| Copyright | (c) 2011-2016 Bryan O'Sullivan (c) 2011 MailRank Inc. |
|---|---|
| License | BSD3 |
| Maintainer | Bryan O'Sullivan <bos@serpentine.com> |
| Stability | experimental |
| Portability | portable |
| Safe Haskell | Safe-Inferred |
| Language | Haskell2010 |
Data.Aeson.Types
Description
Types for working with JSON data.
Synopsis
- data Value
- data Key
- type Encoding = Encoding' Value
- unsafeToEncoding :: Builder -> Encoding' a
- fromEncoding :: Encoding' tag -> Builder
- data Series
- type Array = Vector Value
- emptyArray :: Value
- type Pair = (Key, Value)
- type Object = KeyMap Value
- emptyObject :: Value
- newtype DotNetTime = DotNetTime {}
- typeMismatch :: String -> Value -> Parser a
- unexpected :: Value -> Parser a
- data Parser a
- data Result a
- class FromJSON a where
- fromJSON :: FromJSON a => Value -> Result a
- parse :: (a -> Parser b) -> a -> Result b
- parseEither :: (a -> Parser b) -> a -> Either String b
- parseMaybe :: (a -> Parser b) -> a -> Maybe b
- parseFail :: String -> Parser a
- modifyFailure :: (String -> String) -> Parser a -> Parser a
- prependFailure :: String -> Parser a -> Parser a
- parserThrowError :: JSONPath -> String -> Parser a
- parserCatchError :: Parser a -> (JSONPath -> String -> Parser a) -> Parser a
- data IResult a
- ifromJSON :: FromJSON a => Value -> IResult a
- iparse :: (a -> Parser b) -> a -> IResult b
- iparseEither :: (a -> Parser b) -> a -> Either (JSONPath, String) b
- class ToJSON a where
- toJSON :: a -> Value
- toEncoding :: a -> Encoding
- toJSONList :: [a] -> Value
- toEncodingList :: [a] -> Encoding
- class KeyValue kv where
- class ToJSONKey a where
- toJSONKey :: ToJSONKeyFunction a
- toJSONKeyList :: ToJSONKeyFunction [a]
- data ToJSONKeyFunction a
- = ToJSONKeyText !(a -> Key) !(a -> Encoding' Key)
- | ToJSONKeyValue !(a -> Value) !(a -> Encoding)
- toJSONKeyText :: (a -> Text) -> ToJSONKeyFunction a
- toJSONKeyKey :: (a -> Key) -> ToJSONKeyFunction a
- contramapToJSONKeyFunction :: (b -> a) -> ToJSONKeyFunction a -> ToJSONKeyFunction b
- class FromJSONKey a where
- data FromJSONKeyFunction a where
- FromJSONKeyCoerce :: Coercible Text a => FromJSONKeyFunction a
- FromJSONKeyText :: !(Text -> a) -> FromJSONKeyFunction a
- FromJSONKeyTextParser :: !(Text -> Parser a) -> FromJSONKeyFunction a
- FromJSONKeyValue :: !(Value -> Parser a) -> FromJSONKeyFunction a
- fromJSONKeyCoerce :: Coercible Text a => FromJSONKeyFunction a
- coerceFromJSONKeyFunction :: Coercible a b => FromJSONKeyFunction a -> FromJSONKeyFunction b
- mapFromJSONKeyFunction :: (a -> b) -> FromJSONKeyFunction a -> FromJSONKeyFunction b
- class GetConName f => GToJSONKey f
- genericToJSONKey :: (Generic a, GToJSONKey (Rep a)) => JSONKeyOptions -> ToJSONKeyFunction a
- class (ConstructorNames f, SumFromString f) => GFromJSONKey f
