Evaluating functor application only once

In the absence of applicative functors, I am trying to ensure that 
certain functors are applied only once.  (Without going into too much 
detail, the issue is that a library that needs e.g.
   structure GUInt8Array = CArray(GUInt8)
can't know whether another library has already introduced the same 
structure.)

My approach is to have the functor application in its own SML file:

   <Name>.sml
     structure <Name> = F(X)

With Poly/ML, which doesn't support MLB files, I can have a variant of 
"use" that only processes a file <Name>.sml if there is no existing 
structure <Name>.

With MLB files, I plan to also introduce <Name>.mlb (which contains only 
<Name>.sml) and refer to that, so that it won't have any effect if 
another library has already evaluated <Name>.mlb.  What I am doing is 
inherently complier-specific, so I wondered - is there is any other 
MLton-specific way of achieving the same thing, e.g. MLB extension?

Phil

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