Dumping data structures with circular references.

[Richard Lamson <rsl%max-fleischer.ila-sf.dialnet.symbolics.com@RELAY.CS.NET>]

    Date: Sat, 4 Nov 89 15:06 PST
    From: Robert D. Pfeiffer <RDP@ALAN.LAAC-AI.Dialnet.Symbolics.COM>

	Date: Fri, 3 Nov 89 13:57 PST
	From: rsl@MAX-FLEISCHER.ILA-SF.Dialnet.Symbolics.COM (Richard Lamson)

    Anyway, to the best of my knowledge, I should be reachable with the
    following address:

    RDP@ALAN.KAHUNA.DECNET.LOCKHEED.COM

OK, let's try it.

	    Date: Fri, 3 Nov 89 09:19 PST
	    From: Robert D. Pfeiffer <RDP@ALAN.LAAC-AI.Dialnet.Symbolics.COM>

	    Anyone have an idea how best to solve this?  Maybe write two separate
	    files with SYS:DUMP-FORMS-TO-FILE and then append them after the fact?
	    Is it easy to append two binary files (or are there subtleties of the
	    file format that will screw me)?  Or if I had the equivalent of
	    SYS:DUMP-FORMS-TO-STREAM I guess I would be home free.  Then, I could
	    simply do my own WITH-OPEN-FILE once and call SYS:DUMP-FORMS-TO-STREAM
	    twice on it.

	Here is a synopsis of what I did the last time I needed to do this:

	  (defmethod (dump database) (filename)
	    (si:writing-bin-file (bin-stream filename)
	      (si:dump-attribute-list `(:package ,(package-name *package*) :mode :Lisp) bin-stream) 
	      (do-all-objects (object)
		(si:dump-form-to-eval (creation-form object) bin-stream))
	      (do-all-objects (object)
		(si:dump-form-to-eval (initialization-form object)))))
[...]
		   It's also a good idea not to put in the QUOTE if you can avoid it,
	since this can make your BIN file much larger.  

    Really, "much larger"?  I'm surprised that it's that significant.

I was too.  The BIN file was about 40% bigger when I left in the quotes.
It turns out to contain three or so bytes to reference QUOTE (after the
first reference) plus a couple for the BIN-OP-LIST which constructs the
list `(QUOTE ,whatever) per object.  Many of my objects were small
integers and short strings which only take a few bytes to represent in
the data file.

    --------------------------------------------------------------------------------
	Date: Fri, 03 Nov 89 16:45:58 -0500
	From: kanderso@DINO.BBN.COM

    Well, I see that each of the examples gives me enough raw material to
    accomplish this task.  My final concern is that both RSL and KANDERSO
    use SI:WRITING-BIN-FILE, SI:DUMP-ATTRIBUTE-LIST, and
    SI:DUMP-FORM-TO-EVAL.  I always prefer to avoid using undocumented
    functions when possible.  In this case maybe I can't.  Any opinions on
    how safe these are to build on?  For example, will I still be safe in
    Release 8.0?  Hopefully, in the longer term I can rewrite this stuff
    using the ANSI Common Lisp MAKE-LOAD-FORM that Moon mentioned.

I don't think they will be changing the binary file dumper/loader
functions any time soon; they haven't changed since I first needed to
figure out how to do this kind of thing about 5 years ago.