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Groups > comp.lang.c > #67148

Re: Untyped Variables

From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: Untyped Variables
Date 2015-08-11 17:24 -0700
Organization None to speak of
Message-ID <lnbnedcq0x.fsf@kst-u.example.com> (permalink)
References (5 earlier) <ba0351fd-385d-4bc1-b947-380e83defb2b@googlegroups.com> <lnio8ndvph.fsf@kst-u.example.com> <c56f80ad-fd13-49e6-99d2-fe6e8dd20156@googlegroups.com> <mqbtmh$d1r$1@dont-email.me> <17dea383-12f7-4574-8ffa-7218929f4c48@googlegroups.com>

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David Kleinecke <dkleinecke@gmail.com> writes:
> On Monday, August 10, 2015 at 9:30:54 PM UTC-7, James Kuyper wrote:
[...]
>> An explanation of how you would modify the grammar rules to allow such
>> sequences, and how you would write a constraint to impose those
>> restrictions semantically, would make it much easier for us to
>> understand your objection.
>
> I've done this before.
>
> I want to define "expression" by the following syntax
>    expression = term Infix..
>    term = (Prefix ...) Primitive (Suffix ...)  
> where "..." means repeat as many tiems as desired and "A B.." means
> repeat A separated by B (as in ABABABAB ...). The C syntax is almost
> already in that shape except for two points - one of them in the cast
> expression and the other the tertiary operator. (The tertiary can be
> forced into the right shape by looking at "QUERY expression COLON" as
> an Infix).

I can read the C grammar and, with some work, determine whether a given
expression is valid and how it's evaluated.

I can't do that with your description above, at least not without
knowing what you mean by "Infix", "Prefix", "Primitive", and "Suffix".

Is that intended to be the entire grammar for expressions?  Would you
not have separate rules for additive, multiplicative, shift, and so
forth, expressions?

And you haven't said anyting about constraints.  Would the meaning of
`x + y * z` be specified by the grammar (if so, what you've written above
doesn't do that), or by an English semantic description (if so, you
haven't mentioned it)?

Note that if the binding of `x + y * z` isn't defined by the grammar,
the rule saying that it's equivalent to `x + (y * z)` would not be a
constraint; it would be a semantic description.

(BTW, the "?:" operator is commonly called the *ternary* operator,
though its offical name is the conditional operator.)

-- 
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"

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Thread

Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-07 18:19 -0700
  Re: Untyped Variables Lőrinczy Zsigmond <nospam@for.me> - 2015-08-08 06:53 +0200
  Re: Untyped Variables James Kuyper <jameskuyper@verizon.net> - 2015-08-08 11:09 -0400
    Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-08 12:09 -0700
      Re: Untyped Variables James Kuyper <jameskuyper@verizon.net> - 2015-08-08 14:24 -0400
    Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-08 12:54 -0700
      Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-08 16:06 -0700
        Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-08 17:29 -0700
          Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-09 17:52 -0700
            Re: Untyped Variables Ian Collins <ian-news@hotmail.com> - 2015-08-10 12:57 +1200
            Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-10 08:41 -0700
              Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-10 17:06 -0700
        Re: Untyped Variables Richard Damon <Richard@Damon-Family.org> - 2015-08-08 19:44 -0400
        Re: Untyped Variables James Kuyper <jameskuyper@verizon.net> - 2015-08-08 20:34 -0400
          Re: Untyped Variables glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-09 02:03 +0000
            Re: Untyped Variables Richard Damon <Richard@Damon-Family.org> - 2015-08-08 22:52 -0400
              Re: Untyped Variables glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-09 04:57 +0000
                Re: Untyped Variables Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-08-09 09:58 -0600
                Re: Untyped Variables Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-08-10 03:54 -0700
                Re: Untyped Variables Richard Damon <Richard@Damon-Family.org> - 2015-08-09 16:59 -0400
          Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-09 18:02 -0700
            Re: Untyped Variables James Kuyper <jameskuyper@verizon.net> - 2015-08-10 11:01 -0400
              Re: Untyped Variables James Kuyper <jameskuyper@verizon.net> - 2015-08-10 13:20 -0400
              Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-10 16:54 -0700
                Re: Untyped Variables James Kuyper <jameskuyper@verizon.net> - 2015-08-11 00:20 -0400
            Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-10 08:11 -0700
              Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-10 17:15 -0700
                Re: Untyped Variables James Kuyper <jameskuyper@verizon.net> - 2015-08-11 00:30 -0400
                Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-11 16:50 -0700
                Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-11 17:24 -0700
                Re: Untyped Variables Richard Heathfield <rjh@cpax.org.uk> - 2015-08-12 01:37 +0100
                Re: Untyped Variables glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-12 04:46 +0000
                Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-12 18:12 -0700
                Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-13 12:08 -0700
                Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-13 16:25 -0700
                Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-14 10:36 -0700
                Re: Untyped Variables Bartc <bc@freeuk.com> - 2015-08-14 19:13 +0100
                Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-11 07:58 -0700
          Re: Untyped Variables richard@cogsci.ed.ac.uk (Richard Tobin) - 2015-08-10 13:53 +0000
            Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-10 08:29 -0700
              Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-10 17:01 -0700
                Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-10 17:42 -0700
                Re: Untyped Variables glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-08-11 02:56 +0000
            Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-10 16:50 -0700
              Re: Untyped Variables Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-08-11 01:39 +0100
                Re: Untyped Variables Keith Thompson <kst-u@mib.org> - 2015-08-10 19:03 -0700
                Re: Untyped Variables Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-08-11 11:21 +0100
                Re: Untyped Variables David Kleinecke <dkleinecke@gmail.com> - 2015-08-11 16:37 -0700

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