbox a => MVector MVector (Const a b) | |
Defined in Data.Vector.Unboxed.Base Methods basicLength :: MVector s (Const a b) -> Int Source # basicUnsafeSlice :: Int -> Int -> MVector s (Const a b) -> MVector s (Const a b) Source # basicOverlaps :: MVector s (Const a b) -> MVector s (Const a b) -> Bool Source # basicUnsafeNew :: Int -> ST s (MVector s (Const a b)) Source # basicInitialize :: MVector s (Const a b) -> ST s () Source # basicUnsafeReplicate :: Int -> Const a b -> ST s (MVector s (Const a b)) Source # basicUnsafeRead :: MVector s (Const a b) -> Int -> ST s (Const a b) Source # basicUnsafeWrite :: MVector s (Const a b) -> Int -> Const a b -> ST s () Source # basicClear :: MVector s (Const a b) -> ST s () Source # basicSet :: MVector s (Const a b) -> Const a b -> ST s () Source # basicUnsafeCopy :: MVector s (Const a b) -> MVector s (Const a b) -> ST s () Source # basicUnsafeMove :: MVector s (Const a b) -> MVector s (Const a b) -> ST s () Source # basicUnsafeGrow :: MVector s (Const a b) -> Int -> ST s (MVector s (Const a b)) Source # | |
| FromJSON2 (Const :: Type -> Type -> Type) | |
Defined in Data.Aeson.Types.FromJSON Methods liftParseJSON2 :: (Value -> Parser a) -> (Value -> Parser [a]) -> (Value -> Parser b) -> (Value -> Parser [b]) -> Value -> Parser (Const a b) Source # liftParseJSONList2 :: (Value -> Parser a) -> (Value -> Parser [a]) -> (Value -> Parser b) -> (Value -> Parser [b]) -> Value -> Parser [Const a b] Source # | |
| ToJSON2 (Const :: Type -> Type -> Type) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> Const a b -> Value Source # liftToJSONList2 :: (a -> Value) -> ([a] -> Value) -> (b -> Value) -> ([b] -> Value) -> [Const a b] -> Value Source # liftToEncoding2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> Const a b -> Encoding Source # liftToEncodingList2 :: (a -> Encoding) -> ([a] -> Encoding) -> (b -> Encoding) -> ([b] -> Encoding) -> [Const a b] -> Encoding Source # | |
| Bifunctor (Const :: Type -> Type -> Type) | Since: base-4.8.0.0 |
| NFData2 (Const :: Type -> Type -> Type) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Hashable2 (Const :: Type -> Type -> Type) | |
| Bitraversable1 (Const :: Type -> Type -> Type) | |
Defined in Data.Semigroup.Traversable.Class | |
| FromJSON a => FromJSON1 (Const a :: Type -> Type) | |
| ToJSON a => ToJSON1 (Const a :: Type -> Type) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a0 -> Value) -> ([a0] -> Value) -> Const a a0 -> Value Source # liftToJSONList :: (a0 -> Value) -> ([a0] -> Value) -> [Const a a0] -> Value Source # liftToEncoding :: (a0 -> Encoding) -> ([a0] -> Encoding) -> Const a a0 -> Encoding Source # liftToEncodingList :: (a0 -> Encoding) -> ([a0] -> Encoding) -> [Const a a0] -> Encoding Source # | |
| Foldable (Const m :: Type -> Type) | Since: base-4.7.0.0 |
Defined in Data.Functor.Const Methods fold :: Monoid m0 => Const m m0 -> m0 # foldMap :: Monoid m0 => (a -> m0) -> Const m a -> m0 # foldMap' :: Monoid m0 => (a -> m0) -> Const m a -> m0 # foldr :: (a -> b -> b) -> b -> Const m a -> b # foldr' :: (a -> b -> b) -> b -> Const m a -> b # foldl :: (b -> a -> b) -> b -> Const m a -> b # foldl' :: (b -> a -> b) -> b -> Const m a -> b # foldr1 :: (a -> a -> a) -> Const m a -> a # foldl1 :: (a -> a -> a) -> Const m a -> a # elem :: Eq a => a -> Const m a -> Bool # maximum :: Ord a => Const m a -> a # minimum :: Ord a => Const m a -> a # | |
| Contravariant (Const a :: Type -> Type) | |
| Traversable (Const m :: Type -> Type) | Since: base-4.7.0.0 |
| Monoid m => Applicative (Const m :: Type -> Type) | Since: base-2.0.1 |
| Functor (Const m :: Type -> Type) | Since: base-2.1 |
| NFData a => NFData1 (Const a :: Type -> Type) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Hashable a => Hashable1 (Const a :: Type -> Type) | |
Defined in Data.Hashable.Class | |
| FromJSON a => FromJSON (Const a b) | |
| (FromJSON a, FromJSONKey a) => FromJSONKey (Const a b) | |
Defined in Data.Aeson.Types.FromJSON Methods fromJSONKey :: FromJSONKeyFunction (Const a b) Source # fromJSONKeyList :: FromJSONKeyFunction [Const a b] Source # | |
| ToJSON a => ToJSON (Const a b) | |
| (ToJSON a, ToJSONKey a) => ToJSONKey (Const a b) | |
Defined in Data.Aeson.Types.ToJSON Methods toJSONKey :: ToJSONKeyFunction (Const a b) Source # toJSONKeyList :: ToJSONKeyFunction [Const a b] Source # | |
| IsString a => IsString (Const a b) | Since: base-4.9.0.0 |
Defined in Data.String Methods fromString :: String -> Const a b # | |
| Storable a => Storable (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
| Monoid a => Monoid (Const a b) | Since: base-4.9.0.0 |
| Semigroup a => Semigroup (Const a b) | Since: base-4.9.0.0 |
| Bits a => Bits (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods (.&.) :: Const a b -> Const a b -> Const a b # (.|.) :: Const a b -> Const a b -> Const a b # xor :: Const a b -> Const a b -> Const a b # complement :: Const a b -> Const a b # shift :: Const a b -> Int -> Const a b # rotate :: Const a b -> Int -> Const a b # setBit :: Const a b -> Int -> Const a b # clearBit :: Const a b -> Int -> Const a b # complementBit :: Const a b -> Int -> Const a b # testBit :: Const a b -> Int -> Bool # bitSizeMaybe :: Const a b -> Maybe Int # isSigned :: Const a b -> Bool # shiftL :: Const a b -> Int -> Const a b # unsafeShiftL :: Const a b -> Int -> Const a b # shiftR :: Const a b -> Int -> Const a b # unsafeShiftR :: Const a b -> Int -> Const a b # rotateL :: Const a b -> Int -> Const a b # | |
| FiniteBits a => FiniteBits (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods finiteBitSize :: Const a b -> Int # countLeadingZeros :: Const a b -> Int # countTrailingZeros :: Const a b -> Int # | |
| Bounded a => Bounded (Const a b) | Since: base-4.9.0.0 |
| Enum a => Enum (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods succ :: Const a b -> Const a b # pred :: Const a b -> Const a b # fromEnum :: Const a b -> Int # enumFrom :: Const a b -> [Const a b] # enumFromThen :: Const a b -> Const a b -> [Const a b] # enumFromTo :: Const a b -> Const a b -> [Const a b] # enumFromThenTo :: Const a b -> Const a b -> Const a b -> [Const a b] # | |
| Floating a => Floating (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods exp :: Const a b -> Const a b # log :: Const a b -> Const a b # sqrt :: Const a b -> Const a b # (**) :: Const a b -> Const a b -> Const a b # logBase :: Const a b -> Const a b -> Const a b # sin :: Const a b -> Const a b # cos :: Const a b -> Const a b # tan :: Const a b -> Const a b # asin :: Const a b -> Const a b # acos :: Const a b -> Const a b # atan :: Const a b -> Const a b # sinh :: Const a b -> Const a b # cosh :: Const a b -> Const a b # tanh :: Const a b -> Const a b # asinh :: Const a b -> Const a b # acosh :: Const a b -> Const a b # atanh :: Const a b -> Const a b # log1p :: Const a b -> Const a b # expm1 :: Const a b -> Const a b # | |
| RealFloat a => RealFloat (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods floatRadix :: Const a b -> Integer # floatDigits :: Const a b -> Int # floatRange :: Const a b -> (Int, Int) # decodeFloat :: Const a b -> (Integer, Int) # encodeFloat :: Integer -> Int -> Const a b # exponent :: Const a b -> Int # significand :: Const a b -> Const a b # scaleFloat :: Int -> Const a b -> Const a b # isInfinite :: Const a b -> Bool # isDenormalized :: Const a b -> Bool # isNegativeZero :: Const a b -> Bool # | |
| Generic (Const a b) | |
| Ix a => Ix (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods range :: (Const a b, Const a b) -> [Const a b] # index :: (Const a b, Const a b) -> Const a b -> Int # unsafeIndex :: (Const a b, Const a b) -> Const a b -> Int # inRange :: (Const a b, Const a b) -> Const a b -> Bool # rangeSize :: (Const a b, Const a b) -> Int # unsafeRangeSize :: (Const a b, Const a b) -> Int # | |
| Num a => Num (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
| Read a => Read (Const a b) | This instance would be equivalent to the derived instances of the
Since: base-4.8.0.0 |
| Fractional a => Fractional (Const a b) | Since: base-4.9.0.0 |
| Integral a => Integral (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods quot :: Const a b -> Const a b -> Const a b # rem :: Const a b -> Const a b -> Const a b # div :: Const a b -> Const a b -> Const a b # mod :: Const a b -> Const a b -> Const a b # quotRem :: Const a b -> Const a b -> (Const a b, Const a b) # divMod :: Const a b -> Const a b -> (Const a b, Const a b) # | |
| Real a => Real (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const Methods toRational :: Const a b -> Rational # | |
| RealFrac a => RealFrac (Const a b) | Since: base-4.9.0.0 |
| Show a => Show (Const a b) | This instance would be equivalent to the derived instances of the
Since: base-4.8.0.0 |
| NFData a => NFData (Const a b) | Since: deepseq-1.4.0.0 |
Defined in Control.DeepSeq | |
| Eq a => Eq (Const a b) | Since: base-4.9.0.0 |
| Ord a => Ord (Const a b) | Since: base-4.9.0.0 |
| Hashable a => Hashable (Const a b) | |
| FromFormKey a => FromFormKey (Const a b) | Since: http-api-data-0.4.2 |
Defined in Web.Internal.FormUrlEncoded | |
| ToFormKey a => ToFormKey (Const a b) | Since: http-api-data-0.4.2 |
| Wrapped (Const a x) | |
| Pretty a => Pretty (Const a b) | |
| Unbox a => Unbox (Const a b) | |
Defined in Data.Vector.Unboxed.Base | |
| t ~ Const a' x' => Rewrapped (Const a x) t | |
Defined in Control.Lens.Wrapped | |
| type Rep1 (Const a :: k -> Type) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
| newtype MVector s (Const a b) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep (Const a b) | Since: base-4.9.0.0 |
Defined in Data.Functor.Const | |
| type Unwrapped (Const a x) | |
Defined in Control.Lens.Wrapped | |
| newtype Vector (Const a b) | |
Defined in Data.Vector.Unboxed.Base | |
Lists, but with an Applicative functor based on zipping.
Constructors
| ZipList | |
Fields
| |
Instances
| Foldable ZipList | Since: base-4.9.0.0 |
Defined in Control.Applicative Methods fold :: Monoid m => ZipList m -> m # foldMap :: Monoid m => (a -> m) -> ZipList a -> m # foldMap' :: Monoid m => (a -> m) -> ZipList a -> m # foldr :: (a -> b -> b) -> b -> ZipList a -> b # foldr' :: (a -> b -> b) -> b -> ZipList a -> b # foldl :: (b -> a -> b) -> b -> ZipList a -> b # foldl' :: (b -> a -> b) -> b -> ZipList a -> b # foldr1 :: (a -> a -> a) -> ZipList a -> a # foldl1 :: (a -> a -> a) -> ZipList a -> a # elem :: Eq a => a -> ZipList a -> Bool # maximum :: Ord a => ZipList a -> a # minimum :: Ord a => ZipList a -> a # | |
| Traversable ZipList | Since: base-4.9.0.0 |
| Alternative ZipList | Since: base-4.11.0.0 |
| Applicative ZipList | f <$> ZipList xs1 <*> ... <*> ZipList xsN
= ZipList (zipWithN f xs1 ... xsN)where (\a b c -> stimes c [a, b]) <$> ZipList "abcd" <*> ZipList "567" <*> ZipList [1..]
= ZipList (zipWith3 (\a b c -> stimes c [a, b]) "abcd" "567" [1..])
= ZipList {getZipList = ["a5","b6b6","c7c7c7"]}Since: base-2.1 |
| Functor ZipList | Since: base-2.1 |
| NFData1 ZipList | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Generic1 ZipList | |
| FoldableWithIndex Int ZipList | |
Defined in WithIndex Methods ifoldMap :: Monoid m => (Int -> a -> m) -> ZipList a -> m Source # ifoldMap' :: Monoid m => (Int -> a -> m) -> ZipList a -> m Source # ifoldr :: (Int -> a -> b -> b) -> b -> ZipList a -> b Source # ifoldl :: (Int -> b -> a -> b) -> b -> ZipList a -> b Source # ifoldr' :: (Int -> a -> b -> b) -> b -> ZipList a -> b Source # ifoldl' :: (Int -> b -> a -> b) -> b -> ZipList a -> b Source # | |
| FunctorWithIndex Int ZipList | Same instance as for |
| TraversableWithIndex Int ZipList | |
| Generic (ZipList a) | |
| IsList (ZipList a) | Since: base-4.15.0.0 |
| Read a => Read (ZipList a) | Since: base-4.7.0.0 |
| Show a => Show (ZipList a) | Since: base-4.7.0.0 |
| NFData a => NFData (ZipList a) | Since: deepseq-1.4.0.0 |
Defined in Control.DeepSeq | |
| Eq a => Eq (ZipList a) | Since: base-4.7.0.0 |
| Ord a => Ord (ZipList a) | Since: base-4.7.0.0 |
| AsEmpty (ZipList a) | |
| Wrapped (ZipList a) | |
| t ~ ZipList b => Rewrapped (ZipList a) t | |
Defined in Control.Lens.Wrapped | |
| Cons (ZipList a) (ZipList b) a b | |
| Snoc (ZipList a) (ZipList b) a b | |
| type Rep1 ZipList | Since: base-4.7.0.0 |
Defined in Control.Applicative | |
| type Rep (ZipList a) | Since: base-4.7.0.0 |
Defined in Control.Applicative | |
| type Item (ZipList a) | |
Defined in GHC.IsList | |
| type Unwrapped (ZipList a) | |
Defined in Control.Lens.Wrapped | |
newtype WrappedArrow (a :: Type -> Type -> Type) b c #
Constructors
| WrapArrow | |
Fields
| |
Instances
newtype WrappedMonad (m :: Type -> Type) a #
Constructors
| WrapMonad | |
Fields
| |
Instances
(<$>) :: 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)
(<**>) :: Applicative f => f a -> f (a -> b) -> f b infixl 4 #
A variant of <*> with the arguments reversed.
liftA :: Applicative f => (a -> b) -> f a -> f b #
Lift a function to actions.
Equivalent to Functor's fmap but implemented using only Applicative's methods:
liftA f a = pure f <*> a
As such this function may be used to implement a Functor instance from an Applicative one.
Examples
Using the Applicative instance for Lists:
>>>liftA (+1) [1, 2][2,3]
Or the Applicative instance for Maybe
>>>liftA (+1) (Just 3)Just 4
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d #
Lift a ternary function to actions.
asum :: (Foldable t, Alternative f) => t (f a) -> f a #
The sum of a collection of actions using (<|>), generalizing concat.
asum is just like msum, but generalised to Alternative.
Examples
Basic usage:
>>>asum [Just "Hello", Nothing, Just "World"]Just "Hello"
class Functor (f :: Type -> Type) where #
A type f is a Functor if it provides a function fmap which, given any types a and b
lets you apply any function from (a -> b) to turn an f a into an f b, preserving the
structure of f. Furthermore f needs to adhere to the following:
Note, that the second law follows from the free theorem of the type fmap and
the first law, so you need only check that the former condition holds.
See https://www.schoolofhaskell.com/user/edwardk/snippets/fmap or
https://github.com/quchen/articles/blob/master/second_functor_law.md
for an explanation.
Minimal complete definition
Methods
fmap :: (a -> b) -> f a -> f b #
fmap is used to apply a function of type (a -> b) to a value of type f a,
where f is a functor, to produce a value of type f b.
Note that for any type constructor with more than one parameter (e.g., Either),
only the last type parameter can be modified with fmap (e.g., b in `Either a b`).
