nlffi cvt vs get

I went back to the "no longer foreign" paper and found the following  
snippet of example code:

fun maxx l = let
   fun x l =
     C.Cvt.ml_double
      (C.Get.double
        (IXDB.S_record.f_x
          (C.Ptr.|*| l)))

The idea being that C.Cvt creates and ML object to avoid any nasty  
interaction with malloc/free on the part of the pointer l.

The problem is that I have basically re-created this code and cannot  
get this to work.

The C.Get.double call returns a type which is incompatible with  
C.Cvt.ml_double

Shouldn' it work ?

If I look at C.sig it looks to be that the types _are_ compatible.

???

Brian


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