avers-0.0.10: empty

Safe HaskellNone
LanguageHaskell2010

Avers.TH

Synopsis

Documentation

deriveJSON

Arguments

:: Options

Encoding options.

-> Name

Name of the type for which to generate ToJSON and FromJSON instances.

-> Q [Dec] 

Generates both ToJSON and FromJSON instance declarations for the given data type.

This is a convienience function which is equivalent to calling both deriveToJSON and deriveFromJSON.

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 ResponseType 
FromJSON ZonedTime 
FromJSON Datum 
FromJSON Operation 
FromJSON ObjectId 
FromJSON RevId 
FromJSON ObjId 
FromJSON Path 
FromJSON Object 
FromJSON Patch 
FromJSON Snapshot 
FromJSON Secret 
FromJSON SecretId 
FromJSON Release 
FromJSON Blob 
FromJSON BlobId 
FromJSON Session 
FromJSON SessionId 
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 (IntMap a) 
(Ord a, FromJSON a) => FromJSON (Set a) 
FromJSON v => FromJSON (Tree v) 
FromJSON a => FromJSON (Seq a) 
FromJSON a => FromJSON (Identity a) 
(Eq a, Hashable a, FromJSON a) => FromJSON (HashSet a) 
FromJSON a => FromJSON (Vector a) 
(Vector Vector a, FromJSON a) => FromJSON (Vector a) 
(Storable a, FromJSON a) => FromJSON (Vector a) 
(Prim a, FromJSON a) => FromJSON (Vector 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) 
(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) 

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 Datum 
ToJSON Operation 
ToJSON ObjectId 
ToJSON RevId 
ToJSON ObjId 
ToJSON Path 
ToJSON Object 
ToJSON Patch 
ToJSON Snapshot 
ToJSON Secret 
ToJSON SecretId 
ToJSON Release 
ToJSON Blob 
ToJSON BlobId 
ToJSON Session 
ToJSON SessionId 
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 (IntMap a) 
ToJSON a => ToJSON (Set a) 
ToJSON v => ToJSON (Tree v) 
ToJSON a => ToJSON (Seq a) 
ToJSON a => ToJSON (Identity a) 
ToJSON a => ToJSON (HashSet a) 
ToJSON a => ToJSON (Vector a) 
(Vector Vector a, ToJSON a) => ToJSON (Vector a) 
(Storable a, ToJSON a) => ToJSON (Vector a) 
(Prim a, ToJSON a) => ToJSON (Vector a) 
ToJSON a => ToJSON (Record 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) 
(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)