amazonka-core-1.2.0: Core data types and functionality for Amazonka libraries.

Copyright(c) 2013-2015 Brendan Hay
LicenseMozilla Public License, v. 2.0.
MaintainerBrendan Hay <brendan.g.hay@gmail.com>
Stabilityprovisional
Portabilitynon-portable (GHC extensions)
Safe HaskellNone
LanguageHaskell2010

Network.AWS.Data.JSON

Contents

Description

 

Synopsis

FromJSON

class FromJSON a where

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

When writing an instance, use empty, 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:

{-# LANGUAGE OverloadedStrings #-}

data Coord = 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

Note the use of the OverloadedStrings language extension which enables Text values to be written as string literals.

Instead of manually writing your FromJSON instance, there are three 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 will probably be more efficient than the following two options:
  • Data.Aeson.Generic provides a generic fromJSON function that parses to any type which is an instance of Data.
  • If your compiler has support for the DeriveGeneric and DefaultSignatures language extensions, parseJSON will have a default generic implementation.

To use this, 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

Note that, instead of using DefaultSignatures, it's also possible to parameterize the generic decoding using genericParseJSON applied to your encoding/decoding Options:

instance FromJSON Coord where
    parseJSON = genericParseJSON defaultOptions

Minimal complete definition

Nothing

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

WARNING: Only parse Integers from trusted input since an attacker could easily fill up the memory of the target system by specifying a scientific number with a big exponent like 1e1000000000.

FromJSON Word 
FromJSON Word8 
FromJSON Word16 
FromJSON Word32 
FromJSON Word64 
FromJSON () 
FromJSON Scientific 
FromJSON Number 
FromJSON Text 
FromJSON UTCTime 
FromJSON Value 
FromJSON DotNetTime 
FromJSON Text 
FromJSON IntSet 
FromJSON ZonedTime 
FromJSON Nat 
FromJSON AuthEnv 
FromJSON RequestId 
FromJSON ErrorMessage 
FromJSON ErrorCode 
FromJSON Abbrev 
FromJSON Base64 
FromJSON POSIX 
FromJSON AWSTime 
FromJSON BasicTime 
FromJSON ISO8601 
FromJSON RFC822 
FromJSON [Char] 
FromJSON a => FromJSON [a] 
FromJSON (Ratio Integer) 
FromJSON a => FromJSON (Maybe a) 
HasResolution a => FromJSON (Fixed a)

WARNING: Only parse fixed-precision numbers from trusted input since an attacker could easily fill up the memory of the target system by specifying a scientific number with a big exponent like 1e1000000000.

FromJSON a => FromJSON (Dual a) 
FromJSON a => FromJSON (First a) 
FromJSON a => FromJSON (Last a) 
FromJSON a => FromJSON (Identity a) 
FromJSON a => FromJSON (IntMap a) 
(Ord a, FromJSON a) => FromJSON (Set a) 
FromJSON v => FromJSON (Tree v) 
FromJSON a => FromJSON (Seq a) 
FromJSON a => FromJSON (Vector a) 
(Prim a, FromJSON a) => FromJSON (Vector a) 
(Storable a, FromJSON a) => FromJSON (Vector a) 
(Vector Vector a, FromJSON a) => FromJSON (Vector a) 
(Eq a, Hashable a, FromJSON a) => FromJSON (HashSet a) 
FromJSON a => FromJSON (List1 a) 
FromJSON a => FromJSON (Sensitive a) 
(FromJSON a, FromJSON b) => FromJSON (Either a b) 
(FromJSON a, FromJSON b) => FromJSON (a, b) 
FromJSON v => FromJSON (HashMap String v) 
FromJSON v => FromJSON (HashMap Text v) 
FromJSON v => FromJSON (HashMap Text v) 
FromJSON v => FromJSON (Map String v) 
FromJSON v => FromJSON (Map Text v) 
FromJSON v => FromJSON (Map Text v) 
(Eq k, Hashable k, FromText k, FromJSON v) => FromJSON (Map k v) 
(FromJSON a, FromJSON b, FromJSON c) => FromJSON (a, b, c) 
(FromJSON a, FromJSON b, FromJSON c, FromJSON d) => FromJSON (a, b, c, d) 
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e) => FromJSON (a, b, c, d, e) 
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f) => FromJSON (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) 
(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) 
(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) 
(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) 
(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) 
(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) 
(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) 
(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) 
(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) 

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 expected f value applies f to the Object when value is an Object and fails using typeMismatch expected otherwise.