Some type constructors with two parameters or more have a Bifunctor
Examples
Convert from a Maybe IntMaybe String
using show:
>>>fmap show NothingNothing>>>fmap show (Just 3)Just "3"
Convert from an Either Int IntEither Int String using show:
>>>fmap show (Left 17)Left 17>>>fmap show (Right 17)Right "17"
Double each element of a list:
>>>fmap (*2) [1,2,3][2,4,6]
Apply even to the second element of a pair:
>>>fmap even (2,2)(2,True)
It may seem surprising that the function is only applied to the last element of the tuple
compared to the list example above which applies it to every element in the list.
To understand, remember that tuples are type constructors with multiple type parameters:
a tuple of 3 elements (a,b,c) can also be written (,,) a b c and its Functor instance
is defined for Functor ((,,) a b) (i.e., only the third parameter is free to be mapped over
with fmap).
It explains why fmap can be used with tuples containing values of different types as in the
following example:
>>>fmap even ("hello", 1.0, 4)("hello",1.0,True)
Instances
class Applicative m => Monad (m :: Type -> Type) where #
The Monad class defines the basic operations over a monad,
a concept from a branch of mathematics known as category theory.
From the perspective of a Haskell programmer, however, it is best to
think of a monad as an abstract datatype of actions.
Haskell's do expressions provide a convenient syntax for writing
monadic expressions.
Instances of Monad should satisfy the following:
- Left identity
returna>>=k = k a- Right identity
m>>=return= m- Associativity
m>>=(\x -> k x>>=h) = (m>>=k)>>=h
Furthermore, the Monad and Applicative operations should relate as follows:
The above laws imply:
and that pure and (<*>) satisfy the applicative functor laws.
The instances of Monad for lists, Maybe and IO
defined in the Prelude satisfy these laws.
Minimal complete definition
Methods
(>>=) :: m a -> (a -> m b) -> m b infixl 1 #
Sequentially compose two actions, passing any value produced by the first as an argument to the second.
'as ' can be understood as the >>= bsdo expression
do a <- as bs a
(>>) :: m a -> m b -> m b infixl 1 #
Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.
'as ' can be understood as the >> bsdo expression
do as bs
Inject a value into the monadic type.
Instances
| Monad IResult | |
| Monad Parser | |
| Monad Result | |
| Monad Complex | Since: base-4.9.0.0 |
| Monad Identity | Since: base-4.8.0.0 |
| Monad First | Since: base-4.8.0.0 |
| Monad Last | Since: base-4.8.0.0 |
| Monad Down | Since: base-4.11.0.0 |
| Monad First | Since: base-4.9.0.0 |
| Monad Last | Since: base-4.9.0.0 |
| Monad Max | Since: base-4.9.0.0 |
| Monad Min | Since: base-4.9.0.0 |
| Monad Dual | Since: base-4.8.0.0 |
| Monad Product | Since: base-4.8.0.0 |
| Monad Sum | Since: base-4.8.0.0 |
| Monad NonEmpty | Since: base-4.9.0.0 |
| Monad STM | Since: base-4.3.0.0 |
| Monad Par1 | Since: base-4.9.0.0 |
| Monad P | Since: base-2.1 |
| Monad ReadP | Since: base-2.1 |
| Monad Put | |
| Monad List | |
| Monad Seq | |
| Monad Tree | |
| Monad BatchM | |
| Monad Client | |
| Monad CryptoFailable | |
Defined in Crypto.Error.Types Methods (>>=) :: CryptoFailable a -> (a -> CryptoFailable b) -> CryptoFailable b # (>>) :: CryptoFailable a -> CryptoFailable b -> CryptoFailable b # return :: a -> CryptoFailable a # | |
| Monad DNonEmpty | |
| Monad DList | |
| Monad IO | Since: base-2.1 |
| Monad App Source # | |
| Monad ParserM | |
| Monad ParserResult | |
Defined in Options.Applicative.Types Methods (>>=) :: ParserResult a -> (a -> ParserResult b) -> ParserResult b # (>>) :: ParserResult a -> ParserResult b -> ParserResult b # return :: a -> ParserResult a # | |
| Monad ReadM | |
| Monad Array | |
| Monad SmallArray | |
Defined in Data.Primitive.SmallArray Methods (>>=) :: SmallArray a -> (a -> SmallArray b) -> SmallArray b # (>>) :: SmallArray a -> SmallArray b -> SmallArray b # return :: a -> SmallArray a # | |
| Monad ClientM | |
| Monad DelayedIO | |
| Monad Handler | |
| Monad RouteResult | |
Defined in Servant.Server.Internal.RouteResult Methods (>>=) :: RouteResult a -> (a -> RouteResult b) -> RouteResult b # (>>) :: RouteResult a -> RouteResult b -> RouteResult b # return :: a -> RouteResult a # | |
| Monad I | |
| Monad Q | |
| Monad Memoized | |
| Monad Vector | |
| Monad Id | |
| Monad Stream | |
| Monad Maybe | Since: base-2.1 |
| Monad Solo | Since: base-4.15 |
| Monad List | Since: base-2.1 |
| Representable f => Monad (Co f) | |
| Monad (Parser i) | |
| Monad m => Monad (WrappedMonad m) | Since: base-4.7.0.0 |
Defined in Control.Applicative Methods (>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b # (>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b # return :: a -> WrappedMonad m a # | |
| ArrowApply a => Monad (ArrowMonad a) | Since: base-2.1 |
Defined in Control.Arrow Methods (>>=) :: ArrowMonad a a0 -> (a0 -> ArrowMonad a b) -> ArrowMonad a b # (>>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b # return :: a0 -> ArrowMonad a a0 # | |
| Monad (Either e) | Since: base-4.4.0.0 |
| Monad (Proxy :: Type -> Type) | Since: base-4.7.0.0 |
| Monad (U1 :: Type -> Type) | Since: base-4.9.0.0 |
| DRG gen => Monad (MonadPseudoRandom gen) | |
Defined in Crypto.Random.Types Methods (>>=) :: MonadPseudoRandom gen a -> (a -> MonadPseudoRandom gen b) -> MonadPseudoRandom gen b # (>>) :: MonadPseudoRandom gen a -> MonadPseudoRandom gen b -> MonadPseudoRandom gen b # return :: a -> MonadPseudoRandom gen a # | |
| ParserSource input => Monad (Parser input) | |
| Alternative f => Monad (Cofree f) | |
| Functor f => Monad (Free f) | |
| Monad m => Monad (Yoneda m) | |
| Monad (ReifiedFold s) | |
Defined in Control.Lens.Reified Methods (>>=) :: ReifiedFold s a -> (a -> ReifiedFold s b) -> ReifiedFold s b # (>>) :: ReifiedFold s a -> ReifiedFold s b -> ReifiedFold s b # return :: a -> ReifiedFold s a # | |
| Monad (ReifiedGetter s) | |
Defined in Control.Lens.Reified Methods (>>=) :: ReifiedGetter s a -> (a -> ReifiedGetter s b) -> ReifiedGetter s b # (>>) :: ReifiedGetter s a -> ReifiedGetter s b -> ReifiedGetter s b # return :: a -> ReifiedGetter s a # | |
| Monad m => Monad (ResourceT m) | |
| Monad m => Monad (RouteResultT m) | |
Defined in Servant.Server.Internal.RouteResult Methods (>>=) :: RouteResultT m a -> (a -> RouteResultT m b) -> RouteResultT m b # (>>) :: RouteResultT m a -> RouteResultT m b -> RouteResultT m b # return :: a -> RouteResultT m a # | |
| Semigroup a => Monad (These a) | |
| Semigroup a => Monad (These a) | |
| Monad m => Monad (MaybeT m) | |
| Monoid a => Monad ((,) a) | Since: base-4.9.0.0 |
| Monad m => Monad (Kleisli m a) | Since: base-4.14.0.0 |
| Monad f => Monad (Ap f) | Since: base-4.12.0.0 |
| Monad f => Monad (Alt f) | Since: base-4.8.0.0 |
| Monad f => Monad (Rec1 f) | Since: base-4.9.0.0 |
| (Applicative f, Monad f) => Monad (WhenMissing f x) | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods (>>=) :: WhenMissing f x a -> (a -> WhenMissing f x b) -> WhenMissing f x b # (>>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b # return :: a -> WhenMissing f x a # | |
| (Alternative f, Monad w) => Monad (CofreeT f w) | |
| (Functor f, Monad m) => Monad (FreeT f m) | |
| Monad (Indexed i a) | |
| (Monad (Rep p), Representable p) => Monad (Prep p) | |
| Monad (Tagged s) | |
| (Monoid w, Functor m, Monad m) => Monad (AccumT w m) | |
| Monad m => Monad (ExceptT e m) | |
| Monad m => Monad (IdentityT m) | |
| Monad m => Monad (ReaderT r m) | |
| Monad m => Monad (SelectT r m) | |
| Monad m => Monad (StateT s m) | |
| Monad m => Monad (StateT s m) | |
| Monad m => Monad (WriterT w m) | |
| (Monoid w, Monad m) => Monad (WriterT w m) | |
| (Monoid w, Monad m) => Monad (WriterT w m) | |
| Monad m => Monad (Reverse m) | Derived instance. |
| (Monoid a, Monoid b) => Monad ((,,) a b) | Since: base-4.14.0.0 |
| (Monad f, Monad g) => Monad (Product f g) | Since: base-4.9.0.0 |
| (Monad f, Monad g) => Monad (f :*: g) | Since: base-4.9.0.0 |
| Monad (ConduitT i o m) | |
| (Monad f, Applicative f) => Monad (WhenMatched f x y) | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods (>>=) :: WhenMatched f x y a -> (a -> WhenMatched f x y b) -> WhenMatched f x y b # (>>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b # return :: a -> WhenMatched f x y a # | |
| (Applicative f, Monad f) => Monad (WhenMissing f k x) | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal Methods (>>=) :: WhenMissing f k x a -> (a -> WhenMissing f k x b) -> WhenMissing f k x b # (>>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b # return :: a -> WhenMissing f k x a # | |
| Monad (Codensity f) | |
| Monad (ContT r m) | |
| (Monoid a, Monoid b, Monoid c) => Monad ((,,,) a b c) | Since: base-4.14.0.0 |
| Monad ((->) r) | Since: base-2.1 |
| Monad f => Monad (M1 i c f) | Since: base-4.9.0.0 |
| (Monad f, Applicative f) => Monad (WhenMatched f k x y) | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal Methods (>>=) :: WhenMatched f k x y a -> (a -> WhenMatched f k x y b) -> WhenMatched f k x y b # (>>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b # return :: a -> WhenMatched f k x y a # | |
| Monad m => Monad (RWST r w s m) | |
| (Monoid w, Monad m) => Monad (RWST r w s m) | |
| (Monoid w, Monad m) => Monad (RWST r w s m) | |
| Monad state => Monad (Builder collection mutCollection step state err) | |
Defined in Basement.MutableBuilder Methods (>>=) :: Builder collection mutCollection step state err a -> (a -> Builder collection mutCollection step state err b) -> Builder collection mutCollection step state err b # (>>) :: Builder collection mutCollection step state err a -> Builder collection mutCollection step state err b -> Builder collection mutCollection step state err b # return :: a -> Builder collection mutCollection step state err a # | |
| Monad m => Monad (Pipe l i o u m) | |
class Monad m => MonadFail (m :: Type -> Type) where #
When a value is bound in do-notation, the pattern on the left
hand side of <- might not match. In this case, this class
provides a function to recover.
A Monad without a MonadFail instance may only be used in conjunction
with pattern that always match, such as newtypes, tuples, data types with
only a single data constructor, and irrefutable patterns (~pat).
Instances of MonadFail should satisfy the following law: fail s should
be a left zero for >>=,
fail s >>= f = fail s
If your Monad is also MonadPlus, a popular definition is
fail _ = mzero
fail s should be an action that runs in the monad itself, not an
exception (except in instances of MonadIO). In particular,
fail should not be implemented in terms of error.
Since: base-4.9.0.0
Instances
class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where #
Monads that also support choice and failure.
Minimal complete definition
Nothing
Methods
The identity of mplus. It should also satisfy the equations
mzero >>= f = mzero v >> mzero = mzero
The default definition is
mzero = empty
An associative operation. The default definition is
mplus = (<|>)
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
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.
'join bssdo expression
do bs <- bss bs
Examples
A common use of join is to run an IO computation returned from
an STM transaction, since STM transactions
can't perform IO directly. Recall that
atomically :: STM a -> IO a
is used to run STM transactions atomically. So, by
specializing the types of atomically and join to
atomically:: STM (IO b) -> IO (IO b)join:: IO (IO b) -> IO b
we can compose them as
join.atomically:: STM (IO b) -> IO b
forever :: Applicative f => f a -> f b #
Repeat an action indefinitely.
Examples
A common use of forever is to process input from network sockets,
Handles, and channels
(e.g. MVar and
Chan).
For example, here is how we might implement an echo
server, using
forever both to listen for client connections on a network socket
and to echo client input on client connection handles:
echoServer :: Socket -> IO () echoServer socket =forever$ do client <- accept socketforkFinally(echo client) (\_ -> hClose client) where echo :: Handle -> IO () echo client =forever$ hGetLine client >>= hPutStrLn client
Note that "forever" isn't necessarily non-terminating.
If the action is in a MonadPlusforevermzero, effectively short-circuiting its caller.
guard :: Alternative f => Bool -> f () #
Conditional failure of Alternative computations. Defined by
guard True =pure() guard False =empty
Examples
Common uses of guard include conditionally signaling an error in
an error monad and conditionally rejecting the current choice in an
Alternative-based parser.
As an example of signaling an error in the error monad Maybe,
consider a safe division function safeDiv x y that returns
Nothing when the denominator y is zero and Just (x `div`
y)
>>>safeDiv 4 0Nothing
>>>safeDiv 4 2Just 2
A definition of safeDiv using guards, but not guard:
safeDiv :: Int -> Int -> Maybe Int
safeDiv x y | y /= 0 = Just (x `div` y)
| otherwise = Nothing
A definition of safeDiv using guard and Monad do-notation:
safeDiv :: Int -> Int -> Maybe Int safeDiv x y = do guard (y /= 0) return (x `div` y)
(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 #
Same as >>=, but with the arguments interchanged.
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.
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
liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r #
Promote a function to a monad, scanning the monadic arguments from
left to right (cf. liftM2).
liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r #
Promote a function to a monad, scanning the monadic arguments from
left to right (cf. liftM2).
liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r #
Promote a function to a monad, scanning the monadic arguments from
left to right (cf. liftM2).
filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] #
This generalizes the list-based filter function.
(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1 #
Left-to-right composition of Kleisli arrows.
'(bs ' can be understood as the >=> cs) ado expression
do b <- bs a cs b
mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c]) #
The mapAndUnzipM function maps its first argument over a list, returning
the result as a pair of lists. This function is mainly used with complicated
data structures or a state monad.
zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] #
zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () #
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 xm
If 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.
replicateM :: Applicative m => Int -> m a -> m [a] #
replicateM n actact n times,
and then returns the list of results:
Examples
>>>import Control.Monad.State>>>runState (replicateM 3 $ state $ \s -> (s, s + 1)) 1([1,2,3],4)
replicateM_ :: Applicative m => Int -> m a -> m () #
unless :: Applicative f => Bool -> f () -> f () #
The reverse of when.
module Data.Functor
class (forall a. Functor (p a)) => Bifunctor (p :: Type -> Type -> Type) where #
A bifunctor is a type constructor that takes
two type arguments and is a functor in both arguments. That
is, unlike with Functor, a type constructor such as Either
does not need to be partially applied for a Bifunctor
instance, and the methods in this class permit mapping
functions over the Left value or the Right value,
or both at the same time.
Formally, the class Bifunctor represents a bifunctor
from Hask -> Hask.
Intuitively it is a bifunctor where both the first and second arguments are covariant.
You can define a Bifunctor by either defining bimap or by
defining both first and second. A partially applied Bifunctor
must be a Functor and the second method must agree with fmap.
From this it follows that:
secondid=id
If you supply bimap, you should ensure that:
bimapidid≡id
If you supply first and second, ensure:
firstid≡idsecondid≡id
If you supply both, you should also ensure:
bimapf g ≡firstf.secondg
These ensure by parametricity:
bimap(f.g) (h.i) ≡bimapf h.bimapg ifirst(f.g) ≡firstf.firstgsecond(f.g) ≡secondf.secondg
Since 4.18.0.0 Functor is a superclass of 'Bifunctor.
