From mboxrd@z Thu Jan  1 00:00:00 1970
Subject: Re: [9fans] same functions everywhere
From: John Murdie <john@cs.york.ac.uk>
To: 9fans@cse.psu.edu
Cc: john@cs.york.ac.uk
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Date: Sat, 10 May 2003 18:17:05 +0100
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On Fri, 2003-05-09 at 19:24, northern snowfall wrote:
> >
> >
> >And then what should one do? Suppose that a "genuinely surprising
> >condition" occurs when a launch vehicle is a few tens of seconds off the
> >ground; just what should the program do?
> >
> Hopefully, the programmer would have enough sense to
> see this coming? The point of smart design is to facilitate
> the unexpected, I don't think that means exceptions are
> the answer. Certainly, this argument is slightly dramatic,
> wouldn't you agree, John?

That's precisely my point (and, yes, it is slightly dramatic but, then,
people do code launch vehicle control systems). I'm glad we agree. I
would hope that the analyst/programmer[s] would have designed the code
in such a way that it straightforwardly describes what should be done in
all anticipatable circumstances. I don't think it is worth betting that
ad hoc exception-handling code can cope with the "genuinely surprising
condition".

I think that exceptions encourage careless, lazy, analysis and
programming, and produce code that is unclear and (more) difficult to
reason about than traditional sequential, predicate-transforming, code.
Yes, they can be used as a short-hand notation to code e.g. the rule
"whenever an arithmetic overflow occurs in this section of code, I don't
care; just quit (or do the calculation again with different parameters,
or whatever)", but they are also used as an inadequate substitute for
proper systems analysis and coding. I think that this was Rob Pike's
point, with which I agree.

(To counter my own argument, though, I remember reading something that -
I think - Doug McIlroy wrote about error handling code in telephone
exchanges; the code had been known to recover successfully from errors
that the designers had not anticipated. That said, I'd rather not trust
to such luck.)

John A. Murdie