Groups > comp.lang.c > #162027

Re: How to disambiguate macro?

From	Bart <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: How to disambiguate macro?
Date	2021-07-21 20:47 +0100
Organization	A noiseless patient Spider
Message-ID	<sd9tkt$edf$1@dont-email.me> (permalink)
References	(8 earlier) <8735s7ls5z.fsf@bsb.me.uk> <sd9a5q$qs0$1@dont-email.me> <87sg07k82m.fsf@bsb.me.uk> <sd9ib5$qh1$1@dont-email.me> <sd9mhe$q8b$1@dont-email.me>

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On 21/07/2021 18:46, David Brown wrote:
> On 21/07/2021 18:34, Bart wrote:
>> On 21/07/2021 16:20, Ben Bacarisse wrote:
>>> Bart <bc@freeuk.com> writes:
>>>
>>>> On 21/07/2021 14:20, Ben Bacarisse wrote:
>>>>> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>>>>
>>>>>> Neither B nor BCPL had short-circuit logical operators, relying
>>>>>> instead
>>>>>> on bitwise & and |, as did early C.
>>>>> Minor correction.  B didn't have short-circuit & and | as such, but it
>>>>> had a weird rule that in conditional contexts like
>>>>>      if (a & b) ...
>>>>> the operator short-circuited!  C rightly ditched this contextual
>>>>> interpretation in favour of explicitly short-circuiting operators.
>>>>
>>>> That's not so weird. I used to have something similar (not in C) where
>>>> 'A and B' (ie. logical and, also 'or') short-circuited in conditional
>>>> expressions as used in 'if' and 'while' control expressions, which
>>>> tended to be implemented with branching.
>>>>
>>>> But in ordinary expressions, they didn't.
>>>
>>> I'm don't see how this would persuade someone that it's not weird.  A
>>> private language is never going to be used by someone other than the
>>> world authority on its semantics.
>>>
>>> In public-facing languages, such context-sensitive semantics seem to me
>>> to be the epitome of "weird".
>>>
>>
>> In BASIC, "=" was used for assignments, and "=" was also used as an
>> equality operator.
>>
>> Those two contexts didn't clash, so there wasn't any confusion.
>>
>> It's similar with the special expression that follows if, while etc; the
>> language can simply say that is a separate context.
>>
>> In my case, because control expression were expected to be full of
>> branching anyway, but expressions had linear execution. Nowadays
>> branchless code is fashionable.
> 
> That makes little sense.
> 
> In an "if", etc., your controlling expression is an expression.  In an
> assignment, or other expression, you are using an expression.
> 
> Are you suggesting that:
> 
> 	x = a && b;
> 
> 	if (a && b) ...
> 
> are clearly different contexts and should have different semantics,
> despite "a && b" being an expression in each case?

These do different things. One results in a concrete 1 or 0 boolean 
value. The other determines whether or not you jump to some label.



> What about
> 
> 	if a && b 	(for languages that don't need parenthesis)
> 
> and
> 
> 	if (a && b)
> 
> ?
> 
> What about
> 
> 	x = a && b;
> 	if (x) ....
> 
> 
> It's fine to have the same symbol used in different contexts - look at
> how often commas are used in most languages.  Having an operator give
> different meanings depending on other code around it (other than the
> operands), is asking for trouble.

I'm not good at keeping old versions of languages. But one I've just 
tried didn't even allow && in a normal expresion. It meant having to write:

    x = a && b;

as the equivalent of:

    x = (a && b ? 1 : 0);

So here && still has one behaviour.

But now all my languages support short-circuiting logic ops in any 
context. One idea for non-short-circuiting versions of && and || was 
dropped (I had too many features already), but it would have allowed:

   if task1() andb task2() then
       println "Both succeeded"
   end

Here these are independent and you want to attempt both even if the 
other failed.

Thread

How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-20 11:15 +0000
  Re: How to disambiguate macro? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-20 13:49 +0100
    Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-20 12:56 +0000
      Re: How to disambiguate macro? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-20 15:36 +0100
        Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-21 01:48 +0000
          Re: How to disambiguate macro? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-07-20 19:18 -0700
          Re: How to disambiguate macro? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-20 20:27 -0700
            Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-21 04:15 +0000
              Re: How to disambiguate macro? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-21 02:00 -0700
              Re: How to disambiguate macro? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-07-21 06:02 -0400
          Re: How to disambiguate macro? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-07-21 06:00 -0400
            Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-21 10:10 +0000
              Re: How to disambiguate macro? Bart <bc@freeuk.com> - 2021-07-21 11:30 +0100
              Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-21 13:31 +0200
              Re: How to disambiguate macro? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-21 13:02 +0100
                Re: How to disambiguate macro? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-21 14:20 +0100
                Re: How to disambiguate macro? Bart <bc@freeuk.com> - 2021-07-21 15:15 +0100
                Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-21 16:28 +0200
                Re: How to disambiguate macro? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-21 16:20 +0100
                Re: How to disambiguate macro? Bart <bc@freeuk.com> - 2021-07-21 17:34 +0100
                Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-21 19:46 +0200
                Re: How to disambiguate macro? Manfred <noname@add.invalid> - 2021-07-21 20:42 +0200
                Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-22 08:37 +0200
                Re: How to disambiguate macro? Bart <bc@freeuk.com> - 2021-07-21 20:47 +0100
                Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-22 08:47 +0200
                Re: How to disambiguate macro? Bart <bc@freeuk.com> - 2021-07-22 11:31 +0100
                Re: How to disambiguate macro? antispam@math.uni.wroc.pl - 2021-07-22 14:37 +0000
                Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-22 18:15 +0200
                Re: How to disambiguate macro? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-21 21:19 +0100
                Re: How to disambiguate macro? Manfred <noname@add.invalid> - 2021-07-21 15:42 +0200
                Re: How to disambiguate macro? scott@slp53.sl.home (Scott Lurndal) - 2021-07-21 15:39 +0000
              Re: How to disambiguate macro? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-07-21 09:22 -0700
              Re: How to disambiguate macro? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-07-21 17:24 -0400
                Re: How to disambiguate macro? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-21 16:42 -0700
                Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-22 05:49 +0000
                Re: How to disambiguate macro? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-07-22 19:11 -0400
                Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-22 05:30 +0000
                Re: How to disambiguate macro? scott@slp53.sl.home (Scott Lurndal) - 2021-07-22 14:14 +0000
                Re: How to disambiguate macro? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-07-22 17:06 +0100
                OT: possessive adjectives (Was: How to disambiguate macro?) Manfred <noname@add.invalid> - 2021-07-22 15:04 +0200
                Re: OT: possessive adjectives Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 13:37 -0700
          Re: How to disambiguate macro? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 13:58 -0700
  Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-20 14:50 +0200
    Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-20 13:19 +0000
      Re: How to disambiguate macro? Bart <bc@freeuk.com> - 2021-07-20 14:40 +0100
        Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-20 21:02 +0200
      Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-20 21:00 +0200
      Re: How to disambiguate macro? David Brown <david.brown@hesbynett.no> - 2021-07-21 08:15 +0200
      Re: How to disambiguate macro? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 23:17 -0700
  Re: How to disambiguate macro? John Forkosh <forkosh@panix.com> - 2021-07-20 12:51 +0000
  Re: How to disambiguate macro? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-07-20 08:47 -0700

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