Since: base-4.8.0.0
Methods
Instances
| Bifunctor ConcurrentlyE | |
Defined in Control.Concurrent.Async.Internal Methods bimap :: (a -> b) -> (c -> d) -> ConcurrentlyE a c -> ConcurrentlyE b d # first :: (a -> b) -> ConcurrentlyE a c -> ConcurrentlyE b c # second :: (b -> c) -> ConcurrentlyE a b -> ConcurrentlyE a c # | |
| Bifunctor Either | Since: base-4.8.0.0 |
| Bifunctor Arg | Since: base-4.9.0.0 |
| Bifunctor RequestF | |
| Bifunctor Either | |
| Bifunctor These | |
| Bifunctor Pair | |
| Bifunctor These | |
| Bifunctor (,) | Class laws for tuples hold only up to laziness. Both
Since: base-4.8.0.0 |
| Bifunctor (Const :: Type -> Type -> Type) | Since: base-4.8.0.0 |
| Functor f => Bifunctor (CofreeF f) | |
| Functor f => Bifunctor (FreeF f) | |
| Bifunctor (Tagged :: Type -> Type -> Type) | |
| Bifunctor (Constant :: Type -> Type -> Type) | |
| Bifunctor ((,,) x1) | Since: base-4.8.0.0 |
| Bifunctor (K1 i :: Type -> Type -> Type) | Since: base-4.9.0.0 |
| Bifunctor ((,,,) x1 x2) | Since: base-4.8.0.0 |
| Functor f => Bifunctor (Clown f :: Type -> Type -> Type) | |
| Bifunctor p => Bifunctor (Flip p) | |
| Functor g => Bifunctor (Joker g :: Type -> Type -> Type) | |
| Bifunctor p => Bifunctor (WrappedBifunctor p) | |
Defined in Data.Bifunctor.Wrapped Methods bimap :: (a -> b) -> (c -> d) -> WrappedBifunctor p a c -> WrappedBifunctor p b d # first :: (a -> b) -> WrappedBifunctor p a c -> WrappedBifunctor p b c # second :: (b -> c) -> WrappedBifunctor p a b -> WrappedBifunctor p a c # | |
| Bifunctor ((,,,,) x1 x2 x3) | Since: base-4.8.0.0 |
| (Bifunctor f, Bifunctor g) => Bifunctor (Product f g) | |
| (Bifunctor p, Bifunctor q) => Bifunctor (Sum p q) | |
| Bifunctor ((,,,,,) x1 x2 x3 x4) | Since: base-4.8.0.0 |
| (Functor f, Bifunctor p) => Bifunctor (Tannen f p) | |
| Bifunctor ((,,,,,,) x1 x2 x3 x4 x5) | Since: base-4.8.0.0 |
| (Bifunctor p, Functor f, Functor g) => Bifunctor (Biff p f g) | |
module Data.Function
module Data.Functor.Identity
module Data.Int
module Data.Word
module Data.Void
module Data.Bool
module Data.Char
module Data.Ord
Boolean monoid under disjunction (||).
Any x <> Any y = Any (x || y)
Examples
>>>Any True <> mempty <> Any FalseAny {getAny = True}
>>>mconcat (map (\x -> Any (even x)) [2,4,6,7,8])Any {getAny = True}
>>>Any False <> memptyAny {getAny = False}
Instances
The class of semigroups (types with an associative binary operation).
Instances should satisfy the following:
You can alternatively define sconcat instead of (<>), in which case the
laws are:
Since: base-4.9.0.0
Methods
(<>) :: a -> a -> a infixr 6 #
An associative operation.
Examples
>>>[1,2,3] <> [4,5,6][1,2,3,4,5,6]
>>>Just [1, 2, 3] <> Just [4, 5, 6]Just [1,2,3,4,5,6]
>>>putStr "Hello, " <> putStrLn "World!"Hello, World!
Reduce a non-empty list with <>
The default definition should be sufficient, but this can be overridden for efficiency.
Examples
For the following examples, we will assume that we have:
>>>import Data.List.NonEmpty (NonEmpty (..))
>>>sconcat $ "Hello" :| [" ", "Haskell", "!"]"Hello Haskell!"
>>>sconcat $ Just [1, 2, 3] :| [Nothing, Just [4, 5, 6]]Just [1,2,3,4,5,6]
>>>sconcat $ Left 1 :| [Right 2, Left 3, Right 4]Right 2
stimes :: Integral b => b -> a -> a #
Repeat a value n times.
The default definition will raise an exception for a multiplier that is <= 0.
This may be overridden with an implementation that is total. For monoids
it is preferred to use stimesMonoid.
By making this a member of the class, idempotent semigroups
and monoids can upgrade this to execute in \(\mathcal{O}(1)\) by
picking stimes = or stimesIdempotentstimes =
respectively.stimesIdempotentMonoid
Examples
>>>stimes 4 [1][1,1,1,1]
>>>stimes 5 (putStr "hi!")hi!hi!hi!hi!hi!
>>>stimes 3 (Right ":)")Right ":)"
Instances
Monoid under addition.
Sum a <> Sum b = Sum (a + b)
Examples
>>>Sum 1 <> Sum 2 <> memptySum {getSum = 3}
>>>mconcat [ Sum n | n <- [3 .. 9]]Sum {getSum = 42}
Instances
Monoid under multiplication.
Product x <> Product y == Product (x * y)
Examples
>>>Product 3 <> Product 4 <> memptyProduct {getProduct = 12}
>>>mconcat [ Product n | n <- [2 .. 10]]Product {getProduct = 3628800}
Constructors
| Product | |
Fields
| |
Instances
Beware that Data.Semigroup.Last is different from
Data.Monoid.Last. The former simply returns the last value,
so x <> Data.Semigroup.Last Nothing = Data.Semigroup.Last Nothing.
The latter returns the last non-Nothing,
thus x <> Data.Monoid.Last Nothing = x.
Examples
>>>Last 0 <> Last 10Last {getLast = 10}
>>>sconcat $ Last 1 :| [ Last n | n <- [2..]]Last {getLast = * hangs forever *
Instances
| FromJSON1 Last | |
| ToJSON1 Last | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Last a -> Value Source # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Last a] -> Value Source # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Last a -> Encoding Source # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Last a] -> Encoding Source # | |
| MonadFix Last | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| Foldable Last | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods fold :: Monoid m => Last m -> m # foldMap :: Monoid m => (a -> m) -> Last a -> m # foldMap' :: Monoid m => (a -> m) -> Last a -> m # foldr :: (a -> b -> b) -> b -> Last a -> b # foldr' :: (a -> b -> b) -> b -> Last a -> b # foldl :: (b -> a -> b) -> b -> Last a -> b # foldl' :: (b -> a -> b) -> b -> Last a -> b # foldr1 :: (a -> a -> a) -> Last a -> a # foldl1 :: (a -> a -> a) -> Last a -> a # elem :: Eq a => a -> Last a -> Bool # maximum :: Ord a => Last a -> a # | |
| Traversable Last | Since: base-4.9.0.0 |
| Applicative Last | Since: base-4.9.0.0 |
| Functor Last | Since: base-4.9.0.0 |
| Monad Last | Since: base-4.9.0.0 |
| NFData1 Last | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Traversable1 Last | |
| Generic1 Last | |
| Unbox a => Vector Vector (Last a) | |
Defined in Data.Vector.Unboxed.Base Methods basicUnsafeFreeze :: Mutable Vector s (Last a) -> ST s (Vector (Last a)) Source # basicUnsafeThaw :: Vector (Last a) -> ST s (Mutable Vector s (Last a)) Source # basicLength :: Vector (Last a) -> Int Source # basicUnsafeSlice :: Int -> Int -> Vector (Last a) -> Vector (Last a) Source # basicUnsafeIndexM :: Vector (Last a) -> Int -> Box (Last a) Source # basicUnsafeCopy :: Mutable Vector s (Last a) -> Vector (Last a) -> ST s () Source # | |
| Unbox a => MVector MVector (Last a) | |
Defined in Data.Vector.Unboxed.Base Methods basicLength :: MVector s (Last a) -> Int Source # basicUnsafeSlice :: Int -> Int -> MVector s (Last a) -> MVector s (Last a) Source # basicOverlaps :: MVector s (Last a) -> MVector s (Last a) -> Bool Source # basicUnsafeNew :: Int -> ST s (MVector s (Last a)) Source # basicInitialize :: MVector s (Last a) -> ST s () Source # basicUnsafeReplicate :: Int -> Last a -> ST s (MVector s (Last a)) Source # basicUnsafeRead :: MVector s (Last a) -> Int -> ST s (Last a) Source # basicUnsafeWrite :: MVector s (Last a) -> Int -> Last a -> ST s () Source # basicClear :: MVector s (Last a) -> ST s () Source # basicSet :: MVector s (Last a) -> Last a -> ST s () Source # basicUnsafeCopy :: MVector s (Last a) -> MVector s (Last a) -> ST s () Source # basicUnsafeMove :: MVector s (Last a) -> MVector s (Last a) -> ST s () Source # basicUnsafeGrow :: MVector s (Last a) -> Int -> ST s (MVector s (Last a)) Source # | |
| FromJSON a => FromJSON (Last a) | |
| ToJSON a => ToJSON (Last a) | |
| Data a => Data (Last a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Last a -> c (Last a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Last a) # toConstr :: Last a -> Constr # dataTypeOf :: Last a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Last a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Last a)) # gmapT :: (forall b. Data b => b -> b) -> Last a -> Last a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Last a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Last a -> r # gmapQ :: (forall d. Data d => d -> u) -> Last a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Last a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Last a -> m (Last a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Last a -> m (Last a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Last a -> m (Last a) # | |
| Semigroup (Last a) | Since: base-4.9.0.0 |
| Bounded a => Bounded (Last a) | Since: base-4.9.0.0 |
| Enum a => Enum (Last a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| Generic (Last a) | |
| Read a => Read (Last a) | Since: base-4.9.0.0 |
| Show a => Show (Last a) | Since: base-4.9.0.0 |
| NFData a => NFData (Last a) | Since: deepseq-1.4.2.0 |
Defined in Control.DeepSeq | |
| Eq a => Eq (Last a) | Since: base-4.9.0.0 |
| Ord a => Ord (Last a) | Since: base-4.9.0.0 |
| Hashable a => Hashable (Last a) | |
| FromFormKey a => FromFormKey (Last a) | |
Defined in Web.Internal.FormUrlEncoded | |
| ToFormKey a => ToFormKey (Last a) | |
| Wrapped (Last a) | |
| Unbox a => Unbox (Last a) | |
Defined in Data.Vector.Unboxed.Base | |
| t ~ Last b => Rewrapped (Last a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep1 Last | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| newtype MVector s (Last a) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep (Last a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| type Unwrapped (Last a) | |
Defined in Control.Lens.Wrapped | |
| newtype Vector (Last a) | |
Defined in Data.Vector.Unboxed.Base | |
Beware that Data.Semigroup.First is different from
Data.Monoid.First. The former simply returns the first value,
so Data.Semigroup.First Nothing <> x = Data.Semigroup.First Nothing.
The latter returns the first non-Nothing,
thus Data.Monoid.First Nothing <> x = x.
Examples
>>>First 0 <> First 10First 0
>>>sconcat $ First 1 :| [ First n | n <- [2 ..] ]First 1
Instances
| FromJSON1 First | |
| ToJSON1 First | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> First a -> Value Source # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [First a] -> Value Source # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> First a -> Encoding Source # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [First a] -> Encoding Source # | |
| MonadFix First | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| Foldable First | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods fold :: Monoid m => First m -> m # foldMap :: Monoid m => (a -> m) -> First a -> m # foldMap' :: Monoid m => (a -> m) -> First a -> m # foldr :: (a -> b -> b) -> b -> First a -> b # foldr' :: (a -> b -> b) -> b -> First a -> b # foldl :: (b -> a -> b) -> b -> First a -> b # foldl' :: (b -> a -> b) -> b -> First a -> b # foldr1 :: (a -> a -> a) -> First a -> a # foldl1 :: (a -> a -> a) -> First a -> a # elem :: Eq a => a -> First a -> Bool # maximum :: Ord a => First a -> a # minimum :: Ord a => First a -> a # | |
| Traversable First | Since: base-4.9.0.0 |
| Applicative First | Since: base-4.9.0.0 |
| Functor First | Since: base-4.9.0.0 |
| Monad First | Since: base-4.9.0.0 |
| NFData1 First | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Traversable1 First | |
| Generic1 First | |
| Unbox a => Vector Vector (First a) | |
Defined in Data.Vector.Unboxed.Base Methods basicUnsafeFreeze :: Mutable Vector s (First a) -> ST s (Vector (First a)) Source # basicUnsafeThaw :: Vector (First a) -> ST s (Mutable Vector s (First a)) Source # basicLength :: Vector (First a) -> Int Source # basicUnsafeSlice :: Int -> Int -> Vector (First a) -> Vector (First a) Source # basicUnsafeIndexM :: Vector (First a) -> Int -> Box (First a) Source # basicUnsafeCopy :: Mutable Vector s (First a) -> Vector (First a) -> ST s () Source # | |
| Unbox a => MVector MVector (First a) | |
Defined in Data.Vector.Unboxed.Base Methods basicLength :: MVector s (First a) -> Int Source # basicUnsafeSlice :: Int -> Int -> MVector s (First a) -> MVector s (First a) Source # basicOverlaps :: MVector s (First a) -> MVector s (First a) -> Bool Source # basicUnsafeNew :: Int -> ST s (MVector s (First a)) Source # basicInitialize :: MVector s (First a) -> ST s () Source # basicUnsafeReplicate :: Int -> First a -> ST s (MVector s (First a)) Source # basicUnsafeRead :: MVector s (First a) -> Int -> ST s (First a) Source # basicUnsafeWrite :: MVector s (First a) -> Int -> First a -> ST s () Source # basicClear :: MVector s (First a) -> ST s () Source # basicSet :: MVector s (First a) -> First a -> ST s () Source # basicUnsafeCopy :: MVector s (First a) -> MVector s (First a) -> ST s () Source # basicUnsafeMove :: MVector s (First a) -> MVector s (First a) -> ST s () Source # basicUnsafeGrow :: MVector s (First a) -> Int -> ST s (MVector s (First a)) Source # | |
| FromJSON a => FromJSON (First a) | |
| ToJSON a => ToJSON (First a) | |
| Data a => Data (First a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> First a -> c (First a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (First a) # toConstr :: First a -> Constr # dataTypeOf :: First a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (First a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (First a)) # gmapT :: (forall b. Data b => b -> b) -> First a -> First a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> First a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> First a -> r # gmapQ :: (forall d. Data d => d -> u) -> First a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> First a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> First a -> m (First a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> First a -> m (First a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> First a -> m (First a) # | |
| Semigroup (First a) | Since: base-4.9.0.0 |
| Bounded a => Bounded (First a) | Since: base-4.9.0.0 |
| Enum a => Enum (First a) | Since: base-4.9.0.0 |
| Generic (First a) | |
| Read a => Read (First a) | Since: base-4.9.0.0 |
| Show a => Show (First a) | Since: base-4.9.0.0 |
| NFData a => NFData (First a) | Since: deepseq-1.4.2.0 |
Defined in Control.DeepSeq | |
| Eq a => Eq (First a) | Since: base-4.9.0.0 |
| Ord a => Ord (First a) | Since: base-4.9.0.0 |
| Hashable a => Hashable (First a) | |
| FromFormKey a => FromFormKey (First a) | |
Defined in Web.Internal.FormUrlEncoded | |
| ToFormKey a => ToFormKey (First a) | |
| Wrapped (First a) | |
| Unbox a => Unbox (First a) | |
Defined in Data.Vector.Unboxed.Base | |
| t ~ First b => Rewrapped (First a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep1 First | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| newtype MVector s (First a) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep (First a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| type Unwrapped (First a) | |
Defined in Control.Lens.Wrapped | |
| newtype Vector (First a) | |
Defined in Data.Vector.Unboxed.Base | |
The Min Monoid and Semigroup always choose the smaller element as
by the Ord instance and min of the contained type.