- genericFromJSONKey :: forall a. (Generic a, GFromJSONKey (Rep a)) => JSONKeyOptions -> FromJSONKeyFunction a
- class FromJSON1 f where
- parseJSON1 :: (FromJSON1 f, FromJSON a) => Value -> Parser (f a)
- class FromJSON2 f where
- parseJSON2 :: (FromJSON2 f, FromJSON a, FromJSON b) => Value -> Parser (f a b)
- class ToJSON1 f 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
- toJSON1 :: (ToJSON1 f, ToJSON a) => f a -> Value
- toEncoding1 :: (ToJSON1 f, ToJSON a) => f a -> Encoding
- class ToJSON2 f 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
- toJSON2 :: (ToJSON2 f, ToJSON a, ToJSON b) => f a b -> Value
- toEncoding2 :: (ToJSON2 f, ToJSON a, ToJSON b) => f a b -> Encoding
- class GFromJSON arity f
- data FromArgs arity a
- type GToJSON = GToJSON' Value
- type GToEncoding = GToJSON' Encoding
- class GToJSON' enc arity f
- data ToArgs res arity a
- data Zero
- data One
- genericToJSON :: (Generic a, GToJSON' Value Zero (Rep a)) => Options -> a -> Value
- 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
- 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)
- 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
- pairs :: Series -> Encoding
- foldable :: (Foldable t, ToJSON a) => t a -> Encoding
- (.:) :: 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
- object :: [Pair] -> Value
- parseField :: FromJSON a => Object -> Key -> Parser a
- parseFieldMaybe :: FromJSON a => Object -> Key -> Parser (Maybe a)
- parseFieldMaybe' :: FromJSON a => Object -> Key -> Parser (Maybe a)
- explicitParseField :: (Value -> Parser a) -> Object -> Key -> Parser a
- explicitParseFieldMaybe :: (Value -> Parser a) -> Object -> Key -> Parser (Maybe a)
- explicitParseFieldMaybe' :: (Value -> Parser a) -> Object -> Key -> Parser (Maybe a)
- listEncoding :: (a -> Encoding) -> [a] -> Encoding
- listValue :: (a -> Value) -> [a] -> Value
- listParser :: (Value -> Parser a) -> Value -> Parser [a]
- data Options
- fieldLabelModifier :: Options -> String -> String
- constructorTagModifier :: Options -> String -> String
- allNullaryToStringTag :: Options -> Bool
- omitNothingFields :: Options -> Bool
- sumEncoding :: Options -> SumEncoding
- unwrapUnaryRecords :: Options -> Bool
- tagSingleConstructors :: Options -> Bool
- rejectUnknownFields :: Options -> Bool
- data SumEncoding
- camelTo :: Char -> String -> String
- camelTo2 :: Char -> String -> String
- defaultOptions :: Options
- defaultTaggedObject :: SumEncoding
- data JSONKeyOptions
- keyModifier :: JSONKeyOptions -> String -> String
- defaultJSONKeyOptions :: JSONKeyOptions
- (<?>) :: Parser a -> JSONPathElement -> Parser a
- type JSONPath = [JSONPathElement]
- data JSONPathElement
- formatPath :: JSONPath -> String
- formatRelativePath :: JSONPath -> String
- formatError :: JSONPath -> String -> String
Core JSON types
A JSON value represented as a Haskell value.
