Re: x === x

Path	csiph.com!weretis.net!feeder4.news.weretis.net!news.mb-net.net!open-news-network.org!.POSTED!not-for-mail
From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups	comp.lang.javascript
Subject	Re: x === x
Date	Wed, 31 May 2017 23:39:41 +0200
Organization	PointedEars Software (PES)
Lines	32
Message-ID	<2276977.Lt9SDvczpP@PointedEars.de> (permalink)
References	<JavaScript-20170530123255@ram.dialup.fu-berlin.de> <874lw231ui.fsf@bsb.me.uk> <context-20170530144535@ram.dialup.fu-berlin.de> <2872662.aeNJFYEL58@PointedEars.de> <87inkh28sf.fsf@bsb.me.uk> <19437984.EfDdHjke4D@PointedEars.de> <87efv4zr3k.fsf@bsb.me.uk>
Reply-To	Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
NNTP-Posting-Host	47.229.197.178.dynamic.wless.zhbmb00p-cgnat.res.cust.swisscom.ch
Mime-Version	1.0
Content-Type	text/plain; charset="UTF-8"
Content-Transfer-Encoding	8Bit
X-Trace	gwaiyur.mb-net.net 1496266782 28872 178.197.229.47 (31 May 2017 21:39:42 GMT)
X-Complaints-To	abuse@open-news-network.org
NNTP-Posting-Date	Wed, 31 May 2017 21:39:42 +0000 (UTC)
User-Agent	KNode/4.14.2
X-Face	%i>XG-yXR'\"2P/C_aO%~;2o~?g0pPKmbOw^=NT`tprDEf++D.m7"}HW6.#=U:?2GGctkL,f89@H46O$ASoW&?s}.k+&.<b';Md8`dH6iqhT)6C^.Px\|[=M@7=Ik[_w<%n1Up"LPQNu2m8\|L!/3iby{-]A+#YE}Kl{Cw$\U!kD%K}\2jz"QQP6Uqr],./"?;=4v
Face	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
Xref	csiph.com comp.lang.javascript:33460

Show key headers only | View raw

Ben Bacarisse wrote:

> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:
>> | > {} === {}
>> | <- false
>> | {} === {};
>> | (x) Uncaught SyntaxError: Unexpected token ===
>>
>> I assume that the explicit semicolon there is considered an
>> /EmptyStatement/ that switches back to statement context.
> 
> I can't find any reference to "statement context" or "expression
> context" in the language standard.  I assume it's your own terminology,
> but I don't see how it helps explain why [] === []; is OK but {} === {};
> is a syntax error.  (I know why, I'm just wondering how talking about
> === making expression context and ; switching back helps to explain this
> difference.)

Simply put, ECMAScript syntax is ambiguous, and it depends on the context 
how it is parsed.  For example, “{}” can be parsed either as an empty 
/Block/ *statement* (which can only be produced by the /Statement/ 
production) or as an empty Object initializer; the latter is an *expression* 
(it can only be produced by the /Expression/ production).  A further 
complication is the /ExpressionStatement/ production (IIRC).

I will consider the rest of your posting later.

-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | <http://PointedEars.de/es-matrix>
<https://github.com/PointedEars> | <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | Please do not cc me./Bitte keine Kopien per E-Mail.

Thread

Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-30 14:34 +0100
  Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-30 15:02 +0100
  Re: x === x Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-30 16:22 +0200
    Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-31 01:02 +0100
      Re: x === x Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-31 12:39 +0200
        Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-31 21:52 +0100
          Re: x === x Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-31 23:39 +0200
            Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-01 01:46 +0100
              Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 00:14 -0700
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-01 10:39 +0100
                Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 03:37 -0700
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-01 18:54 +0100
                Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-01 21:54 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-02 11:06 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-02 11:08 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-02 10:56 +0100
                Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-04 12:50 +0100
                Re: x === x John G Harris <niam@jghnorth.org.uk.invalid> - 2017-06-04 14:30 +0100
                Re: x === x Dr J R Stockton <J.R.Stockton@physics.org> - 2017-06-04 09:03 -0700
                Re: x === x Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-01 14:45 +0100
                Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 07:00 -0700
        Re: x === x Julio Di Egidio <julio@diegidio.name> - 2017-06-01 00:00 -0700

csiph-web