amazonka-core-2.0: Core data types and functionality for Amazonka libraries.
Copyright(c) 2013-2023 Brendan Hay
LicenseMozilla Public License, v. 2.0.
MaintainerBrendan Hay <brendan.g.hay+amazonka@gmail.com>
Stabilityprovisional
Portabilitynon-portable (GHC extensions)
Safe HaskellSafe-Inferred
LanguageHaskell2010

Amazonka.Data.JSON

Description

 
Synopsis

FromJSON

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 
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Defined in Data.Aeson.Types.FromJSON

FromJSON Value 
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Defined in Data.Aeson.Types.FromJSON

FromJSON Base64 Source # 
Instance details

Defined in Amazonka.Data.Base64

FromJSON AWSTime Source # 
Instance details

Defined in Amazonka.Data.Time

FromJSON BasicTime Source # 
Instance details

Defined in Amazonka.Data.Time

FromJSON ISO8601 Source # 
Instance details

Defined in Amazonka.Data.Time

FromJSON POSIX Source # 
Instance details

Defined in Amazonka.Data.Time

FromJSON RFC822 Source # 
Instance details

Defined in Amazonka.Data.Time

FromJSON Abbrev Source # 
Instance details

Defined in Amazonka.Types

FromJSON AccessKey Source # 
Instance details

Defined in Amazonka.Types

FromJSON AuthEnv Source # 
Instance details

Defined in Amazonka.Types

FromJSON ErrorCode Source # 
Instance details

Defined in Amazonka.Types

FromJSON ErrorMessage Source # 
Instance details

Defined in Amazonka.Types

FromJSON Region Source # 
Instance details

Defined in Amazonka.Types

FromJSON RequestId Source # 
Instance details

Defined in Amazonka.Types

FromJSON SecretKey Source # 
Instance details

Defined in Amazonka.Types

FromJSON SessionToken Source # 
Instance details

Defined in Amazonka.Types

FromJSON Version 
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Defined in Data.Aeson.Types.FromJSON

FromJSON Void 
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FromJSON CTime 
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FromJSON Int16 
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FromJSON Int32 
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FromJSON Int64 
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FromJSON Int8 
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FromJSON Word16 
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FromJSON Word32 
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FromJSON Word64 
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FromJSON Word8 
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FromJSON IntSet 
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FromJSON Ordering 
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FromJSON Scientific 
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FromJSON Text 
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FromJSON Text 
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FromJSON ShortText

Since: aeson-2.0.2.0

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FromJSON CalendarDiffDays 
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FromJSON Day 
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FromJSON Month 
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FromJSON Quarter 
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FromJSON QuarterOfYear 
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FromJSON DayOfWeek 
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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 
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FromJSON UTCTime 
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FromJSON CalendarDiffTime 
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FromJSON LocalTime 
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FromJSON TimeOfDay 
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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

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FromJSON UUID 
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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.

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FromJSON Natural 
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FromJSON () 
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Methods

parseJSON :: Value -> Parser () #

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

FromJSON Bool 
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FromJSON Char 
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FromJSON Double 
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FromJSON Float 
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FromJSON Int 
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FromJSON Word 
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FromJSON v => FromJSON (KeyMap v)

Since: aeson-2.0.1.0

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FromJSON a => FromJSON (Sensitive a) Source # 
Instance details

Defined in Amazonka.Data.Sensitive

FromJSON a => FromJSON (Identity a) 
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FromJSON a => FromJSON (First a) 
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FromJSON a => FromJSON (Last a) 
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FromJSON a => FromJSON (First a) 
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FromJSON a => FromJSON (Last a) 
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FromJSON a => FromJSON (Max a) 
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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) 
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FromJSON a => FromJSON (Dual a) 
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(FromJSON a, Integral a) => FromJSON (Ratio a) 
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FromJSON a => FromJSON (IntMap a) 
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FromJSON a => FromJSON (Seq a) 
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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) 
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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

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

Since: aeson-2.1.0.0

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FromJSON a => FromJSON (Array a) 
Instance details

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

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FromJSON a => FromJSON (SmallArray a) 
Instance details

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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

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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

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

Defined in Data.Aeson.Types.FromJSON

FromJSON a => FromJSON (NonEmpty a) 
Instance details

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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

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(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)] #

class FromJSONKey a where #

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

instance FromJSONKey Color where
  fromJSONKey = genericFromJSONKey defaultJSONKeyOptions

Minimal complete definition

Nothing

Methods

fromJSONKey :: FromJSONKeyFunction a #

Strategy for parsing the key of a map-like container.

fromJSONKeyList :: FromJSONKeyFunction [a] #

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.

