yesod-core-1.6.24.2: Creation of type-safe, RESTful web applications.
Safe HaskellSafe-Inferred
LanguageHaskell2010

Yesod.Core.Json

Synopsis

Convert from a JSON value

defaultLayoutJson Source #

Arguments

:: (Yesod site, ToJSON a) 
=> WidgetFor site ()

HTML

-> HandlerFor site a

JSON

-> HandlerFor site TypedContent 

Provide both an HTML and JSON representation for a piece of data, using the default layout for the HTML output (defaultLayout).

Since: 0.3.0

jsonToRepJson :: (Monad m, ToJSON a) => a -> m Value Source #

Deprecated: Use returnJson instead

Wraps a data type in a RepJson. The data type must support conversion to JSON via ToJSON.

Since: 0.3.0

returnJson :: (Monad m, ToJSON a) => a -> m Value Source #

Convert a value to a JSON representation via aeson's toJSON function.

Since: 1.2.1

returnJsonEncoding :: (Monad m, ToJSON a) => a -> m Encoding Source #

Convert a value to a JSON representation via aeson's toEncoding function.

Since: 1.4.21

provideJson :: (Monad m, ToJSON a) => a -> Writer (Endo [ProvidedRep m]) () Source #

Provide a JSON representation for usage with selectReps, using aeson's toJSON (aeson >= 0.11: toEncoding) function to perform the conversion.

Since: 1.2.1

Convert to a JSON value

parseCheckJsonBody :: (MonadHandler m, FromJSON a) => m (Result a) Source #

Parse the request body to a data type as a JSON value. The data type must support conversion from JSON via FromJSON. If you want the raw JSON value, just ask for a Result Value.

The MIME type must indicate JSON content. Requiring a JSON content-type helps secure your site against CSRF attacks (browsers will perform POST requests for form and text/plain content-types without doing a CORS check, and those content-types can easily contain valid JSON).

Note that this function will consume the request body. As such, calling it twice will result in a parse error on the second call, since the request body will no longer be available.

Since: 0.3.0

parseInsecureJsonBody :: (MonadHandler m, FromJSON a) => m (Result a) Source #

Same as parseCheckJsonBody, but does not check that the mime type indicates JSON content.

Note: This function is vulnerable to CSRF attacks.

Since: 1.6.11

requireCheckJsonBody :: (MonadHandler m, FromJSON a) => m a Source #

Same as parseCheckJsonBody, but return an invalid args response on a parse error.

requireInsecureJsonBody :: (MonadHandler m, FromJSON a) => m a Source #

Same as parseInsecureJsonBody, but return an invalid args response on a parse error.

Since: 1.6.11

Deprecated JSON conversion

parseJsonBody :: (MonadHandler m, FromJSON a) => m (Result a) Source #

Deprecated: Use parseCheckJsonBody or parseInsecureJsonBody instead

Same as parseInsecureJsonBody

Since: 0.3.0

parseJsonBody_ :: (MonadHandler m, FromJSON a) => m a Source #

Deprecated: Use requireCheckJsonBody or requireInsecureJsonBody instead

Same as parseInsecureJsonBody, but return an invalid args response on a parse error.

requireJsonBody :: (MonadHandler m, FromJSON a) => m a Source #

Deprecated: Use requireCheckJsonBody or requireInsecureJsonBody instead

Same as parseInsecureJsonBody, but return an invalid args response on a parse error.

Produce JSON values

data Value #

A JSON value represented as a Haskell value.

