GHC.Tc.Deriv.Generics

The deriving code for the Generic class

Documentation

canDoGenerics :: DerivInstTys -> Validity' [DeriveGenericsErrReason]

canDoGenerics1 :: DerivInstTys -> Validity' [DeriveGenericsErrReason]

data GenericKind

Constructors

Gen0

Gen1

gen_Generic_binds :: GenericKind -> SrcSpan -> DerivInstTys -> TcM (LHsBinds GhcPs, [LSig GhcPs])

gen_Generic_fam_inst :: GenericKind -> (Name -> Fixity) -> SrcSpan -> DerivInstTys -> TcM FamInst

get_gen1_constrained_tys :: TyVar -> Type -> [Type]

Called by inferConstraints; generates a list of types, each of which must be a Functor in order for the Generic1 instance to work. For instance, if we have:

data Foo a = MkFoo Int a (Maybe a) (Either Int (Maybe a))

Then get_gen1_constrained_tys a (f (g a)) would return [Either Int], as a derived Generic1 instance would need to call fmap at that type. Invoking get_gen1_constrained_tys a on any of the other fields would return [].

get_gen1_constrained_tys is very similar in spirit to deepSubtypesContaining in GHC.Tc.Deriv.Functor. Just like with deepSubtypesContaining, it is important that the TyVar argument come from dataConUnivTyVars. (See #22167 for what goes wrong if tyConTyVars is used.)