Re: LL vs LR, was Programming language and IDE design

From	Ivan Godard <ivan@ootbcomp.com>
Newsgroups	comp.compilers
Subject	Re: LL vs LR, was Programming language and IDE design
Date	2014-03-01 20:31 -0800
Organization	A noiseless patient Spider
Message-ID	<14-03-004@comp.compilers> (permalink)
References	<13-11-016@comp.compilers> <13-11-018@comp.compilers> <14-03-003@comp.compilers>

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On 3/1/2014 4:03 PM, Hannah wrote:
<snip>

> 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.

The standard way to handle this, and many such other cases where a
formal grammar is not LL, is to introduce a function (in recursive
descent) or rule (in parser generators) that recognizes "parenthesized
thingy" and then figure it out later. Yes, that amounts to LR, but you
only need it in a few specialized places. There's an equivalent trick
in "DOI=1," in Fortran, where you let the lexer resolve it so the
parser sees proper lexemes, not characters.

C and its descendants are well known for being inhumane (as well as
parser-unfriendly) in their excessive overloading of parens and braces.
More friendly (or less keystroke-obsessed) languages require all
syntactic regions to have both openers and closers, unique for each kind
of region, to avoid the canonical C bug of mismatched closers; Algol68
is an early example of doing it right.
[C++ is unusually bad, with some parts just plain ambiguous.  In the example
a few messages back, I gather that the rule is that if you can parse it as a
declaration, it's a declaration, otherwise it's something else. -John]

Thread

Re: Programming language and IDE design Martin Ward <martin@gkc.org.uk> - 2013-11-16 15:55 +0000
  Re: Programming language and IDE design Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2013-11-16 19:48 +0100
  Re: Programming language and IDE design George Neuner <gneuner2@comcast.net> - 2013-11-18 19:02 -0500
    Re: Programming language and IDE design "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2013-11-19 15:36 +0000
    Re: Programming language and IDE design George Neuner <gneuner2@comcast.net> - 2013-11-19 12:41 -0500
      Re: Parsing Fortran, was Programming language and IDE design glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-11-19 20:18 +0000
        Re: Parsing Fortran, was Programming language and IDE design glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-11-21 21:22 +0000
    Re: Programming language and IDE design wclodius@earthlink.net (William Clodius) - 2013-11-22 18:27 -0700
    Re: Programming language and IDE design "robin" <robin51@dodo.com.au> - 2013-11-25 10:33 +1100
      Re: Programming language and IDE design Martin Ward <martin@gkc.org.uk> - 2013-12-03 15:15 +0000
        Re: Programming language and IDE design Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2013-12-05 03:35 +0100
    Re: Programming language and IDE design hu47121@usenet.kitty.sub.org (Hannah) - 2014-03-02 00:03 +0000
      Re: LL vs LR, was Programming language and IDE design Ivan Godard <ivan@ootbcomp.com> - 2014-03-01 20:31 -0800
        Re: LL vs LR, was Programming language and IDE design Kaz Kylheku <kaz@kylheku.com> - 2014-03-02 18:41 +0000
      Re: Programming language and IDE design George Neuner <gneuner2@comcast.net> - 2014-03-02 12:21 -0500
  Re: Programming language and IDE design Jonathan Thornburg <jonathan@cobalt.astro.indiana.edu> - 2013-11-19 19:39 +0000

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