Automatically deriving toJSON/fromJSON using the instances of the inner type of a newtype

Question

In my code I use a lot of newtype declarations, like:

newtype PersonName = PersonName { personName :: Text }
newtype PetName = PetName { petName :: Text }

(In practice I use lenses to avoid the cumbersome names for the accessor functions.)

However, if I derive the instance from ToJSON and FromJSON automatically, the resulting JSON will be of the form:

{ "personName": "The person name" }
{ "petName": "The pet name" }

Is there a way to avoid the boilerplate of declaring trivial instances of ToJSON and FromJSON for the newtypes above, in such a way that the resulting JSON objects will be of the form:

"The person name"
"The pet name"

Answer 1

You can use GeneralizedNewtypeDeriving to derive the instances.

{-# LANGUAGE GeneralizedNewtypeDeriving #-}

newtype PersonName = PersonName { personName :: Text }
    deriving (ToJSON, FromJSON)