Instances
| Arbitrary Value Source # | Since: 2.0.3.0 |
| CoArbitrary Value Source # | Since: 2.0.3.0 |
Defined in Data.Aeson.Types.Internal | |
| Function Value Source # | Since: 2.0.3.0 |
| FromJSON Value Source # | |
| ToJSON Value Source # | |
| Data Value Source # | |
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 Source # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Value Source # toConstr :: Value -> Constr Source # dataTypeOf :: Value -> DataType Source # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Value) Source # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Value) Source # gmapT :: (forall b. Data b => b -> b) -> Value -> Value Source # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r Source # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r Source # gmapQ :: (forall d. Data d => d -> u) -> Value -> [u] Source # gmapQi :: Int -> (forall d. Data d => d -> u) -> Value -> u Source # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Value -> m Value Source # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value Source # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value Source # | |
| IsString Value Source # | |
Defined in Data.Aeson.Types.Internal Methods fromString :: String -> Value Source # | |
| Generic Value Source # | |
| Read Value Source # | |
| Show Value Source # | Since version 1.5.6.0 version object values are printed in lexicographic key order
|
| NFData Value Source # | |
Defined in Data.Aeson.Types.Internal | |
| Eq Value Source # | |
| Ord Value Source # | The ordering is total, consistent with Since: 1.5.2.0 |
Defined in Data.Aeson.Types.Internal | |
| Hashable Value Source # | |
| Lift Value Source # | Since: 0.11.0.0 |
| GToJSON' Encoding arity (U1 :: Type -> Type) Source # | |
| GToJSON' Encoding arity (V1 :: Type -> Type) Source # | |
| GToJSON' Value arity (U1 :: Type -> Type) Source # | |
| GToJSON' Value arity (V1 :: Type -> Type) Source # | |
| ToJSON1 f => GToJSON' Encoding One (Rec1 f) Source # | |
| ToJSON1 f => GToJSON' Value One (Rec1 f) Source # | |
| (EncodeProduct arity a, EncodeProduct arity b) => GToJSON' Encoding arity (a :*: b) Source # | |
| ToJSON a => GToJSON' Encoding arity (K1 i a :: Type -> Type) Source # | |
| (WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON' Value arity (a :*: b) Source # | |
| ToJSON a => GToJSON' Value arity (K1 i a :: Type -> Type) Source # | |
| (ToJSON1 f, GToJSON' Encoding One g) => GToJSON' Encoding One (f :.: g) Source # | |
| (ToJSON1 f, GToJSON' Value One g) => GToJSON' Value One (f :.: g) Source # | |
| type Rep Value Source # | |
Defined in Data.Aeson.Types.Internal type Rep Value = D1 ('MetaData "Value" "Data.Aeson.Types.Internal" "aeson-2.1.2.1-1YB20WAhI7FDBnxJnrTmE5" '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)))) | |
Instances
unsafeToEncoding :: Builder -> Encoding' a Source #
Make Encoding from Builder.
Use with care! You have to make sure that the passed Builder is a valid JSON Encoding!
fromEncoding :: Encoding' tag -> Builder Source #
Acquire the underlying bytestring builder.
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)emptyArray :: Value Source #
The empty array.
emptyObject :: Value Source #
The empty object.
Convenience types and functions
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
Arguments
| :: String | The name of the JSON type being parsed
( |
| -> Value | The actual value encountered. |
| -> Parser a |
Fail parsing due to a type mismatch, with a descriptive message.
The following wrappers should generally be preferred:
withObject, withArray, withText, withBool.
Error message example
typeMismatch "Object" (String "oops") -- Error: "expected Object, but encountered String"
unexpected :: Value -> Parser a Source #
Fail parsing due to a type mismatch, when the expected types are implicit.
Error message example
unexpected (String "oops") -- Error: "unexpected String"
Type conversion
Parsing
A JSON parser. N.B. This might not fit your usual understanding of
"parser". Instead you might like to think of Parser as a "parse result",
i.e. a parser to which the input has already been applied.
The result of running a Parser.
Instances
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<$>v.:"x"<*>v.:"y"
Instead of manually writing your FromJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
parseJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericFromJSON instance for your datatype without giving
a definition for parseJSON.
For example, the previous example can be simplified to just:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance FromJSON Coord
or using the DerivingVia extension
deriving viaGenericallyCoord instanceFromJSONCoord
The default implementation will be equivalent to
parseJSON = ; if you need different
options, you can customize the generic decoding by defining:genericParseJSON defaultOptions
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceFromJSONCoord whereparseJSON=genericParseJSONcustomOptions
Minimal complete definition
Nothing
Instances
fromJSON :: FromJSON a => Value -> Result a Source #
Convert a value from JSON, failing if the types do not match.
