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Re: Operator precedence

From Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups comp.lang.awk
Subject Re: Operator precedence
Date 2024-05-26 02:06 +0000
Organization A noiseless patient Spider
Message-ID <20240525185349.904@kylheku.com> (permalink)
References (5 earlier) <20240523210755.307@kylheku.com> <87zfsektvi.fsf@axel-reichert.de> <v2tlbf$320cq$1@dont-email.me> <v2tn6n$32bqt$1@dont-email.me> <slrnv55129.2osd.naddy@lorvorc.mips.inka.de>

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On 2024-05-26, Christian Weisgerber <naddy@mips.inka.de> wrote:
> On 2024-05-25, Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:
>
>> People should be anyway aware of the operator precedences in the
>> various programming languages since there are obviously yet worse
>> definitions than the one we've been discussing here.
>
> Which is why BSD has had an operator(7) man page about "C operator
> precedence and order of evaluation" since 1990.

This discussion has convinced me that unary operators must not be
clumped together and put into a single precedence level.

For instance, if we have the C-like expression

  -*p/*q

it should ideally be

  -(*p/*q)

and not as it is now:

  (-*p)/(*q)

due the unary minus being clumped with dereference.

Unary minus should not be a distinct operator from binary minus.
Unary minus should denote the elision of an identity element term,
so that - X not only means the same as 0 - X, but is considered
to be the same notation, just with the additive identity element not
show. We could correctly parse it as a binary minus by putting the
element back in.

This can make a difference easily. Consider that the unsigned types
in C have a definition for unary minus. If *p is of type unsigned
int, and its value is 1, then (-*p) is UINT_MAX. *q is 4 then
we get UINT_MAX / 4.  Under the proposedd rule, we would get
something else: 1/4 producing 0, and that negating to 0.

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca

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Thread

Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-23 16:13 +0200
  Re: Operator precedence Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-23 16:49 +0000
    Re: Operator precedence Axel Reichert <mail@axel-reichert.de> - 2024-05-23 19:14 +0200
      Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-24 01:53 +0200
        Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-24 04:41 +0200
          Re: Operator precedence Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-24 04:32 +0000
            Re: Operator precedence Axel Reichert <mail@axel-reichert.de> - 2024-05-25 13:34 +0200
              Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-25 23:31 +0200
                Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-26 00:03 +0200
                Re: Operator precedence Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-25 22:26 +0000
                Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-30 06:59 +0200
                Re: Operator precedence Axel Reichert <mail@axel-reichert.de> - 2024-05-30 10:24 +0200
                Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-31 17:08 +0200
                Re: Operator precedence Christian Weisgerber <naddy@mips.inka.de> - 2024-05-26 00:37 +0000
                Re: Operator precedence Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-26 02:06 +0000
                Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-30 07:26 +0200
                Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-30 07:06 +0200
                Re: Operator precedence Axel Reichert <mail@axel-reichert.de> - 2024-05-30 10:22 +0200
                Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-31 17:16 +0200
            Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-25 23:31 +0200
              Re: Operator precedence Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-26 01:29 +0000
        Re: Operator precedence Axel Reichert <mail@axel-reichert.de> - 2024-05-30 10:17 +0200
          Re: Operator precedence Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-05-31 17:46 +0200
            Re: Operator precedence Axel Reichert <mail@axel-reichert.de> - 2024-06-01 09:11 +0200
      Re: Operator precedence Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-24 03:45 +0000
        Re: Operator precedence Axel Reichert <mail@axel-reichert.de> - 2024-05-25 13:09 +0200
          Re: Operator precedence Kaz Kylheku <643-408-1753@kylheku.com> - 2024-05-25 22:20 +0000

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