Re: Parentheses as operators

Path	csiph.com!eternal-september.org!feeder.eternal-september.org!mx02.eternal-september.org!.POSTED!not-for-mail
From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: Parentheses as operators
Date	Mon, 17 Aug 2015 14:36:31 -0700
Organization	None to speak of
Lines	56
Message-ID	<lnmvxp61i8.fsf@kst-u.example.com> (permalink)
References	<operator-20150817203200@ram.dialup.fu-berlin.de> <lnr3n1655c.fsf@kst-u.example.com> <21rAx.201505$nx.48087@fx16.am4>
Mime-Version	1.0
Content-Type	text/plain; charset=us-ascii
Injection-Info	mx02.eternal-september.org; posting-host="945944de09706c9b4e29b53c9d2efdc2"; logging-data="9025"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/Zjf2YVupQtPHMnQLU+szG"
User-Agent	Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)
Cancel-Lock	sha1:f0wPdlvF8c/OVh+5jtu43+QMuWY= sha1:yykVtXrZc+L6s83Ni2oTSr8KFpY=
Xref	csiph.com comp.lang.c:67631

Show key headers only | View raw

Richard Heathfield <rjh@cpax.org.uk> writes:
> On 17/08/2015 21:17, Keith Thompson wrote:
>
> <snip>
>
>> N1570 6.5p1 says:
>>
>>      An *expression* is a sequence of operators and operands that
>>      specifies computation of a value, or that designates an object or a
>>      function, or that generates side effects, or that performs a
>>      combination thereof.
>>
>> which is not accurate, since `42` is clearly an expression, but it has
>> no operators and therefore no operands.
>
> It could be argued that it is a sequence of 0 operators and 1 operand 
> that specifies the computation of the value 42.
>
> <snip>

It could -- but not correctly.

N1570 6.4.6p2 defines the word "operand"

    A punctuator is a symbol that has independent syntactic and
    semantic significance.  Depending on context, it may specify an
    operation to be performed (which in turn may yield a value or a
    function designator, produce a side effect, or some combination
    thereof) in which case it is known as an *operator* (other forms
    of operator also exist in some contexts).

I previously says that the standard doesn't define the word "operator".
I was only partially correct; this is a definition, but explicitly an
incomplete one.  It *could* leave the door open to defining parentheses
an an "operator", but if the standard does so I haven't found it.

    An *operand* is an entity on which an operator acts.

Which implies that there can be no operand without an operator acting on
it.

42 certainly *can* be an operand, but in a case like:

    42;

it isn't.

(This is just a bit of sloppy wording.  The grammar defines "expression"
unambiguously, and 42 is clearly *intended* to be an expression; the
definition in 6.5p1 just doesn't capture the intent properly.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

Re: Parentheses as operators Keith Thompson <kst-u@mib.org> - 2015-08-17 13:17 -0700
  Re: Parentheses as operators Richard Heathfield <rjh@cpax.org.uk> - 2015-08-17 20:57 +0100
    Re: Parentheses as operators Keith Thompson <kst-u@mib.org> - 2015-08-17 14:36 -0700
    Re: Parentheses as operators Keith Thompson <kst-u@mib.org> - 2015-08-17 14:40 -0700

csiph-web