module S1: sig .. end
sig
end
type ('a, 'b) writer = 'a Type_class.writer0 -> 'b Type_class.writer0
('a, 'b)
'a Type_class.writer0 -> 'b Type_class.writer0
type ('a, 'b) reader = 'a Type_class.reader0 -> 'b Type_class.reader0
'a Type_class.reader0 -> 'b Type_class.reader0
type ('a, 'b) t = 'a Type_class.t0 -> 'b Type_class.t0
'a Type_class.t0 -> 'b Type_class.t0