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From: mph@lion.inmos.co.uk (Mike Harrison)
Newsgroups: comp.lang.misc
Subject: Re: do...while vs. repeat...until (was: Errors aren't that simple)
Message-ID: <4879@ganymede.inmos.co.uk>
Date: 23 Mar 90 12:51:41 GMT
References: <16188@haddock.ima.isc.com> <9130009@hpavla.AVO.HP.COM> <OVB2S3Bxds13@ficc.uu.net> <16249@haddock.ima.isc.com>
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Reply-To: mph@inmos.co.uk (Mike Harrison)
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In article <16249@haddock.ima.isc.com> karl@haddock.ima.isc.com (Karl Heuer) writes:
>(Followups to comp.lang.misc.  I'm not talking about C; I'm talking about loop
>constructs in general.)
> ...
>To take a concrete example, let's ignore the existence of <ctype.h> and
>suppose that we want to test whether or not a given character is a lowercase
>letter.  I claim that, to me, the condition "(c >= 'a' && c <= 'z')" is a
>simpler expression than "(c < 'a' || c > 'z')".  I immediately recognize the
>idiom in the former, but the latter causes a perceptible delay as I mentally
>translate the condition.  (If you disagree with this example, invent another
>one--unless you want to claim that there is *no* condition that is simpler
>than its inverse.)

But how about:

    subtype LOWER_CASE_LETTERS is CHARACTER range 'a' .. 'z';

    C : CHARACTER;

    GET(C);
    if C in LOWER_CASE_LETTERS then ...

(Guess which language :-))

For loop control structures I always liked Algol 68, where you could do all
the work in the Condition part, with an empty loop body, eg:

    'while' 'if' a[i] > i 'then' i +:= 1; 'true' 'else' 'false' 'fi'
        'do'
            'skip'
        'od'

And for the ultimate in conditional expressions:

    'if' x = 1 'then' y 'else' z 'fi' := x;


Mike,


Michael P. Harrison - Software Group - Inmos Ltd. UK.
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