exportFn and evalStream questions

Dear SML/NJ gurus,

Would it be possible for someone to please answer 1 or more of the
following questions about exportFn and evalStream?

1. Where does exportFn discard the contents of the top-level
   environment?  I've been looking through the source code and if I
   have seen it I certainly have not recognized it.  It is clear that
   this is happening both from the documentation and also from the
   fact that subsequent uses of evalStream or useStream seem to
   complain that all identifiers are undefined.

2. Is it possible to get the same space-saving effect as exportFn
   without having to write a heap image to disk and then exec a fresh
   sml process to load the heap image?  (Another problem this would
   avoid is the fact that exportFn closes all files and clears the
   signal handler table.)  Is it enough to clear the top-level
   environment by hand and then let the garbage collector do its work?
   And does anyone have any example SML code that clears the top-level
   environment correctly?  Can doing this release memory back to the
   system?  If not, can doing this at least reduce the amount of work
   the garbage collector needs to do regularly?

3. Is is possible to preserve some portion of the top-level
   environment across an exportFn?  It would be enough to preserve the
   constructors and type names of some datatypes and built-in types,
   so that evalStream and useStream could still work for parsing, type
   checking, and pretty printing datatype values.

4. Can someone provide an example of constructing a custom environment
   for use with evalStream?  Any example would do.  I already know how
   to do something that seems equivalent to the top-level environment.
   It would be particularly nice if the example showed how to include
   just datatype constructors and type names.

Thanks for your time in considering my questions.  And extra thanks
if anyone answers even just one of my questions!

-- 
Joe


-- 
Heriot-Watt University is a Scottish charity
registered under charity number SC000278.


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