Deriving instances for GADTs

• Eq, Ord, Show can be derived using the StandaloneDeriving extension (implicitly using the stock deriving strategy).

• To derive instances for Some f (where f is your GADT), as well as DSum f g, you will need to use the following libraries :

  • some and dependent-sum - for deriving GEq, GShow, GCompare
  • aeson-gadt-th - for deriving JSON instances
    • Use this in conjunction with dependent-sum-aeson-orphans to get instances for ToJSON (Some f)

• The kind-generics package generalizes the approach of GHC.Generics to GADTs.