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SCL condition system

    Date: Fri, 29 Jun 90 13:59 EDT
    From: Kent M Pitman <KMP@STONY-BROOK.SCRC.Symbolics.COM>

    Boy, I can't believe Barry alluded to all this low-level undocumented
    junk without adding a disclaimer against actually programming
    directly using those things. 

Well, he had already found some of the variables himself, and had
confused their roles; I was simply responding at the same level of
detail as his question.  I hoped he was just trying to *understand* the
implementation, not program with it.  Besides, various people inject
that disclaimer often enough that I don't feel the need to repeat it.
(Also, as a maintainer of code that *does* play with debugger internals
(we have code that dynamically adds type-specific debugger special
commands) I'd be hypocritical if I did.)

Be happy that I revised my message before sending it; an earlier version
also mentioned DBG:*CONDITION-HANDLER-LISTS*, the variable that actually
defines the order in which the various types of handlers are searched
(boy, you could really confuse the condition system by changing this!).

    See the documentation on
    conditions (cited by Barry above) for the full story.  It's much
    too detailed to go into here.

Specifically, the documentation section "Finding a Handler" describes
this mechanism pretty well, but without getting too deep into
implementation details.  For instance, it mentions interactive handlers,
but not the variable *INTERACTIVE-HANDLERS* (which apparently isn't