aeson deriving via

aeson-via.hs

{-# LANGUAGE DeriveGeneric, DerivingVia, FlexibleInstances, UndecidableInstances #-}

import Data.Aeson
import Data.Aeson.Casing
import GHC.Generics

newtype CamelCaseJson a = CamelCaseJson a
  deriving (Eq, Show, Generic)

instance (GToJSON Zero (Rep a), Generic a) => ToJSON (CamelCaseJson a) where
  toJSON (CamelCaseJson a) = genericToJSON (aesonPrefix camelCase) a

data Foo =
  Foo
    { fooBarBaz :: Int
    , fooLaLa :: String
    }
  deriving Generic
  deriving ToJSON via (CamelCaseJson Foo)

-- encode $ Foo 42 "lala"
-- {"barBaz":42,"laLa":"lala"}