deriving-compat

Provides Template Haskell functions that mimic deriving extensions that were introduced or modified in recent versions of GHC. Currently, the following extensions are covered:

• DeriveFoldable
• DeriveFunctor
• DeriveTraversable

The following changes have been backported:

• In GHC 8.0, DeriveFoldable was changed to allow folding over data types with existential constraints.
• In GHC 8.0, DeriveFoldable and DeriveTraversable were changed so as not to generate superfluous mempty or pure expressions in generated code. As a result, this allows deriving Traversable instances for datatypes with unlifted argument types.

Note that some recent GHC extensions are not covered by this package:

• DeriveGeneric, which was introducted in GHC 7.2 for deriving Generic instances, and modified in GHC 7.6 to allow derivation of Generic1 instances. Use Generics.Deriving.TH from generic-deriving to derive Generic(1) using Template Haskell.
• DeriveLift, which was introduced in GHC 8.0 for deriving Lift instances. Use Language.Haskell.TH.Lift from th-lift to derive Lift using Template Haskell.