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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.awk
Subject: Re: Operator precedence
Date: Sun, 26 May 2024 02:06:40 -0000 (UTC)
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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
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