Examples
>>>Min 42 <> Min 3Min 3
>>>sconcat $ Min 1 :| [ Min n | n <- [2 .. 100]]Min {getMin = 1}
Instances
| FromJSON1 Min | |
| ToJSON1 Min | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Min a -> Value Source # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Min a] -> Value Source # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Min a -> Encoding Source # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Min a] -> Encoding Source # | |
| MonadFix Min | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| Foldable Min | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods fold :: Monoid m => Min m -> m # foldMap :: Monoid m => (a -> m) -> Min a -> m # foldMap' :: Monoid m => (a -> m) -> Min a -> m # foldr :: (a -> b -> b) -> b -> Min a -> b # foldr' :: (a -> b -> b) -> b -> Min a -> b # foldl :: (b -> a -> b) -> b -> Min a -> b # foldl' :: (b -> a -> b) -> b -> Min a -> b # foldr1 :: (a -> a -> a) -> Min a -> a # foldl1 :: (a -> a -> a) -> Min a -> a # elem :: Eq a => a -> Min a -> Bool # maximum :: Ord a => Min a -> a # | |
| Traversable Min | Since: base-4.9.0.0 |
| Applicative Min | Since: base-4.9.0.0 |
| Functor Min | Since: base-4.9.0.0 |
| Monad Min | Since: base-4.9.0.0 |
| NFData1 Min | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Traversable1 Min | |
| Generic1 Min | |
| Unbox a => Vector Vector (Min a) | |
Defined in Data.Vector.Unboxed.Base Methods basicUnsafeFreeze :: Mutable Vector s (Min a) -> ST s (Vector (Min a)) Source # basicUnsafeThaw :: Vector (Min a) -> ST s (Mutable Vector s (Min a)) Source # basicLength :: Vector (Min a) -> Int Source # basicUnsafeSlice :: Int -> Int -> Vector (Min a) -> Vector (Min a) Source # basicUnsafeIndexM :: Vector (Min a) -> Int -> Box (Min a) Source # basicUnsafeCopy :: Mutable Vector s (Min a) -> Vector (Min a) -> ST s () Source # | |
| Unbox a => MVector MVector (Min a) | |
Defined in Data.Vector.Unboxed.Base Methods basicLength :: MVector s (Min a) -> Int Source # basicUnsafeSlice :: Int -> Int -> MVector s (Min a) -> MVector s (Min a) Source # basicOverlaps :: MVector s (Min a) -> MVector s (Min a) -> Bool Source # basicUnsafeNew :: Int -> ST s (MVector s (Min a)) Source # basicInitialize :: MVector s (Min a) -> ST s () Source # basicUnsafeReplicate :: Int -> Min a -> ST s (MVector s (Min a)) Source # basicUnsafeRead :: MVector s (Min a) -> Int -> ST s (Min a) Source # basicUnsafeWrite :: MVector s (Min a) -> Int -> Min a -> ST s () Source # basicClear :: MVector s (Min a) -> ST s () Source # basicSet :: MVector s (Min a) -> Min a -> ST s () Source # basicUnsafeCopy :: MVector s (Min a) -> MVector s (Min a) -> ST s () Source # basicUnsafeMove :: MVector s (Min a) -> MVector s (Min a) -> ST s () Source # basicUnsafeGrow :: MVector s (Min a) -> Int -> ST s (MVector s (Min a)) Source # | |
| FromJSON a => FromJSON (Min a) | |
| ToJSON a => ToJSON (Min a) | |
| Data a => Data (Min a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Min a -> c (Min a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Min a) # dataTypeOf :: Min a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Min a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Min a)) # gmapT :: (forall b. Data b => b -> b) -> Min a -> Min a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Min a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Min a -> r # gmapQ :: (forall d. Data d => d -> u) -> Min a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Min a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Min a -> m (Min a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Min a -> m (Min a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Min a -> m (Min a) # | |
| (Ord a, Bounded a) => Monoid (Min a) | Since: base-4.9.0.0 |
| Ord a => Semigroup (Min a) | Since: base-4.9.0.0 |
| Bounded a => Bounded (Min a) | Since: base-4.9.0.0 |
| Enum a => Enum (Min a) | Since: base-4.9.0.0 |
| Generic (Min a) | |
| Num a => Num (Min a) | Since: base-4.9.0.0 |
| Read a => Read (Min a) | Since: base-4.9.0.0 |
| Show a => Show (Min a) | Since: base-4.9.0.0 |
| NFData a => NFData (Min a) | Since: deepseq-1.4.2.0 |
Defined in Control.DeepSeq | |
| Eq a => Eq (Min a) | Since: base-4.9.0.0 |
| Ord a => Ord (Min a) | Since: base-4.9.0.0 |
| Hashable a => Hashable (Min a) | |
| FromFormKey a => FromFormKey (Min a) | |
Defined in Web.Internal.FormUrlEncoded | |
| ToFormKey a => ToFormKey (Min a) | |
| Wrapped (Min a) | |
| Unbox a => Unbox (Min a) | |
Defined in Data.Vector.Unboxed.Base | |
| t ~ Min b => Rewrapped (Min a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep1 Min | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| newtype MVector s (Min a) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep (Min a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| type Unwrapped (Min a) | |
Defined in Control.Lens.Wrapped | |
| newtype Vector (Min a) | |
Defined in Data.Vector.Unboxed.Base | |
The Max Monoid and Semigroup always choose the bigger element as
by the Ord instance and max of the contained type.
Examples
>>>Max 42 <> Max 3Max 42
>>>sconcat $ Max 1 :| [ Max n | n <- [2 .. 100]]Max {getMax = 100}
Instances
| FromJSON1 Max | |
| ToJSON1 Max | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Max a -> Value Source # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Max a] -> Value Source # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Max a -> Encoding Source # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Max a] -> Encoding Source # | |
| MonadFix Max | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| Foldable Max | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods fold :: Monoid m => Max m -> m # foldMap :: Monoid m => (a -> m) -> Max a -> m # foldMap' :: Monoid m => (a -> m) -> Max a -> m # foldr :: (a -> b -> b) -> b -> Max a -> b # foldr' :: (a -> b -> b) -> b -> Max a -> b # foldl :: (b -> a -> b) -> b -> Max a -> b # foldl' :: (b -> a -> b) -> b -> Max a -> b # foldr1 :: (a -> a -> a) -> Max a -> a # foldl1 :: (a -> a -> a) -> Max a -> a # elem :: Eq a => a -> Max a -> Bool # maximum :: Ord a => Max a -> a # | |
| Traversable Max | Since: base-4.9.0.0 |
| Applicative Max | Since: base-4.9.0.0 |
| Functor Max | Since: base-4.9.0.0 |
| Monad Max | Since: base-4.9.0.0 |
| NFData1 Max | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Traversable1 Max | |
| Generic1 Max | |
| Unbox a => Vector Vector (Max a) | |
Defined in Data.Vector.Unboxed.Base Methods basicUnsafeFreeze :: Mutable Vector s (Max a) -> ST s (Vector (Max a)) Source # basicUnsafeThaw :: Vector (Max a) -> ST s (Mutable Vector s (Max a)) Source # basicLength :: Vector (Max a) -> Int Source # basicUnsafeSlice :: Int -> Int -> Vector (Max a) -> Vector (Max a) Source # basicUnsafeIndexM :: Vector (Max a) -> Int -> Box (Max a) Source # basicUnsafeCopy :: Mutable Vector s (Max a) -> Vector (Max a) -> ST s () Source # | |
| Unbox a => MVector MVector (Max a) | |
Defined in Data.Vector.Unboxed.Base Methods basicLength :: MVector s (Max a) -> Int Source # basicUnsafeSlice :: Int -> Int -> MVector s (Max a) -> MVector s (Max a) Source # basicOverlaps :: MVector s (Max a) -> MVector s (Max a) -> Bool Source # basicUnsafeNew :: Int -> ST s (MVector s (Max a)) Source # basicInitialize :: MVector s (Max a) -> ST s () Source # basicUnsafeReplicate :: Int -> Max a -> ST s (MVector s (Max a)) Source # basicUnsafeRead :: MVector s (Max a) -> Int -> ST s (Max a) Source # basicUnsafeWrite :: MVector s (Max a) -> Int -> Max a -> ST s () Source # basicClear :: MVector s (Max a) -> ST s () Source # basicSet :: MVector s (Max a) -> Max a -> ST s () Source # basicUnsafeCopy :: MVector s (Max a) -> MVector s (Max a) -> ST s () Source # basicUnsafeMove :: MVector s (Max a) -> MVector s (Max a) -> ST s () Source # basicUnsafeGrow :: MVector s (Max a) -> Int -> ST s (MVector s (Max a)) Source # | |
| FromJSON a => FromJSON (Max a) | |
| ToJSON a => ToJSON (Max a) | |
| Data a => Data (Max a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Max a -> c (Max a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Max a) # dataTypeOf :: Max a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Max a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Max a)) # gmapT :: (forall b. Data b => b -> b) -> Max a -> Max a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Max a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Max a -> r # gmapQ :: (forall d. Data d => d -> u) -> Max a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Max a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Max a -> m (Max a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Max a -> m (Max a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Max a -> m (Max a) # | |
| (Ord a, Bounded a) => Monoid (Max a) | Since: base-4.9.0.0 |
| Ord a => Semigroup (Max a) | Since: base-4.9.0.0 |
| Bounded a => Bounded (Max a) | Since: base-4.9.0.0 |
| Enum a => Enum (Max a) | Since: base-4.9.0.0 |
| Generic (Max a) | |
| Num a => Num (Max a) | Since: base-4.9.0.0 |
| Read a => Read (Max a) | Since: base-4.9.0.0 |
| Show a => Show (Max a) | Since: base-4.9.0.0 |
| NFData a => NFData (Max a) | Since: deepseq-1.4.2.0 |
Defined in Control.DeepSeq | |
| Eq a => Eq (Max a) | Since: base-4.9.0.0 |
| Ord a => Ord (Max a) | Since: base-4.9.0.0 |
| Hashable a => Hashable (Max a) | |
| FromFormKey a => FromFormKey (Max a) | |
Defined in Web.Internal.FormUrlEncoded | |
| ToFormKey a => ToFormKey (Max a) | |
| Wrapped (Max a) | |
| Unbox a => Unbox (Max a) | |
Defined in Data.Vector.Unboxed.Base | |
| t ~ Max b => Rewrapped (Max a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep1 Max | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| newtype MVector s (Max a) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep (Max a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup | |
| type Unwrapped (Max a) | |
Defined in Control.Lens.Wrapped | |
| newtype Vector (Max a) | |
Defined in Data.Vector.Unboxed.Base | |
Boolean monoid under conjunction (&&).
All x <> All y = All (x && y)
Examples
>>>All True <> mempty <> All False)All {getAll = False}
>>>mconcat (map (\x -> All (even x)) [2,4,6,7,8])All {getAll = False}
>>>All True <> memptyAll {getAll = True}
Instances
The monoid of endomorphisms under composition.
Endo f <> Endo g == Endo (f . g)
Examples
>>>let computation = Endo ("Hello, " ++) <> Endo (++ "!")>>>appEndo computation "Haskell""Hello, Haskell!"
>>>let computation = Endo (*3) <> Endo (+1)>>>appEndo computation 16
Instances
| Monoid (Endo a) | Since: base-2.1 |
| Semigroup (Endo a) | Since: base-4.9.0.0 |
| Generic (Endo a) | |
| Default (Endo a) | |
Defined in Data.Default.Class | |
| Wrapped (Endo a) | |
| t ~ Endo b => Rewrapped (Endo a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep (Endo a) | Since: base-4.7.0.0 |
Defined in Data.Semigroup.Internal | |
| type Unwrapped (Endo a) | |
Defined in Control.Lens.Wrapped | |
The dual of a Monoid, obtained by swapping the arguments of mappend.
| The dual of a Monoid, obtained by swapping the arguments of (<>).
Dual a <> Dual b == Dual (b <> a)
Examples
>>>Dual "Hello" <> Dual "World"Dual {getDual = "WorldHello"}
>>>Dual (Dual "Hello") <> Dual (Dual "World")Dual {getDual = Dual {getDual = "HelloWorld"}}
Instances
newtype WrappedMonoid m #
Provide a Semigroup for an arbitrary Monoid.
NOTE: This is not needed anymore since Semigroup became a superclass of
Monoid in base-4.11 and this newtype be deprecated at some point in the future.
Constructors
| WrapMonoid | |
Fields
| |
Instances
type ArgMax a b = Max (Arg a b) #
Examples
>>>Max (Arg 0 ()) <> Max (Arg 1 ())Max {getMax = Arg 1 ()}
>>>maximum [ Arg (length name) name | name <- ["violencia", "lea", "pixie"]]Arg 9 "violencia"
type ArgMin a b = Min (Arg a b) #
Examples
>>>Min (Arg 0 ()) <> Min (Arg 1 ())Min {getMin = Arg 0 ()}
>>>minimum [ Arg (length name) name | name <- ["violencia", "lea", "pixie"]]Arg 3 "lea"
Arg isn't itself a Semigroup in its own right, but it can be
placed inside Min and Max to compute an arg min or arg max.
Examples
>>>minimum [ Arg (x * x) x | x <- [-10 .. 10] ]Arg 0 0
>>>maximum [ Arg (-0.2*x^2 + 1.5*x + 1) x | x <- [-10 .. 10] ]Arg 3.8 4.0
>>>minimum [ Arg (-0.2*x^2 + 1.5*x + 1) x | x <- [-10 .. 10] ]Arg (-34.0) (-10.0)
Constructors
| Arg | |
Instances
| Bifoldable Arg | Since: base-4.10.0.0 |
| Bifunctor Arg | Since: base-4.9.0.0 |
| Bitraversable Arg | Since: base-4.10.0.0 |
Defined in Data.Semigroup Methods bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Arg a b -> f (Arg c d) # | |
| NFData2 Arg | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| Bitraversable1 Arg | |
Defined in Data.Semigroup.Traversable.Class | |
| Generic1 (Arg a :: Type -> Type) | |
| (Unbox a, Unbox b) => Vector Vector (Arg a b) | |
Defined in Data.Vector.Unboxed.Base Methods basicUnsafeFreeze :: Mutable Vector s (Arg a b) -> ST s (Vector (Arg a b)) Source # basicUnsafeThaw :: Vector (Arg a b) -> ST s (Mutable Vector s (Arg a b)) Source # basicLength :: Vector (Arg a b) -> Int Source # basicUnsafeSlice :: Int -> Int -> Vector (Arg a b) -> Vector (Arg a b) Source # basicUnsafeIndexM :: Vector (Arg a b) -> Int -> Box (Arg a b) Source # basicUnsafeCopy :: Mutable Vector s (Arg a b) -> Vector (Arg a b) -> ST s () Source # | |
| (Unbox a, Unbox b) => MVector MVector (Arg a b) | |
Defined in Data.Vector.Unboxed.Base Methods basicLength :: MVector s (Arg a b) -> Int Source # basicUnsafeSlice :: Int -> Int -> MVector s (Arg a b) -> MVector s (Arg a b) Source # basicOverlaps :: MVector s (Arg a b) -> MVector s (Arg a b) -> Bool Source # basicUnsafeNew :: Int -> ST s (MVector s (Arg a b)) Source # basicInitialize :: MVector s (Arg a b) -> ST s () Source # basicUnsafeReplicate :: Int -> Arg a b -> ST s (MVector s (Arg a b)) Source # basicUnsafeRead :: MVector s (Arg a b) -> Int -> ST s (Arg a b) Source # basicUnsafeWrite :: MVector s (Arg a b) -> Int -> Arg a b -> ST s () Source # basicClear :: MVector s (Arg a b) -> ST s () Source # basicSet :: MVector s (Arg a b) -> Arg a b -> ST s () Source # basicUnsafeCopy :: MVector s (Arg a b) -> MVector s (Arg a b) -> ST s () Source # basicUnsafeMove :: MVector s (Arg a b) -> MVector s (Arg a b) -> ST s () Source # basicUnsafeGrow :: MVector s (Arg a b) -> Int -> ST s (MVector s (Arg a b)) Source # | |
| Foldable (Arg a) | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods fold :: Monoid m => Arg a m -> m # foldMap :: Monoid m => (a0 -> m) -> Arg a a0 -> m # foldMap' :: Monoid m => (a0 -> m) -> Arg a a0 -> m # foldr :: (a0 -> b -> b) -> b -> Arg a a0 -> b # foldr' :: (a0 -> b -> b) -> b -> Arg a a0 -> b # foldl :: (b -> a0 -> b) -> b -> Arg a a0 -> b # foldl' :: (b -> a0 -> b) -> b -> Arg a a0 -> b # foldr1 :: (a0 -> a0 -> a0) -> Arg a a0 -> a0 # foldl1 :: (a0 -> a0 -> a0) -> Arg a a0 -> a0 # elem :: Eq a0 => a0 -> Arg a a0 -> Bool # maximum :: Ord a0 => Arg a a0 -> a0 # minimum :: Ord a0 => Arg a a0 -> a0 # | |
| Traversable (Arg a) | Since: base-4.9.0.0 |
| Functor (Arg a) | Since: base-4.9.0.0 |
| NFData a => NFData1 (Arg a) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
| (Data a, Data b) => Data (Arg a b) | Since: base-4.9.0.0 |
Defined in Data.Semigroup Methods gfoldl :: (forall d b0. Data d => c (d -> b0) -> d -> c b0) -> (forall g. g -> c g) -> Arg a b -> c (Arg a b) # gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Arg a b) # toConstr :: Arg a b -> Constr # dataTypeOf :: Arg a b -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Arg a b)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Arg a b)) # gmapT :: (forall b0. Data b0 => b0 -> b0) -> Arg a b -> Arg a b # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Arg a b -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Arg a b -> r # gmapQ :: (forall d. Data d => d -> u) -> Arg a b -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Arg a b -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Arg a b -> m (Arg a b) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Arg a b -> m (Arg a b) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Arg a b -> m (Arg a b) # | |
| Generic (Arg a b) | |
| (Read a, Read b) => Read (Arg a b) | Since: base-4.9.0.0 |
| (Show a, Show b) => Show (Arg a b) | Since: base-4.9.0.0 |
| (NFData a, NFData b) => NFData (Arg a b) | Since: deepseq-1.4.2.0 |
Defined in Control.DeepSeq | |
| Eq a => Eq (Arg a b) | Since: base-4.9.0.0 |
| Ord a => Ord (Arg a b) | Since: base-4.9.0.0 |
| Hashable a => Hashable (Arg a b) | Note: Prior to Since: hashable-1.3.0.0 |
| (Unbox a, Unbox b) => Unbox (Arg a b) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep1 (Arg a :: Type -> Type) | Since: base-4.9.0.0 |
Defined in Data.Semigroup type Rep1 (Arg a :: Type -> Type) = D1 ('MetaData "Arg" "Data.Semigroup" "base" 'False) (C1 ('MetaCons "Arg" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1)) | |
| newtype MVector s (Arg a b) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep (Arg a b) | Since: base-4.9.0.0 |
Defined in Data.Semigroup type Rep (Arg a b) = D1 ('MetaData "Arg" "Data.Semigroup" "base" 'False) (C1 ('MetaCons "Arg" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 b))) | |
| newtype Vector (Arg a b) | |
Defined in Data.Vector.Unboxed.Base | |
stimesIdempotent :: Integral b => b -> a -> a #
stimesIdempotentMonoid :: (Integral b, Monoid a) => b -> a -> a #
stimesMonoid :: (Integral b, Monoid a) => b -> a -> a #
mtimesDefault :: (Integral b, Monoid a) => b -> a -> a #
Repeat a value n times.
mtimesDefault n a = a <> a <> ... <> a -- using <> (n-1) times
In many cases, stimes 0 aMonoid will produce mempty.
