Data.Aeson.Types

Core JSON types

data Value

A JSON value represented as a Haskell value.

Constructors

Object Object

Array Array

String Text

Number Number

Bool !Bool

Null

Instances

Eq Value

Data Value

Show Value

Typeable Value

IsString Value

NFData Value

FromJSON Value

ToJSON Value

type Array = Vector Value

A JSON "array" (sequence).

emptyArray :: Value

The empty array.

type Pair = (Text, Value)

A key/value pair for an Object.

type Object = Map Text Value

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

emptyObject :: Value

The empty object.

Convenience types and functions

newtype DotNetTime

A newtype wrapper for UTCTime that uses the same non-standard serialization format as Microsoft .NET.

Constructors

DotNetTime

Fields

fromDotNetTime :: UTCTime

Instances

Eq DotNetTime

Ord DotNetTime

Read DotNetTime

Show DotNetTime

Typeable DotNetTime

FormatTime DotNetTime

FromJSON DotNetTime

ToJSON DotNetTime

typeMismatch

Arguments

:: String

The name of the type you are trying to parse.

-> Value

The actual value encountered.

-> Parser a

Fail parsing due to a type mismatch, with a descriptive message.

Type conversion

data Parser a

A continuation-based parser type.

Instances

Monad Parser

Functor Parser

MonadPlus Parser

Applicative Parser

Alternative Parser

Monoid (Parser a)

data Result a

The result of running a Parser.

Constructors

Error String

Success a

Instances

Typeable1 Result

Eq a => Eq (Result a)

Show a => Show (Result a)

class FromJSON a where

A type that can be converted from JSON, with the possibility of failure.

When writing an instance, use mzero or fail to make a conversion fail, e.g. if an Object is missing a required key, or the value is of the wrong type.

An example type and instance:

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

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

-- A non-Object value is of the wrong type, so use mzero to fail.
   parseJSON _          = mzero

Methods

parseJSON :: Value -> Parser a

Instances

FromJSON Bool

FromJSON Char

FromJSON Double

FromJSON Float

FromJSON Int

FromJSON Int8

FromJSON Int16

FromJSON Int32

FromJSON Int64

FromJSON Integer

FromJSON Word

FromJSON Word8

FromJSON Word16

FromJSON Word32

FromJSON Word64

FromJSON ()

FromJSON ByteString

FromJSON ByteString

FromJSON Number

FromJSON Text

FromJSON Text

FromJSON IntSet

FromJSON UTCTime

FromJSON DotNetTime

FromJSON Value

FromJSON [Char]

FromJSON a => FromJSON [a]

FromJSON (Ratio Integer)

FromJSON a => FromJSON (Maybe a)

FromJSON a => FromJSON (Dual a)

FromJSON a => FromJSON (First a)

FromJSON a => FromJSON (Last a)

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

FromJSON a => FromJSON (Vector a)

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

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

FromJSON v => FromJSON (Map String v)

FromJSON v => FromJSON (Map ByteString v)

FromJSON v => FromJSON (Map ByteString v)

FromJSON v => FromJSON (Map Text v)

FromJSON v => FromJSON (Map Text v)

FromJSON v => FromJSON (HashMap String v)

FromJSON v => FromJSON (HashMap ByteString v)

FromJSON v => FromJSON (HashMap ByteString v)

FromJSON v => FromJSON (HashMap Text v)

FromJSON v => FromJSON (HashMap Text v)

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

fromJSON :: FromJSON a => Value -> Result a

Convert a value from JSON, failing if the types do not match.

parse :: (a -> Parser b) -> a -> Result b

Run a Parser.

class ToJSON a where

A type that can be converted to JSON.

An example type and instance:

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

instance ToJSON Coord where
   toJSON (Coord x y) = object ["x" .= x, "y" .= y]

Methods

toJSON :: a -> Value

Instances

ToJSON Bool

ToJSON Char

ToJSON Double

ToJSON Float

ToJSON Int

ToJSON Int8

ToJSON Int16

ToJSON Int32

ToJSON Int64

ToJSON Integer

ToJSON Word

ToJSON Word8

ToJSON Word16

ToJSON Word32

ToJSON Word64

ToJSON ()

ToJSON ByteString

ToJSON ByteString

ToJSON Number

ToJSON Text

ToJSON Text

ToJSON IntSet

ToJSON UTCTime

ToJSON DotNetTime

ToJSON Value

ToJSON [Char]

ToJSON a => ToJSON [a]

ToJSON (Ratio Integer)

ToJSON a => ToJSON (Maybe a)

ToJSON a => ToJSON (Dual a)

ToJSON a => ToJSON (First a)

ToJSON a => ToJSON (Last a)

ToJSON a => ToJSON (Set a)

ToJSON a => ToJSON (Vector a)

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

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

ToJSON v => ToJSON (Map String v)

ToJSON v => ToJSON (Map ByteString v)

ToJSON v => ToJSON (Map ByteString v)

ToJSON v => ToJSON (Map Text v)

ToJSON v => ToJSON (Map Text v)

ToJSON v => ToJSON (HashMap String v)

ToJSON v => ToJSON (HashMap ByteString v)

ToJSON v => ToJSON (HashMap ByteString v)

ToJSON v => ToJSON (HashMap Text v)

ToJSON v => ToJSON (HashMap Text v)

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

Constructors and accessors

(.=) :: ToJSON a => Text -> a -> Pair

Construct a Pair from a key and a value.

(.:) :: FromJSON a => Object -> Text -> 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 -> Text -> 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 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.

object :: [Pair] -> Value

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