rec.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE OverloadedLabels #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE DataKinds #-}

import SuperRecord
import Data.Aeson
import Data.ByteString (ByteString)

main = do
  print $ decodeIntsNewtype sample
  print $ decodeIntsRecord sample

sample :: ByteString
sample = "{\"ints\": [1,2,3]}"

-----------------------------------------------------------
-- With a newtype
-----------------------------------------------------------

newtype Ints = Ints {ints :: [Int]}

instance FromJSON Ints where
  parseJSON = withObject "ints" $ \o -> 
    Ints <$> o .: "ints"

decodeIntsNewtype :: ByteString -> Maybe [Int]
decodeIntsNewtype = 
  fmap ints .
  decodeStrict

-----------------------------------------------------------
-- With a record
-----------------------------------------------------------

decodeIntsRecord :: ByteString -> Maybe [Int]
decodeIntsRecord = 
  fmap (get #ints) .
  decodeStrict @(Rec '["ints" := [Int]])