Instances

Instances details
Arbitrary Value

Since: aeson-2.0.3.0

Instance details

Defined in Data.Aeson.Types.Internal

Methods

arbitrary :: Gen Value #

shrink :: Value -> [Value] #

CoArbitrary Value

Since: aeson-2.0.3.0

Instance details

Defined in Data.Aeson.Types.Internal

Methods

coarbitrary :: Value -> Gen b -> Gen b #

Function Value

Since: aeson-2.0.3.0

Instance details

Defined in Data.Aeson.Types.Internal

Methods

function :: (Value -> b) -> Value :-> b #

FromJSON Value 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromString Encoding 
Instance details

Defined in Data.Aeson.Types.ToJSON

FromString Value 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

fromString :: String -> Value

ToJSON Value 
Instance details

Defined in Data.Aeson.Types.ToJSON

Data Value 
Instance details

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 #

toConstr :: Value -> Constr #

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 
Instance details

Defined in Data.Aeson.Types.Internal

Methods

fromString :: String -> Value #

Generic Value 
Instance details

Defined in Data.Aeson.Types.Internal

Associated Types

type Rep Value :: Type -> Type #

Methods

from :: Value -> Rep Value x #

to :: Rep Value x -> Value #

Read Value 
Instance details

Defined in Data.Aeson.Types.Internal

Show Value

Since version 1.5.6.0 version object values are printed in lexicographic key order

>>> toJSON $ H.fromList [("a", True), ("z", False)]
Object (fromList [("a",Bool True),("z",Bool False)])
>>> toJSON $ H.fromList [("z", False), ("a", True)]
Object (fromList [("a",Bool True),("z",Bool False)])
Instance details

Defined in Data.Aeson.Types.Internal

Methods

showsPrec :: Int -> Value -> ShowS #

show :: Value -> String #

showList :: [Value] -> ShowS #

NFData Value 
Instance details

Defined in Data.Aeson.Types.Internal

Methods

rnf :: Value -> () #

Eq Value 
Instance details

Defined in Data.Aeson.Types.Internal

Methods

(==) :: Value -> Value -> Bool #

(/=) :: Value -> Value -> Bool #

Ord Value

The ordering is total, consistent with Eq instance. However, nothing else about the ordering is specified, and it may change from environment to environment and version to version of either this package or its dependencies (hashable and 'unordered-containers').

Since: aeson-1.5.2.0

Instance details

Defined in Data.Aeson.Types.Internal

Methods

compare :: Value -> Value -> Ordering #

(<) :: Value -> Value -> Bool #

(<=) :: Value -> Value -> Bool #

(>) :: Value -> Value -> Bool #

(>=) :: Value -> Value -> Bool #

max :: Value -> Value -> Value #

min :: Value -> Value -> Value #

Hashable Value 
Instance details

Defined in Data.Aeson.Types.Internal

Methods

hashWithSalt :: Int -> Value -> Int #

hash :: Value -> Int #

ToJavascript Value 
Instance details

Defined in Text.Julius

HasContentType Encoding Source # 
Instance details

Defined in Yesod.Core.Content

HasContentType Value Source # 
Instance details

Defined in Yesod.Core.Content

ToContent Encoding Source # 
Instance details

Defined in Yesod.Core.Content

ToContent Value Source # 
Instance details

Defined in Yesod.Core.Content

ToTypedContent Encoding Source # 
Instance details

Defined in Yesod.Core.Content

ToTypedContent Value Source # 
Instance details

Defined in Yesod.Core.Content

Lift Value

Since: aeson-0.11.0.0

Instance details

Defined in Data.Aeson.Types.Internal

Methods

lift :: Quote m => Value -> m Exp #

liftTyped :: forall (m :: Type -> Type). Quote m => Value -> Code m Value #

(GToJSON' Encoding arity a, ConsToJSON Encoding arity a, Constructor c) => SumToJSON' TwoElemArray Encoding arity (C1 c a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

sumToJSON' :: Options -> ToArgs Encoding arity a0 -> C1 c a a0 -> Tagged TwoElemArray Encoding

(GToJSON' Value arity a, ConsToJSON Value arity a, Constructor c) => SumToJSON' TwoElemArray Value arity (C1 c a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

sumToJSON' :: Options -> ToArgs Value arity a0 -> C1 c a a0 -> Tagged TwoElemArray Value

GToJSON' Encoding arity (U1 :: TYPE LiftedRep -> Type) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Encoding arity a -> U1 a -> Encoding

