Issue: PRINT-CIRCLE-STRUCTURE (Version 1)

[Jon L White <jonl@lucid.com>]

re:     Date: 5 Oct 88 20:47 PDT
	From: masinter.pa@Xerox.COM

	Circularities need only be detected for
	objects that would normally be printed by the default structure
	print-function.

    I cannot accept any proposal with this kludgey restriction in it.  If
    circularities are going to be detected at all, they should be done
    right.  It's not difficult to call the user-defined print-function once
    with a special stream argument that detects what the function prints
    (i.e. what calls to WRITE and equivalent functions and FORMAT directives
    it makes using that stream), and use that for circularity detection.
    That's how the Symbolics Genera implementation works.

A "first cut" implementation is merely to descend all components of objects
when looking for circularities.  At worst this will cause spurious #n='s 
to appear in the output (which CLtL doesn't seem to proscribe), and may 
impose some extra traffic on the "looker" (probably a hash-table).

-- JonL --