Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!news.glorb.com!news-out.readnews.com!news-xxxfer.readnews.com!news.misty.com!news.iecc.com!.POSTED!nerds-end
From: hu47121@usenet.kitty.sub.org (Hannah)
Newsgroups: comp.compilers
Subject: Re: Programming language and IDE design
Date: Sun, 2 Mar 2014 00:03:18 +0000 (UTC)
Organization: The Pond
Lines: 53
Sender: news@iecc.com
Approved: comp.compilers@iecc.com
Message-ID: <14-03-003@comp.compilers>
References: <13-11-016@comp.compilers> <13-11-018@comp.compilers>
NNTP-Posting-Host: news.iecc.com
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
X-Trace: miucha.iecc.com 1393732684 7031 64.57.183.58 (2 Mar 2014 03:58:04 GMT)
X-Complaints-To: abuse@iecc.com
NNTP-Posting-Date: Sun, 2 Mar 2014 03:58:04 +0000 (UTC)
Keywords: design, C++
Posted-Date: 01 Mar 2014 22:58:04 EST
X-submission-address: compilers@iecc.com
X-moderator-address: compilers-request@iecc.com
X-FAQ-and-archives: http://compilers.iecc.com
Xref: csiph.com comp.compilers:1125

George Neuner <gneuner2@comcast.net> wrote:
>On Sat, 16 Nov 2013 15:55:10 +0000, Martin Ward <martin@gkc.org.uk>
>wrote:

>>On Friday 08 Nov 2013 at 21:04, George Neuner <gneuner2@comcast.net> wrote:

>>> The majority of successful languages are LL(k) for small k.  It's hard
>>> to get much simpler than that for parsing.

>>C is not LL(K), neither is COBOL, nor C++, nor I think is Java.
>>That probably covers the majority of successful languages:
>>if "success" is defined as "total lines of code in production".

>They _all_ are LL(k).  More specifically, I believe all of your
>examples are, at most, LL(2).

I don't think C++ is LL(2).

Think e.g.

  T(a)++;
vs.
  T(a)[5];

(Example from n3485, page 131).

The former is a statement, while the latter is a declaration, and you
can decide this only very late. As the first four tokens are the same,
C++ can't be LL(4), at least.

As you can substitute '('^n x ')' ^n for a in this example (i.e. enclose
that identifier in any number of parentheses), C++ isn't LL(n) for any n.
(In the first case, "a" is a subexpression, that can be parenthesized,
while in the second case, it's the declarator-id that can also be
parenthesized).

Then, in C99, in function parameter declarations
(i.e. parameter-type-list, then in the single parameter-declaration,
after declaration-specifiers, even if you left-factor those), you have
to decide whether you're to descend into declarator or into
abstract-declarator_opt.

FIRST_k(declarator), however, includes "("^k, as does
FIRST_k(abstract-declarator_opt):

The former via k recursions of declarator -> direct-declarator -> ( declarator )
the latter via k recursions of
  abstract-declarator -> direct-abstract-declarator -> ( abstract-declarator )

So the C grammar is not LL(k) for any k, either. You can probably parse
that particular part of the C/C++ grammar easily using LR.

Hannah.