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Groups > comp.lang.c > #91662

Re: Synthetic 'unless' keyword

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Keith Thompson <kst-u@mib.org> writes:

> supercat@casperkitty.com writes:
>> On Thursday, August 4, 2016 at 10:52:33 AM UTC-5, Keith Thompson wrote:
>>> One drawback of the `if (!expr)` form is that `!` is a single
>>> character that can sometimes be easy to miss.  Adding a space:
>>> `if (! expr)` helps a bit.  One nice thing about Perl is that you can
>>> write `not` rather than `!`. You can do the same in C with `#include
>>> <iso646.h>`, but that's unfamiliar enough that I don't use it myself.
>>
>> IMHO, that's less of an issue than the fact that ! only binds to the first
>> term, rather than inverting the entire expression.  Given a collection
>> of "if" statements some of which test affirmative conditions and some of
>> which test negative conditions, it becomes necessary to either use different
>> levels of nesting on positive and negative expressions, use doubled-up
>> parentheses on the positive expressions, or else add a redundant double-
>> invert on the positive ones.
>>
>> Extending the grammar by having "if" and "while" accept a
>> "conditional-expression" which is satisfied by either "(expression)"
>> or "!conditional-expression" would quite easily resolve that issue,
>> though I doubt the issue is a big enough problem to justify the change.
>
> So the meaning of
>
>     ! x == y
>
> would differ depending on whether it appears as the condition for an
> "if" or "while" (or, presumably "for", or "do-while", or "?:") or in
> some other context.
>
> No thanks!

I think the suggestion is that you could write if !(exp) and/or
while !(exp) thus avoiding the extra parentheses.  (The required grammar
is sketched in supercats's text, but I think it's been brought up
before.)

-- 
Ben.

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Thread

Synthetic 'unless' keyword jt@toerring.de (Jens Thoms Toerring) - 2016-08-04 09:44 +0000
  Re: Synthetic 'unless' keyword David Brown <david.brown@hesbynett.no> - 2016-08-04 12:21 +0200
  Re: Synthetic 'unless' keyword Mark Storkamp <mstorkamp@yahoo.com> - 2016-08-04 07:01 -0500
    Re: Synthetic 'unless' keyword bert <bert.hutchings@btinternet.com> - 2016-08-04 05:42 -0700
    Re: Synthetic 'unless' keyword Keith Thompson <kst-u@mib.org> - 2016-08-04 08:45 -0700
      Re: Synthetic 'unless' keyword Philip Lantz <prl@canterey.us> - 2016-08-04 21:55 -0700
      Re: Synthetic 'unless' keyword BartC <bc@freeuk.com> - 2016-08-05 10:08 +0100
    Re: Synthetic 'unless' keyword Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-05 01:17 -0700
      Re: Synthetic 'unless' keyword BartC <bc@freeuk.com> - 2016-08-05 10:01 +0100
        Re: Synthetic 'unless' keyword Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-05 04:34 -0700
      Re: Synthetic 'unless' keyword Mark Storkamp <mstorkamp@yahoo.com> - 2016-08-05 09:37 -0500
        Re: Synthetic 'unless' keyword Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-08-06 02:28 -0700
  Re: Synthetic 'unless' keyword jt@toerring.de (Jens Thoms Toerring) - 2016-08-04 13:38 +0000
  Re: Synthetic 'unless' keyword BartC <bc@freeuk.com> - 2016-08-04 15:04 +0100
  Re: Synthetic 'unless' keyword mark.bluemel@gmail.com - 2016-08-04 07:06 -0700
  Re: Synthetic 'unless' keyword Keith Thompson <kst-u@mib.org> - 2016-08-04 08:52 -0700
    Re: Synthetic 'unless' keyword supercat@casperkitty.com - 2016-08-04 09:45 -0700
      Re: Synthetic 'unless' keyword Keith Thompson <kst-u@mib.org> - 2016-08-04 10:23 -0700
        Re: Synthetic 'unless' keyword Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-04 19:39 +0100
          Re: Synthetic 'unless' keyword supercat@casperkitty.com - 2016-08-04 12:02 -0700
            Re: Synthetic 'unless' keyword Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-04 20:33 +0100
            Re: Synthetic 'unless' keyword BartC <bc@freeuk.com> - 2016-08-04 20:42 +0100
              Re: Synthetic 'unless' keyword David Brown <david.brown@hesbynett.no> - 2016-08-05 13:14 +0200
                Re: Synthetic 'unless' keyword Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-05 12:41 +0100
    Re: Synthetic 'unless' keyword mark.bluemel@gmail.com - 2016-08-05 00:53 -0700
  Re: Synthetic 'unless' keyword Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-04 16:43 -0400
    Re: Synthetic 'unless' keyword David Brown <david.brown@hesbynett.no> - 2016-08-05 13:16 +0200
  Re: Synthetic 'unless' keyword jt@toerring.de (Jens Thoms Toerring) - 2016-08-04 23:16 +0000
    Re: Synthetic 'unless' keyword Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-08-05 00:35 +0100
    Re: Synthetic 'unless' keyword Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-04 20:13 -0700
    Re: Synthetic 'unless' keyword Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-05 04:57 -0700
      Re: Synthetic 'unless' keyword BartC <bc@freeuk.com> - 2016-08-05 13:15 +0100
        Re: Synthetic 'unless' keyword Tim Rentsch <txr@alumni.caltech.edu> - 2016-08-18 08:11 -0700
          Re: Synthetic 'unless' keyword BartC <bc@freeuk.com> - 2016-08-18 16:36 +0100
            Re: Synthetic 'unless' keyword supercat@casperkitty.com - 2016-08-18 10:20 -0700
  Re: Synthetic 'unless' keyword Paul N <gw7rib@aol.com> - 2016-08-07 12:56 -0700

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