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From: throopw@dg_rtp.UUCP (Wayne Throop)
Newsgroups: net.lang.c
Subject: Re: Boolean Operators Slighted in C
Message-ID: <345@dg_rtp.UUCP>
Date: Thu, 8-May-86 16:36:34 EDT
Article-I.D.: dg_rtp.345
Posted: Thu May  8 16:36:34 1986
Date-Received: Sun, 11-May-86 00:32:57 EDT
References: <838@ihwpt.UUCP> <778@bentley.UUCP> <12329@ucla-cs.ARPA>
Lines: 32

> jimc@ucla-cs.ARPA (Jim Carter)
>>  kwh@bentley.UUCP (KW Heuer)
>>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,
> 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;

The point is not that it isn't useful to collapse multiple array (or
other clumsy) references.  The point is that in "e1 = e1 < e2", the "<"
operator assumes arguments with numeric semantics and yeilds a value
with boolean semantics.  Since e1 is both an argument and a result, this
expression isn't very meaningful.  The fact that C overloads the numeric
types with boolean meaning doesn't make this a useful thing to do.
Interestingly, if e2 also has boolean semantics, the "e1 < e2" gives the
same result as "!e1 && e2" (ignoring side effects).  Doesn't seem like a
primitive to clammor for in the language, nor does "<" seem like a good
symbol for it if it were a primitive.

Now, I know what all you hackers are saying.  You're saying "But Wayne,
how did you become a LOVE GOD?" (What's that?  net.lang.c?  Not
net.panting.singles?  Sorry, I mean) "But Wayne, I just don't care
diddly about numeric vs boolean type safety debates.  I just want
something that'll WORK." Ok.  Fine.  But you'll probably be looking for
subtle and disgusting bugs in programs that contain oddities like
"e1 = e1 < e2" long after others are happily using working programs that
don't.  So there.
-- 
Wayne Throop      <the-known-world>!mcnc!rti-sel!dg_rtp!throopw