GToJSON' Encoding arity (V1 :: TYPE LiftedRep -> Type) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Encoding arity a -> V1 a -> Encoding

GToJSON' Value arity (U1 :: TYPE LiftedRep -> Type) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Value arity a -> U1 a -> Value

GToJSON' Value arity (V1 :: TYPE LiftedRep -> Type) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Value arity a -> V1 a -> Value

ToJSON1 f => GToJSON' Encoding One (Rec1 f) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Encoding One a -> Rec1 f a -> Encoding

ToJSON1 f => GToJSON' Value One (Rec1 f) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Value One a -> Rec1 f a -> Value

(EncodeProduct arity a, EncodeProduct arity b) => GToJSON' Encoding arity (a :*: b) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Encoding arity a0 -> (a :*: b) a0 -> Encoding

ToJSON a => GToJSON' Encoding arity (K1 i a :: TYPE LiftedRep -> Type) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Encoding arity a0 -> K1 i a a0 -> Encoding

(WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON' Value arity (a :*: b) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Value arity a0 -> (a :*: b) a0 -> Value

ToJSON a => GToJSON' Value arity (K1 i a :: TYPE LiftedRep -> Type) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Value arity a0 -> K1 i a a0 -> Value

(ToJSON1 f, GToJSON' Encoding One g) => GToJSON' Encoding One (f :.: g) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Encoding One a -> (f :.: g) a -> Encoding

(ToJSON1 f, GToJSON' Value One g) => GToJSON' Value One (f :.: g) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

gToJSON :: Options -> ToArgs Value One a -> (f :.: g) a -> Value

FromPairs Value (DList Pair) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

fromPairs :: DList Pair -> Value

v ~ Value => KeyValuePair v (DList Pair) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

pair :: Key -> v -> DList Pair

type Rep Value 
Instance details

Defined in Data.Aeson.Types.Internal

class ToJSON a where #

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 write Text literals.
{-# LANGUAGE OverloadedStrings #-}

data Coord = Coord { x :: Double, y :: Double }

instance ToJSON Coord where
  toJSON (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 Generic clause to your datatype and declare a ToJSON 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 via Generically Coord instance ToJSON Coord

If on the other hand you wish to customize the generic decoding, you have to implement both methods:

customOptions = defaultOptions
                { fieldLabelModifier = map toUpper
                }

instance ToJSON Coord where
    toJSON     = genericToJSON customOptions
    toEncoding = genericToEncoding customOptions

Previous versions of this library only had the toJSON method. Adding toEncoding had two reasons:

  1. toEncoding is more efficient for the common case that the output of toJSON is directly serialized to a ByteString. Further, expressing either method in terms of the other would be non-optimal.
  2. The choice of defaults allows a smooth transition for existing users: Existing instances that do not define toEncoding still compile and have the correct semantics. This is ensured by making the default implementation of toEncoding use toJSON. This produces correct results, but since it performs an intermediate conversion to a Value, it will be less efficient than directly emitting an Encoding. (this also means that specifying nothing more than instance ToJSON Coord would be sufficient as a generically decoding instance, but there probably exists no good reason to not specify toEncoding in new instances.)

Minimal complete definition

Nothing

Methods

toJSON :: a -> Value #

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.

instance ToJSON Coord where
    toEncoding = genericToEncoding defaultOptions

toJSONList :: [a] -> Value #

toEncodingList :: [a] -> Encoding #

Instances

Instances details
ToJSON Key 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON DotNetTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Value 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Number 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Version 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Void 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON CTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Int16 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Int32 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Int64 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Int8 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Word16 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Word32 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Word64 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Word8 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON IntSet 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Ordering 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Scientific 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Text 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Text 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON ShortText

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON CalendarDiffDays 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Day 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Month 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Quarter 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON QuarterOfYear 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON DayOfWeek 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON DiffTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON NominalDiffTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON SystemTime

