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From: kwh@bentley.UUCP (KW Heuer)
Newsgroups: net.lang.c
Subject: Re: Boolean Operators Slighted in C
Message-ID: <795@bentley.UUCP>
Date: Tue, 6-May-86 09:44:24 EDT
Article-I.D.: bentley.795
Posted: Tue May  6 09:44:24 1986
Date-Received: Wed, 7-May-86 06:10:35 EDT
References: <12329@ucla-cs.ARPA>
Organization: AT&T Bell Laboratories, Liberty Corner
Lines: 39

In article <12329@ucla-cs.ARPA> jimc@ucla-cs.ARPA (Jim Carter) writes:
>In article <778@bentley.UUCP> kwh@bentley.UUCP (KW Heuer) writes:
>>Btw, you can't have *all* operators extended with "=".  How would you write
>>"v = v < e;"?  (Not that it's useful.)
>
>I think it's useful!  As written, of course, it's semantically invalid,

Whoa!  The operator I was referring to was "v = v < e", which is the clear
generalization of "op=" on operator "<".  This is meaningful in C, because
the boolean result of "<" will be interpreted as an integer.  But it is not
generally useful, because one does not normally use a boolean argument to a
comparison operator like "<".

>but what you really mean is "v <= e" (sic) or, to demonstrate where it's
>really useful,
>     array[horrendous] [subscript] [list] <= bigexpr;
>  rather than 
>     if (array[h][s][l] < bigexpr) array[h][s][l] = bigexpr;

Now we're discussing "if (v < e) v = e;" which means "v = max(v,e);".  This
is indeed a useful operation, but the operator is now "max" rather than "<".

>Now "<=" already means something else so this syntax is not acceptable.
>How about "v < = e" with a mandatory blank?  This is atrocious human
>engineering but at least is parseable.  Anybody have any better ideas?

Yes.  I already mentioned this in the discussion about builtins, but I think
it bears repeating.

Introduce a new operator "<>" for max (and "><" for min).
Add the corresponding assignment operator "<>=" (and "><=") with the above
meaning.

The symbol "<>" is currently meaningless in C, though basic and pascal users
would have a fit.  "|>" and "<|" may be better choices.  "\/" and "/\" would
mimic the mathematical notation, but there may be reasons to avoid the use
of backslash in program source.

Karl W. Z. Heuer (ihnp4!bentley!kwh), The Walking Lint