However, there are situations when it cannot do so. In particular,
the following situation is fairly common:
data T a = ... class Constraint1 a class Constraint1 a => Constraint2 a
instance Constraint1 a =>Semigroup(T a) instance Constraint2 a =>Monoid(T a)
Since Constraint1 is insufficient to implement mempty,
stimes for T a cannot do so.
When working with such a type, or when working polymorphically with
Semigroup instances, mtimesDefault should be used when the
multiplier might be zero. It is implemented using stimes when
the multiplier is nonzero and mempty when it is zero.
Examples
>>>mtimesDefault 0 "bark"[]
>>>mtimesDefault 3 "meow""meowmeowmeow"
Boolean monoid under disjunction (||).
Any x <> Any y = Any (x || y)
Examples
>>>Any True <> mempty <> Any FalseAny {getAny = True}
>>>mconcat (map (\x -> Any (even x)) [2,4,6,7,8])Any {getAny = True}
>>>Any False <> memptyAny {getAny = False}
Instances
class Semigroup a => Monoid a where #
The class of monoids (types with an associative binary operation that has an identity). Instances should satisfy the following:
- Right identity
x<>mempty= x- Left identity
mempty<>x = x- Associativity
x(<>(y<>z) = (x<>y)<>zSemigrouplaw)- Concatenation
mconcat=foldr(<>)mempty
You can alternatively define mconcat instead of mempty, in which case the
laws are:
- Unit
mconcat(purex) = x- Multiplication
mconcat(joinxss) =mconcat(fmapmconcatxss)- Subclass
mconcat(toListxs) =sconcatxs
The method names refer to the monoid of lists under concatenation, but there are many other instances.
Some types can be viewed as a monoid in more than one way,
e.g. both addition and multiplication on numbers.
In such cases we often define newtypes and make those instances
of Monoid, e.g. Sum and Product.
NOTE: Semigroup is a superclass of Monoid since base-4.11.0.0.
Methods
Identity of mappend
Examples
>>>"Hello world" <> mempty"Hello world"
>>>mempty <> [1, 2, 3][1,2,3]
An associative operation
NOTE: This method is redundant and has the default
implementation mappend = (<>)mappend is a synonym for
(<>), it is expected that the two functions are defined the same
way. In a future GHC release mappend will be removed from Monoid.
Fold a list using the monoid.
For most types, the default definition for mconcat will be
used, but the function is included in the class definition so
that an optimized version can be provided for specific types.
>>>mconcat ["Hello", " ", "Haskell", "!"]"Hello Haskell!"
Instances
Monoid under addition.
Sum a <> Sum b = Sum (a + b)
Examples
>>>Sum 1 <> Sum 2 <> memptySum {getSum = 3}
>>>mconcat [ Sum n | n <- [3 .. 9]]Sum {getSum = 42}
Instances
Monoid under multiplication.
Product x <> Product y == Product (x * y)
Examples
>>>Product 3 <> Product 4 <> memptyProduct {getProduct = 12}
>>>mconcat [ Product n | n <- [2 .. 10]]Product {getProduct = 3628800}
Constructors
| Product | |
Fields
| |
Instances
newtype Alt (f :: k -> Type) (a :: k) #
Monoid under <|>.
Alt l <> Alt r == Alt (l <|> r)
Examples
>>>Alt (Just 12) <> Alt (Just 24)Alt {getAlt = Just 12}
>>>Alt Nothing <> Alt (Just 24)Alt {getAlt = Just 24}
Since: base-4.8.0.0
Instances
| Generic1 (Alt f :: k -> Type) | |
| Unbox (f a) => Vector Vector (Alt f a) | |
Defined in Data.Vector.Unboxed.Base Methods basicUnsafeFreeze :: Mutable Vector s (Alt f a) -> ST s (Vector (Alt f a)) Source # basicUnsafeThaw :: Vector (Alt f a) -> ST s (Mutable Vector s (Alt f a)) Source # basicLength :: Vector (Alt f a) -> Int Source # basicUnsafeSlice :: Int -> Int -> Vector (Alt f a) -> Vector (Alt f a) Source # basicUnsafeIndexM :: Vector (Alt f a) -> Int -> Box (Alt f a) Source # basicUnsafeCopy :: Mutable Vector s (Alt f a) -> Vector (Alt f a) -> ST s () Source # | |
| Unbox (f a) => MVector MVector (Alt f a) | |
Defined in Data.Vector.Unboxed.Base Methods basicLength :: MVector s (Alt f a) -> Int Source # basicUnsafeSlice :: Int -> Int -> MVector s (Alt f a) -> MVector s (Alt f a) Source # basicOverlaps :: MVector s (Alt f a) -> MVector s (Alt f a) -> Bool Source # basicUnsafeNew :: Int -> ST s (MVector s (Alt f a)) Source # basicInitialize :: MVector s (Alt f a) -> ST s () Source # basicUnsafeReplicate :: Int -> Alt f a -> ST s (MVector s (Alt f a)) Source # basicUnsafeRead :: MVector s (Alt f a) -> Int -> ST s (Alt f a) Source # basicUnsafeWrite :: MVector s (Alt f a) -> Int -> Alt f a -> ST s () Source # basicClear :: MVector s (Alt f a) -> ST s () Source # basicSet :: MVector s (Alt f a) -> Alt f a -> ST s () Source # basicUnsafeCopy :: MVector s (Alt f a) -> MVector s (Alt f a) -> ST s () Source # basicUnsafeMove :: MVector s (Alt f a) -> MVector s (Alt f a) -> ST s () Source # basicUnsafeGrow :: MVector s (Alt f a) -> Int -> ST s (MVector s (Alt f a)) Source # | |
| Foldable f => Foldable (Alt f) | Since: base-4.12.0.0 |
Defined in Data.Foldable Methods fold :: Monoid m => Alt f m -> m # foldMap :: Monoid m => (a -> m) -> Alt f a -> m # foldMap' :: Monoid m => (a -> m) -> Alt f a -> m # foldr :: (a -> b -> b) -> b -> Alt f a -> b # foldr' :: (a -> b -> b) -> b -> Alt f a -> b # foldl :: (b -> a -> b) -> b -> Alt f a -> b # foldl' :: (b -> a -> b) -> b -> Alt f a -> b # foldr1 :: (a -> a -> a) -> Alt f a -> a # foldl1 :: (a -> a -> a) -> Alt f a -> a # elem :: Eq a => a -> Alt f a -> Bool # maximum :: Ord a => Alt f a -> a # minimum :: Ord a => Alt f a -> a # | |
| Contravariant f => Contravariant (Alt f) | |
| Traversable f => Traversable (Alt f) | Since: base-4.12.0.0 |
| Alternative f => Alternative (Alt f) | Since: base-4.8.0.0 |
| Applicative f => Applicative (Alt f) | Since: base-4.8.0.0 |
| Functor f => Functor (Alt f) | Since: base-4.8.0.0 |
| Monad f => Monad (Alt f) | Since: base-4.8.0.0 |
| MonadPlus f => MonadPlus (Alt f) | Since: base-4.8.0.0 |
| Traversable1 f => Traversable1 (Alt f) | |
| Alternative f => Monoid (Alt f a) | Since: base-4.8.0.0 |
| Alternative f => Semigroup (Alt f a) | Since: base-4.9.0.0 |
| Enum (f a) => Enum (Alt f a) | Since: base-4.8.0.0 |
| Generic (Alt f a) | |
| Num (f a) => Num (Alt f a) | Since: base-4.8.0.0 |
| Read (f a) => Read (Alt f a) | Since: base-4.8.0.0 |
| Show (f a) => Show (Alt f a) | Since: base-4.8.0.0 |
| Eq (f a) => Eq (Alt f a) | Since: base-4.8.0.0 |
| Ord (f a) => Ord (Alt f a) | Since: base-4.8.0.0 |
Defined in Data.Semigroup.Internal | |
| Wrapped (Alt f a) | |
| Unbox (f a) => Unbox (Alt f a) | |
Defined in Data.Vector.Unboxed.Base | |
| t ~ Alt g b => Rewrapped (Alt f a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep1 (Alt f :: k -> Type) | Since: base-4.8.0.0 |
Defined in Data.Semigroup.Internal | |
| newtype MVector s (Alt f a) | |
Defined in Data.Vector.Unboxed.Base | |
| type Rep (Alt f a) | Since: base-4.8.0.0 |
Defined in Data.Semigroup.Internal | |
| type Unwrapped (Alt f a) | |
Defined in Control.Lens.Wrapped | |
| newtype Vector (Alt f a) | |
Defined in Data.Vector.Unboxed.Base | |
Boolean monoid under conjunction (&&).
All x <> All y = All (x && y)
Examples
>>>All True <> mempty <> All False)All {getAll = False}
>>>mconcat (map (\x -> All (even x)) [2,4,6,7,8])All {getAll = False}
>>>All True <> memptyAll {getAll = True}
Instances
The monoid of endomorphisms under composition.
Endo f <> Endo g == Endo (f . g)
Examples
>>>let computation = Endo ("Hello, " ++) <> Endo (++ "!")>>>appEndo computation "Haskell""Hello, Haskell!"
>>>let computation = Endo (*3) <> Endo (+1)>>>appEndo computation 16
Instances
| Monoid (Endo a) | Since: base-2.1 |
| Semigroup (Endo a) | Since: base-4.9.0.0 |
| Generic (Endo a) | |
| Default (Endo a) | |
Defined in Data.Default.Class | |
| Wrapped (Endo a) | |
| t ~ Endo b => Rewrapped (Endo a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep (Endo a) | Since: base-4.7.0.0 |
Defined in Data.Semigroup.Internal | |
| type Unwrapped (Endo a) | |
Defined in Control.Lens.Wrapped | |
The dual of a Monoid, obtained by swapping the arguments of mappend.
| The dual of a Monoid, obtained by swapping the arguments of (<>).
Dual a <> Dual b == Dual (b <> a)
Examples
>>>Dual "Hello" <> Dual "World"Dual {getDual = "WorldHello"}
>>>Dual (Dual "Hello") <> Dual (Dual "World")Dual {getDual = Dual {getDual = "HelloWorld"}}
Instances
newtype Ap (f :: k -> Type) (a :: k) #
This data type witnesses the lifting of a Monoid into an
Applicative pointwise.
Examples
>>>Ap (Just [1, 2, 3]) <> Ap NothingAp {getAp = Nothing}
>>>Ap [Sum 10, Sum 20] <> Ap [Sum 1, Sum 2]Ap {getAp = [Sum {getSum = 11},Sum {getSum = 12},Sum {getSum = 21},Sum {getSum = 22}]}
Since: base-4.12.0.0
Instances
| Generic1 (Ap f :: k -> Type) | |
| MonadFail f => MonadFail (Ap f) | Since: base-4.12.0.0 |
Defined in Data.Monoid | |
| Foldable f => Foldable (Ap f) | Since: base-4.12.0.0 |
Defined in Data.Foldable Methods fold :: Monoid m => Ap f m -> m # foldMap :: Monoid m => (a -> m) -> Ap f a -> m # foldMap' :: Monoid m => (a -> m) -> Ap f a -> m # foldr :: (a -> b -> b) -> b -> Ap f a -> b # foldr' :: (a -> b -> b) -> b -> Ap f a -> b # foldl :: (b -> a -> b) -> b -> Ap f a -> b # foldl' :: (b -> a -> b) -> b -> Ap f a -> b # foldr1 :: (a -> a -> a) -> Ap f a -> a # foldl1 :: (a -> a -> a) -> Ap f a -> a # elem :: Eq a => a -> Ap f a -> Bool # maximum :: Ord a => Ap f a -> a # | |
| Traversable f => Traversable (Ap f) | Since: base-4.12.0.0 |
| Alternative f => Alternative (Ap f) | Since: base-4.12.0.0 |
| Applicative f => Applicative (Ap f) | Since: base-4.12.0.0 |
| Functor f => Functor (Ap f) | Since: base-4.12.0.0 |
| Monad f => Monad (Ap f) | Since: base-4.12.0.0 |
| MonadPlus f => MonadPlus (Ap f) | Since: base-4.12.0.0 |
| (Applicative f, Monoid a) => Monoid (Ap f a) | Since: base-4.12.0.0 |
| (Applicative f, Semigroup a) => Semigroup (Ap f a) | Since: base-4.12.0.0 |
| (Applicative f, Bounded a) => Bounded (Ap f a) | Since: base-4.12.0.0 |
| Enum (f a) => Enum (Ap f a) | Since: base-4.12.0.0 |
Defined in Data.Monoid | |
| Generic (Ap f a) | |
| (Applicative f, Num a) => Num (Ap f a) | Note that even if the underlying Commutativity:
Additive inverse:
Distributivity:
Since: base-4.12.0.0 |
| Read (f a) => Read (Ap f a) | Since: base-4.12.0.0 |
| Show (f a) => Show (Ap f a) | Since: base-4.12.0.0 |
| Eq (f a) => Eq (Ap f a) | Since: base-4.12.0.0 |
| Ord (f a) => Ord (Ap f a) | Since: base-4.12.0.0 |
| Wrapped (Ap f a) | |
| t ~ Ap g b => Rewrapped (Ap f a) t | |
Defined in Control.Lens.Wrapped | |
| type Rep1 (Ap f :: k -> Type) | Since: base-4.12.0.0 |
Defined in Data.Monoid | |
| type Rep (Ap f a) | Since: base-4.12.0.0 |
Defined in Data.Monoid | |
| type Unwrapped (Ap f a) | |
Defined in Control.Lens.Wrapped | |
(<>) :: Semigroup a => a -> a -> a infixr 6 #
An associative operation.
Examples
>>>[1,2,3] <> [4,5,6][1,2,3,4,5,6]
>>>Just [1, 2, 3] <> Just [4, 5, 6]Just [1,2,3,4,5,6]
>>>putStr "Hello, " <> putStrLn "World!"Hello, World!
module Data.Maybe
module Data.Either
module Data.Foldable
module Data.Traversable
module Data.Tuple
module Data.String
(++) :: [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.
WARNING: This function takes linear time in the number of elements of the first list.
foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b #
Right-associative fold of a structure, lazy in the accumulator.
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, given an
operator lazy in its right argument, foldr can produce a terminating
expression from an unbounded list.
For a general Foldable structure this should be semantically identical
to,
foldr f z =foldrf z .toList
Examples
Basic usage:
>>>foldr (||) False [False, True, False]True
>>>foldr (||) False []False
>>>foldr (\c acc -> acc ++ [c]) "foo" ['a', 'b', 'c', 'd']"foodcba"
Infinite structures
⚠️ Applying foldr to infinite structures usually doesn't terminate.
