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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: John McCarthy died today. |
| Date | 2011-11-09 13:50 -0800 |
| Organization | None to speak of |
| Message-ID | <lnvcqt9d9l.fsf@nuthaus.mib.org> (permalink) |
| References | (11 earlier) <8a3ee570-307b-46b4-8e39-996082e716fc@s5g2000vbe.googlegroups.com> <ln7h3acl4i.fsf@nuthaus.mib.org> <j9ca4i$gt7$1@speranza.aioe.org> <lnr51ib0bn.fsf@nuthaus.mib.org> <j9eceq$jb3$1@speranza.aioe.org> |
Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> writes:
> Keith Thompson wrote:
>> Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> writes:
>>> Keith Thompson wrote:
>> [...]
>>>> Using "=" for assignment was not, in my opinion, a good idea. Any
>>>> attempt to change it now would be far worse.
>>>
>>> With this attitude, the language will never improve!
>>
>> With any other attitude, the language will die.
>>
>> If you think that changing the C language to use ":=" rather than for
>> assignment is a good idea, that's not an unreasonable opinion, at least
>> at first glance. Frankly, I *wish* I could agree. But if you want to
>> propose such a change and have it taken seriously, you need to address
>> the problems it could cause (as I did in my previous message).
>>
>> So tell us, how would you address the problem of existing code that uses
>> "=" for assignment, and of new code using ":=" for assignment that would
>> no longer compile with older compilers? Similarly, how would you
>> address the legions of C programmers who believe (rightly or wrongly)
>> that using "=" for assignment and "==" for equality is ok, and doesn't
>> need to be fixed?
>>
>> Please be specific.
>
> Python has dealt with this problem very successfully, Kieth: see http://
> www.python.org/dev/peps/pep-0005/ for some general approaches, but also
> http://docs.python.org/release/3.0/whatsnew/3.0.html for details about
> transitioning to "the first ever intentionally backwards incompatible
> Python release".
>
> One of the key planks supporting upgrades to Python 3.0 is an automated
> conversion tool, 2to3 (http://docs.python.org/release/3.0/
> library/2to3.html#to3-reference), which automatically upgrades 2.x source
> code to valid 3.0 Python syntax.
>
> It would be a simple matter to write a converter that read a C source
> file and replaced all = assignment operators with :=
Ok, that's not a bad answer. I still don't think that it would be
at all practical to change C's assignment operator from "=" to ":=".
The overhead would be substantial, probably enough to cause many
implementers and programmers to ignore any new standard that made
such a change. (Getting C99 adopted has been difficult enough.)
C programming culture is not Python programming culture. And I'll
note that Python 2 is not dying with the introduction of Python 3.
> Incidentally, Python has many convenient features that could easily be
> added to C, e.g. multiple comparisons behave correctly (a < b > c etc);
> array and string slicing e.g. s[4:7] as a shortcut for strndup(s+4,3);
> else clauses on loops; and many more. Unfortunately the current fashion
> seems to be to try to preserve C in aspic.
"a < b > c" already has a meaning in C; it's equivalent to
"(a < b) > c", where "(a < b)" yields either 0 or 1. I suspect
that such constructs are used in error more often than they're used
correctly, but the committee is rightly hesitant to make changes
that can break existing code. And it's not *that* hard to write
"a < b && b > c".
I can't think of a way to define "s[4:7]" consistently in C without
radically changing the way C deals with strings and arrays. Suppose
s is a string with the value "Hello, world"; it's represented as an
array containing those 12 characters followed by a terminating '\0'.
s[4:7] should be the string "o, w", but that requires building an
array somewhere in memory with a '\0' immediately following the
'w'; you can't just treat a subset of "Hello, world" as "o, w".
And that means you have to deal with allocating, initializing,
and deallocating it.
I'm not saying that C's string and array handling are an ideal
solution, but there are uncounted millions of lines of code that
depend on it.
As for "preserv[ing] C in aspic", I refer you to
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf, the latest
(?) draft of the upcoming C201X standard. It adds threading,
alignment support, Unicode support, type-generic expressions,
static assertions, optional support for bounds-checking interfaces,
and a number of other things.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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