Encoded as number

Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON UTCTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON CalendarDiffTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON LocalTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON TimeOfDay 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON ZonedTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON UUID 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Integer 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Natural 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON () 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: () -> Value #

toEncoding :: () -> Encoding #

toJSONList :: [()] -> Value #

toEncodingList :: [()] -> Encoding #

ToJSON Bool 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Char 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Double 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Float 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Int 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON Word 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON v => ToJSON (KeyMap v) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Identity a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (First a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Last a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (First a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Last a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Max a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Max a -> Value #

toEncoding :: Max a -> Encoding #

toJSONList :: [Max a] -> Value #

toEncodingList :: [Max a] -> Encoding #

ToJSON a => ToJSON (Min a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Min a -> Value #

toEncoding :: Min a -> Encoding #

toJSONList :: [Min a] -> Value #

toEncodingList :: [Min a] -> Encoding #

ToJSON a => ToJSON (WrappedMonoid a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Dual a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(ToJSON a, Integral a) => ToJSON (Ratio a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (IntMap a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Seq a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Seq a -> Value #

toEncoding :: Seq a -> Encoding #

toJSONList :: [Seq a] -> Value #

toEncodingList :: [Seq a] -> Encoding #

ToJSON a => ToJSON (Set a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Set a -> Value #

toEncoding :: Set a -> Encoding #

toJSONList :: [Set a] -> Value #

toEncodingList :: [Set a] -> Encoding #

ToJSON v => ToJSON (Tree v) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON1 f => ToJSON (Fix f)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Fix f -> Value #

toEncoding :: Fix f -> Encoding #

toJSONList :: [Fix f] -> Value #

toEncodingList :: [Fix f] -> Encoding #

(ToJSON1 f, Functor f) => ToJSON (Mu f)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Mu f -> Value #

toEncoding :: Mu f -> Encoding #

toJSONList :: [Mu f] -> Value #

toEncodingList :: [Mu f] -> Encoding #

(ToJSON1 f, Functor f) => ToJSON (Nu f)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Nu f -> Value #

toEncoding :: Nu f -> Encoding #

toJSONList :: [Nu f] -> Value #

toEncodingList :: [Nu f] -> Encoding #

ToJSON a => ToJSON (DNonEmpty a)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (DList a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(Generic a, GToJSON' Value Zero (Rep a), GToJSON' Encoding Zero (Rep a)) => ToJSON (Generically a)

Since: aeson-2.1.0.0

Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Array a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(Prim a, ToJSON a) => ToJSON (PrimArray a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (SmallArray a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Maybe a)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (HashSet a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(Prim a, ToJSON a) => ToJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(Storable a, ToJSON a) => ToJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(Vector Vector a, ToJSON a) => ToJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (NonEmpty a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (Maybe a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON a => ToJSON (a)

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a) -> Value #

toEncoding :: (a) -> Encoding #

toJSONList :: [(a)] -> Value #

toEncodingList :: [(a)] -> Encoding #

ToJSON a => ToJSON [a] 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: [a] -> Value #

toEncoding :: [a] -> Encoding #

toJSONList :: [[a]] -> Value #

toEncodingList :: [[a]] -> Encoding #

(ToJSON a, ToJSON b) => ToJSON (Either a b) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Either a b -> Value #

toEncoding :: Either a b -> Encoding #

toJSONList :: [Either a b] -> Value #

toEncodingList :: [Either a b] -> Encoding #

HasResolution a => ToJSON (Fixed a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSON (Proxy a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(ToJSON v, ToJSONKey k) => ToJSON (Map k v) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Map k v -> Value #

toEncoding :: Map k v -> Encoding #

toJSONList :: [Map k v] -> Value #

toEncodingList :: [Map k v] -> Encoding #

(ToJSON a, ToJSON b) => ToJSON (Either a b)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Either a b -> Value #

toEncoding :: Either a b -> Encoding #

toJSONList :: [Either a b] -> Value #

toEncodingList :: [Either a b] -> Encoding #

(ToJSON a, ToJSON b) => ToJSON (These a b)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: These a b -> Value #

toEncoding :: These a b -> Encoding #

toJSONList :: [These a b] -> Value #

toEncodingList :: [These a b] -> Encoding #

(ToJSON a, ToJSON b) => ToJSON (Pair a b)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Pair a b -> Value #

toEncoding :: Pair a b -> Encoding #

toJSONList :: [Pair a b] -> Value #

toEncodingList :: [Pair a b] -> Encoding #

(ToJSON a, ToJSON b) => ToJSON (These a b)

