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Re: *print-circle*

    Date: Wed, 21 Jan 87 22:12 EST
    From: David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>

    Symbolics' implementation of *print-circle* looks for shared 
    substructures, and it wouldn't surprise me if a lot of other 
    implementations also do so.  It seems like a good idea.  

This is the sort of information I was looking for.  If this is indeed the
common practice, and we all agree it is a good idea, then it should be 
standardized.  So far I have had a number of requests for my code and 
one reply from a person who thought this behavior already was specified 
in the manual.  I have yet to hear any negative comments.

    I could imagine a user demand for separate control
    of circularity detecting and sharing detection....

So could I, but I suspect that it would be harder to get everyone to agree
on introducing a separate control mechanism than it would for us to agree to
make *print-circle* do this, especially if *print-circle* already behaves
this way in many implementations.

I might add that an additional reason to provide a standardized way to
print shared structures is that it's not possible for an ordinary user
to write a general purpose routine to do this without knowing how to get
at the internal representation of structures generated via defstruct.