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Re: Operator precedence

From Axel Reichert <mail@axel-reichert.de>
Newsgroups comp.lang.awk
Subject Re: Operator precedence
Date 2024-05-25 13:34 +0200
Organization A noiseless patient Spider
Message-ID <87zfsektvi.fsf@axel-reichert.de> (permalink)
References (1 earlier) <20240523092856.646@kylheku.com> <87sey8movv.fsf@axel-reichert.de> <v2okuh$1vrvh$1@dont-email.me> <v2ouo9$2547f$1@dont-email.me> <20240523210755.307@kylheku.com>

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Kaz Kylheku <643-408-1753@kylheku.com> writes:

> Now in the C grammar, we have multiplication also occuping a
> precedence rung between unary plus/minus and additive expressions.
>
> Thus -A*B means (-A)*B, whereas X - A*B means X-(A*B).
>
> In this case it doesn't matter because the unary minus is
> a kind of product. -A can be regarded as a shorthand for (-1)*A.
>
> More importantly the identity (-A)*B = -(A*B) holds.
>
> This creates a problem if we naively wedge exponentiation into
> the grammar, by sticking it into a precedence level above
> multiplication, but below unary.
>
> The identity does not hold in exponentiation: (-A)**B
> is not -(A**B).

Very nice explanation, many thanks. I will likely pass it to a friend
(geodesist), who had a heated argument with the math teacher of her son
about whether

    2
  -3

is -9 or +9. I think the mathematical conventions are clear (and
probably established for centuries), but the teacher might be confused
and think Excel is the reference, see

  https://en.wikipedia.org/wiki/Order_of_operations#Unary_minus_sign

It would be interesting to learn about the motivation for spreadsheets
and "bc" to deviate from the mathematical convention.

Best regards

Axel

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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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