Since: aeson-1.5.1.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: These a b -> Value #

toEncoding :: These a b -> Encoding #

toJSONList :: [These a b] -> Value #

toEncodingList :: [These a b] -> Encoding #

(ToJSON v, ToJSONKey k) => ToJSON (HashMap k v) 
Instance details

Defined in Data.Aeson.Types.ToJSON

(ToJSON a, ToJSON b) => ToJSON (a, b) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b) -> Value #

toEncoding :: (a, b) -> Encoding #

toJSONList :: [(a, b)] -> Value #

toEncodingList :: [(a, b)] -> Encoding #

ToJSON a => ToJSON (Const a b) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Const a b -> Value #

toEncoding :: Const a b -> Encoding #

toJSONList :: [Const a b] -> Value #

toEncodingList :: [Const a b] -> Encoding #

ToJSON b => ToJSON (Tagged a b) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Tagged a b -> Value #

toEncoding :: Tagged a b -> Encoding #

toJSONList :: [Tagged a b] -> Value #

toEncodingList :: [Tagged a b] -> Encoding #

(ToJSON1 f, ToJSON1 g, ToJSON a) => ToJSON (These1 f g a)

Since: aeson-1.5.1.0

Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: These1 f g a -> Value #

toEncoding :: These1 f g a -> Encoding #

toJSONList :: [These1 f g a] -> Value #

toEncodingList :: [These1 f g a] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c) => ToJSON (a, b, c) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c) -> Value #

toEncoding :: (a, b, c) -> Encoding #

toJSONList :: [(a, b, c)] -> Value #

toEncodingList :: [(a, b, c)] -> Encoding #

(ToJSON1 f, ToJSON1 g, ToJSON a) => ToJSON (Product f g a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Product f g a -> Value #

toEncoding :: Product f g a -> Encoding #

toJSONList :: [Product f g a] -> Value #

toEncodingList :: [Product f g a] -> Encoding #

(ToJSON1 f, ToJSON1 g, ToJSON a) => ToJSON (Sum f g a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Sum f g a -> Value #

toEncoding :: Sum f g a -> Encoding #

toJSONList :: [Sum f g a] -> Value #

toEncodingList :: [Sum f g a] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d) => ToJSON (a, b, c, d) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d) -> Value #

toEncoding :: (a, b, c, d) -> Encoding #

toJSONList :: [(a, b, c, d)] -> Value #

toEncodingList :: [(a, b, c, d)] -> Encoding #

(ToJSON1 f, ToJSON1 g, ToJSON a) => ToJSON (Compose f g a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: Compose f g a -> Value #

toEncoding :: Compose f g a -> Encoding #

toJSONList :: [Compose f g a] -> Value #

toEncodingList :: [Compose f g a] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e) => ToJSON (a, b, c, d, e) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e) -> Value #

toEncoding :: (a, b, c, d, e) -> Encoding #

toJSONList :: [(a, b, c, d, e)] -> Value #

toEncodingList :: [(a, b, c, d, e)] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f) => ToJSON (a, b, c, d, e, f) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f) -> Value #

toEncoding :: (a, b, c, d, e, f) -> Encoding #

toJSONList :: [(a, b, c, d, e, f)] -> Value #

toEncodingList :: [(a, b, c, d, e, f)] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g) => ToJSON (a, b, c, d, e, f, g) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g) -> Value #

toEncoding :: (a, b, c, d, e, f, g) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g)] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h) => ToJSON (a, b, c, d, e, f, g, h) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h)] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i) => ToJSON (a, b, c, d, e, f, g, h, i) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h, i) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h, i) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h, i)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h, i)] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i, ToJSON j) => ToJSON (a, b, c, d, e, f, g, h, i, j) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h, i, j) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h, i, j) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h, i, j)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h, i, j)] -> Encoding #

