$ mkConApp data_con [Var len_var, Var repr_var]
to_prod repr_vars@(r : _)
- (ProdRepr { prod_components = tys
+ (ProdRepr { prod_components = tys@(ty : _)
, prod_arr_tycon = tycon
, prod_arr_data_con = data_con })
= do
- len <- lengthPA (Var r)
+ len <- lengthPA ty (Var r)
return . wrapFamInstBody tycon tys
. mkConApp data_con
$ map Type tys ++ len : map Var repr_vars