Xref: utzoo comp.lang.c:11520 comp.arch:5717
Newsgroups: comp.lang.c,comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: compiler detection of potential run-time errors
Message-ID: <1988Jul27.202049.21589@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1988Jul23.221743.22169@utzoo.uucp> <477@m3.mfci.UUCP> <1075@garth.UUCP>
Date: Wed, 27 Jul 88 20:20:49 GMT

In article <1075@garth.UUCP> smryan@garth.UUCP (Steven Ryan) writes:
>Depends on whether all possible programs (including those of monkey
>programmers) or just `practical' programs are considerred. Formal proofs
>of all possible programs are impossible, flat out, no appeal. Formal proofs
>of practical programs depend on how powerful practical has to be to remain
>useful.

My standing comment on this one is "programmers do not write arbitrary
programs".  I have no objection to monkey programmers being told "this
program is so poorly written that verifying the absence of run-time errors
is beyond this compiler's ability".  In fact, I have no objection to real
programmers occasionally getting the same message, provided some attempt
is made to identify the source of the problem.  As it is, I occasionally
have to modify my programs to keep less-than-perfect implementations of
cc or lint happy; an absence-of-run-time-errors checker that required
"unnecessary" changes once in a while would still be worth having.

(I also wonder whether proving absence of run-time errors is sufficiently
weaker than proving correctness that it is fundamentally easier, but
on reflection it seems to me that in the [irrelevant] general case it is
probably equivalent to the halting problem.)
-- 
MSDOS is not dead, it just     |     Henry Spencer at U of Toronto Zoology
smells that way.               | uunet!mnetor!utzoo!henry henry@zoo.toronto.edu