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Puzzlement about DumpSave (and/or DownValues)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg110145] Puzzlement about DumpSave (and/or DownValues)
  • From: James Stein <mathgroup at stein.org>
  • Date: Fri, 4 Jun 2010 08:01:22 -0400 (EDT)

This looks like a bug to me, but I know appearances can deceive!
Cell 1 below defines two symbols: foo and list.
After evaluation of Cell1, I thought
Cell 2 would dump and restore symbol 'foo' but it does not.
Now here is puzzlement:  If you change DumpSave's second argument
from 'list' to '{foo}', the code works !-- even though these are
"identical" expressions:  {foo} === list  evaluates to True.
Here is a clue to what might be the problem: Despite the fact that
foo === list [ [ 1 ] ], they have different DownValues.
Can two symbols with different DownValues really be identical?
(Well, to quibble, they are not both symbols... )

 (* Define a list of Symbols used in compound Heads: *)
ClearAll [ foo, list ];
foo[ 1 ] = { 1, 2, 3 };
list = { foo };

(* Cell 2 fails *)
DumpSave [ "foo.mx", list ];
ClearAll [ foo ];
Get [ "foo.mx" ];   (* Get what was dumped *)

Definition[foo]      (* Alas-- we get'Null'  for foo! *)


This is a simplified example, of course.  I have hundreds of symbols,

not just 'foo', and each is used as a compound head in several different
ways.

I was hoping to dump all these definitions to a single file.

I hope I'm missing something that will make me feel dumb...



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