yaml-0.11.11.2: Support for parsing and rendering YAML documents.
Safe HaskellSafe-Inferred
LanguageHaskell2010

Data.Yaml

Description

Provides a high-level interface for processing YAML files.

This module reuses most of the infrastructure from the aeson package. This means that you can use all of the existing tools for JSON processing for processing YAML files. As a result, much of the documentation below mentions JSON; do not let that confuse you, it's intentional.

For the most part, YAML content translates directly into JSON, and therefore there is very little data loss. If you need to deal with YAML more directly (e.g., directly deal with aliases), you should use the Text.Libyaml module instead.

For documentation on the aeson types, functions, classes, and operators, please see the Data.Aeson module of the aeson package.

Look in the examples directory of the source repository for some initial pointers on how to use this library.

Synopsis

Encoding

encode :: ToJSON a => a -> ByteString Source #

Encode a value into its YAML representation.

encodeWith :: ToJSON a => EncodeOptions -> a -> ByteString Source #

Encode a value into its YAML representation with custom styling.

Since: 0.10.2.0

encodeFile :: ToJSON a => FilePath -> a -> IO () Source #

Encode a value into its YAML representation and save to the given file.

encodeFileWith :: ToJSON a => EncodeOptions -> FilePath -> a -> IO () Source #

Encode a value into its YAML representation with custom styling and save to the given file.

Since: 0.10.2.0

Decoding

decodeEither' :: FromJSON a => ByteString -> Either ParseException a Source #

More helpful version of decodeEither which returns the YamlException .

Since: 0.8.3

decodeFileEither :: FromJSON a => FilePath -> IO (Either ParseException a) Source #

A version of decodeFile which should not throw runtime exceptions.

Since: 0.8.4

decodeFileWithWarnings :: FromJSON a => FilePath -> IO (Either ParseException ([Warning], a)) Source #

A version of decodeFileEither that returns warnings along with the parse result.

Since: 0.10.0

decodeThrow :: (MonadThrow m, FromJSON a) => ByteString -> m a Source #

A version of decodeEither' lifted to MonadThrow

Since: 0.8.31

decodeFileThrow :: (MonadIO m, FromJSON a) => FilePath -> m a Source #

A version of decodeFileEither lifted to MonadIO

Since: 0.8.31

Decoding multiple documents

For situations where we need to be able to parse multiple documents separated by `---` in a YAML stream, these functions decode a list of values rather than a single value.

decodeAllEither' :: FromJSON a => ByteString -> Either ParseException [a] Source #

Like decodeEither' , but decode multiple documents.

Since: 0.11.5.0

decodeAllFileEither :: FromJSON a => FilePath -> IO (Either ParseException [a]) Source #

Like decodeFileEither , but decode multiple documents.

Since: 0.11.5.0

decodeAllFileWithWarnings :: FromJSON a => FilePath -> IO (Either ParseException ([Warning], [a])) Source #

Like decodeFileWithWarnings , but decode multiple documents.

Since: 0.11.5.0

decodeAllThrow :: (MonadThrow m, FromJSON a) => ByteString -> m [a] Source #

Like decodeThrow , but decode multiple documents.

Since: 0.11.5.0

decodeAllFileThrow :: (MonadIO m, FromJSON a) => FilePath -> m [a] Source #

Like decodeFileThrow , but decode multiple documents.

Since: 0.11.5.0

More control over decoding

decodeHelper :: FromJSON a => ConduitM () Event Parse () -> IO (Either ParseException ([Warning], Either String a)) Source #

Types

data Value #

A JSON value represented as a Haskell value.

Constructors

Object !Object
Array !Array
String !Text
Number !Scientific
Bool !Bool
Null

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

Methods

fromString :: String -> Encoding

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 #

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

type Rep Value = D1 ('MetaData "Value" "Data.Aeson.Types.Internal" "aeson-2.1.2.1-4QFSJ9mRhdxDvTHHXtJzK8" 'False) ((C1 ('MetaCons "Object" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Object)) :+: (C1 ('MetaCons "Array" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Array)) :+: C1 ('MetaCons "String" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Text)))) :+: (C1 ('MetaCons "Number" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Scientific)) :+: (C1 ('MetaCons "Bool" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'SourceStrict 'DecidedStrict) (Rec0 Bool)) :+: C1 ('MetaCons "Null" 'PrefixI 'False) (U1 :: Type -> Type))))

data Parser a #

A JSON parser. N.B. This might not fit your usual understanding of "parser". Instead you might like to think of Parser as a "parse result", i.e. a parser to which the input has already been applied.