Instances

Instances details
FromJSONKey Key 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Version 
Instance details

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FromJSONKey Void

Since: aeson-2.1.2.0

Instance details

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FromJSONKey Int16 
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FromJSONKey Int32 
Instance details

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FromJSONKey Int64 
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FromJSONKey Int8 
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Defined in Data.Aeson.Types.FromJSON

FromJSONKey Word16 
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FromJSONKey Word32 
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Defined in Data.Aeson.Types.FromJSON

FromJSONKey Word64 
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FromJSONKey Word8 
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FromJSONKey Text 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Text 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey ShortText

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Day 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Month 
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Defined in Data.Aeson.Types.FromJSON

FromJSONKey Quarter 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey QuarterOfYear 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey DayOfWeek 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey UTCTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey LocalTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey TimeOfDay 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey ZonedTime 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey UUID 
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Defined in Data.Aeson.Types.FromJSON

FromJSONKey Integer 
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Defined in Data.Aeson.Types.FromJSON

FromJSONKey Natural 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Bool 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Char 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Double 
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Defined in Data.Aeson.Types.FromJSON

FromJSONKey Float 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Int 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey Word 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey a => FromJSONKey (Identity a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

FromJSONKey a => FromJSONKey (a)

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.FromJSON

(FromJSONKey a, FromJSON a) => FromJSONKey [a] 
Instance details

Defined in Data.Aeson.Types.FromJSON

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

Defined in Data.Aeson.Types.FromJSON

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

Defined in Data.Aeson.Types.FromJSON

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

Defined in Data.Aeson.Types.FromJSON

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

Defined in Data.Aeson.Types.FromJSON

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

Defined in Data.Aeson.Types.FromJSON

Methods

fromJSONKey :: FromJSONKeyFunction (a, b, c, d) #

fromJSONKeyList :: FromJSONKeyFunction [(a, b, c, d)] #

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.

Parser a

withObject :: String -> (Object -> Parser a) -> Value -> Parser a #

withObject name f value applies f 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"

(.:) :: 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.

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

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 #

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"

Either String a

ToJSON

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 Base64 Source # 
Instance details

Defined in Amazonka.Data.Base64

ToJSON AWSTime Source # 
Instance details

Defined in Amazonka.Data.Time

ToJSON BasicTime Source # 
Instance details

Defined in Amazonka.Data.Time

ToJSON ISO8601 Source # 
Instance details

Defined in Amazonka.Data.Time

ToJSON POSIX Source # 
Instance details

Defined in Amazonka.Data.Time

ToJSON RFC822 Source # 
Instance details

Defined in Amazonka.Data.Time

ToJSON AccessKey Source # 
Instance details

Defined in Amazonka.Types

ToJSON Region Source # 
Instance details

Defined in Amazonka.Types

ToJSON SecretKey Source # 
Instance details

Defined in Amazonka.Types

ToJSON SessionToken Source # 
Instance details

Defined in Amazonka.Types

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 (Sensitive a) Source # 
Instance details

Defined in Amazonka.Data.Sensitive

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 ToJSONKey a where #

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 Foo

That'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:

instance ToJSONKey Color where
  toJSONKey = genericToJSONKey defaultJSONKeyOptions

Low-level implementations

Expand

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.Encoding

The 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.Encoding

This 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 #

Strategy for rendering the key for a map-like container.

toJSONKeyList :: ToJSONKeyFunction [a] #

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.

Instances

Instances details
ToJSONKey Key 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Version 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Void

Since: aeson-2.1.2.0

Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Int16 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Int32 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Int64 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Int8 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Word16 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Word32 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Word64 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Word8 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Scientific 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Text 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Text 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey ShortText

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Day 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Month 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Quarter 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey QuarterOfYear 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey DayOfWeek 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey UTCTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey LocalTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey TimeOfDay 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey ZonedTime 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey UUID 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Integer 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Natural 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Bool 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Char 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Double 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Float 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Int 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey Word 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey a => ToJSONKey (Identity a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

ToJSONKey a => ToJSONKey (a)

Since: aeson-2.0.2.0

Instance details

Defined in Data.Aeson.Types.ToJSON

(ToJSONKey a, ToJSON a) => ToJSONKey [a] 
Instance details

Defined in Data.Aeson.Types.ToJSON

HasResolution a => ToJSONKey (Fixed a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

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

Defined in Data.Aeson.Types.ToJSON

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

Defined in Data.Aeson.Types.ToJSON

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

Defined in Data.Aeson.Types.ToJSON

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

Defined in Data.Aeson.Types.ToJSON

Methods

toJSONKey :: ToJSONKeyFunction (a, b, c) #

toJSONKeyList :: ToJSONKeyFunction [(a, b, c)] #

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

Defined in Data.Aeson.Types.ToJSON

Methods

toJSONKey :: ToJSONKeyFunction (a, b, c, d) #

toJSONKeyList :: ToJSONKeyFunction [(a, b, c, d)] #

data Value #

A JSON value represented as a Haskell value.

Constructors

Object !Object 

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

ToBody Value Source # 
Instance details

Defined in Amazonka.Data.Body

ToHashedBody Value Source # 
Instance details

Defined in Amazonka.Data.Body

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 #

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

ToBody (KeyMap Value) Source # 
Instance details

Defined in Amazonka.Data.Body

ToHashedBody (KeyMap Value) Source # 
Instance details

Defined in Amazonka.Data.Body

type Rep Value 
Instance details

Defined in Data.Aeson.Types.Internal

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 #