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Re: Remembering C's operator precedence rules

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Bart <bc@freeuk.com> writes:

> On 09/03/2019 20:54, Joe Pfeiffer wrote:
>> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>
>>> I was going to post this as a reply, but once finished I thought it
>>> should be a new thread.
>>>
>>> Prompted by recent posts about remembering C's 15 precedence levels for
>>> its 49 operators, I thought I would gather together some remarks about
>>> why I think you can work most of it out for yourself.  I certainly don't
>>> know them all, but I think of them in big blocks (unary, arithmetic,
>>> relational, and so on) which are easy to relate to each other, and only
>>> every now and then do I need to consider the structure within these
>>> blocks of operators.
>>
>> <snip>
>>
>> This isn't unexpected; they are in the order that seemed most intuitive
>> to K&R in 1974 or thereabouts (doing something like putting + above *
>> would have been downright perverse).
>
> That doesn't explain why there are so many.
>
> WHY do &, | and ^ each need, not only a separate level from all other
> operators, but even separate from each other?! What could possibly be
> the advantage?

The advantage could possibly be having to use fewer ()s.  Note (because
I know how you flip arguments around) that I am not saying that there is
no associated disadvantage.  Another might be to allow the language to
gain operators during its development without breaking any old code.
That is explanation given for two of them.

>> The thing is, what's most intuitive depends on everything from context
>> in the program to the current phase of the moon.
>
> There is nothing intuitive about C's operators apart from the 4 levels
> that everyone should know:
>
>    * /        (from school)
>    + -
>    == etc     (from use of 'equals' in school)
>    &&         (from use of 'and' in English)

That unary operators are above these is also, I suspect, intuitive even
to you.  And I can't see how you could argue that having pre- and
post-fix operators separate, and in the order they come, is not also
intuitive.  What else could be done with them without making code clumsy.

> One more level for || needs to be added (I don't know the reasoning
> for that one although I can guess), but after that there was no reason
> for any more really:

Where do assignment operators come?  If you put them in with something
else you might still need another rule because assignment should be
right-associative and most other groups should probably associate to the
left.

So what would be your preferred table?

-- 
Ben.

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Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-09 16:53 +0000
  Re: Remembering C's operator precedence rules Richard Damon <Richard@Damon-Family.org> - 2019-03-09 15:21 -0500
    Re: Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-09 21:41 +0000
  Re: Remembering C's operator precedence rules Keith Thompson <kst-u@mib.org> - 2019-03-09 12:32 -0800
    Re: Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-09 21:21 +0000
      Re: Remembering C's operator precedence rules Richard Damon <Richard@Damon-Family.org> - 2019-03-09 16:42 -0500
        Re: Remembering C's operator precedence rules "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-03-09 14:01 -0800
      Re: Remembering C's operator precedence rules Keith Thompson <kst-u@mib.org> - 2019-03-09 14:17 -0800
        Re: Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-10 00:42 +0000
  Re: Remembering C's operator precedence rules Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-03-09 13:54 -0700
    Re: Remembering C's operator precedence rules Bart <bc@freeuk.com> - 2019-03-09 21:37 +0000
      Re: Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-09 22:01 +0000
      Re: Remembering C's operator precedence rules Richard Damon <Richard@Damon-Family.org> - 2019-03-09 18:59 -0500
        Re: Remembering C's operator precedence rules Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-03-13 09:26 -0700
    Re: Remembering C's operator precedence rules Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-03-13 10:11 -0700
      Re: Remembering C's operator precedence rules Bart <bc@freeuk.com> - 2019-03-13 17:40 +0000
        Re: Remembering C's operator precedence rules Keith Thompson <kst-u@mib.org> - 2019-03-13 15:24 -0700
          Re: Remembering C's operator precedence rules Bart <bc@freeuk.com> - 2019-03-13 23:43 +0000
            Re: Remembering C's operator precedence rules Keith Thompson <kst-u@mib.org> - 2019-03-13 17:43 -0700
        Re: Remembering C's operator precedence rules Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-03-18 08:53 -0700
      Re: Remembering C's operator precedence rules Wouter Verhelst <w@uter.be> - 2019-03-13 22:24 +0200
        Re: Remembering C's operator precedence rules Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-03-13 14:06 -0700
        Re: Remembering C's operator precedence rules Ian Collins <ian-news@hotmail.com> - 2019-03-14 14:28 +1300
          Re: Remembering C's operator precedence rules scott@slp53.sl.home (Scott Lurndal) - 2019-03-14 13:35 +0000
            Re: Remembering C's operator precedence rules Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-03-14 06:55 -0700
            Re: Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-14 16:39 +0000
              Re: Remembering C's operator precedence rules scott@slp53.sl.home (Scott Lurndal) - 2019-03-14 17:37 +0000
                Re: Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-14 20:42 +0000
              Re: Remembering C's operator precedence rules Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-03-14 10:42 -0700
                Re: Remembering C's operator precedence rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-14 23:08 +0000
                Re: Remembering C's operator precedence rules Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-03-15 02:53 -0700
                Re: Remembering C's operator precedence rules Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-03-15 17:52 -0600
  Re: Remembering C's operator precedence rules Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-03-13 12:56 -0700
  Re: Remembering C's operator precedence rules Jens Stuckelberger <Jens_Stuckelberger@nowhere.net> - 2019-03-13 20:14 +0000
  Re: Remembering C's operator precedence rules fir <profesor.fir@gmail.com> - 2019-03-19 14:17 -0700

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