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

[ bsd3, json, library, program ] [ Propose Tags ]

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


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Versions [faq] 0.1.0.0, 0.1.1.0, 0.1.2.0, 0.1.2.1, 0.2.0.0, 0.2.1.0, 0.2.1.1, 0.2.1.2
Change log ChangeLog.md
Dependencies aeson, aeson-gadt-th, base (>=4.11 && <4.13), containers, dependent-map, dependent-sum, template-haskell, transformers [details]
License BSD-3-Clause
Copyright 2019 Obsidian Systems LLC
Author Obsidian Systems LLC
Maintainer maintainer@obsidian.systems
Revised Revision 1 made by phadej at Tue Oct 8 19:24:34 UTC 2019
Category JSON
Source repo head: git clone git://github.com/obsidiansystems/aeson-gadt-th.git
Uploaded by abrar at Thu May 9 21:22:58 UTC 2019
Distributions NixOS:0.2.1.2
Executables readme
Downloads 951 total (240 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by rule of succession]
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Readme for aeson-gadt-th-0.2.1.0

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aeson-gadt-th

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

Example Usage:

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

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

import Data.Dependent.Map (DMap)
import Data.Dependent.Sum (DSum)
import Data.Functor.Identity
import Data.GADT.Compare

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 a

data C t :: * -> * where
  C_t :: t -> C t t

deriveJSONGADT ''A
deriveJSONGADT ''B
deriveJSONGADT ''C

-- Some real-world-ish examples.

-- | Edit operations for `LabelledGraph`
data LabelledGraphEdit v vm em :: * -> * where
  LabelledGraphEdit_ClearAll :: LabelledGraphEdit v vm em ()
  LabelledGraphEdit_AddVertex :: vm -> LabelledGraphEdit v vm em v
  LabelledGraphEdit_AddEdge :: v -> v -> em -> LabelledGraphEdit v vm em ()
  LabelledGraphEdit_SetVertexProperties :: v -> vm -> LabelledGraphEdit v vm em ()
  LabelledGraphEdit_SetEdgeProperties :: v -> v -> em -> LabelledGraphEdit v vm em ()

-- | PropertyGraphEdit operatios for `PropertyGraph`
data PropertyGraphEdit v vp ep r where
  PropertyGraphEdit_ClearAll :: PropertyGraphEdit v vp ep ()
  PropertyGraphEdit_AddVertex :: (DMap vp Identity) -> PropertyGraphEdit v vp ep v
  PropertyGraphEdit_AddEdge :: v -> v -> (DMap ep Identity) -> PropertyGraphEdit v vp ep ()
  PropertyGraphEdit_SetVertexProperty :: GCompare vp => v -> DSum vp Identity -> PropertyGraphEdit v vp ep ()
  PropertyGraphEdit_SetEdgeProperty :: GCompare ep => v -> v -> DSum ep Identity -> PropertyGraphEdit v vp ep ()

-- | View operations for `LabelledGraph`
data LabelledGraphView v vm em :: * -> * where
  LabelledGraphView_All :: LabelledGraphView v vm em ()
  LabelledGraphView_GetVertexProperties :: v -> LabelledGraphView v vm em vm
  LabelledGraphView_GetEdgeProperties :: v -> v -> LabelledGraphView v vm em em

deriveJSONGADT ''LabelledGraphEdit
deriveJSONGADT ''PropertyGraphEdit
deriveJSONGADT ''LabelledGraphView

main :: IO ()
main = return ()

Encoding:

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

Decoding:

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