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Re: New C operator -- would it be a good idea?

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On 2012-09-10, mike3 <mike4ty4@yahoo.com> wrote:
> Hi.
>
> I was wondering about this. I saw this posting on this site:
>
> http://stackoverflow.com/questions/1642028/what-is-the-name-of-this-operator
>
> where they were mentioning a fake "operator", an artifact of how the C
> language is interpreted, that looked like it caused the value of a
> variable to "go to" another. Namely, "x --> 0" in the code was just
> "x-- > 0", giving it the appearance of having the effect of
> "incrementing x toward 0". Now, I was wondering: would this be a good
> idea for a new real operator for the C language? Namely, "a -->
> b" (and "b <-- a") as real operators that could increment a toward b.
> Or would it be pretty worthless?

I can give you five reasons why not.

1. It would be worthless because using it would make your code nonportable to all
   the compilers which have decided to ignore implementing such a thing.
   The best feature of C is stability, and the best dialect for that is ISO C90,
   (with perhaps some very judicious use of new-fangled libraries from C99 and C11.)

2. The --> and <-- syntax has an existing meaning. It is tokenized as {--}{>}
   and {<}{--}.  The expression a-->b is already valid C. It means (a--) > (b).
   In other words, decrement a, and test whether the prior value is greater than b.
   So your proposal horribly breaks the current language, making it a complete
   nonstarter.

3. Not having b <-- a, you have to write something like a = (a < b) ? a + 1 : a - 1;
   This is not a big deal and you can hide it behind a macro, except that it evaluates
   a twice:

     #define INCTOWARD(A, B) ((A) = (A) < (B) ? (A) + 1 : (A) - 1)

   See? You can implement the operator in C already, just not with the syntax you want,
   and with a small semantic concession. But this means that the --> operator
   does not express anything which cannot be expressed already, it just makes a
   small, incremental semantic improvement over the macro. A small, incremental
   improvement is harder to justify. Moreover, the syntax that you want breaks
   the existing syntax (point 2 above), whereas the INCTOWARD macro doesn't.

4. There is no corresponding machine instruction in any popular machine
   instruction set, so you're not going to get better code by providing an inctoward
   operator in the language.  And even if there is a single machine instruction
   for doing (A < B ? A + 1 : A - 1), a compiler just has to recognize this
   syntax tree pattern, and check a few constraints and then use the
   instruction. It is not strictly necessary to have a dedicated operator. 
   For instance, some instruction sets have a division instruction which yields both
   the quotient and the modulus. Compilers recognize code like
   a = b / c; d = b % c and emit just one division instruction from which the
   quotient and modulus are obtained for a and d.

5. A trivial new arithmetic operator is not going to lend expressivity to the C language.
   And anyway, programmers don't need C to be expressive. By and large they
   need it to be a "portable assembler". If you want expressivity, you invent
   another programming language and then interpret it with C, or compile it to C.
   That language can easily have an A <-- B operator, which expands into
   the appropriate C (with clean evaluation semantics and everything).

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Thread

New C operator -- would it be a good idea? mike3 <mike4ty4@yahoo.com> - 2012-09-10 12:48 -0700
  Re: New C operator -- would it be a good idea? "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2012-09-11 14:27 -0400
    Re: New C operator -- would it be a good idea? "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-09-11 16:53 -0700
  Re: New C operator -- would it be a good idea? Kaz Kylheku <kaz@kylheku.com> - 2012-09-11 19:24 +0000
    Re: New C operator -- would it be a good idea? "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2012-09-11 15:56 -0400
      Re: New C operator -- would it be a good idea? Keith Thompson <kst-u@mib.org> - 2012-09-11 14:15 -0700
      Re: New C operator -- would it be a good idea? mike3 <mike4ty4@yahoo.com> - 2012-09-11 15:56 -0700
        Re: New C operator -- would it be a good idea? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-09-12 00:56 -0700
          Re: New C operator -- would it be a good idea? "BartC" <bc@freeuk.com> - 2012-09-12 10:55 +0100
            Re: New C operator -- would it be a good idea? "io_x" <a@b.c.invalid> - 2012-09-13 07:47 +0200
              Re: New C operator -- would it be a good idea? "BartC" <bc@freeuk.com> - 2012-09-13 10:47 +0100
    Re: New C operator -- would it be a good idea? mike3 <mike4ty4@yahoo.com> - 2012-09-11 15:25 -0700
      Re: New C operator -- would it be a good idea? David Brown <david@westcontrol.removethisbit.com> - 2012-09-12 09:39 +0200
        Re: New C operator -- would it be a good idea? mike3 <mike4ty4@yahoo.com> - 2012-09-12 08:33 -0700
          Re: New C operator -- would it be a good idea? David Brown <david@westcontrol.removethisbit.com> - 2012-09-13 09:53 +0200
    Re: New C operator -- would it be a good idea? falk@rahul.net (Edward A. Falk) - 2012-09-12 17:43 +0000
      Re: New C operator -- would it be a good idea? mike3 <mike4ty4@yahoo.com> - 2012-09-12 15:35 -0700
      Re: New C operator -- would it be a good idea? Ike Naar <ike@iceland.freeshell.org> - 2012-09-13 06:34 +0000
        Re: New C operator -- would it be a good idea? "BartC" <bc@freeuk.com> - 2012-09-13 11:47 +0100
      Re: New C operator -- would it be a good idea? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-09-13 23:52 -0700
        Re: New C operator -- would it be a good idea? Ike Naar <ike@iceland.freeshell.org> - 2012-09-14 07:53 +0000
          Re: New C operator -- would it be a good idea? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-09-14 11:46 +0100
            Re: New C operator -- would it be a good idea? JohnF <john@please.see.sig.for.email.com> - 2012-09-14 13:17 +0000
          Re: New C operator -- would it be a good idea? John Bode <jfbode1029@gmail.com> - 2012-09-14 11:35 -0700
        Re: New C operator -- would it be a good idea? Keith Thompson <kst-u@mib.org> - 2012-09-14 02:04 -0700
        Re: New C operator -- would it be a good idea? Kaz Kylheku <kaz@kylheku.com> - 2012-09-14 21:11 +0000
      Re: New C operator -- would it be a good idea? Ben Pfaff <blp@cs.stanford.edu> - 2012-09-14 11:39 -0700
  Re: New C operator -- would it be a good idea? "BartC" <bc@freeuk.com> - 2012-09-11 22:32 +0100
    Re: New C operator -- would it be a good idea? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-09-11 15:19 -0700
  Re: New C operator -- would it be a good idea? gordonb.22y0w@burditt.org (Gordon Burditt) - 2012-09-11 17:27 -0500
    Re: New C operator -- would it be a good idea? mike3 <mike4ty4@yahoo.com> - 2012-09-11 18:51 -0700
      Re: New C operator -- would it be a good idea? "BartC" <bc@freeuk.com> - 2012-09-12 10:49 +0100
      Re: New C operator -- would it be a good idea? Greg Martin <greg@softsprocket.com> - 2012-09-12 23:23 -0700
        Re: New C operator -- would it be a good idea? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-09-13 12:08 +0100
          Re: New C operator -- would it be a good idea? Keith Thompson <kst-u@mib.org> - 2012-09-13 15:20 -0700
      Re: New C operator -- would it be a good idea? gordonb.h093l@burditt.org (Gordon Burditt) - 2012-09-14 15:13 -0500
  Re: New C operator -- would it be a good idea? Rui Maciel <rui.maciel@gmail.com> - 2012-09-14 20:38 +0100

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