(.:) :: 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.

(.!=) :: 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.

An example type and instance:

@{-# LANGUAGE OverloadedStrings #-}

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

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

Note the use of the OverloadedStrings language extension which enables Text values to be written as string literals.

Instead of manually writing your ToJSON instance, there are three 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 will probably be more efficient than the following two options:
  • Data.Aeson.Generic provides a generic toJSON function that accepts any type which is an instance of Data.
  • If your compiler has support for the DeriveGeneric and DefaultSignatures language extensions (GHC 7.2 and newer), toJSON will have a default generic implementation.

To use the latter option, simply add a deriving Generic clause to your datatype and declare a ToJSON instance for your datatype without giving a definition for toJSON.

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 ToJSON Coord @

Note that, instead of using DefaultSignatures, it's also possible to parameterize the generic encoding using genericToJSON applied to your encoding/decoding Options:

instance ToJSON Coord where
    toJSON = genericToJSON defaultOptions

Minimal complete definition

Nothing

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 Scientific 
ToJSON Number 
ToJSON Text 
ToJSON UTCTime 
ToJSON Value 
ToJSON DotNetTime 
ToJSON Text 
ToJSON IntSet 
ToJSON ZonedTime 
ToJSON Nat 
ToJSON Base64 
ToJSON POSIX 
ToJSON AWSTime 
ToJSON BasicTime 
ToJSON ISO8601 
ToJSON RFC822 
ToJSON [Char] 
ToJSON a => ToJSON [a] 
ToJSON (Ratio Integer) 
ToJSON a => ToJSON (Maybe a) 
HasResolution a => ToJSON (Fixed a) 
ToJSON a => ToJSON (Dual a) 
ToJSON a => ToJSON (First a) 
ToJSON a => ToJSON (Last a) 
ToJSON a => ToJSON (Identity a) 
ToJSON a => ToJSON (IntMap a) 
ToJSON a => ToJSON (Set a) 
ToJSON v => ToJSON (Tree v) 
ToJSON a => ToJSON (Seq a) 
ToJSON a => ToJSON (Vector a) 
(Prim a, ToJSON a) => ToJSON (Vector a) 
(Storable a, ToJSON a) => ToJSON (Vector a) 
(Vector Vector a, ToJSON a) => ToJSON (Vector a) 
ToJSON a => ToJSON (HashSet a) 
ToJSON a => ToJSON (List1 a) 
ToJSON a => ToJSON (Sensitive a) 
(ToJSON a, ToJSON b) => ToJSON (Either a b) 
(ToJSON a, ToJSON b) => ToJSON (a, b) 
ToJSON v => ToJSON (HashMap String v) 
ToJSON v => ToJSON (HashMap Text v) 
ToJSON v => ToJSON (HashMap Text v) 
ToJSON v => ToJSON (Map String v) 
ToJSON v => ToJSON (Map Text v) 
ToJSON v => ToJSON (Map Text v) 
(Eq k, Hashable k, ToText k, ToJSON v) => ToJSON (Map k v) 
(ToJSON a, ToJSON b, ToJSON c) => ToJSON (a, b, c) 
(ToJSON a, ToJSON b, ToJSON c, ToJSON d) => ToJSON (a, b, c, d) 
(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e) => ToJSON (a, b, c, d, e) 
(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f) => ToJSON (a, b, c, d, e, f) 
(ToJSON a, ToJSON b, ToJSON c, ToJSON d, ToJSON e, ToJSON f, ToJSON g) => ToJSON (a, b, c, d, e, f, g) 
(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) 
(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) 
(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) 
(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) 
(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) 
(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) 
(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) 
(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) 

data Value :: *

A JSON value represented as a Haskell value.

Constructors

Object !Object 

object :: [Pair] -> Value

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

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

Construct a Pair from a key and a value.