Parser error handling
modifyFailure :: (String -> String) -> Parser a -> Parser a Source #
If the inner Parser failed, modify the failure message using the
provided function. This allows you to create more descriptive error messages.
For example:
parseJSON (Object o) = modifyFailure
("Parsing of the Foo value failed: " ++)
(Foo <$> o .: "someField")Since 0.6.2.0
prependFailure :: String -> Parser a -> Parser a Source #
If the inner Parser failed, prepend the given string to the failure
message.
prependFailures =modifyFailure(s++)
parserThrowError :: JSONPath -> String -> Parser a Source #
Throw a parser error with an additional path.
Since: 1.2.1.0
parserCatchError :: Parser a -> (JSONPath -> String -> Parser a) -> Parser a Source #
A handler function to handle previous errors and return to normal execution.
Since: 1.2.1.0
Parsing with paths
The internal result of running a Parser.
Instances
ifromJSON :: FromJSON a => Value -> IResult a Source #
Convert a value from JSON, failing if the types do not match.
Encoding
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 KeyValue kv where Source #
A key-value pair for encoding a JSON object.
Instances
| KeyValue Series Source # | |
| value ~ Value => KeyValue (KeyMap value) Source # | Constructs a singleton |
| (key ~ Key, value ~ Value) => KeyValue (key, value) Source # | |
Keys for maps
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.
default toJSONKey :: ToJSON a => ToJSONKeyFunction a Source #
toJSONKeyList :: ToJSONKeyFunction [a] Source #
This is similar in spirit to the showsList method of Show.
It makes it possible to give Value keys special treatment
without using OverlappingInstances. End users should always
be able to use the default implementation of this method.
default toJSONKeyList :: ToJSON a => ToJSONKeyFunction [a] Source #
Instances
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 Source # | |
Defined in Data.Aeson.Types.ToJSON Methods contramap :: (a' -> a) -> ToJSONKeyFunction a -> ToJSONKeyFunction a' Source # (>$) :: b -> ToJSONKeyFunction b -> ToJSONKeyFunction a Source # | |
toJSONKeyText :: (a -> Text) -> ToJSONKeyFunction a Source #
Helper for creating textual keys.
instanceToJSONKeyMyKey wheretoJSONKey=toJSONKeyTextmyKeyToText where myKeyToText = Text.pack . show -- or showt from text-show
toJSONKeyKey :: (a -> Key) -> ToJSONKeyFunction a Source #
Since: 2.0.0.0
contramapToJSONKeyFunction :: (b -> a) -> ToJSONKeyFunction a -> ToJSONKeyFunction b Source #
Contravariant map, as ToJSONKeyFunction is a contravariant functor.
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.
default fromJSONKey :: FromJSON a => FromJSONKeyFunction a Source #
fromJSONKeyList :: FromJSONKeyFunction [a] Source #
This is similar in spirit to the readList method of Read.
It makes it possible to give Value keys special treatment
without using OverlappingInstances. End users should always
be able to use the default implementation of this method.
default fromJSONKeyList :: FromJSON a => FromJSONKeyFunction [a] Source #
Instances
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 Source # | Only law abiding up to interpretation |
Defined in Data.Aeson.Types.FromJSON Methods fmap :: (a -> b) -> FromJSONKeyFunction a -> FromJSONKeyFunction b Source # (<$) :: a -> FromJSONKeyFunction b -> FromJSONKeyFunction a Source # | |
fromJSONKeyCoerce :: Coercible Text a => FromJSONKeyFunction a Source #
Construct FromJSONKeyFunction for types coercible from Text. This
conversion is still unsafe, as Hashable and Eq instances of a should be
compatible with Text i.e. hash values should be equal for wrapped values as well.
This property will always be maintained if the Hashable and Eq instances
are derived with generalized newtype deriving.
compatible with Text i.e. hash values be equal for wrapped values as well.
