Unions between polymorphic variants behind module types

i’m trying to compose two modules in a Module Function with polymorphic variants A.t and B.t to module C with C.t = [A.t|B.t] for the reason that they both have a PV return typ in A.tryMap and B.tryMap and i want to compose C so that C.tryMap = A.tryMap->B.tryMap so that the return type is expanded to include both, but that doesn’t seem to be expressible i think?