| Copyright | (C) 2015 Oleg Grenrus |
|---|---|
| License | BSD3 |
| Maintainer | Oleg Grenrus <oleg.grenrus@iki.fi> |
| Safe Haskell | None |
| Language | Haskell2010 |
Data.Aeson.Compat
Description
Compatibility notices
decodeetc. work as inaeson >=0.9- but it is generalised to work in any
MonadThrow(that is extra) .:?works as inaeson ||=0.11.:!works as inaeson ||=0.11and as.:?did inaeson ==0.10.*- Orphan instances
FromJSONDayandFromJSONLocalTimeforaeson <0.10 Encodingrelated functionality is not added. It's present only withaeson >=0.10
Synopsis
- decode :: (FromJSON a, MonadThrow m) => ByteString -> m a
- decode' :: (FromJSON a, MonadThrow m) => ByteString -> m a
- newtype AesonException = AesonException String
- eitherDecode :: FromJSON a => ByteString -> Either String a
- eitherDecode' :: FromJSON a => ByteString -> Either String a
- encode :: ToJSON a => a -> ByteString
- decodeStrict :: (FromJSON a, MonadThrow m) => ByteString -> m a
- decodeStrict' :: (FromJSON a, MonadThrow m) => ByteString -> m a
- eitherDecodeStrict :: FromJSON a => ByteString -> Either String a
- eitherDecodeStrict' :: FromJSON a => ByteString -> Either String a
- data Value
- type Encoding = Encoding' Value
- fromEncoding :: Encoding' tag -> Builder
- type Array = Vector Value
- type Object = KeyMap Value
- newtype DotNetTime = DotNetTime {}
- class FromJSON a where
- data Result a
- fromJSON :: FromJSON a => Value -> Result a
- class ToJSON a where
- toJSON :: a -> Value
- toEncoding :: a -> Encoding
- toJSONList :: [a] -> Value
- toEncodingList :: [a] -> Encoding
- class KeyValue kv where
- class GFromJSON arity (f :: Type -> Type)
- type GToJSON = GToJSON' Value
- type GToEncoding = GToJSON' Encoding
- genericToJSON :: (Generic a, GToJSON' Value Zero (Rep a)) => Options -> a -> Value
- genericToEncoding :: (Generic a, GToJSON' Encoding Zero (Rep a)) => Options -> a -> Encoding
- genericParseJSON :: (Generic a, GFromJSON Zero (Rep a)) => Options -> Value -> Parser a
- defaultOptions :: Options
- withObject :: String -> (Object -> Parser a) -> Value -> Parser a
- withText :: String -> (Text -> Parser a) -> Value -> Parser a
- withArray :: String -> (Array -> Parser a) -> Value -> Parser a
- withNumber :: String -> (Number -> 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
- data Series
- pairs :: Series -> Encoding
- foldable :: (Foldable t, ToJSON a) => t a -> Encoding
- (.:) :: FromJSON a => Object -> Text -> Parser a
- (.:?) :: FromJSON a => Object -> Text -> Parser (Maybe a)
- (.:!) :: FromJSON a => Object -> Text -> Parser (Maybe a)
- (.!=) :: Parser (Maybe a) -> a -> Parser a
- object :: [Pair] -> Value
- json :: Parser Value
- json' :: Parser Value
- value :: Parser Value
- value' :: Parser Value
- data Parser a
Encoding and decoding
Direct encoding
decode :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like original decode but in arbitrary MonadThrow.
Parse a top-level JSON value, i.e. also strings, numbers etc.
decode' :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like original decode' but in arbitrary MonadThrow.
newtype AesonException Source #
Exception thrown by decode - family of functions in this module.
Constructors
| AesonException String |
Instances
| Show AesonException Source # | |
Defined in Data.Aeson.Compat Methods showsPrec :: Int -> AesonException -> ShowS # show :: AesonException -> String # showList :: [AesonException] -> ShowS # | |
| Exception AesonException Source # | |
Defined in Data.Aeson.Compat Methods toException :: AesonException -> SomeException # | |
eitherDecode :: FromJSON a => ByteString -> Either String a #
Like decode but returns an error message when decoding fails.
eitherDecode' :: FromJSON a => ByteString -> Either String a #
Like decode' but returns an error message when decoding fails.
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.
Variants for strict bytestrings
decodeStrict :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like original decodeStrict but in arbitrary MonadThrow.
decodeStrict' :: (FromJSON a, MonadThrow m) => ByteString -> m a Source #
Like original decodeStrict' but in arbitrary MonadThrow.
eitherDecodeStrict :: FromJSON a => ByteString -> Either String a #
Like decodeStrict but returns an error message when decoding fails.
eitherDecodeStrict' :: FromJSON a => ByteString -> Either String a #
Like decodeStrict' but returns an error message when decoding fails.