It may still terminate under one of the following conditions:
- the folding function is short-circuiting
- the folding function is lazy on its second argument
Short-circuiting
( short-circuits on ||)True values, so the following terminates
because there is a True value finitely far from the left side:
>>>foldr (||) False (True : repeat False)True
But the following doesn't terminate:
>>>foldr (||) False (repeat False ++ [True])* Hangs forever *
Laziness in the second argument
Applying foldr to infinite structures terminates when the operator is
lazy in its second argument (the initial accumulator is never used in
this case, and so could be left undefined, but [] is more clear):
>>>take 5 $ foldr (\i acc -> i : fmap (+3) acc) [] (repeat 1)[1,4,7,10,13]
null :: Foldable t => t a -> Bool #
Test whether the structure is empty. The default implementation is Left-associative and lazy in both the initial element and the accumulator. Thus optimised for structures where the first element can be accessed in constant time. Structures where this is not the case should have a non-default implementation.
Examples
Basic usage:
>>>null []True
>>>null [1]False
null is expected to terminate even for infinite structures.
The default implementation terminates provided the structure
is bounded on the left (there is a leftmost element).
>>>null [1..]False
Since: base-4.8.0.0
foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b #
Left-associative fold of a structure, lazy in the accumulator. This is rarely what you want, but can work well for structures with efficient right-to-left sequencing and an operator that is lazy in its left argument.
In the case of lists, foldl, when applied to a binary operator, a
starting value (typically the left-identity of the operator), and a
list, reduces the list using the binary operator, from left to right:
foldl f z [x1, x2, ..., xn] == (...((z `f` x1) `f` x2) `f`...) `f` xn
Note that to produce the outermost application of the operator the
entire input list must be traversed. Like all left-associative folds,
foldl will diverge if given an infinite list.
If you want an efficient strict left-fold, you probably want to use
foldl' instead of foldl. The reason for this is that the latter
does not force the inner results (e.g. z `f` x1 in the above
example) before applying them to the operator (e.g. to (`f` x2)).
This results in a thunk chain O(n) elements long, which then must be
evaluated from the outside-in.
For a general Foldable structure this should be semantically identical
to:
foldl f z =foldlf z .toList
Examples
The first example is a strict fold, which in practice is best performed
with foldl'.
>>>foldl (+) 42 [1,2,3,4]52
Though the result below is lazy, the input is reversed before prepending it to the initial accumulator, so corecursion begins only after traversing the entire input string.
>>>foldl (\acc c -> c : acc) "abcd" "efgh""hgfeabcd"
A left fold of a structure that is infinite on the right cannot terminate, even when for any finite input the fold just returns the initial accumulator:
>>>foldl (\a _ -> a) 0 $ repeat 1* Hangs forever *
WARNING: When it comes to lists, you always want to use either foldl' or foldr instead.
foldl' :: Foldable t => (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 structure to a single strict result (e.g. sum).
For a general Foldable structure this should be semantically identical
to,
foldl' f z =foldl'f z .toList
Since: base-4.6.0.0
length :: Foldable t => t a -> Int #
Returns the size/length of a finite structure as an Int. The
default implementation just counts elements starting with the leftmost.
Instances for structures that can compute the element count faster
than via element-by-element counting, should provide a specialised
implementation.
Examples
Basic usage:
>>>length []0
>>>length ['a', 'b', 'c']3>>>length [1..]* Hangs forever *
Since: base-4.8.0.0
foldl1 :: Foldable t => (a -> a -> a) -> t a -> a #
A variant of foldl that has no base case,
and thus may only be applied to non-empty structures.
This function is non-total and will raise a runtime exception if the structure happens to be empty.
foldl1f =foldl1f .toList
Examples
Basic usage:
>>>foldl1 (+) [1..4]10
>>>foldl1 (+) []*** Exception: Prelude.foldl1: empty list
>>>foldl1 (+) Nothing*** Exception: foldl1: empty structure
>>>foldl1 (-) [1..4]-8
>>>foldl1 (&&) [True, False, True, True]False
>>>foldl1 (||) [False, False, True, True]True
>>>foldl1 (+) [1..]* Hangs forever *
sum :: (Foldable t, Num a) => t a -> a #
The sum function computes the sum of the numbers of a structure.
Examples
Basic usage:
>>>sum []0
>>>sum [42]42
>>>sum [1..10]55
>>>sum [4.1, 2.0, 1.7]7.8
>>>sum [1..]* Hangs forever *
Since: base-4.8.0.0
product :: (Foldable t, Num a) => t a -> a #
The product function computes the product of the numbers of a
structure.
Examples
Basic usage:
>>>product []1
>>>product [42]42
>>>product [1..10]3628800
>>>product [4.1, 2.0, 1.7]13.939999999999998
>>>product [1..]* Hangs forever *
Since: base-4.8.0.0
foldr1 :: Foldable t => (a -> a -> a) -> t a -> a #
A variant of foldr that has no base case,
and thus may only be applied to non-empty structures.
This function is non-total and will raise a runtime exception if the structure happens to be empty.
Examples
Basic usage:
>>>foldr1 (+) [1..4]10
>>>foldr1 (+) []Exception: Prelude.foldr1: empty list
>>>foldr1 (+) Nothing*** Exception: foldr1: empty structure
>>>foldr1 (-) [1..4]-2
>>>foldr1 (&&) [True, False, True, True]False
>>>foldr1 (||) [False, False, True, True]True
>>>foldr1 (+) [1..]* Hangs forever *
maximum :: (Foldable t, Ord a) => t a -> a #
The largest element of a non-empty structure.
This function is non-total and will raise a runtime exception if the structure happens to be empty. A structure that supports random access and maintains its elements in order should provide a specialised implementation to return the maximum in faster than linear time.
Examples
Basic usage:
>>>maximum [1..10]10
>>>maximum []*** Exception: Prelude.maximum: empty list
>>>maximum Nothing*** Exception: maximum: empty structure
WARNING: This function is partial for possibly-empty structures like lists.
Since: base-4.8.0.0
minimum :: (Foldable t, Ord a) => t a -> a #
The least element of a non-empty structure.
This function is non-total and will raise a runtime exception if the structure happens to be empty. A structure that supports random access and maintains its elements in order should provide a specialised implementation to return the minimum in faster than linear time.
Examples
Basic usage:
>>>minimum [1..10]1
>>>minimum []*** Exception: Prelude.minimum: empty list
>>>minimum Nothing*** Exception: minimum: empty structure
WARNING: This function is partial for possibly-empty structures like lists.
Since: base-4.8.0.0
elem :: (Foldable t, Eq a) => a -> t a -> Bool infix 4 #
Does the element occur in the structure?
Note: elem is often used in infix form.
Examples
Basic usage:
>>>3 `elem` []False
>>>3 `elem` [1,2]False
>>>3 `elem` [1,2,3,4,5]True
For infinite structures, the default implementation of elem
terminates if the sought-after value exists at a finite distance
from the left side of the structure:
>>>3 `elem` [1..]True
>>>3 `elem` ([4..] ++ [3])* Hangs forever *
Since: base-4.8.0.0
map :: (a -> b) -> [a] -> [b] #
\(\mathcal{O}(n)\). map f xs is the list obtained by applying f to
each element of xs, i.e.,
map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn] map f [x1, x2, ...] == [f x1, f x2, ...]
>>>map (+1) [1, 2, 3][2,3,4]
The sort function implements a stable sorting algorithm.
It is a special case of sortBy, which allows the programmer to supply
their own comparison function.
Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.
>>>sort [1,6,4,3,2,5][1,2,3,4,5,6]
The argument must be finite.
union :: Eq a => [a] -> [a] -> [a] #
The union function returns the list union of the two lists.
It is a special case of unionBy, which allows the programmer to supply
their own equality test.
For example,
>>>"dog" `union` "cow""dogcw"
If equal elements are present in both lists, an element from the first list will be used. If the second list contains equal elements, only the first one will be retained:
>>>import Data.Semigroup>>>union [Arg () "dog"] [Arg () "cow"][Arg () "dog"]>>>union [] [Arg () "dog", Arg () "cow"][Arg () "dog"]
However if the first list contains duplicates, so will the result:
>>>"coot" `union` "duck""cootduk">>>"duck" `union` "coot""duckot"
union is productive even if both arguments are infinite.
filter :: (a -> Bool) -> [a] -> [a] #
\(\mathcal{O}(n)\). filter, applied to a predicate and a list, returns
the list of those elements that satisfy the predicate; i.e.,
filter p xs = [ x | x <- xs, p x]
>>>filter odd [1, 2, 3][1,3]
zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] #
\(\mathcal{O}(\min(m,n))\). zipWith generalises zip by zipping with the
function given as the first argument, instead of a tupling function.
zipWith (,) xs ys == zip xs ys zipWith f [x1,x2,x3..] [y1,y2,y3..] == [f x1 y1, f x2 y2, f x3 y3..]
For example, zipWith (+)
>>>zipWith (+) [1, 2, 3] [4, 5, 6][5,7,9]
zipWith is right-lazy:
>>>let f = undefined>>>zipWith f [] undefined[]
zipWith is capable of list fusion, but it is restricted to its
first list argument and its resulting list.
sortBy :: (a -> a -> Ordering) -> [a] -> [a] #
The sortBy function is the non-overloaded version of sort.
The argument must be finite.
>>>sortBy (\(a,_) (b,_) -> compare a b) [(2, "world"), (4, "!"), (1, "Hello")][(1,"Hello"),(2,"world"),(4,"!")]
The supplied comparison relation is supposed to be reflexive and antisymmetric,
otherwise, e. g., for _ _ -> GT, the ordered list simply does not exist.
The relation is also expected to be transitive: if it is not then sortBy
might fail to find an ordered permutation, even if it exists.
genericLength :: Num i => [a] -> i #
\(\mathcal{O}(n)\). The genericLength function is an overloaded version
of length. In particular, instead of returning an Int, it returns any
type which is an instance of Num. It is, however, less efficient than
length.
>>>genericLength [1, 2, 3] :: Int3>>>genericLength [1, 2, 3] :: Float3.0
Users should take care to pick a return type that is wide enough to contain
the full length of the list. If the width is insufficient, the overflow
behaviour will depend on the (+) implementation in the selected Num
instance. The following example overflows because the actual list length
of 200 lies outside of the Int8 range of -128..127.
>>>genericLength [1..200] :: Int8-56
maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a #
The largest element of a non-empty structure with respect to the given comparison function.
Examples
Basic usage:
>>>maximumBy (compare `on` length) ["Hello", "World", "!", "Longest", "bar"]"Longest"
WARNING: This function is partial for possibly-empty structures like lists.
minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a #
The least element of a non-empty structure with respect to the given comparison function.
Examples
Basic usage:
>>>minimumBy (compare `on` length) ["Hello", "World", "!", "Longest", "bar"]"!"
WARNING: This function is partial for possibly-empty structures like lists.
genericReplicate :: Integral i => i -> a -> [a] #
The genericReplicate function is an overloaded version of replicate,
which accepts any Integral value as the number of repetitions to make.
genericTake :: Integral i => i -> [a] -> [a] #
The genericTake function is an overloaded version of take, which
accepts any Integral value as the number of elements to take.
genericDrop :: Integral i => i -> [a] -> [a] #
The genericDrop function is an overloaded version of drop, which
accepts any Integral value as the number of elements to drop.
genericSplitAt :: Integral i => i -> [a] -> ([a], [a]) #
The genericSplitAt function is an overloaded version of splitAt, which
accepts any Integral value as the position at which to split.
genericIndex :: Integral i => [a] -> i -> a #
The genericIndex function is an overloaded version of !!, which
accepts any Integral value as the index.
head :: HasCallStack => [a] -> a #
\(\mathcal{O}(1)\). Extract the first element of a list, which must be non-empty.
>>>head [1, 2, 3]1>>>head [1..]1>>>head []*** Exception: Prelude.head: empty list
WARNING: This function is partial. You can use case-matching, uncons or
listToMaybe instead.
group :: Eq a => [a] -> [[a]] #
The group function takes a list and returns a list of lists such
that the concatenation of the result is equal to the argument. Moreover,
each sublist in the result is non-empty and all elements are equal
to the first one. For example,
>>>group "Mississippi"["M","i","ss","i","ss","i","pp","i"]
group is a special case of groupBy, which allows the programmer to supply
their own equality test.
It's often preferable to use Data.List.NonEmpty.group,
which provides type-level guarantees of non-emptiness of inner lists.
groupBy :: (a -> a -> Bool) -> [a] -> [[a]] #
The groupBy function is the non-overloaded version of group.
When a supplied relation is not transitive, it is important to remember that equality is checked against the first element in the group, not against the nearest neighbour:
>>>groupBy (\a b -> b - a < 5) [0..19][[0,1,2,3,4],[5,6,7,8,9],[10,11,12,13,14],[15,16,17,18,19]]
It's often preferable to use Data.List.NonEmpty.groupBy,
which provides type-level guarantees of non-emptiness of inner lists.
unfoldr :: (b -> Maybe (a, b)) -> b -> [a] #
The unfoldr function is a `dual' to foldr: while foldr
reduces a list to a summary value, unfoldr builds a list from
a seed value. The function takes the element and returns Nothing
if it is done producing the list or returns Just (a,b), in which
case, a is a prepended to the list and b is used as the next
element in a recursive call. For example,
iterate f == unfoldr (\x -> Just (x, f x))
In some cases, unfoldr can undo a foldr operation:
unfoldr f' (foldr f z xs) == xs
if the following holds:
f' (f x y) = Just (x,y) f' z = Nothing
A simple use of unfoldr:
>>>unfoldr (\b -> if b == 0 then Nothing else Just (b, b-1)) 10[10,9,8,7,6,5,4,3,2,1]
The transpose function transposes the rows and columns of its argument.
For example,
>>>transpose [[1,2,3],[4,5,6]][[1,4],[2,5],[3,6]]
If some of the rows are shorter than the following rows, their elements are skipped:
>>>transpose [[10,11],[20],[],[30,31,32]][[10,20,30],[11,31],[32]]
For this reason the outer list must be finite; otherwise transpose hangs:
>>>transpose (repeat [])* Hangs forever *
sortOn :: Ord b => (a -> b) -> [a] -> [a] #
Sort a list by comparing the results of a key function applied to each
element. sortOn fsortBy (comparing f)f once for each element in the
input list. This is called the decorate-sort-undecorate paradigm, or
Schwartzian transform.
Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.
>>>sortOn fst [(2, "world"), (4, "!"), (1, "Hello")][(1,"Hello"),(2,"world"),(4,"!")]
The argument must be finite.
Since: base-4.8.0.0
cycle :: HasCallStack => [a] -> [a] #
cycle ties a finite list into a circular one, or equivalently,
the infinite repetition of the original list. It is the identity
on infinite lists.
>>>cycle []*** Exception: Prelude.cycle: empty list>>>cycle [42][42,42,42,42,42,42,42,42,42,42...>>>cycle [2, 5, 7][2,5,7,2,5,7,2,5,7,2,5,7...
concat :: Foldable t => t [a] -> [a] #
The concatenation of all the elements of a container of lists.
Examples
Basic usage:
>>>concat (Just [1, 2, 3])[1,2,3]
>>>concat (Left 42)[]
>>>concat [[1, 2, 3], [4, 5], [6], []][1,2,3,4,5,6]
zip :: [a] -> [b] -> [(a, b)] #
\(\mathcal{O}(\min(m,n))\). zip takes two lists and returns a list of
corresponding pairs.
>>>zip [1, 2] ['a', 'b'][(1,'a'),(2,'b')]
If one input list is shorter than the other, excess elements of the longer list are discarded, even if one of the lists is infinite:
>>>zip [1] ['a', 'b'][(1,'a')]>>>zip [1, 2] ['a'][(1,'a')]>>>zip [] [1..][]>>>zip [1..] [][]
zip is right-lazy:
>>>zip [] undefined[]>>>zip undefined []*** Exception: Prelude.undefined ...
zip is capable of list fusion, but it is restricted to its
first list argument and its resulting list.
tail :: HasCallStack => [a] -> [a] #
\(\mathcal{O}(1)\). Extract the elements after the head of a list, which must be non-empty.
>>>tail [1, 2, 3][2,3]>>>tail [1][]>>>tail []*** Exception: Prelude.tail: empty list
WARNING: This function is partial. You can use case-matching or uncons
instead.
last :: HasCallStack => [a] -> a #
\(\mathcal{O}(n)\). Extract the last element of a list, which must be finite and non-empty.
