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Re: String Constants

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>> Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>>>BruceMcF <agila61@netscape.net> wrote:
>>>And neither would I, but when writing portable programs that will run
>>>on systems you've never seen and may not yet exist, it makes sense to
>>>apply Postel's principle:
>>>
>>>Be conservative in what you send; be liberal in what you accept.
>> 
>> Maybe so, but that's not a good basis for designing standards.
>
>No, but it's a really, really good way to write portable programs.

Maybe.  But writing programs to comply with an interpretation of a
standard that cannot be tested without implementing a new system (the
"devil's system") is not practical and therefore not a good way; it
also does not increase the real-world portability in any way.

>>>Which, in this case, means that if you program for "the devil's
>>>implementation" of Forth, one that satisfies the letter of the law,
>>>but is as perversely written as possible, your program will be robust
>>>even in the presence of occasional foibles of implementation.
>> 
>> Sure, that may be heaven for language lawyers, but in practice most
>> programmers write programs such that they work on the real systems
>> they expect their program to be used with. 
>
>This has nothing to do with language lawyers, but about writing robust
>portable programs.

"Letter of the law" has everything to do with language lawyers.

It also has nothing to do with writing robust portable programs.  As
an example, in classical C,

n<n-1

is an efficient test for checking whether x was the smallest number of
its type (and that's even true for ones-complement and sign-magnitude
arithmetic).  In ANSI C, this is only guaranteed for unsigned numbers,
and gcc -O, the devil's implementation, goes ahead and "optimizes"
this to "0".  Now a language lawyer told me that I could write

n < (long)(((unsigned long)n)-1)

instead to get the C compiler to produce the code I want while
"satisfying the letter of the law".  So I try this with the devil's
implementation and find: gcc 2.95, 3.3 and 3.4 all produce 0 with -O
for both code variants and produce the intended code (apart from quite
a bit of inefficiency) without -O for both variants of the code.  Only
gcc 4.1 (among the gcc versions I tested) works as the language lawyer
promised.

In conclusion, I did not get a robust and portable program by
satisfying the letter of the law.

>> And that's the sane approach, because there is no test whether a
>> program will work on a "devil's implementation".  E.g., As a result,
>> most portable Forth code assumes 1 chars=1, because all maintained
>> systems implement that, we cannot test code that tries to cater for
>> the "devil's system" in this area.
>
>That's good practice: it makes sense to program for a somewhat
>modified standard, with 1 chars=1.

And in all maintained systems UNUSED bytes after here are accessible,
so anything else cannot be tested.

>> If you change the standard in the way you suggested ("I'd simply make
>> it clear that using HERE before it was allotted was nonstandard"),
>> there would be no way for programmers to test whether their program
>> violates this restriction.
>
>You can't test for portability on a single system anyway, so this is a
>complete red herring.

I am not sure why you bring up a red herring only to denounce it as
such.  To be clear: Nobody but you has talked about testing on a
single system.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2010: http://www.euroforth.org/ef10/

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Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-18 20:52 -0700
  Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-19 03:44 -0500
    Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-21 21:34 -0700
      Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-22 03:20 -0500
        Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-22 07:37 -0700
          Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-22 11:12 -0500
            Re: String Constants anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-04-22 17:36 +0000
              Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-22 13:05 -0500
                Re: String Constants anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-04-22 18:17 +0000
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-23 03:22 -0500
                Re: String Constants anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-04-23 11:35 +0000
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-23 11:37 -0500
                Re: String Constants anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-04-23 12:07 +0000
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-23 11:40 -0500
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-22 12:22 -0700
            Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-22 12:13 -0700
              Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-23 03:30 -0500
                Re: String Constants anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-04-23 11:44 +0000
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-23 11:47 -0500
                Re: String Constants anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-04-26 09:23 +0000
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-26 06:49 -0500
                Re: String Constants Paul Rubin <no.email@nospam.invalid> - 2011-04-25 00:50 -0700
                Re: String Constants anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-04-26 10:08 +0000
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-23 10:14 -0700
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-24 03:15 -0500
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-24 13:26 -0700
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-24 17:03 -0500
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-24 19:05 -0700
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-25 03:08 -0500
                Re: String Constants kenney@cix.compulink.co.uk - 2011-04-25 07:07 -0500
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-25 08:00 -0700
                Re: String Constants Elizabeth D Rather <erather@forth.com> - 2011-04-25 08:56 -1000
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-25 07:45 -0700
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-26 03:42 -0500
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-26 11:20 -0700
                Re: String Constants Alex McDonald <blog@rivadpm.com> - 2011-04-26 11:02 -0700
                Re: String Constants Bernd Paysan <bernd.paysan@gmx.de> - 2011-04-26 21:59 +0200
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-27 03:26 -0500
                Re: String Constants Alex McDonald <blog@rivadpm.com> - 2011-04-27 09:12 -0700
                Re: String Constants Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-04-27 11:28 -0500
                Re: String Constants Alex McDonald <blog@rivadpm.com> - 2011-04-27 10:47 -0700
                Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-27 10:20 -0700
            Re: String Constants BruceMcF <agila61@netscape.net> - 2011-04-22 12:37 -0700

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