--- make the coercion associated with a newtype
-mkNewTypeCoercion :: Name -> TyCon -> [TyVar] -> Type -> TyCon
-mkNewTypeCoercion name tycon tvs rhs_ty
- = ASSERT (length tvs == tyConArity tycon)
- mkCoercionTyCon name (tyConArity tycon) rule
+-- See note [Newtype coercions] in TyCon
+mkNewTypeCoercion :: Name -> TyCon -> ([TyVar], Type) -> TyCon
+mkNewTypeCoercion name tycon (tvs, rhs_ty)
+ = mkCoercionTyCon name co_con_arity rule
+ where
+ co_con_arity = length tvs
+
+ rule args = ASSERT( co_con_arity == length args )
+ (TyConApp tycon args, substTyWith tvs args rhs_ty)
+
+-- Coercion identifying a data/newtype representation type and its family
+-- instance. It has the form `Co tvs :: F ts :=: R tvs', where `Co' is the
+-- coercion tycon built here, `F' the family tycon and `R' the (derived)
+-- representation tycon.
+--
+mkDataInstCoercion :: Name -- unique name for the coercion tycon
+ -> [TyVar] -- type parameters of the coercion (`tvs')
+ -> TyCon -- family tycon (`F')
+ -> [Type] -- type instance (`ts')
+ -> TyCon -- representation tycon (`R')
+ -> TyCon -- => coercion tycon (`Co')
+mkDataInstCoercion name tvs family instTys rep_tycon
+ = mkCoercionTyCon name coArity rule