>>>last [1, 2, 3]3>>>last [1..]* Hangs forever *>>>last []*** Exception: Prelude.last: empty list
WARNING: This function is partial. You can use reverse with case-matching,
uncons or listToMaybe instead.
init :: HasCallStack => [a] -> [a] #
foldl1' :: HasCallStack => (a -> a -> a) -> [a] -> a #
A strict version of foldl1.
scanl :: (b -> a -> b) -> b -> [a] -> [b] #
\(\mathcal{O}(n)\). scanl is similar to foldl, but returns a list of
successive reduced values from the left:
scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
Note that
last (scanl f z xs) == foldl f z xs
>>>scanl (+) 0 [1..4][0,1,3,6,10]>>>scanl (+) 42 [][42]>>>scanl (-) 100 [1..4][100,99,97,94,90]>>>scanl (\reversedString nextChar -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']["foo","afoo","bafoo","cbafoo","dcbafoo"]>>>scanl (+) 0 [1..]* Hangs forever *
scanl1 :: (a -> a -> a) -> [a] -> [a] #
\(\mathcal{O}(n)\). scanl1 is a variant of scanl that has no starting
value argument:
scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
>>>scanl1 (+) [1..4][1,3,6,10]>>>scanl1 (+) [][]>>>scanl1 (-) [1..4][1,-1,-4,-8]>>>scanl1 (&&) [True, False, True, True][True,False,False,False]>>>scanl1 (||) [False, False, True, True][False,False,True,True]>>>scanl1 (+) [1..]* Hangs forever *
scanr :: (a -> b -> b) -> b -> [a] -> [b] #
\(\mathcal{O}(n)\). scanr is the right-to-left dual of scanl. Note that the order of parameters on the accumulating function are reversed compared to scanl.
Also note that
head (scanr f z xs) == foldr f z xs.
>>>scanr (+) 0 [1..4][10,9,7,4,0]>>>scanr (+) 42 [][42]>>>scanr (-) 100 [1..4][98,-97,99,-96,100]>>>scanr (\nextChar reversedString -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']["abcdfoo","bcdfoo","cdfoo","dfoo","foo"]>>>force $ scanr (+) 0 [1..]*** Exception: stack overflow
scanr1 :: (a -> a -> a) -> [a] -> [a] #
\(\mathcal{O}(n)\). scanr1 is a variant of scanr that has no starting
value argument.
>>>scanr1 (+) [1..4][10,9,7,4]>>>scanr1 (+) [][]>>>scanr1 (-) [1..4][-2,3,-1,4]>>>scanr1 (&&) [True, False, True, True][False,False,True,True]>>>scanr1 (||) [True, True, False, False][True,True,False,False]>>>force $ scanr1 (+) [1..]*** Exception: stack overflow
iterate :: (a -> a) -> a -> [a] #
iterate f x returns an infinite list of repeated applications
of f to x:
iterate f x == [x, f x, f (f x), ...]
Note that iterate is lazy, potentially leading to thunk build-up if
the consumer doesn't force each iterate. See iterate' for a strict
variant of this function.
>>>take 10 $ iterate not True[True,False,True,False...>>>take 10 $ iterate (+3) 42[42,45,48,51,54,57,60,63...
repeat x is an infinite list, with x the value of every element.
>>>repeat 17[17,17,17,17,17,17,17,17,17...
replicate :: Int -> a -> [a] #
replicate n x is a list of length n with x the value of
every element.
It is an instance of the more general genericReplicate,
in which n may be of any integral type.
>>>replicate 0 True[]>>>replicate (-1) True[]>>>replicate 4 True[True,True,True,True]
takeWhile :: (a -> Bool) -> [a] -> [a] #
takeWhile, applied to a predicate p and a list xs, returns the
longest prefix (possibly empty) of xs of elements that satisfy p.
>>>takeWhile (< 3) [1,2,3,4,1,2,3,4][1,2]>>>takeWhile (< 9) [1,2,3][1,2,3]>>>takeWhile (< 0) [1,2,3][]
take n, applied to a list xs, returns the prefix of xs
of length n, or xs itself if n >= .length xs
>>>take 5 "Hello World!""Hello">>>take 3 [1,2,3,4,5][1,2,3]>>>take 3 [1,2][1,2]>>>take 3 [][]>>>take (-1) [1,2][]>>>take 0 [1,2][]
It is an instance of the more general genericTake,
in which n may be of any integral type.
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.
splitAt :: Int -> [a] -> ([a], [a]) #
splitAt n xs returns a tuple where first element is xs prefix of
length n and second element is the remainder of the list:
>>>splitAt 6 "Hello World!"("Hello ","World!")>>>splitAt 3 [1,2,3,4,5]([1,2,3],[4,5])>>>splitAt 1 [1,2,3]([1],[2,3])>>>splitAt 3 [1,2,3]([1,2,3],[])>>>splitAt 4 [1,2,3]([1,2,3],[])>>>splitAt 0 [1,2,3]([],[1,2,3])>>>splitAt (-1) [1,2,3]([],[1,2,3])
It is equivalent to ( when take n xs, drop n xs)n is not _|_
(splitAt _|_ xs = _|_).
splitAt is an instance of the more general genericSplitAt,
in which n may be of any integral type.
span :: (a -> Bool) -> [a] -> ([a], [a]) #
span, applied to a predicate p and a list xs, returns a tuple where
first element is longest prefix (possibly empty) of xs of elements that
satisfy p and second element is the remainder of the list:
>>>span (< 3) [1,2,3,4,1,2,3,4]([1,2],[3,4,1,2,3,4])>>>span (< 9) [1,2,3]([1,2,3],[])>>>span (< 0) [1,2,3]([],[1,2,3])
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],[])
reverse xs returns the elements of xs in reverse order.
xs must be finite.
>>>reverse [][]>>>reverse [42][42]>>>reverse [2,5,7][7,5,2]>>>reverse [1..]* Hangs forever *
and :: Foldable t => t Bool -> Bool #
and returns the conjunction of a container of Bools. For the
result to be True, the container must be finite; False, however,
results from a False value finitely far from the left end.
Examples
Basic usage:
>>>and []True
>>>and [True]True
>>>and [False]False
>>>and [True, True, False]False
>>>and (False : repeat True) -- Infinite list [False,True,True,True,...False
>>>and (repeat True)* Hangs forever *
or :: Foldable t => t Bool -> Bool #
or returns the disjunction of a container of Bools. For the
result to be False, the container must be finite; True, however,
results from a True value finitely far from the left end.
Examples
Basic usage:
>>>or []False
>>>or [True]True
>>>or [False]False
>>>or [True, True, False]True
>>>or (True : repeat False) -- Infinite list [True,False,False,False,...True
>>>or (repeat False)* Hangs forever *
any :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether any element of the structure satisfies the predicate.
Examples
Basic usage:
>>>any (> 3) []False
>>>any (> 3) [1,2]False
>>>any (> 3) [1,2,3,4,5]True
>>>any (> 3) [1..]True
>>>any (> 3) [0, -1..]* Hangs forever *
all :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether all elements of the structure satisfy the predicate.
Examples
Basic usage:
>>>all (> 3) []True
>>>all (> 3) [1,2]False
>>>all (> 3) [1,2,3,4,5]False
>>>all (> 3) [1..]False
>>>all (> 3) [4..]* Hangs forever *
notElem :: (Foldable t, Eq a) => a -> t a -> Bool infix 4 #
notElem is the negation of elem.
Examples
Basic usage:
>>>3 `notElem` []True
>>>3 `notElem` [1,2]True
>>>3 `notElem` [1,2,3,4,5]False
For infinite structures, notElem terminates if the value exists at a
finite distance from the left side of the structure:
>>>3 `notElem` [1..]False
>>>3 `notElem` ([4..] ++ [3])* Hangs forever *
concatMap :: Foldable t => (a -> [b]) -> t a -> [b] #
Map a function over all the elements of a container and concatenate the resulting lists.
Examples
Basic usage:
>>>concatMap (take 3) [[1..], [10..], [100..], [1000..]][1,2,3,10,11,12,100,101,102,1000,1001,1002]
>>>concatMap (take 3) (Just [1..])[1,2,3]
(!!) :: HasCallStack => [a] -> Int -> a infixl 9 #
List index (subscript) operator, starting from 0.
It is an instance of the more general genericIndex,
which takes an index of any integral type.
>>>['a', 'b', 'c'] !! 0'a'>>>['a', 'b', 'c'] !! 2'c'>>>['a', 'b', 'c'] !! 3*** Exception: Prelude.!!: index too large>>>['a', 'b', 'c'] !! (-1)*** Exception: Prelude.!!: negative index
WARNING: This function is partial. You can use atMay instead.
zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d] #
The zipWith3 function takes a function which combines three
elements, as well as three lists and returns a list of the function applied
to corresponding elements, analogous to zipWith.
It is capable of list fusion, but it is restricted to its
first list argument and its resulting list.
zipWith3 (,,) xs ys zs == zip3 xs ys zs zipWith3 f [x1,x2,x3..] [y1,y2,y3..] [z1,z2,z3..] == [f x1 y1 z1, f x2 y2 z2, f x3 y3 z3..]
unzip :: [(a, b)] -> ([a], [b]) #
unzip transforms a list of pairs into a list of first components
and a list of second components.
>>>unzip []([],[])>>>unzip [(1, 'a'), (2, 'b')]([1,2],"ab")
dropWhileEnd :: (a -> Bool) -> [a] -> [a] #
The dropWhileEnd function drops the largest suffix of a list
in which the given predicate holds for all elements. For example:
>>>dropWhileEnd isSpace "foo\n""foo"
>>>dropWhileEnd isSpace "foo bar""foo bar"
dropWhileEnd isSpace ("foo\n" ++ undefined) == "foo" ++ undefinedSince: base-4.5.0.0
stripPrefix :: Eq a => [a] -> [a] -> Maybe [a] #
\(\mathcal{O}(\min(m,n))\). The stripPrefix function drops the given
prefix from a list. It returns Nothing if the list did not start with the
prefix given, or Just the list after the prefix, if it does.
>>>stripPrefix "foo" "foobar"Just "bar"
>>>stripPrefix "foo" "foo"Just ""
>>>stripPrefix "foo" "barfoo"Nothing
>>>stripPrefix "foo" "barfoobaz"Nothing
elemIndices :: Eq a => a -> [a] -> [Int] #
The elemIndices function extends elemIndex, by returning the
indices of all elements equal to the query element, in ascending order.
>>>elemIndices 'o' "Hello World"[4,7]
findIndices :: (a -> Bool) -> [a] -> [Int] #
The findIndices function extends findIndex, by returning the
indices of all elements satisfying the predicate, in ascending order.
>>>findIndices (`elem` "aeiou") "Hello World!"[1,4,7]
isPrefixOf :: Eq a => [a] -> [a] -> Bool #
\(\mathcal{O}(\min(m,n))\). The isPrefixOf function takes two lists and
returns True iff the first list is a prefix of the second.
>>>"Hello" `isPrefixOf` "Hello World!"True>>>"Hello" `isPrefixOf` "Wello Horld!"False
For the result to be True, the first list must be finite;
False, however, results from any mismatch:
>>>[0..] `isPrefixOf` [1..]False>>>[0..] `isPrefixOf` [0..99]False>>>[0..99] `isPrefixOf` [0..]True>>>[0..] `isPrefixOf` [0..]* Hangs forever *
isSuffixOf :: Eq a => [a] -> [a] -> Bool #
The isSuffixOf function takes two lists and returns True iff
the first list is a suffix of the second.
>>>"ld!" `isSuffixOf` "Hello World!"True>>>"World" `isSuffixOf` "Hello World!"False
The second list must be finite; however the first list may be infinite:
>>>[0..] `isSuffixOf` [0..99]False>>>[0..99] `isSuffixOf` [0..]* Hangs forever *
isInfixOf :: Eq a => [a] -> [a] -> Bool #
The isInfixOf function takes two lists and returns True
iff the first list is contained, wholly and intact,
anywhere within the second.
>>>isInfixOf "Haskell" "I really like Haskell."True>>>isInfixOf "Ial" "I really like Haskell."False
For the result to be True, the first list must be finite;
for the result to be False, the second list must be finite:
>>>[20..50] `isInfixOf` [0..]True>>>[0..] `isInfixOf` [20..50]False>>>[0..] `isInfixOf` [0..]* Hangs forever *
\(\mathcal{O}(n^2)\). The nub function removes duplicate elements from a
list. In particular, it keeps only the first occurrence of each element. (The
name nub means `essence'.) It is a special case of nubBy, which allows
the programmer to supply their own equality test.
>>>nub [1,2,3,4,3,2,1,2,4,3,5][1,2,3,4,5]
If the order of outputs does not matter and there exists instance Ord a,
it's faster to use
map Data.List.NonEmpty.head . Data.List.NonEmpty.group . sort,
which takes only \(\mathcal{O}(n \log n)\) time.
(\\) :: Eq a => [a] -> [a] -> [a] infix 5 #
The \\ function is list difference (non-associative).
In the result of xs \\ ys, the first occurrence of each element of
ys in turn (if any) has been removed from xs. Thus
(xs ++ ys) \\ xs == ys.
>>>"Hello World!" \\ "ell W""Hoorld!"
It is a special case of deleteFirstsBy, which allows the programmer
to supply their own equality test.
The second list must be finite, but the first may be infinite.
>>>take 5 ([0..] \\ [2..4])[0,1,5,6,7]>>>take 5 ([0..] \\ [2..])* Hangs forever *
intersect :: Eq a => [a] -> [a] -> [a] #
The intersect function takes the list intersection of two lists.
It is a special case of intersectBy, which allows the programmer to
supply their own equality test.
For example,
>>>[1,2,3,4] `intersect` [2,4,6,8][2,4]
If equal elements are present in both lists, an element from the first list will be used, and all duplicates from the second list quashed:
>>>import Data.Semigroup>>>intersect [Arg () "dog"] [Arg () "cow", Arg () "cat"][Arg () "dog"]
However if the first list contains duplicates, so will the result.
>>>"coot" `intersect` "heron""oo">>>"heron" `intersect` "coot""o"
If the second list is infinite, intersect either hangs
or returns its first argument in full. Otherwise if the first list
is infinite, intersect might be productive:
>>>intersect [100..] [0..][100,101,102,103...>>>intersect [0] [1..]* Hangs forever *>>>intersect [1..] [0]* Hangs forever *>>>intersect (cycle [1..3]) [2][2,2,2,2...
intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] #
The intersectBy function is the non-overloaded version of intersect.
It is productive for infinite arguments only if the first one
is a subset of the second.
intersperse :: a -> [a] -> [a] #
\(\mathcal{O}(n)\). The intersperse function takes an element and a list
and `intersperses' that element between the elements of the list. For
example,
>>>intersperse ',' "abcde""a,b,c,d,e"
intercalate :: [a] -> [[a]] -> [a] #
intercalate xs xss is equivalent to (.
It inserts the list concat (intersperse xs xss))xs in between the lists in xss and concatenates the
result.
>>>intercalate ", " ["Lorem", "ipsum", "dolor"]"Lorem, ipsum, dolor"
partition :: (a -> Bool) -> [a] -> ([a], [a]) #
The partition function takes a predicate and a list, and returns
the pair of lists of elements which do and do not satisfy the
predicate, respectively; i.e.,
partition p xs == (filter p xs, filter (not . p) xs)
>>>partition (`elem` "aeiou") "Hello World!"("eoo","Hll Wrld!")
mapAccumL :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b) #
The mapAccumL function behaves like a combination of fmap
and foldl; it applies a function to each element of a structure,
passing an accumulating parameter from left to right, and returning
a final value of this accumulator together with the new structure.
Examples
Basic usage:
>>>mapAccumL (\a b -> (a + b, a)) 0 [1..10](55,[0,1,3,6,10,15,21,28,36,45])
>>>mapAccumL (\a b -> (a <> show b, a)) "0" [1..5]("012345",["0","01","012","0123","01234"])
mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b) #
The mapAccumR function behaves like a combination of fmap
and foldr; it applies a function to each element of a structure,
passing an accumulating parameter from right to left, and returning
a final value of this accumulator together with the new structure.
Examples
Basic usage:
>>>mapAccumR (\a b -> (a + b, a)) 0 [1..10](55,[54,52,49,45,40,34,27,19,10,0])
>>>mapAccumR (\a b -> (a <> show b, a)) "0" [1..5]("054321",["05432","0543","054","05","0"])
insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a] #
\(\mathcal{O}(n)\). The non-overloaded version of insert.
zipWith7 :: (a -> b -> c -> d -> e -> f -> g -> h) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [h] #
deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] #
The deleteFirstsBy function takes a predicate and two lists and
returns the first list with the first occurrence of each element of
the second list removed. This is the non-overloaded version of (\\).
The second list must be finite, but the first may be infinite.
The inits function returns all initial segments of the argument,
shortest first. For example,
>>>inits "abc"["","a","ab","abc"]
Note that inits has the following strictness property:
inits (xs ++ _|_) = inits xs ++ _|_
In particular,
inits _|_ = [] : _|_
inits is semantically equivalent to map reverse . scanl (flip (:)) []reverse.
subsequences :: [a] -> [[a]] #
The subsequences function returns the list of all subsequences of the argument.
