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Re: Import "HeldExpression" element of MX file

• To: mathgroup at smc.vnet.net
• Subject: [mg103324] Re: Import "HeldExpression" element of MX file
• From: dr DanW <dmaxwarren at gmail.com>
• Date: Tue, 15 Sep 2009 04:26:09 -0400 (EDT)
• References: <200909101125.HAA18361@smc.vnet.net> <h8d54o$112$1@smc.vnet.net>

I have been looking at this for a couple of weeks (I may be the poster
of the "previous question" that started this thread).

I started this with the mistaken impression that a .mx file was simply
a binary form of a .m file, but I am coming to appreciate that the
nature of the data stored in these files is fundamentally different.
Most of Mathematica input is in the form of expressions; a .m file
stores a literal, ASCII representation of these expressions as could
be input directly from a keyboard. However, Mathematica interprets
input expressions to build internal tables of values and attributes,
which we can get a peek at using Information[], ??, UpValues[], or
DownValues[].  DumpSave[] creates a binary dump of these internal
value tables to a .mx file, in a format I am presuming is a close
mirror of the internal memory registers.

So, when we read in a .mx file, we should not expect to get the
expressions the programmer typed in (in Held form or otherwise), but
the somewhat pre-digested form that Mathematica uses internally.  This
may still provide us some insight into how a function works, but not
as insightful as seeing the original code.

Daniel

• References:
  • Import "HeldExpression" element of MX file
    • From: Szabolcs Horvát <szhorvat@gmail.com>