Instances

Instances details
MonadFail Parser
Instance details

Defined in Data.Aeson.Types.Internal

Methods

fail :: String -> Parser a #

MonadFix Parser

Since: aeson-2.1.0.0

Instance details

Defined in Data.Aeson.Types.Internal

Methods

mfix :: (a -> Parser a) -> Parser a #

Alternative Parser
Instance details

Defined in Data.Aeson.Types.Internal

Methods

empty :: Parser a #

(<|>) :: Parser a -> Parser a -> Parser a #

some :: Parser a -> Parser [a] #

many :: Parser a -> Parser [a] #

Applicative Parser
Instance details

Defined in Data.Aeson.Types.Internal

Methods

pure :: a -> Parser a #

(<*>) :: Parser (a -> b) -> Parser a -> Parser b #

liftA2 :: (a -> b -> c) -> Parser a -> Parser b -> Parser c #

(*>) :: Parser a -> Parser b -> Parser b #

(<*) :: Parser a -> Parser b -> Parser a #

Functor Parser
Instance details

Defined in Data.Aeson.Types.Internal

Methods

fmap :: (a -> b) -> Parser a -> Parser b #

(<$) :: a -> Parser b -> Parser a #

Monad Parser
Instance details

Defined in Data.Aeson.Types.Internal

Methods

(>>=) :: Parser a -> (a -> Parser b) -> Parser b #

(>>) :: Parser a -> Parser b -> Parser b #

return :: a -> Parser a #

MonadPlus Parser
Instance details

Defined in Data.Aeson.Types.Internal

Methods

mzero :: Parser a #

mplus :: Parser a -> Parser a -> Parser a #

Monoid (Parser a)
Instance details

Defined in Data.Aeson.Types.Internal

Methods

mempty :: Parser a #

mappend :: Parser a -> Parser a -> Parser a #

mconcat :: [Parser a] -> Parser a #

Semigroup (Parser a)
Instance details

Defined in Data.Aeson.Types.Internal

Methods

(<>) :: Parser a -> Parser a -> Parser a #

sconcat :: NonEmpty (Parser a) -> Parser a #

stimes :: Integral b => b -> Parser a -> Parser a #

type Object = KeyMap Value #

A JSON "object" (key/value map).

type Array = Vector Value #

A JSON "array" (sequence).

data ParseException Source #

Constructors

NonScalarKey
UnknownAlias
UnexpectedEvent
InvalidYaml (Maybe YamlException)
MultipleDocuments
AesonException String
OtherParseException SomeException
NonStringKey JSONPath
NonStringKeyAlias AnchorName Value
CyclicIncludes
LoadSettingsException FilePath ParseException

Instances

Instances details
Exception ParseException Source #
Instance details

Defined in Data.Yaml.Internal

Show ParseException Source #
Instance details

Defined in Data.Yaml.Internal

prettyPrintParseException :: ParseException -> String Source #

Alternative to show to display a ParseException on the screen. Instead of displaying the data constructors applied to their arguments, a more textual output is returned. For example, instead of printing:

InvalidYaml (Just (YamlParseException {yamlProblem = "did not find expected ',' or '}'", yamlContext = "while parsing a flow mapping", yamlProblemMark = YamlMark {yamlIndex = 42, yamlLine = 2, yamlColumn = 12}})))

It looks more pleasant to print:

YAML parse exception at line 2, column 12,
while parsing a flow mapping:
did not find expected ',' or '}'

Since 0.8.11

data YamlException #

Constructors

YamlException String
YamlParseException

problem, context, index, position line, position column

Instances

Instances details
Exception YamlException
Instance details

Defined in Text.Libyaml

Show YamlException
Instance details

Defined in Text.Libyaml

data YamlMark #

The pointer position

Constructors

YamlMark

Instances

Instances details
Show YamlMark
Instance details

Defined in Text.Libyaml

Constructors and accessors

object :: [Pair] -> Value #

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

array :: [Value] -> Value Source #

Construct a new Value from a list of Value s.

(.=) :: (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.

(.:?) :: 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"

With helpers (since 0.8.23)

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"

withText :: String -> (Text -> Parser a) -> Value -> Parser a #

withText name f value applies f to the Text when value is a String and fails otherwise.

Error message example

withText "MyType" f Null
-- Error: "parsing MyType failed, expected String, but encountered Null"

withArray :: String -> (Array -> Parser a) -> Value -> Parser a #

withArray expected f value applies f to the Array when value is an Array and fails otherwise.

