-- non-recursive newtypes
all_coercions = True
tvs = tyConTyVars tycon
- rhs_ty = ASSERT(not (null (dataConInstOrigDictsAndArgTys con (mkTyVarTys tvs))))
- -- head (dataConInstOrigArgTys con (mkTyVarTys tvs))
- head (dataConInstOrigDictsAndArgTys con (mkTyVarTys tvs))
+ inst_con_ty = applyTys (dataConUserType con) (mkTyVarTys tvs)
+ rhs_ty = ASSERT( isFunTy inst_con_ty ) funArgTy inst_con_ty
-- Instantiate the data con with the
-- type variables from the tycon
- -- NB: a newtype DataCon has no existentials; hence the
- -- call to dataConInstOrigArgTys has the right type args
+ -- NB: a newtype DataCon has a type that must look like
+ -- forall tvs. <arg-ty> -> T tvs
+ -- Note that we *can't* use dataConInstOrigArgTys here because
+ -- the newtype arising from class Foo a => Bar a where {}
+ -- has a single argument (Foo a) that is a *type class*, so
+ -- dataConInstOrigArgTys returns [].
etad_tvs :: [TyVar] -- Matched lazily, so that mkNewTypeCoercion can
etad_rhs :: Type -- return a TyCon without pulling on rhs_ty