aeson-gadt-th: Derivation of Aeson instances for GADTs

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Template Haskell for generating ToJSON and FromJSON instances for GADTs. See for examples.

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Versions,,,,,,,,, 0.2.2, 0.2.3, 0.2.4,,,
Change log None available
Dependencies aeson, aeson-gadt-th, base (>=4.8 && <4.13), dependent-sum, template-haskell, transformers [details]
License BSD-3-Clause
Copyright 2019 Obsidian Systems LLC
Author Obsidian Systems LLC
Category JSON
Source repo head: git clone git://
Uploaded by abrar at 2019-02-14T23:37:02Z



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Readme for aeson-gadt-th-

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Provides Template Haskell expressions for deriving ToJSON and FromJSON instances for GADTs.

Example Usage:

{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}

import Data.Aeson
import Data.Aeson.GADT.TH

data A :: * -> * where
  A_a :: A a
  A_b :: Int -> A ()

data B c :: * -> * where
  B_a :: c -> A a -> B c a
  B_x :: B c x

deriveJSONGADT ''A
deriveJSONGADT ''B

main :: IO ()
main = return ()


encode A_a
> "[\"A_a\",[]]"


When decoding a JSON-encoded GADT, the result will be wrapped using Data.Some.This.

case (decode $ encode A_a) :: Maybe (Some A) of
  Nothing -> error "Couldn't decode
  Just (This A_a) -> putStrLn "it worked"
  Just (This A_b) -> putStrLn "wat"
> it worked