Core JSON types
A JSON value represented as a Haskell value.
Instances
| Eq 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 # | |
| Ord Value | The ordering is total, consistent with Since: aeson-1.5.2.0 |
| Read Value | |
| Show Value | Since version 1.5.6.0 version object values are printed in lexicographic key order
|
| IsString Value | |
Defined in Data.Aeson.Types.Internal Methods fromString :: String -> Value # | |
| Generic Value | |
| Hashable Value | |
Defined in Data.Aeson.Types.Internal | |
| ToJSON Value | |
Defined in Data.Aeson.Types.ToJSON | |
| KeyValue Object | Constructs a singleton |
| KeyValue Pair | |
| FromJSON Value | |
| NFData Value | |
Defined in Data.Aeson.Types.Internal | |
| FromString Encoding | |
Defined in Data.Aeson.Types.ToJSON Methods fromString :: String -> Encoding | |
| FromString Value | |
Defined in Data.Aeson.Types.ToJSON Methods fromString :: String -> Value | |
| Lift Value | Since: aeson-0.11.0.0 |
| GToJSON' Encoding arity (U1 :: Type -> Type) | |
| GToJSON' Value arity (V1 :: Type -> Type) | |
| GToJSON' Value arity (U1 :: Type -> Type) | |
| ToJSON1 f => GToJSON' Encoding One (Rec1 f) | |
| ToJSON1 f => GToJSON' Value One (Rec1 f) | |
| ToJSON a => GToJSON' Encoding arity (K1 i a :: Type -> Type) | |
| (EncodeProduct arity a, EncodeProduct arity b) => GToJSON' Encoding arity (a :*: b) | |
| ToJSON a => GToJSON' Value arity (K1 i a :: Type -> Type) | |
| (WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON' Value arity (a :*: b) | |
| (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 | |
| (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 | |
| type Rep Value | |
Defined in Data.Aeson.Types.Internal type Rep Value = D1 ('MetaData "Value" "Data.Aeson.Types.Internal" "aeson-2.0.0.0-F54dplBS5yq6DxV4Jkg3Jx" '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)))) | |
fromEncoding :: Encoding' tag -> Builder #
Acquire the underlying bytestring builder.
Convenience types
newtype DotNetTime #
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
Type conversion
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
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
The result of running a Parser.
Instances
| Monad Result | |
| Functor Result | |
| MonadFail Result | |
Defined in Data.Aeson.Types.Internal | |
| Applicative Result | |
| 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 | |
| MonadPlus Result | |
| Eq a => Eq (Result a) | |
| Show a => Show (Result a) | |
| Semigroup (Result a) | |
| Monoid (Result a) | |
| NFData a => NFData (Result a) | |
Defined in Data.Aeson.Types.Internal | |
fromJSON :: FromJSON a => Value -> Result a #
Convert a value from JSON, failing if the types do not match.
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
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:
- toEncoding is more efficient for the common case that the output of
toJSONis 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 key-value pair for encoding a JSON object.
Generic JSON classes and options
class GFromJSON arity (f :: Type -> Type) #
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 | |
| GFromJSON arity a => GFromJSON arity (M1 i c a) | |
Defined in Data.Aeson.Types.FromJSON | |
| (FromJSON1 f, GFromJSON One g) => GFromJSON One (f :.: g) | |
Defined in Data.Aeson.Types.FromJSON | |
type GToEncoding = GToJSON' Encoding #
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.
genericToEncoding :: (Generic a, GToJSON' Encoding Zero (Rep a)) => Options -> a -> Encoding #
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.
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 }
Inspecting Values
ValueswithObject :: String -> (Object -> Parser a) -> Value -> Parser a #
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"
withNumber :: String -> (Number -> Parser a) -> Value -> Parser a Source #
Deprecated: Use withScientific instead
withNumber expected f valuef to the Number when value
is a Number and fails using typeMismatch expected
withScientific :: String -> (Scientific -> Parser a) -> Value -> Parser a #
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 #
Decode a nested JSON-encoded string.
Constructors and accessors
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)(.:?) :: FromJSON a => Object -> Text -> 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 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.
This operator is consistent in aeson >=0.7 && <0.11
(.!=) :: Parser (Maybe a) -> a -> Parser a #
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"
Parsing
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.
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'.
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.