CATCH-ALL

[Bernard S. Greenberg <BSG@SCRC-STONY-BROOK.ARPA>]

    Date: 19 Nov 1985 1641-PST
    From: Rem@IMSSS

    MacLISP and ZetaLisp (Symbolics LISP Machine) had/have that feature too.
    CATCH-ALL was/is a macro that generates the appropriate (:CATCH NIL form).
    But the ZetaLisp manual says if you think you need this you probably want
    UNWIND-PROTECT instead.
    Perhaps what we really need is an extra feature in UNWIND-PROTECT, whereby
    the cleaup forms can find out why they are being called. Some global
    variable can be SETQ'd by the unwinding mechanism, to NIL in the case of
    falling out of the main form nomally, to ERROR in the case of an error
    signal that is being passed up to an errset, or to the tag if a THROW
    is happening. This would give the cleanup form the opportunity to
    intercept certain tags in the same way CATCH-ALL did in MacLISP, but
    maybe be a bit cleaner? Or maybe we really need CATCH-ALL because it
    woul be cleaner than the enhanced UNWIND-PROTECT. Esthetic opinion anybody?
    -------

I think this is all pretty disgusting, and a blatant controversion of
modularity.  I'd like to hear the proposed use of CATCH-ALL, or
whatever.  Please don't confuse it with a need to catch all -errors-,
which is a function of an error system, not catch/throw semantics.