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From: gwyn@BRL.ARPA (VLD/VMB)
Newsgroups: net.lang.c
Subject: Re:  Boolean Operators Slighted in C
Message-ID: <825@brl-smoke.ARPA>
Date: Tue, 13-May-86 22:15:18 EDT
Article-I.D.: brl-smok.825
Posted: Tue May 13 22:15:18 1986
Date-Received: Sun, 25-May-86 06:39:49 EDT
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Index to participants:
	>>> Steven Brian McKechnie Sargent
	>> Doug Gwyn
	> Jim Cottrell

>>> New operators like "< =", in addition to being hard to spell and
>>> understand,
>>> facilitate usages that just aren't that common.  I hardly ever want to
>>> say x = (x < y), and I don't mind typing the extra characters. I'm not
>>> interested in paying compiler vendors money for supporting this
>>> (or any other dubious misfeature pounded into the language for
>>> "completeness'sake.")
>>
>> Here is an example where proper use of Boolean data would be violated.
>> A statement like
>> 	x = x < y;
>> should NEVER be used, since it assigns a Boolean result to an
>> arithmetic variable.  This means that a "< =" operator is not
>> a good idea.
> 
> Wrong you are, Doug. You have been thinking in this Boolean paradigm
> for so long that you are missing another Good thing. Implication!
> Given that P and Q are `Boolean' variables (0 or 1), the Logical
> Implication is described by the operator `<='. Thus, the statement
> `x = p <= q;' sets the `boolean' value x to a `boolean' expression.
> Since there are no such things as booleans :-), x, p, & q are integers.
> It's all a matter of interpretation. APL has no `boolean exclusive or'
> operator because the operator `!=' does the same thing (when given
> only zero's or one's). There are sixteen different boolean functions
> with two inputs and one output. They all fit nicely into C operators:
> [table omitted]

Even Boole knew that Boolean operations can be performed
by appropriate arithmetic on {0,1} operands; that is irrelevant.

The original example, x "< =" y;, interpreted as you suggest, would
mean `set x to "x is not implied by y"', if and only if x and y were
Boolean in the first place.  Not only is this of negligible practical
value, but that meaning of the operator differs from its meaning
when applied to non-Boolean values (the general case, and the one I
had in mind when I argued that it was a bad idea).

>> I find data abstraction to be a Good Thing, and have produced
>> much better code since defining a Boolean data type and using
>> it in a strictly type-correct manner.
> 
> This fact doesn't bother people who write in APL, widely considered
> to be the most mathematical language.

APL doesn't offer real facilities for data abstraction.

> Why does it bother you?

Because as a conscientious software engineer I have to produce
reliable and maintainable systems for people to use.
This requires quality standards well beyond what hackers might
feel to be necessary.