Let_syntax.Let_syntax
val return : 'a -> ('a, _, _) X.t
val map : ('a, 'd, 'e) X.t -> f:('a -> 'b) -> ('b, 'd, 'e) X.t
val both : ('a, 'd, 'e) X.t -> ('b, 'd, 'e) X.t -> ('a * 'b, 'd, 'e) X.t
module Open_on_rhs : Intf.S