(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g, ToJSON h, ToJSON i, ToJSON j, ToJSON k) => ToJSON (a, b, c, d, e, f, g, h, i, j, k) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h, i, j, k) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h, i, j, k) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h, i, j, k)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h, i, j, k)] -> Encoding #

(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 (a, b, c, d, e, f, g, h, i, j, k, l) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h, i, j, k, l) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h, i, j, k, l) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h, i, j, k, l)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h, i, j, k, l)] -> Encoding #

(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) => ToJSON (a, b, c, d, e, f, g, h, i, j, k, l, m) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m)] -> Encoding #

(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, ToJSON n) => ToJSON (a, b, c, d, e, f, g, h, i, j, k, l, m, n) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)] -> Encoding #

(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, ToJSON n, ToJSON o) => ToJSON (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

toJSON :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Value #

toEncoding :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Encoding #

toJSONList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)] -> Value #

toEncodingList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)] -> Encoding #

class FromJSON a where #

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:

  • fail yields a custom error message: it is the recommended way of reporting a failure;
  • empty (or mzero) is uninformative: use it when the error is meant to be caught by some (<|>);
  • typeMismatch can be used to report a failure when the encountered value is not of the expected JSON type; unexpected is 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 write Text literals.
{-# LANGUAGE OverloadedStrings #-}

data Coord = Coord { x :: Double, y :: Double }

instance FromJSON Coord where
    parseJSON (Object v) = Coord
        <$> v .: "x"
        <*> v .: "y"

    -- We do not expect a non-Object value here.
    -- We could use empty to fail, but typeMismatch
    -- gives a much more informative error message.
    parseJSON invalid    =
        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:

instance FromJSON Coord where
    parseJSON = 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 Generic clause to your datatype and declare a FromJSON 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 via Generically Coord instance FromJSON Coord

The default implementation will be equivalent to parseJSON = genericParseJSON defaultOptions; if you need different options, you can customize the generic decoding by defining:

customOptions = defaultOptions
                { fieldLabelModifier = map toUpper
                }

instance FromJSON Coord where
    parseJSON = genericParseJSON customOptions

Minimal complete definition

Nothing

Methods

parseJSON :: Value -> Parser a #

parseJSONList :: Value -> Parser [a] #

Instances

Instances details
FromJSON Key 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON DotNetTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Value 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Version 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Void 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON CTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Int16 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Int32 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Int64 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Int8 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Word16 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Word32 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Word64 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Word8 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON IntSet 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Ordering 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Scientific 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Text 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Text 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON ShortText

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON CalendarDiffDays 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Day 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Month 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Quarter 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON QuarterOfYear 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON DayOfWeek 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON DiffTime

This instance includes a bounds check to prevent maliciously large inputs to fill up the memory of the target system. You can newtype Scientific and provide your own instance using withScientific if you want to allow larger inputs.

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON NominalDiffTime

This instance includes a bounds check to prevent maliciously large inputs to fill up the memory of the target system. You can newtype Scientific and provide your own instance using withScientific if you want to allow larger inputs.

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON SystemTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON UTCTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON CalendarDiffTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON LocalTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON TimeOfDay 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON ZonedTime

Supported string formats:

YYYY-MM-DD HH:MM Z YYYY-MM-DD HH:MM:SS Z YYYY-MM-DD HH:MM:SS.SSS Z

The first space may instead be a T, and the second space is optional. The Z represents UTC. The Z may be replaced with a time zone offset of the form +0000 or -08:00, where the first two digits are hours, the : is optional and the second two digits (also optional) are minutes.