On pre GHC 7.8 this is unconstrained function.
coerceFromJSONKeyFunction :: Coercible a b => FromJSONKeyFunction a -> FromJSONKeyFunction b Source #
Semantically the same as coerceFromJSONKeyFunction = fmap coerce = coerce.
See note on fromJSONKeyCoerce.
mapFromJSONKeyFunction :: (a -> b) -> FromJSONKeyFunction a -> FromJSONKeyFunction b Source #
Same as fmap. Provided for the consistency with ToJSONKeyFunction.
Generic keys
class GetConName f => GToJSONKey f Source #
Instances
| GetConName f => GToJSONKey (f :: k -> Type) Source # | |
Defined in Data.Aeson.Types.ToJSON | |
genericToJSONKey :: (Generic a, GToJSONKey (Rep a)) => JSONKeyOptions -> ToJSONKeyFunction a Source #
class (ConstructorNames f, SumFromString f) => GFromJSONKey f Source #
Instances
| (ConstructorNames f, SumFromString f) => GFromJSONKey f Source # | |
Defined in Data.Aeson.Types.FromJSON | |
genericFromJSONKey :: forall a. (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
Liftings to unary and binary type constructors
class FromJSON1 f 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 #
default liftParseJSON :: (Generic1 f, GFromJSON One (Rep1 f)) => (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser (f a) Source #
liftParseJSONList :: (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser [f a] Source #
Instances
parseJSON1 :: (FromJSON1 f, FromJSON a) => Value -> Parser (f a) Source #
Lift the standard parseJSON function through the type constructor.
class FromJSON2 f 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
parseJSON2 :: (FromJSON2 f, FromJSON a, FromJSON b) => Value -> Parser (f a b) Source #
Lift the standard parseJSON function through the type constructor.
class ToJSON1 f 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 #
default liftToJSON :: (Generic1 f, GToJSON' Value One (Rep1 f)) => (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 #
default liftToEncoding :: (Generic1 f, GToJSON' Encoding One (Rep1 f)) => (a -> Encoding) -> ([a] -> Encoding) -> f a -> Encoding Source #
liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [f a] -> Encoding Source #
Instances
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.
class ToJSON2 f 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 Source # | |
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 Source # | Since: 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 Source # | Since: 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 Source # | Since: 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 Source # | Since: 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 (,) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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) Source # | |
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 # | |
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.
Generic JSON classes
class GFromJSON arity f Source #
Class of generic representation types that can be converted from JSON.
Minimal complete definition
gParseJSON
Instances
| GFromJSON One Par1 Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| GFromJSON arity (V1 :: Type -> Type) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| FromJSON1 f => GFromJSON One (Rec1 f) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| (GFromJSON' arity a, Datatype d) => GFromJSON arity (D1 d a) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| FromJSON a => GFromJSON arity (K1 i a :: Type -> Type) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| (FromJSON1 f, GFromJSON One g) => GFromJSON One (f :.: g) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| GFromJSON arity a => GFromJSON arity (M1 i c a) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
type GToEncoding = GToJSON' Encoding Source #
class GToJSON' enc arity f Source #
Class of generic representation types that can be converted to JSON.
