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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: John McCarthy died today. |
| Date | 2011-11-08 07:05 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <j9b5v5$67b$1@dont-email.me> (permalink) |
| References | (8 earlier) <20111104214808.434@kylheku.com> <j98dee$fmo$1@dont-email.me> <20111107114608.386@kylheku.com> <4EB84456.7030800@verizon.net> <ad819d7c-54f6-4e23-8aad-1fbe29d16ff3@o13g2000vbo.googlegroups.com> |
On 11/08/2011 03:38 AM, Nick Keighley wrote:
> On Nov 7, 8:49�pm, James Kuyper <jameskuy...@verizon.net> wrote:
>> On 11/07/2011 02:49 PM, Kaz Kylheku wrote:
>> ...
>>
>>> What if in some insane language, subtraction were written "++" and addition
>>> "+"?
>>
>>> Would you fix the language with some insane restructuring of its fundamental
>>> rules, or would you fix the damn spelling of "++" to "-"?
>>
>> I would not recommend any change to C itself, because the need for
>> backwards compatibility prevents any meaningful fix to this problem.
>> Either change would be "insane" because of the huge amount of existing
>> code that would be broken.
>>
>> As a feature of a brand new language, I wouldn't characterize the idea
>> that assignment should be a statement type and not an expression type
>> insane. It's a normal feature of many existing languages.
>
> so are assignment expressions
>
> I've always quite liked the idiom
>
> int c;
>
> while ((c = getchar ()) != EOF)
> process_char (c);
>
> it often saves clumsy code
>
> int c = getchar ();
>
> while (c != EOF)
> {
> process_char (c);
> c = getchar ();
> }
I use the idiom myself frequently. I like the fact that it allows me to
write only a single call to getchar(). However, I think it is a clumsy
construct.
There's a need I've felt for a long time, and I just realized that
there's a feature that could be defined which would meet that need. I'm
inventing this idea while I'm writing this, so please be patient with
any lack of elegance.
What I want is to define a condition for a looping construct, and two
separate blocks of code that get executed repeatedly until the condition
is met, but the condition is tested between the two blocks, rather than
before or after a single block. It would be sort-of half-way between a
while() and a do-while(). I'm horrible at naming things - I'll just use
"token_n" to indicate the new as-yet unnamed keywords. The grammar
productions for this new kind of iteration statement would be:
token_1 statement_1 while (condition) statement_2 token_2
token_1 declaration while (condition) statement_3 token_2
The semantics would be to execute statement_1 unconditionally, then test
the condition. If the condition is false, terminate the entire
statement. Otherwise, execute the second statement, followed by the
first statement, and test the condition again; repeat until the
condition is false. If the both statements are compound statements, they
are treated as a single block for purposes of scope rules. If
statement_1 is a compound statement, and statement_2 is not, statement_2
is treated for purposes of scope rules as being inside of statement_1's
block. The break and continue statements work exactly as they do in
other iteration statements.
The second grammar rule is treated as being equivalent to
token_1 {declaration} while (condition) statement_3 token_2
The example you gave above could then be written as
token_1
int c = getchar();
while(c != EOF)
process_char(c);
token_2
I would prefer that to either of the alternatives you gave above. Note,
among other things, that the scope of 'c' is restricted to this new
iteration statement, something that's not possible with the other
alternatives.
--
James Kuyper
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John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-10-25 00:44 +0000
Re: John McCarthy died today. Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-25 01:27 -0700
Re: John McCarthy died today. Kleuskes & Moos <kleuske@somewhere.else.net> - 2011-10-25 09:27 +0000
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Re: John McCarthy died today. Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-30 08:20 -0700
Re: John McCarthy died today. Ark <akhasin@macroexpressions.com> - 2011-11-04 05:20 -0400
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-04 15:53 +0000
Re: John McCarthy died today. James Kuyper <jameskuyper@verizon.net> - 2011-11-04 12:16 -0400
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-04 17:58 +0000
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Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-07 19:49 +0000
Re: John McCarthy died today. James Kuyper <jameskuyper@verizon.net> - 2011-11-07 15:49 -0500
Re: John McCarthy died today. Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-08 00:38 -0800
Re: John McCarthy died today. James Kuyper <jameskuyper@verizon.net> - 2011-11-08 07:05 -0500
Re: John McCarthy died today. lawrence.jones@siemens.com - 2011-11-08 09:12 -0500
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-08 16:48 +0000
Re: John McCarthy died today. James Kuyper <jameskuyper@verizon.net> - 2011-11-08 12:12 -0500
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-08 23:27 +0000
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-08 14:10 -0800
Re: John McCarthy died today. James Kuyper <jameskuyper@verizon.net> - 2011-11-08 17:16 -0500
Re: John McCarthy died today. lawrence.jones@siemens.com - 2011-11-09 13:51 -0500
Re: Looping Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-11-09 19:21 -0700
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Re: John McCarthy died today. Quentin Carbonneaux <qcarbonn@invalid.com> - 2011-11-09 11:59 +0000
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Re: John McCarthy died today. Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-08 18:31 +0200
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-07 14:06 -0800
Re: John McCarthy died today. "BartC" <bc@freeuk.com> - 2011-11-08 02:01 +0000
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-07 23:16 -0800
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-08 05:18 +0000
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-07 23:17 -0800
Re: John McCarthy died today. Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-11-08 01:46 -0800
Re: John McCarthy died today. "BartC" <bc@freeuk.com> - 2011-11-08 13:02 +0000
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-08 14:19 -0800
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Re: John McCarthy died today. James Kuyper <jameskuyper@verizon.net> - 2011-11-08 18:13 -0500
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-08 23:38 +0000
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-08 23:18 +0000
Re: John McCarthy died today. Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-10 12:40 +0200
Re: John McCarthy died today. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-10 11:39 +0000
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Re: John McCarthy died today. 88888 Dihedral <dihedral88888@googlemail.com> - 2011-11-10 05:38 -0800
Re: John McCarthy died today. Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-10 17:29 +0200
Re: John McCarthy died today. David Thompson <dave.thompson2@verizon.net> - 2011-11-21 02:39 -0500
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Re: John McCarthy died today. Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-11-09 23:47 -0800
Re: John McCarthy died today. Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-10 00:21 -0800
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-10 03:04 -0800
Re: John McCarthy died today. gazelle@shell.xmission.com (Kenny McCormack) - 2011-11-10 15:20 +0000
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Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-13 01:44 +0000
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Re: John McCarthy died today. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-14 20:13 +0000
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Re: John McCarthy died today. Lauri Alanko <la@iki.fi> - 2011-11-10 15:26 +0000
Re: John McCarthy died today. Kaz Kylheku <kaz@kylheku.com> - 2011-11-10 01:51 +0000
Re: John McCarthy died today. Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2011-11-09 17:15 +0000
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Re: John McCarthy died today. "BartC" <bc@freeuk.com> - 2011-11-09 22:02 +0000
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-09 14:14 -0800
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-09 13:50 -0800
Re: John McCarthy died today. James Kuyper <jameskuyper@verizon.net> - 2011-11-08 07:10 -0500
Re: John McCarthy died today. Keith Thompson <kst-u@mib.org> - 2011-11-04 14:51 -0700
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