If you want to give the latest open higher priority, you can add !
to it.
open! Blah
But this is a last resort, it is better to do the following:
Write the module name in front of the first field of a record to explicitly tell the type system from which module it is imported.
let x = { Meh.data: 7 }
let y = { Blah.data: 9 }
And it is necessary because you may indeed ending up misguiding the type system.
Generally, I’d use open very sparingly. If you have a module with a very long name that you use quite often you can also alias it:
module MyAlias = MyVeryVeryLongModuleName