Minimal complete definition
gToJSON
Instances
| GToJSON' enc One Par1 Source # | |
| GToJSON' Encoding arity (U1 :: Type -> Type) Source # | |
| GToJSON' Encoding arity (V1 :: Type -> Type) Source # | |
| GToJSON' Value arity (U1 :: Type -> Type) Source # | |
| GToJSON' Value arity (V1 :: Type -> Type) Source # | |
| ToJSON1 f => GToJSON' Encoding One (Rec1 f) Source # | |
| ToJSON1 f => GToJSON' Value One (Rec1 f) Source # | |
| (EncodeProduct arity a, EncodeProduct arity b) => GToJSON' Encoding arity (a :*: b) Source # | |
| ToJSON a => GToJSON' Encoding arity (K1 i a :: Type -> Type) Source # | |
| (WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON' Value arity (a :*: b) Source # | |
| ToJSON a => GToJSON' Value arity (K1 i a :: Type -> Type) Source # | |
| (AllNullary (a :+: b) allNullary, SumToJSON enc arity (a :+: b) allNullary) => GToJSON' enc arity (a :+: b) Source # | |
Defined in Data.Aeson.Types.ToJSON | |
| ConsToJSON enc arity a => GToJSON' enc arity (C1 c a) Source # | |
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)) Source # | |
| (ToJSON1 f, GToJSON' Encoding One g) => GToJSON' Encoding One (f :.: g) Source # | |
| (ToJSON1 f, GToJSON' Value One g) => GToJSON' Value One (f :.: g) Source # | |
| GToJSON' enc arity a => GToJSON' enc arity (M1 i c a) Source # | |
Defined in Data.Aeson.Types.ToJSON | |
A type-level indicator that ToJSON1 or FromJSON1 is being derived generically.
Instances
| GFromJSON One Par1 Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| GToJSON' enc One Par1 Source # | |
| ToJSON1 f => GToJSON' Encoding One (Rec1 f) Source # | |
| ToJSON1 f => GToJSON' Value One (Rec1 f) Source # | |
| (ToJSON1 f, GToJSON' Encoding One g) => GToJSON' Encoding One (f :.: g) Source # | |
| (ToJSON1 f, GToJSON' Value One g) => GToJSON' Value One (f :.: g) Source # | |
| FromJSON1 f => GFromJSON One (Rec1 f) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
| (FromJSON1 f, GFromJSON One g) => GFromJSON One (f :.: g) Source # | |
Defined in Data.Aeson.Types.FromJSON | |
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.
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.
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.
Inspecting Values
ValueswithObject :: 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"
parseFieldMaybe' :: FromJSON a => Object -> Key -> Parser (Maybe a) Source #
Function variant of .:!.
explicitParseField :: (Value -> Parser a) -> Object -> Key -> Parser a Source #
Variant of .: with explicit parser function.
E.g. explicitParseField parseJSON1 :: (FromJSON1 f, FromJSON a) -> Object -> Text -> Parser (f a)
explicitParseFieldMaybe :: (Value -> Parser a) -> Object -> Key -> Parser (Maybe a) Source #
Variant of .:? with explicit parser function.
explicitParseFieldMaybe' :: (Value -> Parser a) -> Object -> Key -> Parser (Maybe a) Source #
Variant of .:! with explicit parser function.
listEncoding :: (a -> Encoding) -> [a] -> Encoding Source #
Helper function to use with liftToEncoding.
Useful when writing own ToJSON1 instances.
newtype F a = F [a] -- This instance encodesValueas an array of chars instanceToJSON1F whereliftToJSONtj _ (F xs) =liftToJSONtj (listValuetj) xsliftToEncodingte _ (F xs) =liftToEncodingte (listEncodingte) xs instanceFromJSON1F whereliftParseJSONp _ v = F <$>liftParseJSONp (listParserp) v
listValue :: (a -> Value) -> [a] -> Value Source #
Helper function to use with liftToJSON, see listEncoding.
listParser :: (Value -> Parser a) -> Value -> Parser [a] Source #
Helper function to use with liftParseJSON. See listEncoding.
Generic and TH encoding configuration
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.
