sig
val ( ++ ) :
('a, 'b) Dispatch_arg.Spec.t ->
('c, 'a) Dispatch_arg.Spec.t -> ('c, 'b) Dispatch_arg.Spec.t
val ( --> ) :
('a, 'b) Dispatch_arg.Spec.t ->
('a, 'c) Dispatch_arg.Spec.Result.t -> ('c, 'b) Dispatch_arg.Spec.t
end