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON UUID 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Integer

This instance includes a bounds check to prevent maliciously large inputs to fill up the memory of the target system. You can newtype Scientific and provide your own instance using withScientific if you want to allow larger inputs.

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Natural 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON () 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser () #

parseJSONList :: Value -> Parser [()] #

FromJSON Bool 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Char 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Double 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Float 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Int 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON Word 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON v => FromJSON (KeyMap v)

Since: aeson-2.0.1.0

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Identity a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (First a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Last a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (First a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Last a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Max a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Max a) #

parseJSONList :: Value -> Parser [Max a] #

FromJSON a => FromJSON (Min a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Min a) #

parseJSONList :: Value -> Parser [Min a] #

FromJSON a => FromJSON (WrappedMonoid a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Dual a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(FromJSON a, Integral a) => FromJSON (Ratio a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (IntMap a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Seq a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Seq a) #

parseJSONList :: Value -> Parser [Seq a] #

(Ord a, FromJSON a) => FromJSON (Set a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Set a) #

parseJSONList :: Value -> Parser [Set a] #

FromJSON v => FromJSON (Tree v) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON1 f => FromJSON (Fix f)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Fix f) #

parseJSONList :: Value -> Parser [Fix f] #

(FromJSON1 f, Functor f) => FromJSON (Mu f)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Mu f) #

parseJSONList :: Value -> Parser [Mu f] #

(FromJSON1 f, Functor f) => FromJSON (Nu f)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Nu f) #

parseJSONList :: Value -> Parser [Nu f] #

FromJSON a => FromJSON (DNonEmpty a)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (DList a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(Generic a, GFromJSON Zero (Rep a)) => FromJSON (Generically a)

Since: aeson-2.1.0.0

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Array a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(Prim a, FromJSON a) => FromJSON (PrimArray a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (SmallArray a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Maybe a)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

(Eq a, Hashable a, FromJSON a) => FromJSON (HashSet a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(Prim a, FromJSON a) => FromJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(Storable a, FromJSON a) => FromJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(Vector Vector a, FromJSON a) => FromJSON (Vector a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (NonEmpty a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (Maybe a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (a)

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a) #

parseJSONList :: Value -> Parser [(a)] #

FromJSON a => FromJSON [a] 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser [a] #

parseJSONList :: Value -> Parser [[a]] #

(FromJSON a, FromJSON b) => FromJSON (Either a b) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Either a b) #

parseJSONList :: Value -> Parser [Either a b] #

HasResolution a => FromJSON (Fixed a)

This instance includes a bounds check to prevent maliciously large inputs to fill up the memory of the target system. You can newtype Scientific and provide your own instance using withScientific if you want to allow larger inputs.

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSON (Proxy a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(FromJSONKey k, Ord k, FromJSON v) => FromJSON (Map k v) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Map k v) #

parseJSONList :: Value -> Parser [Map k v] #

(FromJSON a, FromJSON b) => FromJSON (Either a b)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Either a b) #

parseJSONList :: Value -> Parser [Either a b] #

(FromJSON a, FromJSON b) => FromJSON (These a b)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (These a b) #

parseJSONList :: Value -> Parser [These a b] #

(FromJSON a, FromJSON b) => FromJSON (Pair a b)

Since: aeson-1.5.3.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Pair a b) #

parseJSONList :: Value -> Parser [Pair a b] #

(FromJSON a, FromJSON b) => FromJSON (These a b)

Since: aeson-1.5.1.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (These a b) #

parseJSONList :: Value -> Parser [These a b] #

(FromJSON v, FromJSONKey k, Eq k, Hashable k) => FromJSON (HashMap k v) 
Instance details

Defined in Data.Aeson.Types.FromJSON

(FromJSON a, FromJSON b) => FromJSON (a, b) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b) #

parseJSONList :: Value -> Parser [(a, b)] #

FromJSON a => FromJSON (Const a b) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Const a b) #

parseJSONList :: Value -> Parser [Const a b] #

FromJSON b => FromJSON (Tagged a b) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Tagged a b) #

parseJSONList :: Value -> Parser [Tagged a b] #

(FromJSON1 f, FromJSON1 g, FromJSON a) => FromJSON (These1 f g a)