Options fields
The functions here are in fact record fields of the Options type.
fieldLabelModifier :: Options -> String -> String Source #
Function applied to field labels. Handy for removing common record prefixes for example.
constructorTagModifier :: Options -> String -> String Source #
Function applied to constructor tags which could be handy for lower-casing them for example.
allNullaryToStringTag :: Options -> Bool Source #
If True the constructors of a datatype, with all
nullary constructors, will be encoded to just a string with
the constructor tag. If False the encoding will always
follow the sumEncoding.
omitNothingFields :: Options -> Bool Source #
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
sumEncoding :: Options -> SumEncoding Source #
Specifies how to encode constructors of a sum datatype.
unwrapUnaryRecords :: Options -> Bool Source #
Hide the field name when a record constructor has only one field, like a newtype.
tagSingleConstructors :: Options -> Bool Source #
Encode types with a single constructor as sums,
so that allNullaryToStringTag and sumEncoding apply.
rejectUnknownFields :: Options -> Bool Source #
Applies only to FromJSON instances. If a field appears in
the parsed object map, but does not appear in the target object, parsing
will fail, with an error message indicating which fields were unknown.
Options utilities
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 Source # | |
Defined in Data.Aeson.Types.Internal | |
| Eq SumEncoding Source # | |
Defined in Data.Aeson.Types.Internal Methods (==) :: SumEncoding -> SumEncoding -> Bool Source # (/=) :: SumEncoding -> SumEncoding -> Bool Source # | |
camelTo :: Char -> String -> String Source #
Deprecated: Use camelTo2 for better results
Converts from CamelCase to another lower case, interspersing
the character between all capital letters and their previous
entries, except those capital letters that appear together,
like API.
For use by Aeson template haskell calls.
camelTo '_' 'CamelCaseAPI' == "camel_case_api"
camelTo2 :: Char -> String -> String Source #
Better version of camelTo. Example where it works better:
camelTo '_' "CamelAPICase" == "camel_apicase" camelTo2 '_' "CamelAPICase" == "camel_api_case"
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" }
Options for object keys
data JSONKeyOptions Source #
Options for encoding keys with genericFromJSONKey and
genericToJSONKey.
keyModifier :: JSONKeyOptions -> String -> String Source #
Function applied to keys. Its result is what goes into the encoded
Value.
Example
The following instances encode the constructor Bar to lower-case keys
"bar".
data Foo = Bar derivingGenericopts ::JSONKeyOptionsopts =defaultJSONKeyOptions{keyModifier=toLower} instanceToJSONKeyFoo wheretoJSONKey=genericToJSONKeyopts instanceFromJSONKeyFoo wherefromJSONKey=genericFromJSONKeyopts
defaultJSONKeyOptions :: JSONKeyOptions Source #
Default JSONKeyOptions:
defaultJSONKeyOptions =JSONKeyOptions{keyModifier=id}
Parsing context
(<?>) :: 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
type JSONPath = [JSONPathElement] Source #
data JSONPathElement Source #
Elements of a JSON path used to describe the location of an error.
Constructors
| Key Key | JSON path element of a key into an object, "object.key". |
| Index !Int | JSON path element of an index into an array, "array[index]". |
Instances
| Show JSONPathElement Source # | |
Defined in Data.Aeson.Types.Internal | |
| NFData JSONPathElement Source # | |
Defined in Data.Aeson.Types.Internal Methods rnf :: JSONPathElement -> () Source # | |
| Eq JSONPathElement Source # | |
Defined in Data.Aeson.Types.Internal Methods (==) :: JSONPathElement -> JSONPathElement -> Bool Source # (/=) :: JSONPathElement -> JSONPathElement -> Bool Source # | |
| Ord JSONPathElement Source # | |
Defined in Data.Aeson.Types.Internal Methods compare :: JSONPathElement -> JSONPathElement -> Ordering Source # (<) :: JSONPathElement -> JSONPathElement -> Bool Source # (<=) :: JSONPathElement -> JSONPathElement -> Bool Source # (>) :: JSONPathElement -> JSONPathElement -> Bool Source # (>=) :: JSONPathElement -> JSONPathElement -> Bool Source # max :: JSONPathElement -> JSONPathElement -> JSONPathElement Source # min :: JSONPathElement -> JSONPathElement -> JSONPathElement Source # | |
formatPath :: JSONPath -> String Source #
formatRelativePath :: JSONPath -> String Source #