Error message example

withArray "MyType" f (String "oops")
-- Error: "parsing MyType failed, expected Array, but encountered String"

withScientific :: String -> (Scientific -> Parser a) -> Value -> Parser a #

withScientific name f value applies f to the Scientific number when value is a Number and fails using typeMismatch otherwise.

Warning: If you are converting from a scientific to an unbounded type such as Integer you may want to add a restriction on the size of the exponent (see withBoundedScientific) to prevent malicious input from filling up the memory of the target system.

Error message example

withScientific "MyType" f (String "oops")
-- Error: "parsing MyType failed, expected Number, but encountered String"

withBool :: String -> (Bool -> Parser a) -> Value -> Parser a #

withBool expected f value applies f to the Value when value is a Boolean and fails otherwise.

Error message example

withBool "MyType" f (String "oops")
-- Error: "parsing MyType failed, expected Boolean, but encountered String"

Parsing

parseMonad :: MonadFail m => (a -> Parser b) -> a -> m b Source #

Deprecated: With the MonadFail split, this function is going to be removed in the future. Please migrate to parseEither.

parseEither :: (a -> Parser b) -> a -> Either String b #

Run a Parser with an Either result type. If the parse fails, the Left payload will contain an error message.

parseMaybe :: (a -> Parser b) -> a -> Maybe b #

Run a Parser with a Maybe result type.

Classes

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

Methods

toJSON :: Last a -> Value #

toEncoding :: Last a -> Encoding #

toJSONList :: [Last a] -> Value #

toEncodingList :: [Last a] -> Encoding #

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

Methods

toJSON :: Last a -> Value #

toEncoding :: Last a -> Encoding #

toJSONList :: [Last a] -> Value #

toEncodingList :: [Last a] -> Encoding #

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

Methods

toJSON :: Dual a -> Value #

toEncoding :: Dual a -> Encoding #

toJSONList :: [Dual a] -> Value #

toEncodingList :: [Dual a] -> Encoding #

(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

Methods

toJSON :: Tree v -> Value #

toEncoding :: Tree v -> Encoding #

toJSONList :: [Tree v] -> Value #

toEncodingList :: [Tree v] -> Encoding #

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

Methods

toJSON :: HashMap k v -> Value #

toEncoding :: HashMap k v -> Encoding #

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

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

(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

Methods

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

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

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

Methods

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

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

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

Methods

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

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

(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

Methods

parseJSON :: Value -> Parser (Tree v) #

parseJSONList :: Value -> Parser [Tree v] #

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

Methods

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

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

(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)] #

Custom encoding

isSpecialString :: Text -> Bool Source #

Determine whether a string must be quoted in YAML and can't appear as plain text. Useful if you want to use setStringStyle.

Since: 0.10.2.0

data EncodeOptions Source #

Since: 0.10.2.0

defaultEncodeOptions :: EncodeOptions Source #

Since: 0.10.2.0

defaultStringStyle :: StringStyle Source #

Since: 0.11.2.0

setStringStyle :: (Text -> (Tag, Style)) -> EncodeOptions -> EncodeOptions Source #

Set the string style in the encoded YAML. This is a function that decides for each string the type of YAML string to output.

WARNING: You must ensure that special strings (like "yes"/"no"/"null"/"1234") are not encoded with the Plain style, because then they will be decoded as boolean, null or numeric values. You can use isSpecialString to detect them.

By default, strings are encoded as follows:

Since: 0.10.2.0

setFormat :: FormatOptions -> EncodeOptions -> EncodeOptions Source #

Set the encoding formatting for the encoded YAML. By default, this is defaultFormatOptions .

Since: 0.10.2.0

data FormatOptions #

Contains options relating to the formatting (indendation, width) of the YAML output.

Since: libyaml-0.10.2.0

defaultFormatOptions :: FormatOptions #

Since: libyaml-0.10.2.0

setWidth :: Maybe Int -> FormatOptions -> FormatOptions #

Set the maximum number of columns in the YAML output, or Nothing for infinite. By default, the limit is 80 characters.

Since: libyaml-0.10.2.0

Deprecated

decode :: FromJSON a => ByteString -> Maybe a Source #

Deprecated: Please use decodeEither or decodeThrow, which provide information on how the decode failed

decodeFile :: FromJSON a => FilePath -> IO (Maybe a) Source #

Deprecated: Please use decodeFileEither, which does not confused type-directed and runtime exceptions.

decodeEither :: FromJSON a => ByteString -> Either String a Source #

Deprecated: Please use decodeEither' or decodeThrow, which provide more useful failures

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