>>>subsequences "abc"["","a","b","ab","c","ac","bc","abc"]
This function is productive on infinite inputs:
>>>take 8 $ subsequences ['a'..]["","a","b","ab","c","ac","bc","abc"]
permutations :: [a] -> [[a]] #
The permutations function returns the list of all permutations of the argument.
>>>permutations "abc"["abc","bac","cba","bca","cab","acb"]
The permutations function is maximally lazy:
for each n, the value of permutations xstake n xsdrop n xs
This function is productive on infinite inputs:
>>>take 6 $ map (take 3) $ permutations ['a'..]["abc","bac","cba","bca","cab","acb"]
Note that the order of permutations is not lexicographic. It satisfies the following property:
map (take n) (take (product [1..n]) (permutations ([1..n] ++ undefined))) == permutations [1..n]
Splits the argument into a list of lines stripped of their terminating
\n characters. The \n terminator is optional in a final non-empty
line of the argument string.
For example:
>>>lines "" -- empty input contains no lines[]>>>lines "\n" -- single empty line[""]>>>lines "one" -- single unterminated line["one"]>>>lines "one\n" -- single non-empty line["one"]>>>lines "one\n\n" -- second line is empty["one",""]>>>lines "one\ntwo" -- second line is unterminated["one","two"]>>>lines "one\ntwo\n" -- two non-empty lines["one","two"]
When the argument string is empty, or ends in a \n character, it can be
recovered by passing the result of lines to the unlines function.
Otherwise, unlines appends the missing terminating \n. This makes
unlines . lines idempotent:
(unlines . lines) . (unlines . lines) = (unlines . lines)
isSubsequenceOf :: Eq a => [a] -> [a] -> Bool #
The isSubsequenceOf function takes two lists and returns True if all
the elements of the first list occur, in order, in the second. The
elements do not have to occur consecutively.
isSubsequenceOf x yelem x (subsequences y)
>>>isSubsequenceOf "GHC" "The Glorious Haskell Compiler"True>>>isSubsequenceOf ['a','d'..'z'] ['a'..'z']True>>>isSubsequenceOf [1..10] [10,9..0]False
For the result to be True, the first list must be finite;
for the result to be False, the second list must be finite:
>>>[0,2..10] `isSubsequenceOf` [0..]True>>>[0..] `isSubsequenceOf` [0,2..10]False>>>[0,2..] `isSubsequenceOf` [0..]* Hangs forever*
Since: base-4.8.0.0
class Default a where Source #
A class for types with a default value.
Minimal complete definition
Nothing
Instances
Representable types of kind *.
This class is derivable in GHC with the DeriveGeneric flag on.
A Generic instance must satisfy the following laws:
from.to≡idto.from≡id
Instances
The class Typeable allows a concrete representation of a type to
be calculated.
Minimal complete definition
typeRep#
type HasCallStack = ?callStack :: CallStack #
Request a CallStack.
NOTE: The implicit parameter ?callStack :: CallStack is an
implementation detail and should not be considered part of the
CallStack API, we may decide to change the implementation in the
future.
Since: base-4.9.0.0
Containers
A Map from keys k to values a.
The Semigroup operation for Map is union, which prefers
values from the left operand. If m1 maps a key k to a value
a1, and m2 maps the same key to a different value a2, then
their union m1 <> m2 maps k to a1.
Instances
| Bifoldable Map | Since: containers-0.6.3.1 |
| Eq2 Map | Since: containers-0.5.9 |
| Ord2 Map | Since: containers-0.5.9 |
Defined in Data.Map.Internal | |
| Show2 Map | Since: containers-0.5.9 |
| Hashable2 Map | Since: hashable-1.3.4.0 |
| FoldableWithIndex k (Map k) | |
Defined in WithIndex Methods ifoldMap :: Monoid m => (k -> a -> m) -> Map k a -> m Source # ifoldMap' :: Monoid m => (k -> a -> m) -> Map k a -> m Source # ifoldr :: (k -> a -> b -> b) -> b -> Map k a -> b Source # ifoldl :: (k -> b -> a -> b) -> b -> Map k a -> b Source # | |
| FunctorWithIndex k (Map k) | |
| TraversableWithIndex k (Map k) | |
| Ord k => TraverseMax k (Map k) | |
Defined in Control.Lens.Traversal Methods traverseMax :: IndexedTraversal' k (Map k v) v Source # | |
| Ord k => TraverseMin k (Map k) | |
Defined in Control.Lens.Traversal Methods traverseMin :: IndexedTraversal' k (Map k v) v Source # | |
| (Lift k, Lift a) => Lift (Map k a :: Type) | Since: containers-0.6.6 |
| (FromJSONKey k, Ord k) => FromJSON1 (Map k) | |
| ToJSONKey k => ToJSON1 (Map k) | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Map k a -> Value Source # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Map k a] -> Value Source # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Map k a -> Encoding Source # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Map k a] -> Encoding Source # | |
| Foldable (Map k) | Folds in order of increasing key. |
Defined in Data.Map.Internal Methods fold :: Monoid m => Map k m -> m # foldMap :: Monoid m => (a -> m) -> Map k a -> m # foldMap' :: Monoid m => (a -> m) -> Map k a -> m # foldr :: (a -> b -> b) -> b -> Map k a -> b # foldr' :: (a -> b -> b) -> b -> Map k a -> b # foldl :: (b -> a -> b) -> b -> Map k a -> b # foldl' :: (b -> a -> b) -> b -> Map k a -> b # foldr1 :: (a -> a -> a) -> Map k a -> a # foldl1 :: (a -> a -> a) -> Map k a -> a # elem :: Eq a => a -> Map k a -> Bool # maximum :: Ord a => Map k a -> a # minimum :: Ord a => Map k a -> a # | |
| Eq k => Eq1 (Map k) | Since: containers-0.5.9 |
| Ord k => Ord1 (Map k) | Since: containers-0.5.9 |
Defined in Data.Map.Internal | |
| (Ord k, Read k) => Read1 (Map k) | Since: containers-0.5.9 |
Defined in Data.Map.Internal | |
| Show k => Show1 (Map k) | Since: containers-0.5.9 |
| Traversable (Map k) | Traverses in order of increasing key. |
| Functor (Map k) | |
| Hashable k => Hashable1 (Map k) | Since: hashable-1.3.4.0 |
Defined in Data.Hashable.Class | |
| (FromJSONKey k, Ord k, FromJSON v) => FromJSON (Map k v) | |
| (ToJSON v, ToJSONKey k) => ToJSON (Map k v) | |
| (Data k, Data a, Ord k) => Data (Map k a) | |
Defined in Data.Map.Internal Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Map k a -> c (Map k a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Map k a) # toConstr :: Map k a -> Constr # dataTypeOf :: Map k a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Map k a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Map k a)) # gmapT :: (forall b. Data b => b -> b) -> Map k a -> Map k a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Map k a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Map k a -> r # gmapQ :: (forall d. Data d => d -> u) -> Map k a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Map k a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Map k a -> m (Map k a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Map k a -> m (Map k a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Map k a -> m (Map k a) # | |
| Ord k => Monoid (Map k v) | |
| Ord k => Semigroup (Map k v) | |
| Ord k => IsList (Map k v) | Since: containers-0.5.6.2 |
| (Ord k, Read k, Read e) => Read (Map k e) | |
| (Show k, Show a) => Show (Map k a) | |
| (NFData k, NFData a) => NFData (Map k a) | |
Defined in Data.Map.Internal | |
| (Eq k, Eq a) => Eq (Map k a) | |
| (Ord k, Ord v) => Ord (Map k v) | |
| (Hashable k, Hashable v) => Hashable (Map k v) | Since: hashable-1.3.4.0 |
| (Ord k, FromFormKey k, FromHttpApiData v) => FromForm (Map k [v]) | |
| (ToFormKey k, ToHttpApiData v) => ToForm (Map k [v]) | |
| Ord k => At (Map k a) | |
| Ord k => Ixed (Map k a) | |
Defined in Control.Lens.At | |
| AsEmpty (Map k a) | |
| Ord k => Wrapped (Map k a) | |
| (t ~ Map k' a', Ord k) => Rewrapped (Map k a) t | |
Defined in Control.Lens.Wrapped | |
| c ~ d => Each (Map c a) (Map d b) a b |
|
| type Item (Map k v) | |
Defined in Data.Map.Internal | |
| type Index (Map k a) | |
Defined in Control.Lens.At | |
| type IxValue (Map k a) | |
Defined in Control.Lens.At | |
| type Unwrapped (Map k a) | |
Defined in Control.Lens.Wrapped | |
A set of values a.
Instances
| ToJSON1 Set | |
Defined in Data.Aeson.Types.ToJSON Methods liftToJSON :: (a -> Value) -> ([a] -> Value) -> Set a -> Value Source # liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Set a] -> Value Source # liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Set a -> Encoding Source # liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Set a] -> Encoding Source # | |
| Foldable Set | Folds in order of increasing key. |
Defined in Data.Set.Internal Methods fold :: Monoid m => Set m -> m # foldMap :: Monoid m => (a -> m) -> Set a -> m # foldMap' :: Monoid m => (a -> m) -> Set a -> m # foldr :: (a -> b -> b) -> b -> Set a -> b # foldr' :: (a -> b -> b) -> b -> Set a -> b # foldl :: (b -> a -> b) -> b -> Set a -> b # foldl' :: (b -> a -> b) -> b -> Set a -> b # foldr1 :: (a -> a -> a) -> Set a -> a # foldl1 :: (a -> a -> a) -> Set a -> a # elem :: Eq a => a -> Set a -> Bool # maximum :: Ord a => Set a -> a # | |
| Eq1 Set | Since: containers-0.5.9 |
| Ord1 Set | Since: containers-0.5.9 |
Defined in Data.Set.Internal | |
| Show1 Set | Since: containers-0.5.9 |
| Hashable1 Set | Since: hashable-1.3.4.0 |
Defined in Data.Hashable.Class | |
| Lift a => Lift (Set a :: Type) | Since: containers-0.6.6 |
| (Ord a, FromJSON a) => FromJSON (Set a) | |
| ToJSON a => ToJSON (Set a) | |
| (Data a, Ord a) => Data (Set a) | |
Defined in Data.Set.Internal Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Set a -> c (Set a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Set a) # dataTypeOf :: Set a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Set a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Set a)) # gmapT :: (forall b. Data b => b -> b) -> Set a -> Set a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Set a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Set a -> r # gmapQ :: (forall d. Data d => d -> u) -> Set a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Set a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Set a -> m (Set a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Set a -> m (Set a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Set a -> m (Set a) # | |
| Ord a => Monoid (Set a) | |
| Ord a => Semigroup (Set a) | Since: containers-0.5.7 |
| Ord a => IsList (Set a) | Since: containers-0.5.6.2 |
| (Read a, Ord a) => Read (Set a) | |
| Show a => Show (Set a) | |
| NFData a => NFData (Set a) | |
Defined in Data.Set.Internal | |
| Eq a => Eq (Set a) | |
| Ord a => Ord (Set a) | |
| Hashable v => Hashable (Set v) | Since: hashable-1.3.4.0 |
| Ord k => At (Set k) | |
| Ord a => Contains (Set a) | |
| Ord k => Ixed (Set k) | |
Defined in Control.Lens.At | |
| AsEmpty (Set a) | |
| Ord a => Wrapped (Set a) | |
| (t ~ Set a', Ord a) => Rewrapped (Set a) t | |
Defined in Control.Lens.Wrapped | |
| type Item (Set a) | |
Defined in Data.Set.Internal | |
| type Index (Set a) | |
Defined in Control.Lens.At | |
| type IxValue (Set k) | |
Defined in Control.Lens.At | |
| type Unwrapped (Set a) | |
Defined in Control.Lens.Wrapped | |
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.
Instances
Exceptions
class (Typeable e, Show e) => Exception e where #
Any type that you wish to throw or catch as an exception must be an
instance of the Exception class. The simplest case is a new exception
type directly below the root:
data MyException = ThisException | ThatException
deriving Show
instance Exception MyExceptionThe default method definitions in the Exception class do what we need
in this case. You can now throw and catch ThisException and
ThatException as exceptions:
*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
Caught ThisException
In more complicated examples, you may wish to define a whole hierarchy of exceptions:
---------------------------------------------------------------------
-- Make the root exception type for all the exceptions in a compiler
data SomeCompilerException = forall e . Exception e => SomeCompilerException e
instance Show SomeCompilerException where
show (SomeCompilerException e) = show e
instance Exception SomeCompilerException
compilerExceptionToException :: Exception e => e -> SomeException
compilerExceptionToException = toException . SomeCompilerException
compilerExceptionFromException :: Exception e => SomeException -> Maybe e
compilerExceptionFromException x = do
SomeCompilerException a <- fromException x
cast a
---------------------------------------------------------------------
-- Make a subhierarchy for exceptions in the frontend of the compiler
data SomeFrontendException = forall e . Exception e => SomeFrontendException e
instance Show SomeFrontendException where
show (SomeFrontendException e) = show e
instance Exception SomeFrontendException where
toException = compilerExceptionToException
fromException = compilerExceptionFromException
frontendExceptionToException :: Exception e => e -> SomeException
frontendExceptionToException = toException . SomeFrontendException
frontendExceptionFromException :: Exception e => SomeException -> Maybe e
frontendExceptionFromException x = do
SomeFrontendException a <- fromException x
cast a
---------------------------------------------------------------------
-- Make an exception type for a particular frontend compiler exception
data MismatchedParentheses = MismatchedParentheses
deriving Show
instance Exception MismatchedParentheses where
toException = frontendExceptionToException
fromException = frontendExceptionFromExceptionWe can now catch a MismatchedParentheses exception as
MismatchedParentheses, SomeFrontendException or
SomeCompilerException, but not other types, e.g. IOException:
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
*** Exception: MismatchedParentheses
Minimal complete definition
Nothing
Methods
toException :: e -> SomeException #
fromException :: SomeException -> Maybe e #
displayException :: e -> String #
Render this exception value in a human-friendly manner.
Default implementation: show
Since: base-4.8.0.0
Instances
data SomeException #
The SomeException type is the root of the exception type hierarchy.
When an exception of type e is thrown, behind the scenes it is
encapsulated in a SomeException.
Constructors
| Exception e => SomeException e |
Instances
| Exception SomeException | Since: base-3.0 |
Defined in GHC.Exception.Type Methods toException :: SomeException -> SomeException # fromException :: SomeException -> Maybe SomeException # displayException :: SomeException -> String # | |
| Show SomeException | Since: base-3.0 |
Defined in GHC.Exception.Type Methods showsPrec :: Int -> SomeException -> ShowS # show :: SomeException -> String # showList :: [SomeException] -> ShowS # | |
data SomeAsyncException #
Superclass for asynchronous exceptions.
Since: base-4.7.0.0
Constructors
| Exception e => SomeAsyncException e |
Instances
| Exception SomeAsyncException | Since: base-4.7.0.0 |
Defined in GHC.IO.Exception Methods toException :: SomeAsyncException -> SomeException # fromException :: SomeException -> Maybe SomeAsyncException # | |
| Show SomeAsyncException | Since: base-4.7.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> SomeAsyncException -> ShowS # show :: SomeAsyncException -> String # showList :: [SomeAsyncException] -> ShowS # | |
data IOException #
Exceptions that occur in the IO monad.
An IOException records a more specific error type, a descriptive
string and maybe the handle that was used when the error was
flagged.
Instances
| Exception IOException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods toException :: IOException -> SomeException # fromException :: SomeException -> Maybe IOException # displayException :: IOException -> String # | |
| Show IOException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> IOException -> ShowS # show :: IOException -> String # showList :: [IOException] -> ShowS # | |
| Eq IOException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception | |
Prelude
getContents :: MonadIO m => m String Source #
liftIO :: MonadIO m => IO a -> m a #
Lift a computation from the IO monad.
This allows us to run IO computations in any monadic stack, so long as it supports these kinds of operations
(i.e. IO is the base monad for the stack).
Example
import Control.Monad.Trans.State -- from the "transformers" library printState :: Show s => StateT s IO () printState = do state <- get liftIO $ print state
Had we omitted liftIO
• Couldn't match type ‘IO’ with ‘StateT s IO’ Expected type: StateT s IO () Actual type: IO ()
The important part here is the mismatch between StateT s IO () and IO ()
Luckily, we know of a function that takes an IO a(m a): liftIO
> evalStateT printState "hello" "hello" > evalStateT printState 3 3
Functor
(<$$$>) :: (Functor f, Functor g, Functor h) => (a -> b) -> f (g (h a)) -> f (g (h b)) infix 4 Source #