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...