Proposal #1

[David C. Plummer <DCP@QUABBIN.SCRC.Symbolics.COM>]

    Date: Sun, 13 Jul 1986  23:33 EDT
    From: "Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>


    I don't think that your severity proposal can possibly fly.  
One of us is confused.  I see Proposal#1 being to expand 2 classes of
errors to 3.  I see my extension doing the same thing but expanding to 5
classes instead of 3.  We should probably just drop it.
								 The
    decision about whether to signal an error is a function of two things:
    the severity of the effects of the error and the cost of detecting it.
    The cost of detecting various kinds of errors varies tremendously from
    one implementation to another (and the danger posed by non-detection can
    vary as well) so we can't really create a scalar ranking of errors and
    standardize it across all implementations.  This is a multi-dimensional
    problem.

    I thought we had discussed your second point at some length, when Sandra
    Loosemore expressed dismay at having to provide two versions of all
    built-in functions, but I'll try again using your AREF example.

	...

OK.  Sorry if this was already explained as explicitly as you did in
some previous mail.