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From: rcd@nbires.UUCP
Newsgroups: net.lang.c
Subject: Re: Boolean Operators Slighted in C
Message-ID: <754@nbires.UUCP>
Date: Fri, 9-May-86 01:31:54 EDT
Article-I.D.: nbires.754
Posted: Fri May  9 01:31:54 1986
Date-Received: Wed, 14-May-86 01:07:22 EDT
References: <838@ihwpt.UUCP> <778@bentley.UUCP> <12329@ucla-cs.ARPA>
Organization: NBI,Inc, Boulder CO
Lines: 22

> >Btw, you can't have *all* operators extended with "=".  How would you write
> >"v = v < e;"?  (Not that it's useful.)

A more precisely stated rule, for C, would be that you can extend any
dyadic operator whose result type is the same as the type of the first
operand, but...

> 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;

Cf. Icon, in which the success/failure of a conditional is separate from
its value.  Icon's <= operator (as all of its relational operators) yields
the value of its right operand if it succeeds; otherwise it fails (meaning
no result is produced).  The semantics described above in ">" is just that
of Icon's <:= operator.
-- 
Dick Dunn	{hao,ucbvax,allegra}!nbires!rcd		(303)444-5710 x3086
   ...Cerebus for dictator!