| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
Uniform.Json
Contents
Description
the operations on JSON data types
Synopsis
- class AtKey2 vk v where
- class AtKey vk v where
- encodeT :: ToJSON a => a -> Text
- fromJSONmaybe :: FromJSON a => Value -> Maybe a
- fromJSONm :: (FromJSON a, Show a) => Value -> ErrIO a
- fromJSONerrio :: (FromJSON a, Show a) => Value -> ErrIO a
- fromJSONfailError :: (FromJSON a, Show a) => Value -> ErrIO a
- result1 :: (Monad m, MonadFail m) => Result a -> m a
- gak :: AsValue s => s -> Key -> Maybe Value
- mergeLeftPref :: [Value] -> Value
- unions' :: [KeyMap Value] -> KeyMap Value
- mergeRightPref :: [Value] -> Value
- unObject :: Value -> Object
- type ErrIO = ExceptT Text IO
- data Value
- class ToJSON a where
- toJSON :: a -> Value
- toEncoding :: a -> Encoding
- toJSONList :: [a] -> Value
- toEncodingList :: [a] -> Encoding
- class FromJSON a where
- fromJSON :: FromJSON a => Value -> Result a
- decode :: FromJSON a => ByteString -> Maybe a
- omitNothingFields :: Options -> Bool
- eitherDecode :: FromJSON a => ByteString -> Either String a
- object :: [Pair] -> Value
- (.=) :: (KeyValue kv, ToJSON v) => Key -> v -> kv
- genericParseJSON :: (Generic a, GFromJSON Zero (Rep a)) => Options -> Value -> Parser a
- defaultOptions :: Options
- genericToJSON :: (Generic a, GToJSON' Value Zero (Rep a)) => Options -> a -> Value
- fieldLabelModifier :: Options -> String -> String
- fromList :: (Eq k, Hashable k) => [(k, v)] -> HashMap k v
- toList :: HashMap k v -> [(k, v)]
- data Result a
- encode :: ToJSON a => a -> ByteString
- encodePretty :: ToJSON a => a -> ByteString
- parseEither :: (a -> Parser b) -> a -> Either String b
- parseMaybe :: (a -> Parser b) -> a -> Maybe b
Documentation
class AtKey vk v where Source #
get and set at a key
Methods
getAtKey :: vk -> Key -> Maybe v Source #
getAt2Key :: vk -> Key -> Key -> Maybe v Source #
two keys: one after the other
fromJSONfailError :: (FromJSON a, Show a) => Value -> ErrIO a Source #
converts fromJson to a record structure throws error if fails
mergeLeftPref :: [Value] -> Value Source #
The (left-biased) union of two maps. all values must be objects, which can be prooduced with toJSON It prefers the first map when duplicate keys are encountered, http://hackage.haskell.org/package/hashmap-1.3.3/docs/Data-HashMap.html mergeLeftPref = Object . HML.unions . map unObject for ghc 9.2.1
mergeRightPref :: [Value] -> Value Source #
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 Methods coarbitrary :: Value -> Gen b -> Gen b # | |
| 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 | |
Defined in Data.Aeson.Types.ToJSON | |
| 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 | |
Defined in Data.Aeson.Types.Internal | |
| AsJSON Value | |
| AsNumber Value | |
| AsValue Value | |
| Zeros Value Source # | |
| NiceStrings Value Source # | |
| Lift Value | Since: aeson-0.11.0.0 |
| AtKey Value Value Source # | |
| AtKey Value Text Source # | |
| AtKey Value Integer Source # | |
| AtKey Value Bool Source # | |
| ToJSON a => AtKey2 Value a Source # | |
| (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 | |
| GToJSON' Encoding arity (U1 :: TYPE LiftedRep -> Type) | |
| GToJSON' Encoding arity (V1 :: TYPE LiftedRep -> Type) | |
| GToJSON' Value arity (U1 :: TYPE LiftedRep -> Type) | |
| GToJSON' Value arity (V1 :: TYPE LiftedRep -> 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 LiftedRep -> 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 LiftedRep -> 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-2.1.2.1-1CP91TiqJNMKhmZsERtItU" '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 | |
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 #
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 #
toEncodingList :: [a] -> Encoding #
Instances
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
fromJSON :: FromJSON a => Value -> Result a #
Convert a value from JSON, failing if the types do not match.
decode :: FromJSON a => ByteString -> Maybe a #
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.
omitNothingFields :: Options -> Bool #
If True, record fields with a Nothing value will be
omitted from the resulting object. If False, the resulting
object will include those fields mapping to null.
Note that this does not affect parsing: Maybe fields are
optional regardless of the value of omitNothingFields, subject
to the note below.
Note
Setting omitNothingFields to True only affects fields which are of
type Maybe uniformly in the ToJSON instance.
In particular, if the type of a field is declared as a type variable, it
will not be omitted from the JSON object, unless the field is
specialized upfront in the instance.
The same holds for Maybe fields being optional in the FromJSON instance.
Example
The generic instance for the following type Fruit depends on whether
the instance head is Fruit a or Fruit (Maybe a).
data Fruit a = Fruit
{ apples :: a -- A field whose type is a type variable.
, oranges :: Maybe Int
} deriving Generic
-- apples required, oranges optional
-- Even if fromJSON is then specialized to (Fruit (Maybe a)).
instance FromJSON a => FromJSON (Fruit a)
-- apples optional, oranges optional
-- In this instance, the field apples is uniformly of type (Maybe a).
instance FromJSON a => FromJSON (Fruit (Maybe a))
options :: Options
options = defaultOptions { omitNothingFields = True }
-- apples always present in the output, oranges is omitted if Nothing
instance ToJSON a => ToJSON (Fruit a) where
toJSON = genericToJSON options
-- both apples and oranges are omitted if Nothing
instance ToJSON a => ToJSON (Fruit (Maybe a)) where
toJSON = genericToJSON options
eitherDecode :: FromJSON a => ByteString -> Either String a #
Like decode but returns an error message when decoding fails.
genericParseJSON :: (Generic a, GFromJSON Zero (Rep a)) => Options -> Value -> Parser a #
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.
Default encoding Options:
Options{fieldLabelModifier= id ,constructorTagModifier= id ,allNullaryToStringTag= True ,omitNothingFields= False ,sumEncoding=defaultTaggedObject,unwrapUnaryRecords= False ,tagSingleConstructors= False ,rejectUnknownFields= False }
genericToJSON :: (Generic a, GToJSON' Value Zero (Rep a)) => Options -> a -> Value #
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.
fieldLabelModifier :: Options -> String -> String #
Function applied to field labels. Handy for removing common record prefixes for example.
fromList :: (Eq k, Hashable k) => [(k, v)] -> HashMap k v #
\(O(n)\) Construct a map with the supplied mappings. If the list contains duplicate mappings, the later mappings take precedence.
toList :: HashMap k v -> [(k, v)] #
\(O(n)\) Return a list of this map's elements. The list is produced lazily. The order of its elements is unspecified.
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) | |
encode :: ToJSON a => a -> ByteString #
Efficiently serialize a JSON value as a lazy ByteString.
This is implemented in terms of the ToJSON class's toEncoding method.
encodePretty :: ToJSON a => a -> ByteString #
parseEither :: (a -> Parser b) -> a -> Either String b #