Since: aeson-1.5.1.0

Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (These1 f g a) #

parseJSONList :: Value -> Parser [These1 f g a] #

(FromJSON a, FromJSON b, FromJSON c) => FromJSON (a, b, c) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c) #

parseJSONList :: Value -> Parser [(a, b, c)] #

(FromJSON1 f, FromJSON1 g, FromJSON a) => FromJSON (Product f g a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Product f g a) #

parseJSONList :: Value -> Parser [Product f g a] #

(FromJSON1 f, FromJSON1 g, FromJSON a) => FromJSON (Sum f g a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Sum f g a) #

parseJSONList :: Value -> Parser [Sum f g a] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d) => FromJSON (a, b, c, d) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d) #

parseJSONList :: Value -> Parser [(a, b, c, d)] #

(FromJSON1 f, FromJSON1 g, FromJSON a) => FromJSON (Compose f g a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (Compose f g a) #

parseJSONList :: Value -> Parser [Compose f g a] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e) => FromJSON (a, b, c, d, e) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e) #

parseJSONList :: Value -> Parser [(a, b, c, d, e)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f) => FromJSON (a, b, c, d, e, f) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g) => FromJSON (a, b, c, d, e, f, g) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h) => FromJSON (a, b, c, d, e, f, g, h) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i) => FromJSON (a, b, c, d, e, f, g, h, i) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h, i) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h, i)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j) => FromJSON (a, b, c, d, e, f, g, h, i, j) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h, i, j) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h, i, j)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k) => FromJSON (a, b, c, d, e, f, g, h, i, j, k) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h, i, j, k) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h, i, j, k)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h, i, j, k, l) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h, i, j, k, l)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l, FromJSON m) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l, m) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h, i, j, k, l, m) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h, i, j, k, l, m)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l, FromJSON m, FromJSON n) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l, m, n) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h, i, j, k, l, m, n) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)] #

(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l, FromJSON m, FromJSON n, FromJSON o) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

parseJSON :: Value -> Parser (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) #

parseJSONList :: Value -> Parser [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)] #

array :: ToJSON a => [a] -> Value Source #

Convert a list of values to an Value.

object :: [Pair] -> Value #

Create a Value from a list of name/value Pairs. If duplicate keys arise, later keys and their associated values win.

(.=) :: (KeyValue kv, ToJSON v) => Key -> v -> kv infixr 8 #

(.:) :: FromJSON a => Object -> Key -> Parser a #

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.

Convenience functions

jsonOrRedirect Source #

Arguments

:: (MonadHandler m, ToJSON a) 
=> Route (HandlerSite m)

Redirect target

-> a

Data to send via JSON

-> m Value 

jsonOrRedirect simplifies the scenario where a POST handler sends a different response based on Accept headers:

  1. 200 with JSON data if the client prefers application/json (e.g. AJAX, see acceptsJSON).
  2. 3xx otherwise, following the PRG pattern.

jsonEncodingOrRedirect Source #

Arguments

:: (MonadHandler m, ToJSON a) 
=> Route (HandlerSite m)

Redirect target

-> a

Data to send via JSON

-> m Encoding 

jsonEncodingOrRedirect simplifies the scenario where a POST handler sends a different response based on Accept headers:

  1. 200 with JSON data if the client prefers application/json (e.g. AJAX, see acceptsJSON).
  2. 3xx otherwise, following the PRG pattern. @since 1.4.21

acceptsJson :: MonadHandler m => m Bool Source #

Returns True if the client prefers application/json as indicated by the Accept HTTP header.

Checking if data is JSON

contentTypeHeaderIsJson :: ByteString -> Bool Source #

Given the Content-Type header, returns if it is JSON.

This function is currently a simple check for application/json, but in the future may check for alternative representations such as xxx/yyy+json.

Since: 1.6.17