Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!usc!trwind!saturn!simpson
From: simpson@saturn.ind.trw.com (Scott Simpson)
Newsgroups: comp.lang.ada
Subject: Re: Ada functions versus arrays (i.e. () vs [] )
Message-ID: <3011@trwind.UUCP>
Date: 2 Mar 90 23:46:41 GMT
References: <184@trwacs.UUCP> <598@software.software.org> <5619@crdgw1.crd.ge.com> <608@software.software.org> <6281@bd.sei.cmu.edu>
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Reply-To: simpson@trwind.trw.com (Scott Simpson)
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In article <6281@bd.sei.cmu.edu> firth@sei.cmu.edu (Robert Firth) writes:
>In article <608@software.software.org> blakemor@software.org (Alex Blakemore) writes:
>
>>I agree that side effects are best avoided - they definitely mess up this
>>scheme.  I assume the language designers left them in for the 
>>very few times when they are justifiable (e.g. next_random_number).
>>Quite possibly a language design error forced on them by C programmers :-)
>
>As I recall, we left them in for the same reason Algol-60 did: it is
>impossible to rule out the bad uses without also ruling out the good
>ones.  It is the responsibility of the programmer not to employ the
>bad uses.

Meyer summed this up much more beautifully I think in his book
Object-Oriented Software Construction when he said that side-effects
are harmless when they only affect the *concrete* state and not the
*abstract* state.  This division is important.  See section 7.7.3, page
135 of OOSC.
Scott Simpson    TRW Information Networks Division    simpson@trwind.trw.com