CPL Varia

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: 01 Feb 87  1410 PST
    From: Dick Gabriel <RPG@SAIL.STANFORD.EDU>

    Moon's writes:

    ``Oh, right, this only happens if you add the extension that the local
    precedence order of a class can be a partial order rather than a total
    order.  We have that in Flavors, and it comes in handy, but I'm not
    proposing to standardize on it at this time.''

    I'm not sure what this means, but whether the local precedence order
    is partial or total the leftmost siblings must come first.

No, the whole point of a partial local precedence order is that it is not
a total order.  Therefore the classes mentioned in the direct superclass
list are not constrained to appear in the class precedence list in
the same order as they appear in the direct superclass list.  Instead,
one specifies the local precedence order explicitly as a set of pairs
(before, after).  (Well, actually, there is a little syntactic sugar,
but it's basically a set of ordered pairs.)

    The example at the start of this message shows that
    intuition isn't going to help much in all cases.

At this point I firmly believe that for any algorithm an example can be
constructed that can be plausibly argued to be unintuitive.  I think the
important thing is for intuition to help in the cases that people expect
to be simple, not in all cases.